EXPERIMENTAL AND NUMERICAL STUDY OF THE TIME-DEPENDENT PRESSURE RESPONSE OF A SHOCK-WAVE OSCILLATING IN A NOZZLE

In vestigations of flutter in transonic turbine cascades have shown th at the movement of unsteady normal shocks has an important effect on t he excitation of blades. In order to predict this phenomenon correctly , detailed studies concerning the response of unsteady blade pressures versus different parameters of art oscillating shock wave should be p erformed, if possible isolated from other flow effects in cascades. In the present investigation the correlation between an oscillating norm al shock wave and the response of wall-mounted time-dependent pressure transducers was studied experimentally in a nozzle with fluctuating b ack pressure. Excitation frequencies between 0 Hz and 180 Hz were inve stigated. For the measurements, various measuring techniques were empl oyed. The determination of the unsteady shock position was made by a l ine scan camera using the Schlieren flow visualization technique. This allowed the simultaneous use of unsteady pressure transducers to eval uate the behavior of the pressure under the moving shock. A numerical code, based on the fully unsteady Euler equations in conservative form , was developed to simulate the behavior of the shock and the pressure s. The main results of this work were: (1) The boundary layer over an unsteady pressure transducer has a quasi-steady behavior with respect to the phase lag. The pressure amplitude depends on the frequency of t he backpressure. (2) For the geometry investigated the shock amplitude decreased with increasing excitation frequency. (3) The pressure tran sducer sensed the arriving shock before the shock had reached the posi tion of the pressure transducer. (4) The computed unsteady phenomena a gree well with the results of the measurements.