Compressible vortex loops: Effect of nozzle geometry

Abstract

Vortex loops are fundamental building blocks of supersonic free jets. Isolating them allows for an easier study and better understanding of such flows. The present study looks at the behaviour of compressible vortex loops of different shapes, generated due to the diffraction of a shock wave from a shock tube with different exit nozzle geometries. These include a 15mm diameter circular nozzle, two elliptical nozzles with minor to major axis ratios of 0.4 and 0.6, a 30 × 30mm square nozzle, and finally two exotic nozzles resembling a pair of lips with minor to major axis ratios of 0.2 and 0.5. The experiments were performed for diaphragm pressure ratios of P 4 /P 1 = 4, 8, and 12, with P 4 and P 1 being the pressures within the high pressure and low pressure compartments of the shock tube, respectively. High-speed schlieren photography as well as PIV measurements of both stream-wise and head-on flows have been conducted. * Hossein. Zare-Behtash@glasgow.ac.uk

Three-dimensional shock wave distortion in shock-square vortex loop interaction

“…2 (I), (II), and (III), respectively; this is identical to previous studies [10,11]. The shape of the vortex loop alters and reconstructs to the original shape with expansion and contraction.…”

“…6, image (3)), the distorted shock wave around the outer vortex core is affected by the high-speed flow at the vortex corner (C in image (3)). According to a previous study that the velocity field was measured in front of a square nozzle [10], the high-speed flow occurs along the axis of the square nozzle corner. The high-speed flow reduces the shock propagation velocity at the vortex corner (C in image (3)), and the shock wave is distorted towards the centre of the VL.…”

“…The PIV results of Zare-Betash et al [10] indicated that the circulation of a circular vortex loop is higher than that of a non-circular one because the deceleration of some parts of the non-circular vortex loop induce a relatively lower circulation. According to the numerical simulation of Zhang et al [11], a square vortex loop leads to counter-rotating stream-wise vortices at the four corners, and they accelerate mixing in the vortex core because they engulf the surrounding air into the vortex core.…”

“…Different exit nozzle geometries, which are non-circular in shape, change the flow characteristics and induce unsteady and highly three-dimensional flows. Zare-Betash et al [9,10] reported the flow features of non-circular vortex loops from various nozzle geometries such as the square, elliptic, and exotic shapes.…”

Transverse jet-cavity interactions with the influence of an impinging shock

“…A standard Z-type schlieren system was utilised, identical to that used by Zare-Behtash et al 25,26 The light source was a 450W continuous Xenon lamp and a Photron SA-1 highspeed camera was used to capture images at a frame rate of 10kfps with an exposure time of 1µs.…”