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
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
High pressure and large flow rate small-sized cooling fans are used for servers in data centers and there is a strong demand to increase its performance because of increase of quantity of heat from servers. Contra-rot...High pressure and large flow rate small-sized cooling fans are used for servers in data centers and there is a strong demand to increase its performance because of increase of quantity of heat from servers. Contra-rotating rotors have been adopted for some of high pressure and large flow rate cooling fans to meet the demand. The performance curve of the contra-rotating small-sized cooling fan with 40 mm square casing was investigated by an experimental apparatus and its internal flow condition was clarified by the numerical analysis. The fan static pressure of the front rotor was extremely low and it increased significantly at the rear rotor. The uniform flow was achieved at the inlet of the rear rotor because of the special shape of the casing between the front and rear rotors. On the other hand, the tip leakage flow was large enough to influence on the main flow of the test cooling fan by the design specification of high pressure with compact rotor diameter.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
Different from the previous qualitative analysis of linear systems in time and frequency domains, the method for describing nonlinear systems quantitatively is proposed based on correlated dimensions. Nonlinear dynami...Different from the previous qualitative analysis of linear systems in time and frequency domains, the method for describing nonlinear systems quantitatively is proposed based on correlated dimensions. Nonlinear dynamics theory is used to analyze the pressure data of a contrarotating axial flow fan. The delay time is 18 and the embedded dimension varies from 1 to 25 through phase-space reconstruction. In addition, the correlated dimensions are calculated before and after stalling. The results show that the correlated dimensions drop from 1. 428 before stalling to 1. 198 after stalling, so they are sensitive to the stalling signal of the fan and can be used as a characteristic quantity for the judging of the fan stalling.展开更多
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.
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High pressure and large flow rate small-sized cooling fans are used for servers in data centers and there is a strong demand to increase its performance because of increase of quantity of heat from servers. Contra-rotating rotors have been adopted for some of high pressure and large flow rate cooling fans to meet the demand. The performance curve of the contra-rotating small-sized cooling fan with 40 mm square casing was investigated by an experimental apparatus and its internal flow condition was clarified by the numerical analysis. The fan static pressure of the front rotor was extremely low and it increased significantly at the rear rotor. The uniform flow was achieved at the inlet of the rear rotor because of the special shape of the casing between the front and rear rotors. On the other hand, the tip leakage flow was large enough to influence on the main flow of the test cooling fan by the design specification of high pressure with compact rotor diameter.
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Supported by the Natural Science Foundation of Jiangsu Province(BK2005018)the Graduate Research and Innovation Plan of Jiangsu Province(CX07B-061Z)~~
文摘Different from the previous qualitative analysis of linear systems in time and frequency domains, the method for describing nonlinear systems quantitatively is proposed based on correlated dimensions. Nonlinear dynamics theory is used to analyze the pressure data of a contrarotating axial flow fan. The delay time is 18 and the embedded dimension varies from 1 to 25 through phase-space reconstruction. In addition, the correlated dimensions are calculated before and after stalling. The results show that the correlated dimensions drop from 1. 428 before stalling to 1. 198 after stalling, so they are sensitive to the stalling signal of the fan and can be used as a characteristic quantity for the judging of the fan stalling.
