Boundary layer velocity profiles, time-resolved velocity, turbulence level, turbulence dissipation, intermittency and laminar-turbulent transition are measured by the hot-wire anemometry (HWA). Several multichannel HWA systems from Dantec (DISA 56C17 and mini-CTA) are available in the laboratory. Over 100 single and X-wire probes from Dantec are available as well as film sensors from Senflex, see Fig. 4.10. The hot-wire probes are mounted in the same traversing systems as multi-hole probes.
Figure 4.10. A single- and X-wire probes (left), a single-wire probe in the test section (mid) and a wall-mounted Senflex film sensor (right).
The laboratory has a long tradition and experience of using the Hot Wire Anemometry (HWA) technique, see Bakchinov et al. (2001), Chernoray (2007), Chernoray, Ore, Larsson (2010), Chernoray et al. (2010), Jonsson et al. (2018). Custom in-house hot wire probes, miniature hot wire probes and MEMS-probes are manufactured in the laboratory, see e.g. Gibson et al (2004).
The hot wire probes as resistance thermometers (cold wire mode) are used to measure the temperature of the flow. The wall-mounted hot films can be used for laminar-turbulent transition detection and as resistance thermometers for wall temperature measurement. However, our experience shows that the wall film probes can potentially disturb the flow. Specially designed surface cavities can be used to embed the film probes and to minimize the disturbances. Due to these complications, the priority is given to the hot wire probe traversing which are proven do not affect the transition location and more versatile than hot films.
Figure 4.11. Measurement of the turbulence intensity and turbulence decay in the test section from Jonsson et al., 2008 (left). The turbulence intensity and intermittency in the boundary layer to define the transition location from Chernoray, 2015 (right).
References: Bakchinov A.A., Chernoray V., Jørgensen F.E., Löfdahl, L. (2001) Multiwire system for hot-wire measurements in boundary layers, ASME 6th Int. Thermal Anemometry Symp., Melbourne, Australia. Chernoray, V. (2007) Measurement of the Turbulent Length Scales in the LPT/OGV Facility. Internal report, Chalmers. Chernoray, V., Ore, S., Larsson J. (2010) Effect of Geometry Deviations on the Aerodynamic Performance of an Outlet Guide Vane Cascade. Proc. of ASME TURBO EXPO 2010, pp. 381-390. Chernoray, V., Grek, G. R. and Kozlov V. V. (2010) Spatial Hot-Wire Visualization of the Lambda-Structure Transformation into the Turbulent Spot on the Smooth Flat Plate Surface and Riblet Effect on this Process. Journal of Visualization. Vol. 13 (2), pp. 151-158. Chernoray, V. (2015) Prediction of Laminar-Turbulent Transition on an Airfoil at High Level of Free-Stream Turbulence. Progress in Flight Physics Vol. 7, pp. 704-714. Gibson, A.N., Chernoray, V., Löfdahl L. (2004) Time-Resolved Wall Shear Stress Measurements using MEMS. In Proc. of XXI International Congress of Theoretical and Applied Mechanics. Jonsson, I., Chernoary, V., Rojo, B. (2018) Surface Roughness Impact on Secondary Flow and Losses in a Turbine Exhaust Casing. In Proc. of ASME Turbo Expo 2018 (In Press).