Sound and wake characteristics generated by flow past a triangular cylinder at various incident angles

Abstract

Characteristics of sound and wakes generated by flow past a triangular cylinder with Mach number 0.3 at various incident angles are studied by numerically solving the compressible Navier-Stokes equations using OpenFOAM. The Reynolds number in this study is varied from 140 to 180. The mean lift coefficient is zero when the cylinder is symmetric and has a maximum when the incident angle is approximately 30°. The mean drag coefficient varies when the incident angle increases. The root mean square of the lift coefficient increases as the incident angle increases, while that of the drag coefficient is highest at an incident angle of around 36°. When the incident angle is small, the Strouhal number has the value of around 0.21. As an incident angle increases, the Strouhal number increases by approximately 1.5%. When the incident angle exceeds 24°, the Strouhal number drops to its minimum by 25% at an incident angle of 54° then slightly goes up by 4.5% at an incident angle of 60°. Increasing the Reynolds number does not significantly affect the trends of the vortex shedding frequency and the root mean square of the force coefficients. The root mean square of the pressure wave in the transverse and the upstream directions vary in the same manner as those of the lift and drag coefficients, respectively. At an incident angle of 60°, the root mean square of the pressure wave in the transverse direction increases by 115% compared to when the incident angle is small. While that in the upstream direction increases by 159% at an incident angle of 36° and decreases afterwards by 76% at an incident angle of 60°. The nearest vortex streets behind the cylinder are observed to be either the Benard-von Karman vortex street or the P+S-like wake. Both types of wake turn into the secondary vortex street while advected downstream.