Effect of Freestream Turbulence on a Two Dimensional Cascade, with Different Surface Roughness, at High Reynolds Number.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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The present study shows the effects of high freestream turbulence on the performance of a two dimensional cascade. The cascade consisted of seven NACA 65-A506 airfoils with two inches chord. Experiments were carried out at flow Reynolds number per foot in excess of two and a half million. Flow turbulence intensity of 7 was generated upstream of the cascade. Blades with three different categories of surface roughness were studied. High freestream turbulence results in a decrease in total pressure loss coefficient in the cascade and an increase in the total pressure loss coefficient in the wake. The results also show an increase in pressure coefficient, over the suction surface, independent of the amount of surface roughness. The boundary layer thickness, after 50 chord, increases substantially, with an increase in freestream turbulence. This effect is aggravated with higher surface roughness. The effects of high freestream turbulence on boundary layer edge velocity are sensitive to local surface roughness. With low surface roughness, the boundary layer edge velocity increase with freestream turbulence. The results indicate an opposite effect when local surface roughness is increased.
- Fluid Mechanics