J. F. Brouckaert

Unsteady Turbine Blade Wake Characteristics

The paper presents an experimental investigation of large coherent structures, commonly referred to as von Karman vortex street, in the wake of a turbine blade at high subsonic Mach number (M 2.is =0.79) and high Reynolds number (RE = 2.8×10 6 and their effect on the steady and unsteady pressure and temperature distribution in the wake. Ultra short smoke visualizations and two interferometric measurement techniques, holographic interferometry and white light differential interferometry provide insight into the vortex formation and shedding process. In addition, the interferometric measurement provides quantitative information on the stream wise evolution of the minimum density associated with the vortices and on their lateral spreading. Wake traverses are performed with a four-head fork probe carrying a Kiel probe and a fast response Kulite pressure probe for pressure measurements and a thermocouple probe and a cold wire resistance probe for temperature measurements. The results confirm the observation of energy separation in the wake as found by other researchers. The experimental data are a unique source for the validation of unsteady Navies-Stokes codes.

Experimental investigation of the unsteady rotor aerodynamics of a transonic turbine stage

Abstract This paper describes some results of a large experimental programme on unsteady flow through the rotor of a transonic turbine stage in the large Compression Tube Turbine Facility at the von Karman Institute for Fluid Dynamics. The tests were carried out as part of a Brite EURAM project. The test programme covered the investigation of the effects of a variation in the rotational speed of the rotor, the axial stator-rotor distance and the stator trailing-edge coolant flow ejection. The paper aims at presenting the measurements of the relative inlet total pressure and the rotor blade surface pressure at rotor mid-span.

Fast response aerodynamic probes for measurements in turbomachines

Abstract The present paper concentrates on the use of single- and multi-sensor pressure probes designed for the accurate measurement of unsteady total pressure and flow angle for turbo-machinery applications. Fast response pressure probes have the advantage of offering a high analogue bandwidth, a high signal-to-noise ratio, and a good reliability and robustness as compared to hot-wire techniques for instance. In addition to the magnitude and direction of the flow velocity vector, aerodynamic probes also indicate the total and static pressure as time-resolved quantities. Appropriate data processing then allows to retrieve not only the steady, but also the periodic and random components of the measured variables. The design of several single or multi-sensor probes is briefly described in this paper. These probes have been developed, manufactured and fully calibrated at the von Karman Institute to be used in laboratory and in industry environments over the last 8 years. The main objective of this contribution is to address some examples of applications but focus on the capabilities of the technique rather than on flow field analysis.

Experimental characterization of stall phenomena in a single-stage low-pressure axial compressor

The experimental characterization of the rotating stall phenomena appearing in a single-stage high-speed low-pressure axial compressor is presented in this paper. The compressor design is representative of an advanced direct drive turbofan booster. The stage is equipped with both fast response and steady instrumentation. Fast response pressure sensors are placed in the rotor casing and in the hub at the outlet of each row. The former are employed to perform a detailed survey on the tip leakage flows, and the latter allow to determine the extension of the stall cells across the stage. A fast response aerodynamic pressure probe is located at the rotor outlet to detect the size of the stall cells. The global performances of the machine are recorded by time-averaged measurements at the inlet and at the outlet of the stage. Tests recording the stall inception and the complete stall transients are performed at different speed lines in the VKI-R4 closed loop compressor test rig. The inception mechanism is determined by the comparison between the time mean and the time-resolved data. In terms of stall inception, the compressor exhibits long length scale at lower rotational speed and an abrupt stall at higher rotational speed. The characterization of the stall cells is performed in terms of number, size, and speed by using the unsteady data acquired with the fast response instrumentation. The compressor presents a single full span stall cell in all the speed lines investigated.