Investigation of the Flow Structures for Two Tandem Arrangement of Torpedo-Like Geometries

Abstract

Experimental studies on autonomous underwater vehicles for a torpedo-like geometry are limited in the literature. In this study, flow structures of a streamlined torpedo-like geometry having an elliptical nose and tampered stern at a length to diameter aspect ratio of L/D=5 for a single and double tandem arrangement with various spacings have been investigated using Particle Image Velocimetry (PIV) method in a closed loop water channel. Reynolds number defined for length of the geometry (L=200 mm), free stream water velocity of 100 mm/s was taken as Re=20000, the spacing (G) between two identical torpedo-like geometries is changed from 0 to 120 mm. Instantaneous 1000 images and their time-averaged results are comparatively presented for all configurations of the torpedo-like geometry. It is demonstrated that the tandem arrangements depending on the dimensionless spacing ratios (G/L) between 0 to 0.6 are significantly different from the single torpedo-like geometry for the flow patterns of instantaneous and time-averaged velocity field, dimensionless streamwise velocity component and streamline topology. For the contacting case in which the following model nose is placed on the trailing-edge of the front model, wake region of the back geometry is similar to the single model wake but the all of time-averaged flow patterns elongated and symmetrical flow patterns are slightly deformed. When flow area is provided between two models for spacing ratios of 0.15≤G/L≤0.30, chaotic and rotational flow patterns occur due to the impinging separated flow patterns from the front geometry to the nose of the downstream one. As the gap distance increases to the largest value at G/L=0.6, the wake region of both the single and tandem arrangement becomes almost identical. More detailed information for the flow characteristics of the examined torpedo-like geometry can be determined by using computational fluid dynamics after validation with PIV results in the present study.