民机低速风洞试验通气发房设计

通气发房是民机风洞试验中模拟发动机效应的一种有效手段。通过调整通气发房出口面积,可以对通过发房的流量进行控制,实现所需模拟的流量系数,保证进气流场的几何相似性。失速特性是民机的一个重要的性能指标,大量的低速风洞试验工作都着眼于着落构型下失速特性的研究;而在失速特性的适航审定试飞时的发动机将处于慢车功率状态,因此以模拟慢车流量系数作为低速风洞试验通气发房的设计目标,有助于在风洞试验中对失速特性进行预测。慢车功率时,由于发动机风扇压比很小,如保留外涵喷口形状,通气发房还能近似模拟风扇的喷流效应。发动机在慢车功率下的流量系数在0.5附近,为实现这一流量系数,在设计通气发房时,需调整内涵出口面积,使发房的总出口面积接近唇口面积的一半。CFD计算证明这种设计方法得到的通气发房基本能够实现预期的流量系数。

Design of Through-flow Nacelle for Low-speed Wind Tunnel Testing of Civil Aircraft

Through-flow nacelle (TFN) is an effective method of simulating engine effect in wind tunnel Testing.By adjusting the nozzle exit areas of a TFN, the flow passing the TFN could be controlled and the flow ratio (MFR)could be achieved to make sure the similarity around the inlet flow field.As stall characteristics is one of the important factor in defining civil aircraft performance, a great portion of the low speed wind tunnel tests is devoted to thestudy of the stall characteristics of aircraft in landing configuration; and due to the fact that engines tend to be set atan idle condition during airworthy flight tests for stall speed determination, designing a TFN with a MFR corresponding to an idle power setting is desirable for the prediction of stall characteristics in wind tunnel testing. When running at idle conditions, an engine will have a very low fan pressure ratio, which means if the fan nozzle geometryis maintained, TFN can also be used to simulate approximately the jet effects of idle power setting.A engine running idly will have a MFR of around 0.5, which can be achieved on a TFN which is designed such that the totalnozzle area is half of the highlight area. CFD calculation has proved the effectiveness of this methodology.