INVESTIGATION OF TIP LEAKAGE EFFECTS IN TRANSONIC FLOW USING A PARALLEL UNSTRUCTURED NAVIER-STOKES CODE

Calculated results for tip ow around two dierent blade con gurations are presented and compared with experimen-tal data. The rst conguration (case number 1) is a at-plate prole tested in a linear transonic tunnel|the pro-le is an idealized representation of the aft-section of some highly curved turbine blades. The second conguration (case number 2) originates from the outer prole on the last-stage-blade of a steam turbine, however it is also rem-iniscient of a section from a turbine blade with supersonic exit ow. This conguration was tested in an annular cas-cade at Mach numbers representative of engine operating conditions. The computed results were obtained using a parallel 3D unstructured Navier-Stokes code. The code runs on a work-station cluster, as well as being optimized for the 256 pro-cessor Cray T3D at EPFL: the code is capable of giga op performance using more than 3 million cells|adaptive mesh re nement thus allows enhanced resolution within the tip gap region. For each conguration we have calculated two Runs. In both cases, Run-1 is similar to the experimental conditions, so that direct comparison between measured and calcu-lated results is possible. With case number 1/Run-2 we re-calculated the ow without imposing a prescribed in ow boundary-layer along the sidewall. Comparison between the two runs helped reveal how free-stream total pressure can establish itself within the tip gap region. For the sec-ond conguration|in the annular cascade|we were inter-ested in observing the in uence of relative movement be-tween the blade tip and adjacent sidewall. Hence for case number 2/Run-2 we imposed a circumferential velocity on the adjacent sidewall. This modied the eective sidewall boundary-layer and had a noticeable in uence on the devel-opment of the tip-leakage ow