Initial development of noncircular jets leading to axis switching

Abstract

This paper discusses the underlying mechanisms for the deformation of coherent structures which occurs in the initial stage of the axis switching of noncircular jets. The generalized shooting method is applied to jets with elliptic-core and equilateral-triangular-core regions of constant flow. The analysis reveals that in order to have the deformation, three requirements must be present in the behavior of the eigenmodes of noncircular jets: 1) the eigenfunctions are localized without excessive overlapping; 2) the amplification rates of the corresponding eigenmodes are comparable; and 3) sufficient phase speed difference exists between the eigenmodes. The qualitative behavior of the noncircular jets found through the numerical analysis is compared with experimental results and are in good correlation with them.

On Turbulent Jets Issuing from Notched-Rectangular and Circular Orifice Plates

“…This implies a higher rate of entrainment of the surrounding fluid. These deductions are consistent with previous observations for other noncircular jets (e.g., [5,6,[8][9][10]21]). …”

“…In other words, as these flows proceed downstream, their mean-flow cross-section tends to switch the minor and major axes at a certain distance from the nozzle exit (e.g., [4,23]). For corner-containing configurations, the corners promote the formation of finescale streamwise vortices and thus enhance fine-scale turbulence [5,10]. The above phenomena of noncircular jets have also been observed in a number of numerical simulations (e.g.…”

“…10,11 show contours of the root mean squares (RMS) of u, v and w,i.e., u = √ < u 2 >, v = √ < v 2 > and w = √ < w 2 >,in the xy and xz planes of the Contours of the normalized RMS in the minor axis plane of the notched jet a < u 2 > 1/2 /U e = 0.01-0.3; b < v 2 > 1/2 /U e = 0.01-Contours of the normalized RMS in the major axis plane of the notched jet a < u 2 > 1/2 / U e = 0.01-0.3; b < w 2 > 1/2 /U e = 0.01-0.07 notched jet and in the central plane of the circular jet, from x/D e = 0.4 to x/D e = 8.2. Normalization is based on the bulk mean exit velocity U e ; the contour values are indicated on the plots, ranging from u /U e = 0.01 to 0.3, v /U e = 0.01 to 0.11 and w /U e = 0.01 to 0.07.…”

Numerical Simulations of Shock/ Vortex Interaction in Non-Circular Jets

“…It is well known that non-circular jets are more unstable than two-dimensional ones (Krothapalli et al 1981). This is not only because the non-circular jets have large-scale coherent structures and streamwise vortices, but also because of its special features, such as three-dimensional shock/vortex interactions, asymmetrical vorticity distributions and axis-switching (Husain and Hussain 1993, Koshigoe et al 1989, and Tam and Thies 1993). Recently, there has been a growing interest in the use of non-circular jets in high-speed propulsive systems (Raman and Taghavi 1998).…”

The CFD Analysis of Turbulence Characteristics in Combustion Chamber with Non Circular Co-Axial Jets

“…As a result, these flows spread more rapidly in the minor axis plane than in the major axis plane, causing -axis switching‖ at a certain distance from the nozzle exit. [17] , For corner containing configurations, the corners promote the formation of fine scale mixing [6,8] . The above experimental results have also been demonstrated in a number of numerical simulations.…”