An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors ar...An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower rotational speed. （2） A stable head-characteristic curve for flow rate with negative slope appears. （3） As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.展开更多
A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibrati...A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.展开更多
Small-sized axial fans are used as air coolers for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotatio...Small-sized axial fans are used as air coolers for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although it causes the deterioration of the efficiency and the increase of noise.Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of the performance.In the present paper,the performance and the internal flow condition of the small-sized axial fan are shown as a first step of the research for the contra-rotating small-sized axial fan and the important points to apply contra-rotating rotors to the small-sized axial fan are discussed.Furthermore,the numerical flow analysis is conducted to investigate the performance of the contra-rotating small-sized axial fan and internal flow conditions and pressure distributions are clarified and the effect of contra-rotating rotors is considered.展开更多
Influences of tip clearance on the tip flow and associated loss mechanism in a contra-rotating axial flow fan hasbeen studied in the paper, based on three dimensional numerical results. The results with different tip ...Influences of tip clearance on the tip flow and associated loss mechanism in a contra-rotating axial flow fan hasbeen studied in the paper, based on three dimensional numerical results. The results with different tip clearanceare compared in terms of stage efficiency, relative total pressure loss coefficient, flow angle. It is found that theefficiency of the contra-rotating fan changes almost linearly with increment of the tip clearance, however, efficiencyof the rear rotor is observed to decrease more dramatically than that of the forward rotor given same tipclearance variation. The analysis on the flow structure indicates that the tip region flow field is qualitatively similarin both rotors. However, with the same clearance value, the leakage flow in the rear rotor is effected by a tipleakage vortex of greater intensity caused by relative loading levels and the inter rotor interaction.展开更多
Stall in compressors can cause performance degradation and even lead to disasters.These unacceptable consequences can be avoided by timely monitoring stall inception and taking effective measures.This paper focused on...Stall in compressors can cause performance degradation and even lead to disasters.These unacceptable consequences can be avoided by timely monitoring stall inception and taking effective measures.This paper focused on the rotating stall warning in a low-speed axial contra-rotating compressor.Firstly,the stall disturbance characteristics under different speed configurations were analyzed.The results showed that as the speed ratio(RR)increased,the stall disturbance propagation speed based on the rear rotor speed gradually decreased.Subsequently,the standard deviation(SD)method,the cross-correlation(CC)method,and the discrete wavelet transform(DWT)method were employed to obtain the stall initiation moments of three different speed configurations.It was found that the SD and CC methods did not achieve significant stall warning results in all three speed configurations.Besides,the stall initiation moment obtained by the DWT method at RR=1.125 was one period after the stall had fully developed,which was unacceptable.Therefore,a stall warning method was developed in the present work based on the long short-term memory(LSTM)regression model.By applying the LSTM model,the predicted stall initiation moments of three speed configurations were at the 557th,518th,and 333rd revolution,which were44,2,and 74 revolutions ahead of stall onset moments,respectively.Furthermore,in scenarios where a minor disturbance preceded the stall,the stall warning effect of the LSTM was greatly improved in comparison with the aforementioned three methods.In contrast,when the pressure fluctuation before the stall was relatively small,the differences between the stall initiation moments predicted by these four methods were not significant.展开更多
The Contra-Rotating Open Rotor(CROR)design confronts significant noise challenges despite being one of the possible options for future green aeroengines.To efficiently estimate the noise emitted from a CROR,a three-di...The Contra-Rotating Open Rotor(CROR)design confronts significant noise challenges despite being one of the possible options for future green aeroengines.To efficiently estimate the noise emitted from a CROR,a three-dimensional unsteady prediction model based on the meshless method is presented.The unsteady wake flow and the aerodynamic load fluctuations on the blade are solved through the viscous vortex particle method,the blade element momentum theory and vortex lattice method.Then,the acoustic field is obtained through the Farassat’s formulation 1A.Validation of this method is conducted on a CROR,and a mesh-based method,e.g.,Nonlinear Harmonic(NLH)method,is also employed for comparison.It is found that the presented method is three times faster than NLH method while maintaining a comparable precision.A thorough parametric analysis is also carried out to illustrate the effects of rotational speed,rotor-rotor spacing and rear rotor diameter on the noise level.The rotor speed is found to be the most influencing factor,and by optimizing the speed difference between the front and rear rotors,a notable noise reduction can be expected.The current findings not only contribute to a deeper comprehension of the CROR’s aeroacoustic properties but also offer an effective tool for engineering applications.展开更多
The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor(CRAC). Transient numerical simul...The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor(CRAC). Transient numerical simulation was carried out in a single passage of the CRAC. The original transient fluctuation and oscillation of the tip leakage vortex structure with varying flow capacity of the CRAC were revealed using circle-like pattern figure and phase-locked root mean square(PLRMS). Additionally, the tip leakage flow in terms of vortex structure evolution was visualized for the sake of revealing the flow mechanism during pre-stall process. Results show that the unsteady fluctuation first appears at φ=0.3622, and the fluctuation frequency is 2.86 BPF. Unsteady disturbance source is mainly located at the tip side of the downstream rotor leading edge. From the choking point to the near stall condition, tip leakage vortex is always found in the tip leading edge of the upstream rotor. In addition, the tip leakage vortex of upstream rotor remains in the same place over time, i.e., no fluctuation, even when the downstream rotor entered into stall state. Such a phenomenon indicates that the stall point of the contra-rotating compressor is determined by the downstream rotor. Moreover, the maximum fluctuation position is mainly concentrated on the interface between the mainstream and the tip leakage vortex of the downstream rotor. By throttling the compressor, the angle between the main leakage vortex and the circumferential direction decreases gradually. When the main leakage vortex touches and continuously impacts on the leading edge of the adjacent blade, the unsteady disturbance, which is different from that of BPF, appears firstly.展开更多
Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the perfor...Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the performance and stable operation. The wake and potential interference occur between the front and rear rotors and leakage flow from the front rotor tip influences on the flow condition of the rear rotor near the shroud when the blade row distance is small. Therefore, it is important to clarify the flow condition between front and rear rotors. The fan static pressure curves were obtained by the experimental apparatus and the numerical analysis was also conducted to investigate the internal flow between front and rear rotors. The leakage flow from the front rotor tip reaches the leading edge of the rear rotor when the blade row distance is small as L = 10 mm and the pressure fluctuations at the leading edge of the rear rotor tip becomes larger than those at other radial positions. In the present paper, the vorticity contour between front and rear rotors is shown and pressure fluctuations related to the leakage flow from the front rotor is investigated using the numerical analysis result. Then, suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition.展开更多
Fast and accurate prediction of sound radiation of Contra-Rotating Open Rotors(CRORs)is an essential element of design methods of low-noise open rotor propulsion systems.In the present work,a previous frequency-domain...Fast and accurate prediction of sound radiation of Contra-Rotating Open Rotors(CRORs)is an essential element of design methods of low-noise open rotor propulsion systems.In the present work,a previous frequency-domain model is extended to predict CROR noise.It builds explicitly the relationship between harmonic loadings and corresponding tonal noise,by which the influential parameters to noise generation can be clearly understood.The real distribu-tions of steady and unsteady blade loadings are calculated by the Nonlinear Harmonic(NLH)method.In the present hybrid approach,both the CFD and acoustic modules are solved in the fre-quency domain.To assess the accuracy of the developed method,the loading noise of a CROR is calculated and compared against results by using the time-domain FW-H module of NUMECA.The predicted sound directivities by the two methods are in good agreements.The present acoustic model in the frequency domain is proven to be accurate and have high efficiency in far-field noise prediction and data processing.Furthermore,the characteristics of the CROR interaction tonal noise are analyzed and discussed.展开更多
In order to better understand the stall process of a contra-rotating compressor,the detailed characteristic and multi-channel unsteady pressure signals have been achieved by a special layout of high-frequency response...In order to better understand the stall process of a contra-rotating compressor,the detailed characteristic and multi-channel unsteady pressure signals have been achieved by a special layout of high-frequency response pressure sensors.The array consists of thirty-one high-frequency response dynamic sensors coupled with two optical fiber sensors that were installed on the compressor casing in the direction of circumferential and chordwise of the upstream and downstream of the contra-rotating rotors.A significant hysteresis loop during the stall-recovery process of the contra-rotating compressor was captured successfully.The time series of unsteady signals when the compressor was working on the point of stall occurrence,the period of fully stall,and recovery stall were studied and discussed.Results show a large scale,and low-speed disturbance occurred abruptly at the leading-edge plane of the rear rotor and expands until it passes through both rotors.The single stall cell occupied a circumferential range of 135° and moved in the direction of the rear rotor with an 8.3%shaft speed.As the mass flow rate dropped,the stall cell speed decreases.During the stall recovery process,the rotational speed of disturbance suddenly increased from 7.5%to 18%and even increased to 47%just before the moment when flow recovered axisymmetric.Compared with the rear rotor,the front one dropped out unstable conditions earlier.展开更多
Contra-rotating axial flow fan is a kind of the vital equipment in coal mines. Their work conditions directly affect the safety of staff and production. In the paper, the performance of the contra-rotating axial flow ...Contra-rotating axial flow fan is a kind of the vital equipment in coal mines. Their work conditions directly affect the safety of staff and production. In the paper, the performance of the contra-rotating axial flow fan is experi- mentally investigated. The study is focused on the fan performance, the shaft power and the match between the motor and fan efficiency at different blade angles. The results show that the blade angle 43°/26° has the best aerodynamic perfor- mance. The first engine has a greater impact on the fan than the second one. The blade angle with the best aerodynamic performance does not necessarily correspond to the one with the best match between the motor and fan efficiency. The blade angle 43°/24° is the best choice for the operation of the fan in the present study.展开更多
It is thought that small hydropower generation is alternative energy, and the energy potential of small hydropower is large. The efficiency of small hydro turbines is lower than that of large one, and these small hydr...It is thought that small hydropower generation is alternative energy, and the energy potential of small hydropower is large. The efficiency of small hydro turbines is lower than that of large one, and these small hydro turbine’s common problems are out of operation by foreign materials. Then, there are demands for small hydro turbines to keep high per- formance and wide flow passage. Therefore, we adopted contra-rotating rotors which can be expected to achieve high performance and low-solidity rotors with wide flow passage in order to accomplish high performance and stable opera- tion. Final goal on this study is development of an electric appliance type small hydro turbine which has high portability and makes an effective use of the unused small hydro power energy source. In the present paper, the performance and the internal flow conditions in detail of contra-rotating small-sized axial flow hydro turbine are shown as a first step of the research with the numerical flow analysis. Then, a capability adopting contra-rotating rotors to an electric appliance type small hydro turbine was discussed. Furthermore, the high performance design for it was considered by the numeri- cal analysis results.展开更多
This paper focuses on the response of a high aspect ratio,low speed contra-rotating fan with complex inflow distortion.The total pressure at the inlet is artificially distorted by means of two different sets of screen...This paper focuses on the response of a high aspect ratio,low speed contra-rotating fan with complex inflow distortion.The total pressure at the inlet is artificially distorted by means of two different sets of screens with different porosities to generate a hub-strong complex distortion and a tip-strong complex distortion.Detailed flow analyses were conducted for the design speed of rotor-1 in combination with off design speeds of rotor-2 both for the design and the peak pressure mass flow rates.In order to understand the extent of inlet distortion,the distortion sector was rotated circumferentially at intervals of 151 to cover the entire annulus.Detailed measurements of total pressure,static pressure,velocity components and flow angles were carried out at the inlet of the first rotor,between the two rotors and at the exit of the second rotor using three seven hole probes.The study reveals a few interesting aspects on the effect of complex inflow distortion on the flow behavior of a contra-rotating stage.The presence of a low porosity screen reduces the magnitude of axial velocity and generates higher spread of distortion near the localized region of placement of the screen.The hub-strong complex distortion has a greater effect of presence of this low porosity screen in both circumferential and radial directions.This leads to higher stagnation pressure variation at the inlet.On the other hand,for the tip-strong complex distortion case,the extent of distortion is observed to be higher in the circumferential direction towards the casing rather than radial.The localized improvement in the flow(in tip-strong inflow distortion)near the tip region improves the performance both in terms of pressure rise and efficiency of stage compared to hub–strong complex distortion.展开更多
Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contr...Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor.The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine.The contra-rotating turbine is designed by retaining the existing flow path and HP turbine,and redesigning the LP turbine for fixed radial distributions of inlet total temperature,pressure and swirl.A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds.Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis.The LP stage of contra-rotating turbine exhibits a performance improvement by 2%points at design point,as per flow predictions.The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine,which contributed to the performance improvement.A significant reduction of 23%in blade weight and 45% in LP stator vane count is obtained.展开更多
As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the...As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head - flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carded out to understand the complicated internal flow structures in the rotors.展开更多
文摘An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower rotational speed. （2） A stable head-characteristic curve for flow rate with negative slope appears. （3） As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.
基金supported by the National Natural Science Foundation of China(Grant No.51079157)
文摘A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.
基金supports by the project research aid from The University of Tokushima,Japan Science and Technology Agency and Komiya research aid
文摘Small-sized axial fans are used as air coolers for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although it causes the deterioration of the efficiency and the increase of noise.Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of the performance.In the present paper,the performance and the internal flow condition of the small-sized axial fan are shown as a first step of the research for the contra-rotating small-sized axial fan and the important points to apply contra-rotating rotors to the small-sized axial fan are discussed.Furthermore,the numerical flow analysis is conducted to investigate the performance of the contra-rotating small-sized axial fan and internal flow conditions and pressure distributions are clarified and the effect of contra-rotating rotors is considered.
文摘Influences of tip clearance on the tip flow and associated loss mechanism in a contra-rotating axial flow fan hasbeen studied in the paper, based on three dimensional numerical results. The results with different tip clearanceare compared in terms of stage efficiency, relative total pressure loss coefficient, flow angle. It is found that theefficiency of the contra-rotating fan changes almost linearly with increment of the tip clearance, however, efficiencyof the rear rotor is observed to decrease more dramatically than that of the forward rotor given same tipclearance variation. The analysis on the flow structure indicates that the tip region flow field is qualitatively similarin both rotors. However, with the same clearance value, the leakage flow in the rear rotor is effected by a tipleakage vortex of greater intensity caused by relative loading levels and the inter rotor interaction.
基金supported by the National Natural Science Foundation of China(Grant No.52276039)。
文摘Stall in compressors can cause performance degradation and even lead to disasters.These unacceptable consequences can be avoided by timely monitoring stall inception and taking effective measures.This paper focused on the rotating stall warning in a low-speed axial contra-rotating compressor.Firstly,the stall disturbance characteristics under different speed configurations were analyzed.The results showed that as the speed ratio(RR)increased,the stall disturbance propagation speed based on the rear rotor speed gradually decreased.Subsequently,the standard deviation(SD)method,the cross-correlation(CC)method,and the discrete wavelet transform(DWT)method were employed to obtain the stall initiation moments of three different speed configurations.It was found that the SD and CC methods did not achieve significant stall warning results in all three speed configurations.Besides,the stall initiation moment obtained by the DWT method at RR=1.125 was one period after the stall had fully developed,which was unacceptable.Therefore,a stall warning method was developed in the present work based on the long short-term memory(LSTM)regression model.By applying the LSTM model,the predicted stall initiation moments of three speed configurations were at the 557th,518th,and 333rd revolution,which were44,2,and 74 revolutions ahead of stall onset moments,respectively.Furthermore,in scenarios where a minor disturbance preceded the stall,the stall warning effect of the LSTM was greatly improved in comparison with the aforementioned three methods.In contrast,when the pressure fluctuation before the stall was relatively small,the differences between the stall initiation moments predicted by these four methods were not significant.
基金the financial support from the National Natural Science Foundation of China(Nos.52276045 and 52206062)the Fundamental Research Funds for the Central Universities,China(Nos.3122019171,3122021087 and 3122022QD06).
文摘The Contra-Rotating Open Rotor(CROR)design confronts significant noise challenges despite being one of the possible options for future green aeroengines.To efficiently estimate the noise emitted from a CROR,a three-dimensional unsteady prediction model based on the meshless method is presented.The unsteady wake flow and the aerodynamic load fluctuations on the blade are solved through the viscous vortex particle method,the blade element momentum theory and vortex lattice method.Then,the acoustic field is obtained through the Farassat’s formulation 1A.Validation of this method is conducted on a CROR,and a mesh-based method,e.g.,Nonlinear Harmonic(NLH)method,is also employed for comparison.It is found that the presented method is three times faster than NLH method while maintaining a comparable precision.A thorough parametric analysis is also carried out to illustrate the effects of rotational speed,rotor-rotor spacing and rear rotor diameter on the noise level.The rotor speed is found to be the most influencing factor,and by optimizing the speed difference between the front and rear rotors,a notable noise reduction can be expected.The current findings not only contribute to a deeper comprehension of the CROR’s aeroacoustic properties but also offer an effective tool for engineering applications.
基金supported by the National Natural Science Foundation of China (No. 51376150)
文摘The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor(CRAC). Transient numerical simulation was carried out in a single passage of the CRAC. The original transient fluctuation and oscillation of the tip leakage vortex structure with varying flow capacity of the CRAC were revealed using circle-like pattern figure and phase-locked root mean square(PLRMS). Additionally, the tip leakage flow in terms of vortex structure evolution was visualized for the sake of revealing the flow mechanism during pre-stall process. Results show that the unsteady fluctuation first appears at φ=0.3622, and the fluctuation frequency is 2.86 BPF. Unsteady disturbance source is mainly located at the tip side of the downstream rotor leading edge. From the choking point to the near stall condition, tip leakage vortex is always found in the tip leading edge of the upstream rotor. In addition, the tip leakage vortex of upstream rotor remains in the same place over time, i.e., no fluctuation, even when the downstream rotor entered into stall state. Such a phenomenon indicates that the stall point of the contra-rotating compressor is determined by the downstream rotor. Moreover, the maximum fluctuation position is mainly concentrated on the interface between the mainstream and the tip leakage vortex of the downstream rotor. By throttling the compressor, the angle between the main leakage vortex and the circumferential direction decreases gradually. When the main leakage vortex touches and continuously impacts on the leading edge of the adjacent blade, the unsteady disturbance, which is different from that of BPF, appears firstly.
文摘Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the performance and stable operation. The wake and potential interference occur between the front and rear rotors and leakage flow from the front rotor tip influences on the flow condition of the rear rotor near the shroud when the blade row distance is small. Therefore, it is important to clarify the flow condition between front and rear rotors. The fan static pressure curves were obtained by the experimental apparatus and the numerical analysis was also conducted to investigate the internal flow between front and rear rotors. The leakage flow from the front rotor tip reaches the leading edge of the rear rotor when the blade row distance is small as L = 10 mm and the pressure fluctuations at the leading edge of the rear rotor tip becomes larger than those at other radial positions. In the present paper, the vorticity contour between front and rear rotors is shown and pressure fluctuations related to the leakage flow from the front rotor is investigated using the numerical analysis result. Then, suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition.
基金co-supported by the National Natural Science Foundation of China(Nos.52022009,51790514)the National Science and Technology Major Project,China(No.2017-II-003-0015)the Key Laboratory Foundation,China(No.2021-JCJQ-LB-062-0102).
文摘Fast and accurate prediction of sound radiation of Contra-Rotating Open Rotors(CRORs)is an essential element of design methods of low-noise open rotor propulsion systems.In the present work,a previous frequency-domain model is extended to predict CROR noise.It builds explicitly the relationship between harmonic loadings and corresponding tonal noise,by which the influential parameters to noise generation can be clearly understood.The real distribu-tions of steady and unsteady blade loadings are calculated by the Nonlinear Harmonic(NLH)method.In the present hybrid approach,both the CFD and acoustic modules are solved in the fre-quency domain.To assess the accuracy of the developed method,the loading noise of a CROR is calculated and compared against results by using the time-domain FW-H module of NUMECA.The predicted sound directivities by the two methods are in good agreements.The present acoustic model in the frequency domain is proven to be accurate and have high efficiency in far-field noise prediction and data processing.Furthermore,the characteristics of the CROR interaction tonal noise are analyzed and discussed.
基金This work has been supported by the National Natural Science Foundation of China(No.51376150,No.51906205)National Science and Technology Major Project(2017-11-0009-0023).
文摘In order to better understand the stall process of a contra-rotating compressor,the detailed characteristic and multi-channel unsteady pressure signals have been achieved by a special layout of high-frequency response pressure sensors.The array consists of thirty-one high-frequency response dynamic sensors coupled with two optical fiber sensors that were installed on the compressor casing in the direction of circumferential and chordwise of the upstream and downstream of the contra-rotating rotors.A significant hysteresis loop during the stall-recovery process of the contra-rotating compressor was captured successfully.The time series of unsteady signals when the compressor was working on the point of stall occurrence,the period of fully stall,and recovery stall were studied and discussed.Results show a large scale,and low-speed disturbance occurred abruptly at the leading-edge plane of the rear rotor and expands until it passes through both rotors.The single stall cell occupied a circumferential range of 135° and moved in the direction of the rear rotor with an 8.3%shaft speed.As the mass flow rate dropped,the stall cell speed decreases.During the stall recovery process,the rotational speed of disturbance suddenly increased from 7.5%to 18%and even increased to 47%just before the moment when flow recovered axisymmetric.Compared with the rear rotor,the front one dropped out unstable conditions earlier.
文摘Contra-rotating axial flow fan is a kind of the vital equipment in coal mines. Their work conditions directly affect the safety of staff and production. In the paper, the performance of the contra-rotating axial flow fan is experi- mentally investigated. The study is focused on the fan performance, the shaft power and the match between the motor and fan efficiency at different blade angles. The results show that the blade angle 43°/26° has the best aerodynamic perfor- mance. The first engine has a greater impact on the fan than the second one. The blade angle with the best aerodynamic performance does not necessarily correspond to the one with the best match between the motor and fan efficiency. The blade angle 43°/24° is the best choice for the operation of the fan in the present study.
文摘It is thought that small hydropower generation is alternative energy, and the energy potential of small hydropower is large. The efficiency of small hydro turbines is lower than that of large one, and these small hydro turbine’s common problems are out of operation by foreign materials. Then, there are demands for small hydro turbines to keep high per- formance and wide flow passage. Therefore, we adopted contra-rotating rotors which can be expected to achieve high performance and low-solidity rotors with wide flow passage in order to accomplish high performance and stable opera- tion. Final goal on this study is development of an electric appliance type small hydro turbine which has high portability and makes an effective use of the unused small hydro power energy source. In the present paper, the performance and the internal flow conditions in detail of contra-rotating small-sized axial flow hydro turbine are shown as a first step of the research with the numerical flow analysis. Then, a capability adopting contra-rotating rotors to an electric appliance type small hydro turbine was discussed. Furthermore, the high performance design for it was considered by the numeri- cal analysis results.
基金This work was partially funded by the Aeronautics Research and Development Board of India and is gratefully acknowledged.
文摘This paper focuses on the response of a high aspect ratio,low speed contra-rotating fan with complex inflow distortion.The total pressure at the inlet is artificially distorted by means of two different sets of screens with different porosities to generate a hub-strong complex distortion and a tip-strong complex distortion.Detailed flow analyses were conducted for the design speed of rotor-1 in combination with off design speeds of rotor-2 both for the design and the peak pressure mass flow rates.In order to understand the extent of inlet distortion,the distortion sector was rotated circumferentially at intervals of 151 to cover the entire annulus.Detailed measurements of total pressure,static pressure,velocity components and flow angles were carried out at the inlet of the first rotor,between the two rotors and at the exit of the second rotor using three seven hole probes.The study reveals a few interesting aspects on the effect of complex inflow distortion on the flow behavior of a contra-rotating stage.The presence of a low porosity screen reduces the magnitude of axial velocity and generates higher spread of distortion near the localized region of placement of the screen.The hub-strong complex distortion has a greater effect of presence of this low porosity screen in both circumferential and radial directions.This leads to higher stagnation pressure variation at the inlet.On the other hand,for the tip-strong complex distortion case,the extent of distortion is observed to be higher in the circumferential direction towards the casing rather than radial.The localized improvement in the flow(in tip-strong inflow distortion)near the tip region improves the performance both in terms of pressure rise and efficiency of stage compared to hub–strong complex distortion.
基金Authors acknowledge GATET-GTRE,DRDO,India forthe financial assistance in this projectAuthors would like tothank Director and Head-Propulsion Division of CSIR-NAL for their support in carrying out this workAuthorsalso thank‘Turbine Group-GTRE’and Versatile Turbine Test Rig team members.
文摘Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor.The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine.The contra-rotating turbine is designed by retaining the existing flow path and HP turbine,and redesigning the LP turbine for fixed radial distributions of inlet total temperature,pressure and swirl.A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds.Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis.The LP stage of contra-rotating turbine exhibits a performance improvement by 2%points at design point,as per flow predictions.The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine,which contributed to the performance improvement.A significant reduction of 23%in blade weight and 45% in LP stator vane count is obtained.
文摘As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head - flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carded out to understand the complicated internal flow structures in the rotors.
