Determination of flow angle from measurements of vortex shedding frequency downstream of a triangular bluff model using a single-sensor hot-wire probe

Experimental aerodynamic studies often require precise measurements of flow angles. However, the conventional multi-hole probe is unsuitable for measuring small flow angles or for use under low-velocity conditions. To overcome these limitations, a new method has been proposed based on measuring the frequency of vortex shedding downstream of a non-polar symmetric body. This technique utilizes a single-sensor hot-wire probe to measure the frequency of the vortex shedding from an equilateral triangular model at different flow angles ($\alpha )$ by rotating the model using a rotating mechanism. Subsequently, the Strouhal number (St) is determined for each flow angle from the measured vortex shedding frequencies. An empirical correlation is then obtained between the Strouhal number and the flow angle of the form $\alpha =f^{-1}\left(St\right)$, considering the condition where the Strouhal number is solely a function of the flow angle. The range of flow angles for which the proposed method is applicable, along with acceptable repeatability of the vortex shedding frequency and suitable Strouhal number sensitivity to the variations in the flow angle, was determined. An empirical correlation $\alpha =-4153.4{St}^2-1819.9St+189.51$ was established, which can be used to determine flow angles in the range of ±10° with an accuracy of 1°. For this purpose, the triangular model is fixed at an angle of 33° to the principal coordinates. The probe is positioned downstream of the model in the defined range: $3\le x/a<25$, $4.5\le y/a\le 5.1$, where $a$ is the side of the equilateral triangular model, and $x$ and $y$ are probe distances in the flow and perpendicular to the flow direction.