Experimental Techniques; Analysis of Boundary Layer Data.

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Joseph Gransden        Case Study 3: Experimental Techniques        10/05/07

CASE STUDY 3: Experimental Techniques; Analysis of Boundary Layer Data

By Joseph Gransden

Department of Mechanical Engineering, Nottingham University

The following report is an experimental study of Boundary layer data obtained using hot-wire anemometry. In particular, the report presents and analyses mean velocity and turbulence intensity profiles as well as turbulence statistics. The aim is to discover the best methods of presenting and analysing data in order to determine and explain some of the turbulence phenomena by discussion of the data and its implications.

RESULTS  

Firstly the hot wire anemometer output voltage is calibrated using King’s Law against the velocities that are initially measured with a pitot tube or vane anemometer.

This calibration then allows for the mean and fluctuating velocities (turbulence intensity) to be determined. Results are shown below of the mean velocities and intensities along with distance from the wall.

From such data the boundary layer integral parameters can be determined using:

Displacement thickness,        

        Momentum Thickness        ,        

Shape Factor,                        

The boundary layer thickness has been approximated here using the definition provided by F.M White. That is:

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        Boundary Layer thickness,        δ = y   where u = 0.99U0

To find the correct logarithmic velocity profile the Clauser plot technique was employed varying the friction velocity, u* to ‘match’ the logarithmic ...

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