MEASUREMENTS AND PREDICTION OF THE EFFECTS OF SURFACE-ROUGHNESS ON PROFILE LOSSES AND DEVIATION IN A TURBINE CASCADE

Measurements of pressure distributions, profile losses, and flow devia tion were carried out on a planar turbine cascade in incompressible fl ow to assess the effects of partial roughness coverage of the blade su rfaces. Spanwise-oriented bands of roughness were placed at various lo cations on the suction and pressure surfaces of the blades. Roughness height, spacing between roughness elements, and band width were varied . A computational method based on the inviscid/viscous interaction app roach was also developed; its predictions were in good agreement with the experimental results. This indicates that good predictions can be expected for a variety of cascade and roughness configurations from an y two-dimensional analysis that couples an inviscid method with a suit able rough surface boundary-layer analysis The work also suggests that incorporation of the rough wall skin-friction law into a three-dimens ional Navier-Stokes code would enable good predictions of roughness ef fects in three-dimensional situations Roughness was found to have litt le effect on static pressure distribution around the blades and on dev iation angle, provided that it does not precipitate substantial pow se paration. Roughness on the suction surface can cause large increases i n profile losses; roughness height and location of the leading edge of the roughness band are particularly important. Loss increments due to pressure-surface roughness are much smaller than those due to similar roughness on the suction surface.