Comparison of LDA and hot-wire measurements at moderate subsonic mach numbers

Abstract

A detailed comparison of Hot-Wire-Anemometry (HWA) and Laser-Doppler-Anemometry (LDA) measurements in the wake of an airfoil is presented. An evaluation of the capabilities of both techniques in measuring three-dimensional turbulence in turbomachinery applications is made and potential application pitfalls are highlighted. It is shown that the HWA tends to underestimate the turbulence intensity due to damping effects, while the LDA tends to overestimate the turbulence intensity due to the optical setup. The wake flow of a single airfoil at inflow Mach numbers of 0.35 and 0.45 and corresponding Reynolds numbers of 480,000 and 630,000 are used as a reference case. Different HWA probe head designs and various wire diameter are considered, as well as different setups for the LDA measurement device. In a comparison of the two techniques, the turbulence intensity measured differs by up to <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mn>1.3</mml:mn></mml:math></inline-formula> percentage points (pp) in the freestream region and 4.0 pp within the wake. This is primarily due to the resolution of high-frequency fluctuations. For both measuring techniques, potential sources of errors are highlighted, especially regarding the application to turbomachinery flows.