Freestream turbulence and wind tunnel blockage effects on streamwise surface pressures

Wind tunnel experiments were conducted to study the effects of blockage and freestream turbulence on streamwise surface pressures in a separation bubble. Mean and fluctuating pressures were measured near the leading edge of short axisymmetric cylinders in grid-generated turbulence and in smooth flow. Mean pressures were found to be strongly dependent on turbulence intensity but were little affected by turbulence scale. On the other hand, fluctuating pressures were dependent on both turbulence intensity and scale. The parameter σ _u/u (L_x/D)^0.15 provided reasonable correlation of the fluctuating data for L_x/D<2.0 and σ _x/u>0.06. Blockage corrections were obtained for streamwise pressures measured near separation. A blockage ratio of 5% caused the mean pressure to increase in magnitude by ∼ 15% and the standard deviation and peak pressures to increase by ∼ 20%. The results of these experiments demonstrate the importance of minimizing wind tunnel blockage when measuring fluctuating pressures on building models.