DIRECTIONAL SENSITIVITY OF WALL MOUNTED HOT-FILM GAUGES

The directional sensitivity of a constant temperature, thin, wall moun ted hot-film gauge with respect to variations in yaw angle is investig ated. Results obtained for the response of a hot-film gauge in a bound ary layer flow fit the correlation between the effective cooling veloc ity for a hot-wire gauge and the yaw angle suggested by other workers. The yaw factor k(1)(2) used in this correlation is typically less tha n 1.0. Results presented for the hot-film gauge in a boundary layer in dicate that the yaw factor depends on both the distance into the bound ary layer and the magnitude of the free stream velocity. At some veloc ity, close to zero, the results predict a yaw factor greater than unit y. Computer simulations using the k - epsilon turbulence model are pre sented which verify this prediction. Yaw factors greater than one resu lt because diffusion from the edges of the gauge becomes significant a t low velocities with respect to the total heat transferred.