Experimental Investigation of Turbulent Flow Field and Pressure Fluctuations on Flat Surfaces and Cylinders PDF Download

Author: William W. Willmarth
Publisher:
ISBN:
Category :
Languages : en
Pages : 23

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Book Description
The structure of the fluctuating flow field in a turbulent boundary layer has been investigated with the aid of extremely small hot wire probes. Two investigations were conducted. In one investigations of a small X array hot-wire probe, with dimensions (length and spacing) of the order of 2.5 viscous lengths (100 Microns) was constructed and used to measure the small scale structure of the velocity fluctuations and the Reynolds stress near the wall. It was found that very small, intense contributions to the Reynolds stress occur with a scale of the order of the viscous length. In the other investigation a pair of single hot-wires which were of a length of the order of one half the viscous length (50 Microns) were used to demonstrate the existence of shear layers near the wall with an intensity comparable to the mean shear stress at the wall. One primary results is when large scale turbulence is present in the flow upstream of the cylinder, large amplitude, low frequency circumferentially averaged pressure fluctuations are caused by pressure fluctuations in the free stream turbulence and by the aerodynamic interaction of cylinder with the free stream turbulence. A three-sensor hot-wire probe was used to measure the three components of the velocity fluctuations in the free stream at a point 3.5 diameters from the axis of the cylinder. When the free stream turbulence level was low, the instantaneous average of the pressure fluctuations around the circumference could be estimated from the free stream velocity fluctuations near the measuring point on the cylinder.