Comparison between sonic jets with one jet orifice and two opposite orifices into a Ma-3.0 supersonic crossflow through circular ducts

The spatiotemporal distribution characteristics and flow stability of a rocket-based combined-cycle (RBCC) inlet during the ejector-to-ramjet mode transition are investigated numerically. The operational pressure of the embedded rocket is adjusted to three different levels, and the time-sequences of the rocket and back pressure regulation are varied. The pressure in feature sections is monitored to reveal the coupling relationship and stability of the internal flowfield. The inlet is more adaptable to severe disturbances under the “throttle-maintaining” regulation and is susceptible under the “direct-shutdown” regulation. The severe fluctuation period is relatively short within “medium throttle-maintaining,” while is lengthy within the “high throttle-maintaining.” The severe fluctuation under the direct-shutdown develops with the propagation of the regulation and decays with its establishment. The ultimate flowfields driven by different time-sequences reach unanimity with the same adjustable parameters of embedded rocket and back pressure; however, the dynamic evolutions show distinct characteristics. During the mode transition, pressure “valleys” are formed in any selected sections with the rocket regulations, and “peaks” are developed in many sections due to the propagation of back pressure or the instability of the rocket jet. For the medium throttle-maintaining regulation, the effect of time-sequence on the flowfield is relatively weak. For the high throttle-maintaining regulation, the pressure disturbance rises abruptly under the rocket priority regulation, with a most severe amplitude of 100.7%. For the direct-shutdown regulation, the maximum pressure disturbance of 125% is observed within the rocket priority regulation, and the minimum disturbance occurs within the back pressure priority regulation.

Spatiotemporal flow evolution in a rocket-based combined-cycle inlet during ejector-to-ramjet mode transition

Yang,

Tian

et al. 2023

Transition of Edney shock–shock interactions due to the whipping phenomenon of liquid jet in supersonic crossflow

Sebastian,

Muruganandam

2024

In this paper, we experimentally study the unsteady dynamics of shock–shock interaction between the bow shock generated by a liquid jet in supersonic crossflow (LJISC) and an oblique shock. Images of shock–shock interactions were captured using high-speed focusing schlieren. Due to the whipping nature of the liquid jet, a coupling happens between the instantaneous bow shock shape and violent oscillations of the liquid jet. Proper orthogonal decomposition reveals that the dominant coherent structures of LJISC are convective and flapping modes, and these modes are responsible for unsteady variation in the local bow shock angle. An oblique shock emanating from a wedge is made to interact with the oscillating bow shock of a liquid jet near the sonic line. At this shock interaction location and for a constant momentum flux ratio between liquid jet and crossflow, unsteady transitions between the types of Edney shock–shock interactions were observed. The types of Edney shock–shock interactions that can occur depend on the local average bow shock angle and the momentum flux ratio. Support vector machine (SVM) model was used to classify three types of Edney shock–shock interactions based on ten features related to the nearest knee point, shock interaction point, and maximum penetration height. Using the SVM model, three dominant features that affect the type of shock–shock interaction were identified. Experimental results, when compared with shock polar, reveal some short-duration abnormal presence of overall regular interaction instead of overall Mach interaction regime.

Mixing enhancement of transverse jets in supersonic crossflow using an actively controlled novel fluidic oscillator

Maikap,

Rajagopal

2024

This study investigates the fluid dynamics and mixing characteristics of an oscillating sonic jet injected into a supersonic cross flow of Mach 2.1 using experimental and computational techniques. The oscillating jet is produced by a novel fluidic oscillator, which consists of a primary rectangular duct that expands into an outer duct with sudden expansion. Control jets are injected in the lateral direction from the side walls of the sudden expansion in an out-of-phase manner to oscillate the injected jet in the spanwise direction of the crossflow. Experimental and numerical investigations based on wall static pressure and mass fraction fluctuations, respectively, revealed that the injected jet oscillation frequency matches the control jet frequency. The iso-surface of lambda-2 criterion showed the presence of various dominant vortex structures, such as counter-rotating vortex pairs, horseshoe vortex, sidewall vortices, and trailing vortices. Helicity contour plots showed that the streamwise vortices oscillate in the spanwise direction with the control strategy and promote the spread of the injected jet in the spanwise direction. The spatiotemporal reconstruction (z–t plot) of the density gradients at a particular streamwise location revealed that the bow shock produced by the interaction of the injected jet and the crossflow oscillates with the actuation of the control strategy. The power spectral density of the z–t plot revealed that the shock wave oscillation frequency matches the control jet frequency. The oscillating jet produced by the control strategy showed significant mixing enhancement in supersonic crossflow compared to a simple rectangular injection.