Untitled

Abstract

In the context of measurements in the boundary layer, the problem of estimating the skinfriction velocity is relevant because this velocity is proportional to the drag force and therefore is related to the energy wasted by friction in vehicles such as planes, cars, ships, etc. The existing literature is scarce when presenting an overview of the methods appropriate for the estimation in the scenario: (a) flat plate flow, (b) air incompressible regime, (c) outdoor conditions, (d) turbulent flow. As a response to such shortcomings, this manuscript presents an overview of the methods: (1) hot-wire anemometry, (2) hotfilm anemometry and (3) particle image velocimetry (PIV), in the aforementioned scenario. This manuscript reviews the diverse components that these methods require and contrasts the skin-friction velocity measurements stemming from them. Our results show a consistent estimation of the skin-friction velocity with the three methods. Future work is required in assessing the influence of wall proximity on hot-wire measurements and the influence of different Reynolds regimes on the skin-friction velocity estimations. Future work is required in the aspects of comparing the direct measurement of the skinfriction velocity with the hot-wire probe very close to the wall and the assessment of the accuracy of the techniques at different Reynolds numbers. Keyword-Skin-friction, Boundary Layer, Hot-wire, Hot-fil, Turbulent Flow GLOSSARY Free-stream velocity m/s Boundary layer thickness m Kinematic viscosity m 2 /s ℓ Viscous length scale non-dimensional + Viscous scaled parameters non-dimensional Friction velocity m/s Friction coefficient non-dimensional ISSN (Print) : 2319-8613 ISSN (Online) : 0975-4024 Cristian Rendon-Cardona et al.