低Re数下变弯度机翼的非定常气动特性实验研究

利用变弯度机翼模型及相关的风洞实验平台,开展了以弯度变化速率影响为重点的机翼非定常特性研究。实验结果显示,在低Re数(~105)下,机翼弯度非定常变化得到的升阻力系数曲线与准定常条件下的结果存在显著差异。具体表现为:准定常状态下,曲线表现出明显的可逆性;而弯度非定常变化时,曲线在弯度递增区和递减区之间存在明显的迟滞效应,而且随着变形速率的增加,这种迟滞也越明显。流场显示结果表明,这种小St数下出现的流动迟滞是由于弯度变形导致的流动分离的分离点相对机翼运动迟滞所造成的。这说明弯度变化时,分离流场结构的响应时间尺度与弯度变化周期相当,也揭示了该条件下机翼弯度变化对流动的抑制作用主要是通过改变分离区的大小来实现的。

Experimental Study of Unsteady Aerodynamic Characteristics of Variable Camber Wing at Low Reynolds Number

An experimental investigation on unsteady aerodynamic characteristics of variable camber wing was carried out by a low-speed wind tunnel, which focuses on the effect of camber change rate. Experimental results show that at low Re number (~10⁵), the lift and drag coefficient curves exhibit significant difference comparing with that under quasi steady condition due to wing camber unsteady change. For quasi steady flow, curves present significant reversibility; but when camber changes unsteadly, curves present obvious hysteresis between camber increment and camber decrement zones, further more, when camber variation rate goes faster, hysteresis becomes more obvious. Flow visualization results show that for such small St number flow, the unexpected hysteresis is mainly due to the movement retardation of flow separation point resulted from camber change relative to wing movement. This indicates that when camber changes, the response time scale of separation flow structure considerably matches with camber change cycle. This also reveals that under such condition, flow inhibition from wing camber change is achieved mainly by changing separation zone size.