T. Schröder, R.D. Baier, K. Broichhausen

The losses generated by the blade boundary layers contribute to about 30 % to the overall losses in turbomachines. Thus, special attention must be paid to the aerodynamic design of low loss airfoils for compressors and turbines of modern jet engines. Theoretical and cascade test results show that the different objectives of turbomachinery blades, namely high Mach numbers, large incidence and Reynolds number variation, can be achieved by special custom tailored airfoils. The suction side boundary layer of such airfoils is composed of a laminar zone in the accelerating flow part, followed by a zone where the boundary layer undergoes transition from laminar to turbulent state thereby forming a·closed separation bubble and finally a relatively short turbulent zone. In contrast to external flows around wings, fuselage and nacelles, the flow in turbomachines is highly unsteady and composed of superimposed periodic and random (i.e. turbulent) fluctuations. These fluctuations remarkably influence the behaviour of the boundary layer. For instance in the laminar part turbulent spots can be generated when the wakes of an upstream blade row impinge on the blade suction side boundary layer. In particular the transition to turbulence in the closed separation zone is to a great extent influenced by the wakes of the upstream blade rows. Analyses of experimental investigations carried out in a turbine rig test elucidate these unsteady phenomena.

First European Forum on Laminar Flow Technology, Hamburg, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 11 Seiten

DGLR-Bericht, 1992, 1992-06, First European Forum on Laminar Flow Technology; S.201-211; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aerodynamics, boundary layer transition, laminar flow

Bestellbar

1992