Direct measurement of skin friction on magnetically levitated vehicles

Abstract

The goal to design and build a reliable instrument for the direct measurement of skin friction on the surface of Magnetically Levitated (MagLev) trains was successfully achieved. A wall mounted, cantilevered beam device was used to measure the small tangential flow shear force that passes over the non-intrusive floating element. Piezoresistive strain gage units measure the relatively small strain that is generated by the wall shear. By adapting the geometry of the sensing unit, this design can be adapted for a variety of test flows. Measurements were made on two different vehicle geometries provided by Northrop/Grumman and Lockheed/Martin as well as on a special model designed to study the influence of propulsion rails on the Lockheed/Martin model aerodynamics. The obtained values of the skin friction coefficient C_t are deemed reasonable for the type of flow studied. The estimated uncertainty of the gage is ± 5.2%. The data agreed to within 10% with estimated values from an idealized Couette flow analysis.