The Study of Turbomachine Cascade Performances at Off-Design Flow Entry Angles

Аuthors

Mamaev B. I.^1*, Starodumov A. V.^2**, Ermolaev G. V.^1***

1. Lyulka Desing Bureau, 13, Kasatkina str., Moscow, 129301, Russia
2. Ltd “Space Transport Systems”, Moscow, Russia

*e-mail: boris.mamaev35@mail.ru
**e-mail: a.starodumov@s7.ru
***e-mail: grigoriy.ermolaev@okb.umpo.ru, ermolaev_grigory@mail.ru

Abstract

The effect of positive incidence angles on the flow and losses in both sub- and trans-sonic turbine cascades was studied based on multiple test results. Physical causes and general regularities of losses by the inlet angle and outlet velocity were determined by the velocity distribution on the profile and losses values analysis. Geometric and mode parameters, which should be accounted for while losses computing from the incidence angle, were marked out.

Both cascade passage contraction and exit velocity increase leads to reduction of the airfoil relative velocities and outlet diffusion degree, which reduces losses. Losses from incidence are reducing and may become zero ones in cascades with contractile passages at the moderate incidences with the velocity increase up to its limit value of , while at large velocities these losses may be assumed as constant and equal to their minimum values.

The positive incidence changes mainly the flow-around in the inlet part of the cascade passage. All flow-around changes herewith end up as a rule at the back edge prior to the interprofile channel throat, and in the first half of the trough contour. An incidence increase raises the velocity peak on the suction side near the leading edge sometimes up to supersonic values and increases intensity of following flow decelerations with a formation of separation flow. These flow changes on the airfoil suction side effect prevail the effect of flow improvements at the pressure side, and it, probably, is the main cause or the losses occurrence due to the incidence and these losses increasing due to the incidence increase. On the suction side in close to active cascades and the ones with low value of , the incidence may lead to rather high supersonic velocity at the near leading edge peak and following diffusion flow up to the airfoil trailing edge. In that case, incidence losses may grow as the exit velocity increases more than its limit value.

Keywords:

turbomachine cascade, entry edge, incidence angle, airfoil suction side, flow-around, diffusion factor, flow exit velocity, profile losses from incidence angle

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