With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft＇s approach to landing phase. Noise control efforts have therefore been extensively ...With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft＇s approach to landing phase. Noise control efforts have therefore been extensively focused on the airframe noise problems in order to further reduce aircraft overall noise. In this review, various control methods explored in the last decades for noise reduction on airframe components including high-lift devices and landing gears are summarized. We introduce recent major achievements in airframe noise reduction with passive control methods such as fairings, deceleration plates, splitter plates, acoustic liners, slat cove cover and side-edge replacements, and then discuss the potential and control mechanism of some promising active flow control strategies for airframe noise reduction, such as plasma technique and air blowing/suction devices. Based on the knowledge gained throughout the extensively noise control testing, a few design concepts on the landing gear, high-lift devices and whole aircraft are provided for advanced aircraft low-noise design. Finally, discussions and suggestions are given for future research on airframe noise reduction.展开更多
A slat without a cove is built on the basis of a bionic airfoil （i.e. stowed multi-element airfoil）, which is extracted from a long-eared owl wing. The three-dimensional models with a deployed slat and a stowed slat...A slat without a cove is built on the basis of a bionic airfoil （i.e. stowed multi-element airfoil）, which is extracted from a long-eared owl wing. The three-dimensional models with a deployed slat and a stowed slat are measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect： compared with the stowed slat, the deployed slat works more like a spoiler at low angles of attack, but like a conventional slat or slot at high angles of attack. In addition, it can also increase stall angle and maximum lift coefficient, and postpone the decrease in the gradient of the lift coefficient. At the same time, the flow field visualized around both three-dimensional models suggests the leading-edge separation associated with the decrease in the gradient of the lift coefficient, Furthermore, the related two-dimensional simulation well agrees with the analysis of the lift coefficient, as the complement to the experiment. The bionic slat may be used as reference in the design of leading-edge slats without a cove.展开更多
The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the ...The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.展开更多
The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweepin...The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.展开更多
In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54&#...In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.展开更多
To find a better way to estimate the lift force induced by an interceptor on a high-speed mono-hull ship,a series of high-speed mono-hull ship models are designed and investigated under different conditions.Different ...To find a better way to estimate the lift force induced by an interceptor on a high-speed mono-hull ship,a series of high-speed mono-hull ship models are designed and investigated under different conditions.Different lift forces are obtained by numerical calculations and validated by a model test in a towing tank.The factors that influence the force are the interceptor height,velocity,draft,and deadrise angle.The relationship between each factor and the induced lift force is investigated and obtained.We found that the induced lift mainly depends on the interceptor height and advancing velocity,and is proportional to the square of the interceptor height and velocity.The results also showed that the effects of the draft and deadrise angle are relatively less important,and the relationship between the induced lift and these two factors is generally linear.Based on the results,a formula including the combined effect of all factors used to estimate the lift force induced by the interceptor is developed based on systematic analysis.The proposed formula could be used to estimate the lift force induced by interceptors,especially under high-speed condition.展开更多
Adaptive,morphing flaps are taking ever-increasing attention in civil aviation thanks to the expected benefits this technology can bring at the aircraft level in terms of high-lift performance improvement and related ...Adaptive,morphing flaps are taking ever-increasing attention in civil aviation thanks to the expected benefits this technology can bring at the aircraft level in terms of high-lift performance improvement and related fuel burnt reduction per flight.Relying upon morphing capabilities,it is possible to fix a unique setting for the flap and adapt the flap shape to match the aerodynamic requirements for take-off or landing.The proper morphed shapes can assure better high-lift performances than those achievable by referring to a conventional flap.Moreover,standing the unique flap setting for take-off and landing,a dramatic simplification of the flap deployment systems may be achieved.As a consequence of this simplification,the deployment system can be fully hosted in the wing,thus avoiding under-wing nacelles with significantly better aerodynamics and fuel consumption.The first step for a rational design of an adaptive flap consists in defining the target morphed shapes and the unique optimal flap setting in the take-off and landing phases.In this work,aerodynamic optimization analyses are carried out to determine the best flap setting and related morphed shapes in compliance with the take-off and landing requirements of a reference civil transport aircraft.Four different initial conditions are adopted to avoid the optimization falling into local optima,thus obtaining four groups of optimal candidate configurations.After comparing each candidate’s performance through 2D and 3D simulations,the optimal configuration has been selected.2D simulations show that the optimal configuration is characterized by a maximum lift increase of 31.92%in take-off and 9.04%in landing.According to 3D simulations,the rise in maximum lift equals 22.26%in take-off and 3.50%in landing.Numerical results are finally verified through wind tunnel tests,and the aerodynamic mechanism behind the obtained improvements is explained by carefully analyzing the flow field around the flap.展开更多
文摘With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft＇s approach to landing phase. Noise control efforts have therefore been extensively focused on the airframe noise problems in order to further reduce aircraft overall noise. In this review, various control methods explored in the last decades for noise reduction on airframe components including high-lift devices and landing gears are summarized. We introduce recent major achievements in airframe noise reduction with passive control methods such as fairings, deceleration plates, splitter plates, acoustic liners, slat cove cover and side-edge replacements, and then discuss the potential and control mechanism of some promising active flow control strategies for airframe noise reduction, such as plasma technique and air blowing/suction devices. Based on the knowledge gained throughout the extensively noise control testing, a few design concepts on the landing gear, high-lift devices and whole aircraft are provided for advanced aircraft low-noise design. Finally, discussions and suggestions are given for future research on airframe noise reduction.
文摘A slat without a cove is built on the basis of a bionic airfoil （i.e. stowed multi-element airfoil）, which is extracted from a long-eared owl wing. The three-dimensional models with a deployed slat and a stowed slat are measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect： compared with the stowed slat, the deployed slat works more like a spoiler at low angles of attack, but like a conventional slat or slot at high angles of attack. In addition, it can also increase stall angle and maximum lift coefficient, and postpone the decrease in the gradient of the lift coefficient. At the same time, the flow field visualized around both three-dimensional models suggests the leading-edge separation associated with the decrease in the gradient of the lift coefficient, Furthermore, the related two-dimensional simulation well agrees with the analysis of the lift coefficient, as the complement to the experiment. The bionic slat may be used as reference in the design of leading-edge slats without a cove.
基金The project supported by the National Natural Science Foundation of China (19725210)
文摘The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.
基金The project supported by the National Natural Science Foundation of China(10232010)
文摘The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.
基金Foundation item： Supported by Supported by the National Natural Science Foundation of China （Grant No. 51009070）.
文摘In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.
基金financially supported by the National Key Research and Development Program of China(Grant No.2021YFC2800700)the National Natural Science Foundation of China(Grant Nos.52171330,52101379,52101380,51679053)+2 种基金the Project of Research and Development Plan in Key Areas of Guangdong Province(Grant No.2020B1111010002)the Foundation of Key Laboratory of Marine Environmental Survey Technology and Application,Ministry of Natural Resources(Grant No.MESTA-2021-B010)the Natural Science Foundation of Guangdong Province,China(Grant No.2021A1515012134)。
文摘To find a better way to estimate the lift force induced by an interceptor on a high-speed mono-hull ship,a series of high-speed mono-hull ship models are designed and investigated under different conditions.Different lift forces are obtained by numerical calculations and validated by a model test in a towing tank.The factors that influence the force are the interceptor height,velocity,draft,and deadrise angle.The relationship between each factor and the induced lift force is investigated and obtained.We found that the induced lift mainly depends on the interceptor height and advancing velocity,and is proportional to the square of the interceptor height and velocity.The results also showed that the effects of the draft and deadrise angle are relatively less important,and the relationship between the induced lift and these two factors is generally linear.Based on the results,a formula including the combined effect of all factors used to estimate the lift force induced by the interceptor is developed based on systematic analysis.The proposed formula could be used to estimate the lift force induced by interceptors,especially under high-speed condition.
基金co-supported by the National Natural Science Foundation of China (Nos. 12172275, 12090030)the “111” Program, China (No. B18040)
文摘Adaptive,morphing flaps are taking ever-increasing attention in civil aviation thanks to the expected benefits this technology can bring at the aircraft level in terms of high-lift performance improvement and related fuel burnt reduction per flight.Relying upon morphing capabilities,it is possible to fix a unique setting for the flap and adapt the flap shape to match the aerodynamic requirements for take-off or landing.The proper morphed shapes can assure better high-lift performances than those achievable by referring to a conventional flap.Moreover,standing the unique flap setting for take-off and landing,a dramatic simplification of the flap deployment systems may be achieved.As a consequence of this simplification,the deployment system can be fully hosted in the wing,thus avoiding under-wing nacelles with significantly better aerodynamics and fuel consumption.The first step for a rational design of an adaptive flap consists in defining the target morphed shapes and the unique optimal flap setting in the take-off and landing phases.In this work,aerodynamic optimization analyses are carried out to determine the best flap setting and related morphed shapes in compliance with the take-off and landing requirements of a reference civil transport aircraft.Four different initial conditions are adopted to avoid the optimization falling into local optima,thus obtaining four groups of optimal candidate configurations.After comparing each candidate’s performance through 2D and 3D simulations,the optimal configuration has been selected.2D simulations show that the optimal configuration is characterized by a maximum lift increase of 31.92%in take-off and 9.04%in landing.According to 3D simulations,the rise in maximum lift equals 22.26%in take-off and 3.50%in landing.Numerical results are finally verified through wind tunnel tests,and the aerodynamic mechanism behind the obtained improvements is explained by carefully analyzing the flow field around the flap.
