Passive Ventilation of Shocks in Steady and Unsteady Internal Flows

Abstract

Unsteady aerodynamics plays an important role in turbomachinery aeroelastic and aeroacoustic applications. Unsteady fluctuations in the flow arising from blade vibrations or aerodynamic disturbances at the in- or outflow boundaries may cause structural failure of the blading and, possibly, extensive damage of the engine. In the transonic flow regime waves propagate in the flow field and displace shock waves, therefore the time dependent shock movement and the unsteady lift and moment have become an important concern.

In steady external transonic flow the passive control of the shock-boundary layer interaction has been extensively investigated to weaken the shock strength and to reduce losses and separation phenomena, e.g. in flows over airplane wing sections. Application to steady internal flows is more difficult. Therefore, in a first step we apply the method of passive control to steady supersonic compressor flow. Alternatively we show the effectiveness of ventilation by very thin slits instead of a cavity covered by a porous blade.

Finally we apply the method of ventilation to unsteady internal transonic flow. Experiments and numerical results of the Euler equations for inviscid flow modelling agree in tendency and show a reduction of the amplitude of the shock oscillation up to 50%.