Effects of circular and non-circular nozzle exit geometries on subsonic and supersonic jet propagations

Abstract

The mixing enhancement and core length reduction of a jet without significant loss of thrust are essential for reducing infrared radiation, mitigating aeroacoustic noise, improving combustion characteristics, and thrust vectoring. The jet mixing can be improved by manipulating the flow behavior. In subsonic and sonic jets, the flow manipulation may be achieved by utilizing nozzles with non-circular geometries that shed vortices of varying size due to their non-uniform azimuth curvatures. Non-uniform vortices generate differential spreading along the nozzle’s perimeter, causing axis switching and improving entrainment characteristics. Therefore, the present study examines the effects of two non-circular nozzle exit shapes (elliptic and square) on the mixing augmenting efficacy at subsonic and sonic flow conditions. The circular nozzle is tested for comparison. Both quantitative and qualitative analyses evaluate the efficacy of nozzles with non-circular exit geometries. Among the configurations investigated, the elliptic nozzle is superior in shortening the potential core length and enhancing the jet spread. A maximum reduction of 18.75% in core length with rapid jet decay was accomplished with the elliptic nozzle. The measurement of pressure profiles at different streamwise locations reveals that the spread rate is greater for elliptic and square jets than their circular counterpart. The elliptic jet exhibits the highest spread along the minor-axis direction compared to the major-axis direction. The differential jet spread rate in the elliptical jet causes an early axis-switching––direct evidence of mixing augmentation. Shadowgraph images show the asymmetric pattern of shock cell structures and differential spreading in elliptic and square jets.

The effects of spacing to diameter ratio on mixing characteristics of circular and elliptical twin jets

“…It is understood that the simulated numerical results of the SSTK − ω turbulence model are similar to the experimental results of References. 9, 21 and shown good agreement up to 10 jet diameters. Beyond 10 D , the predicted jet decay is slightly higher.…”

“…To validate the present numerical model, computed solutions of single and twin circular jets are compared with the experimental measurements from Anderson and Spall 9 and Thangaraj and Kaushik. 21 As shown in Table 1, five different meshes with 0.8, 1.6, 2.7, 3.1, and 3.7 million cells are employed to check the grid dependency of the simulations. By examining the circular twin jet symmetry line velocity and turbulent intensity at S / D e = 1.25, grid sensitivity was determined.…”

“…From Table 2, the obtained circular single jet velocity with the SSTK − ω turbulence model matches the experimental data of Anderson and Spall 9 and Thangaraj and Kaushik. 21 Figure 7 shows the centreline velocity decay of a M 0.8 jet for a Single Circular jet. It is understood that the simulated numerical results of the SSTK − ω turbulence model are similar to the experimental results of References.…”

“…In recent years, several researchers suggested that RANS modelling is accurate enough to understand the mixing properties of jets. 9,13 There have been a few studies in the past that looked at the mean and turbulent properties of twin jets under various conditions, such as nozzle/orifice geometry, [3][4][5][6][7]20,21 Reynolds number 3,6,8 and S/D e ratio. 2,[9][10][11]13,14 When S/D e is large, the jets behave like two separate single jets due to the reduced mutual interaction between them.…”

“…There have been a few studies in the past that looked at the mean and turbulent properties of twin jets under various conditions, such as nozzle/orifice geometry, 3–7,20,21 Reynolds number 3,6,8 and S / D e ratio. 2,9–11,13,14 When S / D e is large, the jets behave like two separate single jets due to the reduced mutual interaction between them.…”