逆压力梯度下的自由流湍流度对湍流边界层特性的影响

EFFECT OF FREE-STREAM TURBULENCE ON TURBULENT BOUNDARY LAYER BEHAVIOUR UNDER ADVERSE PRESSURE GRADIENT

本文对有逆压力梯度下的自由流湍流度对湍流边界层特性的影响做了较为仔细的测量,做了边界层内平均速度分布、壁面摩擦系数、压力梯度、边界层内三个方向脉动速度以及脉动总压的测量。试验结果指出:自由流湍流度的增加可大大削弱逆压力梯度对湍流边界层的不利影响,可使边界层速度分布饱满,尾迹强度减弱,从而延迟边界层分离。试验还首次得出自由流湍流度的增加可使边界层内的速度脉动和压力脉动分布均匀以及流动趋于稳定,因而可同时改善扩压器出口的静、动态特性。

Careful measurements of the effect of free-stream turbu-lence on turbulent boundary layer behaviour under adverse pressuregradient were made.Measurements of mean velocity distribution inboundary layer,of skin friction coefficient,of pressure gradient,offluctuating velocities and total pressures in three directions insideboundary layer were made.Experimental results show that the increase of free-stream turbu-lence may greatly reduce the unfavovrable effect of adverse pressuregradient on turbulent boundary layer,make the velocity profile full,weaken the wake intensity so that delay the separation of boundaylayer.Experiments show for the first time that the increase of free-stream turbulence may make the distributions of velocity and pressurefluctuations uniform,and make the flow stable.Therefore at the sametime the static and dynamic characteristics at the outlet of diffusermay be improved.