In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal ...In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal of this study is to gain a better understanding and to find the possible ways for enhancing the aerodynamic efficients. The experimental investigations are carried out in two low-speed wind tunnels. The test models are two dimensional airfoils with different section geometries. Four means of excitations have been used in these experiments. (1) The pitch oscillation of the airfoil high-angle-of-attack situation. (2) The moving surface effects of the airfoil with a leading edge rotating cylinder. (3) Oscillating leading edge flaperon. (4) Small oscillating spoiler located near the leading edge of the airfoil. The lift, drag and pitch moment coefficients are measured in these experiments. But, we will put the emphasis only on the 'dynamic amplifying effects' on aerodynamic lift in this paper. Results obtained indicate that the beneficial aerodynamic effects of section lift increase can be obtained at the high angle of attack near stall regime, as long as the frequency and amplitute of the excitation are appropriately selected.展开更多
The unsteady bearing forces of a propeller can be significantly affected by external transverse excitations.This paper numerically studies the unsteady variation characteristics of the bearing forces of a three-blade ...The unsteady bearing forces of a propeller can be significantly affected by external transverse excitations.This paper numerically studies the unsteady variation characteristics of the bearing forces of a three-blade conventional propeller with external transverse excitations or without excitations.The dynamic mesh method combined with the RANS turbulence model is employed.The numerical simulation shows the frequency response in the frequency domain of KT,Kq under external transverse excitations.The frequency of the response is found always equal to twice of the excitation frequency.If the amplitude of the external transverse excitation keeps constant,the amplitude of the response increases with the in crease of the excitation frequency.If the excitation frequency keeps constant,the amplitude of the response increases with the increase of the excitation amplitude,in a power-law relationship.The pressure distribution can be significantly affected by the external transverse excitation,leading to a high irregularity of the flow field.展开更多
文摘In this paper, the techniques to manage and control the flow over airfoils by using the external unsteady excitations are investigated. The mechanisms of these excitation effects are also explored. The principal goal of this study is to gain a better understanding and to find the possible ways for enhancing the aerodynamic efficients. The experimental investigations are carried out in two low-speed wind tunnels. The test models are two dimensional airfoils with different section geometries. Four means of excitations have been used in these experiments. (1) The pitch oscillation of the airfoil high-angle-of-attack situation. (2) The moving surface effects of the airfoil with a leading edge rotating cylinder. (3) Oscillating leading edge flaperon. (4) Small oscillating spoiler located near the leading edge of the airfoil. The lift, drag and pitch moment coefficients are measured in these experiments. But, we will put the emphasis only on the 'dynamic amplifying effects' on aerodynamic lift in this paper. Results obtained indicate that the beneficial aerodynamic effects of section lift increase can be obtained at the high angle of attack near stall regime, as long as the frequency and amplitute of the excitation are appropriately selected.
基金the China Postdoctoral Science Foundation(Grant No.2017M621455).
文摘The unsteady bearing forces of a propeller can be significantly affected by external transverse excitations.This paper numerically studies the unsteady variation characteristics of the bearing forces of a three-blade conventional propeller with external transverse excitations or without excitations.The dynamic mesh method combined with the RANS turbulence model is employed.The numerical simulation shows the frequency response in the frequency domain of KT,Kq under external transverse excitations.The frequency of the response is found always equal to twice of the excitation frequency.If the amplitude of the external transverse excitation keeps constant,the amplitude of the response increases with the in crease of the excitation frequency.If the excitation frequency keeps constant,the amplitude of the response increases with the increase of the excitation amplitude,in a power-law relationship.The pressure distribution can be significantly affected by the external transverse excitation,leading to a high irregularity of the flow field.
