Oszillierender senkrechter Verdichtungsstoss in einer ebenen Düse

Abstract

This investigation centers on the effects of normal shocks in unsteady flow. Systematic measurements in a turbine model in an annular cascade preceded the detailed investigations. This setup was used to detect the phenomena which cause induced flutter. The phenomenon oscillating shock was then isolated and investigated in a 2-D nozzle. The objectives of the investigation were the Installation of a system for the excitation of periodic oscillations of a normal in a nozzle. Measurement of the behaviour of the normal and the unsteady pressures in the frequency range existing in turbomachines (0 to 200 Hz excitation frequency). Investigation of the effects of the boundary layer on the response of an unsteady pressure transducer under the influence of an shock. Creation of a computation program for nonlinearized unsteady flows in nozzles containing an normal shock; emphasis is put on sharp capturing. Introduction of viscosity models in the computational program for estimating the influence of the boundary layer on the behaviour of the and the unsteady pressures. For the measurement, different current methods were used. The determination of the unsteady position was made by both a laser-2-focus-velocimeter and a line scan camera. The unsteady pressures were measured with unsteady pressure transducers at several positions in the side wall of the nozzle. Close to the shock, laser holography was used to obtain information about the zone of interaction between the and the boundary layer. The computation method developed is based on the Euler equations in conservative form. For viscous computations, the viscosity terms are included as perturbing terms inside the system of equations. With the aid of the flux-vector-splitting-method, the domains of physical influence are correctly taken into account. Thus, the is sharply captured (within only two mesh points). The main results of this work are The boundary layer over an unsteady pressure transducer has a quasi-steady behaviour with respect to the phase lag, but not with respect to the pressure amplitude. This means that the pressure fluctuations are in phase with the movement. The pressure amplitude depends on the frequency and on the boundary layer thickness. The wall region influenced by the is increased due to the boundary layer. The pressure increase or decrease takes place in a larger region on the wall. Thus, the pressure transducer sees the arriving before it has actually reached the position of the pressure transducer. The computational program developed was successfully validated with other available computational methods for steady state flows. The computed unsteady phenomena match well the results of the measurements. The computational method is tested and can now be upgraded for the computation of unsteady flows through cascades.