Flow Quality Measurements in the L2000 Wind Tunnel : Boundary Layer Characterization and Data Acquisition Analysis Using Pressure Rakes

Sammanfattning

This thesis describes the processes and methods used to evaluate the boundary layer of the false floor installed in the L2000 wind tunnel. The L2000 wind tunnel was built in the 1960s and was transferred to KTH in 1996. Three key areas were researched: pressure rake design and comparison, boundary layer estimation, and acquisition time. A new curved rake was constructed based on a NASA report which is then compared with an existing straight rake. The boundary layer is estimated and defined using the shape factor as well as the boundary layer height. In addition, acquisition time was investigated using an Allan variance approach in combination with stopping theory. The frequency contents of the digital signal at different sampling frequencies was also investigated. The data was captured and recorded using a Chell microDAQ3 pressure scanner connected to the Streamwise ProCap program. The data was then analysed using MATLAB. The results shows a difference between the two different rakes which is possibly caused by Construction and design defects. The boundary layer at x = 2180mm was observed to be turbulent with a shape factor of H12 ≈ 1.49 and a Reynolds number above the critical value. Different acquisition times were calculated at a tolerance of ε = 1% for three different confidence intervals and sampling frequencies: 95%, 99%, 99.9%, 5 Hz, 50 Hz, 200 Hz, 400 Hz.