An Experimental Investigation Of Wake Effects In Dynamic Stall PDF Download

Flow over an NACA 0015 airfoil undergoing a constant rate of change of angle of attack was experimentally studied over a range of tunnel speeds and rotation rates. Surface pressure transducers coupled with a microcomputer-based data acquisition system were used to collect surface-pressure data at the rate of 4000 samples per second; data reduction was also microcomputer-based. Data was reduced in two forms: (1) C sub l versus alpha curves through stall were determined for each dynamic experimental configuration. This was accomplished by numerical integration of pressure data at a number of angles through stall, each data point representing the average of five experiments at the same experimental conditions. These curves indicated a slight decrease in C sub l - alpha slope with increasing angle of attack angular rate. (2) Increase in stall angle of attack of the dynamic over the static case was plotted against a nondimensional angular rate parameter (defined as the product of one-half the chord length and angular rotation rate, divided by the freestream velocity). This comparison gave rise to an apparently universal curve of nondimensional angular rotation rate versus increase in stall angle of attack. This curve was in agreement in some sense with previous experiments using stall indicators other than the actual stall.