Characterization of the flow field over a NACA 0015 airfoil using stochastic estimation based on surface pressure and hot film measurements

This work focuses on the analysis of baseline and controlled flow over a NACA 0015 airfoil. The stochastic estimation (SE) method is used to correlate the velocity fields from particle image velocimetry (PIV) with surface pressure and hot film measurements taken simultaneously at several locations on the airfoil surface. Data for the airfoil is available at several angles of attack for the unforced flow as well as for forcing at St=2.75 (1250 Hz), but only 20^o is examined here. The analysis focuses on the effect of the type of sensor (pressure, hot film or combination of both) as well as the use of multiple times on the estimation. The SE is also used with the proper orthogonal decomposition (POD) method to estimate the time evolution of the modal amplitude. Results show that a combination of pressure and hot film sensors at a few locations can sometimes recover the flow characteristics better than using the individual sensor types alone. Also, including additional time information helps to improve the estimation, with a nearly identical match after 7 times are used. However, including more times increases the calculation time. The reconstruction based on the POD modal amplitude shows good agreement with the flow. Finally, the time evolution of the flow is analyzed showing reasonable agreement in terms of the magnitude of the velocity, but more work is needed before the flow dynamics can be described with confidence.