We use the rectangular gaseous supersonic ejector as a platform to study the mixing characteristics of a confined supersonic jet. The entrainment ratio (ER) of the ejector, the non-mixed length (LNM), and potential core length (LPC) of the primary supersonic jet are measures to characterize mixing within the supersonic ejector. Experiments are carried out on a low area ratio rectangular supersonic ejector with air as the working fluid in both primary and secondary flows. The design Mach number of the nozzle (MPD = 1.5–3.0) and primary flow stagnation pressure (Pop = 4.89–9.89 bars) are the parameters that are varied during experimentation. Wall static pressure measurements are carried out to understand the performance of the ejector as well as to estimate the LNM (the spatial resolution is limited by the placement of pressure transducers). Well-resolved flow images (with a spatial resolution of 50 μm/pixel and temporal resolution of 1.25 ms) obtained through Planar Laser Mie Scattering (PLMS) show the flow dynamics within the ejector with clarity. The primary flow and secondary flow are seeded separately with acetone that makes the LNM and LPC clearly visible in the flow images. These parameters are extracted from the flow images using in-house image processing routines. A significant development in this work is the definition of new scaling parameters within the ejector. LNM, non-dimensionalized with respect to the fully expanded jet height hJ, is found to be a linear function of the Mach number ratio (Mach number ratio is defined as the ratio of design Mach number (MPD) and fully expanded Mach number (MPJ) of the primary jet). This definition also provides a clear demarcation of under-expanded and over-expanded regimes of operation according to [MPD/MPJ] > 1 and [MPD/MPJ] < 1, respectively. It is observed that the ER increased in over-expanded mode (to 120%) and decreased in under-expanded mode (to 68%). Similarly, LNM decreased (to 21.8%) in over-expanded mode and increased (to 20.4%) in under-expanded mode. Lengthening of LPC by 139% and a reduction of 50% in shock cell spacing have also been observed for specific flow conditions. The details regarding experimentation, analysis, and discussions are described in this article.

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The flow field in a two-dimensional three-ramp hypersonic mixed-compression inlet in a freestream Mach number of M∞ = 5 is numerically solved to understand the unsteady throttling dynamics. Throttling conditions are simulated by varying the exit area of the isolator in the form of plug insets. Different throttling ratios between 0 ≤ ζ ≤ 0.7 in steps of 0.1 are considered. No unsteadiness is observed for ζ ≤ 0.2, and severe unsteadiness is found for 0.3 ≤ ζ ≤ 0.7. The frequency of unsteadiness (f) increases rapidly with ζ. As ζ increases, the amount of reversed mass inside the isolator scales with the frequency and the exit mass flow rate. A general framework is attempted to scale the unsteady events based on the gathered knowledge from the numerical study. The inlet–isolator flow is modeled as an oscillating flow through a duct with known upstream design conditions such as the freestream Mach number (M∞) and the isolator inlet Mach number (Mi). Factors such as the mass occupied by the duct volume, the characteristic unsteady frequency, the throttling ratio, and the exit mass flow rate through the duct are used to form a non-dimensional parameter β, which scales with the upstream design parameter ξ = Mi/M∞. The scaling parameters are further exploited to formulate a semi-empirical relation using the existing experimental results at different throttling ratios from the open literature. The unsteady frequencies from the present two-dimensional numerical exercise are also shown to agree with the proposed scaling and the resulting semi-empirical relation.

Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by using two sharp-tipped lobes. The lobes are placed one on either end of the minor axis in an elliptic nozzle. The design Mach number and the aspect ratio of the elliptic nozzle are 2.0 and 1.65. A two-lobed nozzle with the same exit area and design Mach number as that of the elliptic nozzle is compared when the jet is exhausted to the ambient in an almost perfectly expanded condition. Time-resolved schlieren imaging, longitudinal and cross-sectional planar laser Mie-scattering imaging, planar Particle Image Velocimetry, and near-field microphone measurements are performed. DMD and POD analysis are carried out on the schlieren and the Mie-scattering images. Mixing characteristics are extracted from the Mie-scattering images through the image processing. The flapping elliptic jet consists of two dominant DMD modes, while the lobed nozzle has only one dominant mode, and the flapping is suppressed. The jet column bifurcates in the lobed nozzle enabling closer contact with the ambient fluid and higher mixing rates in the near-field of the nozzle exit. The jet width growth rate of the two-lobed nozzle is about twice as that of the elliptic jet in the near-field, and there is a 40% reduction in the potential core length. PIV contours substantiate the results.

The impinging shock of varying strengths on the free shear layer in a confined supersonic cavity flow is studied numerically using the detached eddy simulation. The resulting spatiotemporal variations are analyzed between the different cases using unsteady statistics, x–t diagrams, spectral analysis, and modal decomposition. A cavity of length to depth ratio [L/D]=2 at a freestream Mach number of M∞=1.71 is considered to be in a confined passage. Impinging shock strength is controlled by changing the ramp angle (θ) on the top wall. The static-pressure ratio across the impinging shock (p2/p1) is used to quantify the impinging shock strength. Five different impinging shock strengths are studied by changing the pressure ratio: 1.0,1.2,1.5,1.7, and 2.0. As the pressure ratio increases from 1.0 to 2.0, the cavity wall experiences a maximum pressure of 25% due to shock loading. At [p2/p1]=1.5, fundamental fluidic mode or Rossiter's frequency corresponding to n = 1 mode vanishes whereas frequencies correspond to higher modes (n = 2 and 4) resonate. Wavefronts interaction from the longitudinal reflections inside the cavity with the transverse disturbances from the shock-shear layer interactions is identified to drive the strong resonant behavior. Due to Mach reflections inside the confined passage at [p2/p1]=2.0, shock-cavity resonance is lost. Based on the present findings, an idea to use a shock-laden confined cavity flow in an enclosed supersonic wall-jet configuration as passive flow control or a fluidic device is also demonstrated.