Investigation of Flow Pattern and Losses in Transonic Turbine Vane and Blade Cascades by Means of Laser Anemometer Measurements and Navier-Stokes Analysis

This paper presents results of a complex numerical and experimental investigation of the flow structure and losses in the Vane (Ma2is = 1.0, Re = 9.8*105) and Blade (Ma2is = 1.12, Re = 7.8*105) straight cascades on transonic modes. The measurements of turbulence pulsation and mean flow velocity upstream, within and downstream of the cascades were made by means of laser anemometer (LA). The static and total pressure fields were measured upstream and downstream of the cascades to determine profile losses. The static pressure distribution on the suction and pressure surfaces was measured as well. Comparisons were made with predictions using 2D Navier–Stokes analysis. The use of the both experimental and numerical approaches allowed to eliminate separated zones more accurately, to define how these zones affected on flow structure and losses.

Wake Recovery Performance Benefit in a High-Speed Axial Compressor

Rotor wakes are an important source of loss in axial compressors. The decay rate of a rotor wake is largely due to both mixing (results in loss) and stretching (no loss accrual). Thus, the actual loss associated with rotor wake decay will vary in proportion to the amounts of mixing and stretching involved. This wake stretching process, referred to by Smith (1996) as recovery, is reversible and for a 2-D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. It will be shown that for the rotor/stator spacing typical of core compressors, wake stretching is the dominant wake decay process within the stator with viscous mixing playing only a secondary role. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated alone and in a stage configuration at near peak efficiency and near stall operating conditions. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model and laser anemometer measurements indicate that rotor wake straining (stretching) is the primary decay process in the stator passage. Some implications of these results on compressor stage design are discussed.

3D Laser Anemometry in a Rotating Cooling Channel

The flow in rotating cooling passages of jet engine turbine rotors is considered. Contrary to thermal data which have been obtained by a lot of people, velocity field data are very few. Nevertheless, in order to validate Navier-Stokes calculations, these two types of data are necessary. In such a flow with complexe secondary structures, 3D laser anemometer is the most suitable tool but its implementation on this application was a challenge. Measurements were made first in static mode at Reynolds numbers of 5,000 and 25,000. The same model sections were then explored during rotation at a Reynolds number of 5,000 and a Rossby number of 0.33. Some results were obtained a Reynolds number of 25,000 and a Rossby numbers of 0.033 and 0.066. The distortion of the axial velocity profile resulting from the Coriolis acceleration appears clearly when comparing the results obtained in the sections of the centrifugal arm. In the transverse plane, the two other velocity components show the secondary flow structures with two contrarotating vortices. The results obtained in the centripetal arm show that the flow depends on the 180 deg straight-corner turn located upstream. These measurements confirm the assumptions made on the organisation of this type of flow, and the simulation results obtained at ONERA with the MATHILDA code and also by other teams who have published papers on the subject. The first results obtained during this experimental work demonstrate the validity of the 3D laser anemometry in such a case. They show also some insufficiencies due to an application deemed difficult.