بررسی تجربی اثر آشفتگی جریان ورودی بر میدان فشار ناپایا و نویز جریان پیرامون استوانه دایرهای

Abstract

Surface pressure fluctuations on a circular cylinder model are the main sources of far- field noise emitted and have complex physical behavior. So far, limited studies have been devoted to identifying the unsteady surface pressure behavior, especially for turbulence incident flow. In the present study to measure the surface pressure fluctuations under both smooth and turbulence incoming flows, a circular cylinder with an outer diameter of 22mm has been used. In order to change the turbulence characteristics of free stream incoming flow, different biplane grids with square meshes were designed. Power spectral density, coherence, autocorrelation and cross-correlation, spanwise length scale, and convection velocity were different interesting parameters which were calculated using measured unsteady pressures in order to better clarify the flow structure and flow noise around the model. The results revealed that the energy level of both tonal and broadband noises is increased when incident flow changes from smooth to turbulent. Moreover, the tonal noise frequency in the turbulence flow ( f ' = 88 Hz ) shifts to low frequencies compared to that of smooth flow ( f = 98 Hz ). Furthermore, results showed that the physical size of eddies and their convection velocity in turbulence flow are greater than corresponding values for smooth flow.