Experimental Study on Aerodynamic Noise Generated from Two-Dimensional Models. 2nd Report. Effect of the Angle of Inclination of Circular Cylinders and the Angle of Attack of Square Cylinders to Aerodynamic Noise.

Abstract

Control of the aerodynamic noise generated from two-dimensional circular and square cylinders are studied experimentally in a low noise wind tunnel. The circular cylinder of 1cm diameter is inclined against the mean flow, whereas the square cylinder of 1cm2 cross section is placed normal to the mean flow, with various angles of attack. Mean velocity of the flow is between 20.6m/s and 41.6m/s. Powere spectra of the radiated noise in various angles of inclination or angles of attack are measured in order to examine the changes in peak levels and the Strouhal numbers of the so-called Aeolian tones. For the circular cylinder, it is found that the Strouhal number based on the frequency of the Aeolian tone and the normal component of the mean velocity to the axis of the circular cylinder stays nearly constant for the angle between 0° and 45°. The peak level of the radiated noise decreases rapidly from the inclined angle from 0° to 15°. but it stays nearly constant for the angle over 15°. For the square cylinder, the Strouhal number is smallest and the peak level is highest at the angle of attack of 0°. The peak level decreases and the Strouhal number increases rapidly with increase of angle of attack up to 13°. For the angle above 15°, both the Strouhal number and the peak level stay almost constant. It is concluded that a circular cylinder should be inclined more than 15°. and a square cylinder should have an angle of attack well over 15° in order to reduce aerodynamic noise generation.