Measurement of Pressure Fluctuation Distribution around a Square Cylinder with Pressure Sensitive Paint

To detect aerodynamic noise sources, it is essential to measure surface pressure fluctuations that mainly generate the aerodynamic noise in the low-speed region where the Mach number M is lower than 0.3. Recently, as a new surface-pressure measurement technique, pressure-sensitive paint (PSP) has been being developed. PSP changes luminescence intensities depending on surrounding air pressure, thus can acquire pressure fluctuation distribution on the painted surface. However, the validation of PSP measurement in the low speed region has not sufficiently been investigated because pressure fluctuation is small at low-speed wind velocity. The objective of this research is to assess the accuracy of pressure-fluctuation measurement by using PSP at M around 0.3. To assess the accuracy, we measured pressure fluctuations on the floor surface behind square cylinders with four different sizes in the turbulent boundary layer in a wind tunnel. The peak pressure fluctuation caused by Karman vortex from the square cylinder at maximum 3,000Hz was detected by measurement using PSP. The peak frequencies were the same as those measured by a pressure transducer, though the peak power spectral density is lower than that of the pressure transducer. The pressure fluctuation distribution at peak frequencies shows that two high pressure-fluctuation areas are generated by Karman vortex behind the square cylinder.