Experimental investigation of the turbulence effect of incoming flow on the unsteady pressure field and the flow noise around circular cylinder

Surface pressure fluctuations on a circular cylinder model are the main sources of far field noise and have complex physical behavior. So far, brief studies have been devoted for identifying the unsteady surface pressure behavior especially for the turbulence incident flow. In the present study to measure the surface pressure fluctuations under smooth and turbulence incident flows, a circular cylinder with outer diameter of 22 mm has been used. In order to change turbulence characteristics of free stream incoming flow, several biplane grids with square meshes were designed. Power spectral density, coherence, auto correlation and cross correlation, spanwise length scale and convection velocity were different parameters which were calculated using measured unsteady pressures to better clarify the flow structure and flow noise around the circle model. The results revealed that the energy level of both tonal and broadband noises is increased when incident flow changes from smooth to turbulence. Moreover, the tonal noise frequency in turbulence flow ( ) shifts to low frequencies compared to that in smooth flow ( ). Other results showed that physical size of eddies and their convection velocity in turbulence flow is greater than that smooth flow.