Experimental study on the flow patterns and acoustic characteristics of surface piercing cylinders

The hydrodynamic characteristics and noise generated from flow around surface-piercing cylinders are a critical issue for many engineering applications. This article presents an experimental study of flow around a surface-piercing cylinder at Froude number 0.87 to 1.73. The bow wave height, wake pattern, air ventilation, and noise generated have been investigated extensively for different cylinders design such as circular and elliptical cylinders. The diameter of the circular and elliptical cylinders is 40 mm, and 53 mm, respectively. An image processing technique is applied to visualize the air entrainment and calculate the air volume fraction underwater. Due to the lack of experimental published data on the noise around the surface-piercing cylinder, a part of the results discussed the acoustic measurements. A hydrophone is used to study acoustic measurements. The result reveals that the wake region and the bow wave increases significantly as the Froude number increase, accompanied by an air cavity and vortex shedding region behind the circular cylinder, while there was less increment in the bow wave height and wake region as well as there was no air cavity for the case of an elliptical cylinder. The processed image indicated that the air volume fraction for the case of a circular cylinder is four-time higher compared to the elliptical cylinder at Froude number 1.73. Moreover, the results observed that the sound pressure level (SPL) increased as the Froude number increased in all frequency ranges. The sound pressure level behind the circular cylinder increased significantly in the frequency range <1000 Hz, while there was no increment in the SPL behind the elliptical cylinder. The major noise source is due to the air-ventilated cavity behind the cylinder. The outcome results of this study are an important reference for submarine mast designers and some other engineering applications.