Direct measurement of the mean flow velocity vector

The response of a single inclined rotating hot wire anemometer was analyzed. The mean flow anemometer response equation was expanded in a Fourier Series about the fundamental frequency of rotation. Utilizing the d-c level and the first two harmonics of the response it is possible to construct the mean flow velocity vector within a solid angle determined by the mounting angle of the wire. The rotating anemometer response was measured using the technique of two phase lock-in detection to determine the first two harmonics and their phases relative to the fundamental frequency of rotation. Determination of the mean flow velocity vector using this technique was found to be feasible.