Jet arrays in supersonic crossflow — An experimental study

Abstract

Jet injection into a supersonic crossflow is a classical fluid dynamics problem with many engineering applications. Several experimental and numerical studies have been taken up to analyze the interaction of a single jet with the incoming crossflow. However, there is a dearth of the literature on the interaction of multiple jets with one another and with the crossflow. Jets in a supersonic crossflow are known to produce a three-dimensional bow-shock structure due to the blockage of the flow. Multiple jets in a streamwise linear array interact with both one another and the incoming supersonic flow. In this paper, a parametric study is carried out to analyze the effect of microjet (sub-mm diameter) injection in a Mach 1.5 supersonic crossflow using flow visualization and velocity field measurements. The variation of the microjet orifice diameter and spacing within an array is used to study the three-dimensional nature of the flow field around the jets. The strength of the microjet-generated shock, scaling of the shock wave angle with the momentum coefficient, averaged streamwise, spanwise, and cross-stream velocity fields, and microjet array trajectories are detailed in the paper. It was found that shock angles of the microjet-generated shocks scale with the momentum coefficient for the three actuator configurations tested. As the microjets issue in the crossflow, a pair of longitudinal counter-rotating vortices (CVPs) are formed. The vortex pairs remain coherent for arrays with larger spanwise spacing between the micro-orifices and exhibit significant three-dimensionality similar to that of a single jet in crossflow. As the spacing between the jets is reduced, the CVPs merge resulting in a more two-dimensional flow field. The bow shock resulting from microjet injection also becomes nearly two-dimensional as the spacing between the micro-orifices is reduced. Trajectory estimations yield that microjets in an array have similar penetration as single jets. A notional schematic depicting the interaction of the microjet arrays with the supersonic crossflow is presented summarizing the principal features of the interaction.

Research on Fuel Mixing in a Non-reacting Situation Simulating a Dual-mode Combustor

“…Ali et al experimentally clarified that CVPs maintained their strength till about 20d downstream from injection point and spanwise extent of CVPs was 9-10d base on the edge of CVPs. 9) In the present study, though St.1 was 22d from injection point, CVPs still affected the plume. However, due to the narrow spacing between orifices (5.7d), the vortices emanated from adjacent orifices interacted with each other while the vortices being adjacent to side-wall remained.…”

Control of incident shock-induced boundary-layer separation using steady micro-jet actuators at M∞ = 3.5

“…However, all the injectors (except MJVG2 ) resulted in a forward push in the separation shock beyond 303 kPa, which may be due to the jet-to-jet interaction that begins to occur for P oj ≥ 208.5 kPa as discussed in Ali and Alvi. 36 This indicates that the jet-to-jet spacing is an important parameter and needs to be carefully maintained.…”

“…Based on the micro-jet exit axis inclination (pitch angle and skew angle), four different configurations MJVG1–4 were fabricated as shown in Figure 2(b) to (e). The purpose of conducting such a study was to vary the blockage created by the barrel shock 36–38 to that of the cross-stream supersonic flow. For MJVG1–3 , there were 14 micro-jet holes with 0.5 mm diameter and 5 mm pitch between each hole at the same time there were 27 holes with 2.5 mm pitch for MJVG4 .…”

“…32 The plasma-based flow control technique seems promising in controlling the separation 33 but comes with a larger cost and requiring complex installation. Recently, more emphasis was given to high-speed micro-jet flow studies 34–37 as they are relatively easy to implement over a wide range of flow-field conditions. Furthermore, the micro-jet devices have been reported to be effective in controlling the unsteadiness induced by the shock interaction with turbulent boundary layer.…”

Implementing Rotating Stall Control in a Radial Diffuser Using Microjet Arrays

“…AFC of Separated Flows-Control of flow separation is an flow application where microjet-based control has been particularly effective. The primary reason for this is the JICF induced, enhanced mixing which energizes the near-wall, low momentum fluid by efficiently mixing it with the higher momentum fluid in the upper region of the boundary layer [25][26][27]. Separation control has been examined extensively, starting with very fundamental flows and advancing to more complex, realistic, applicationdriven configurations-a very brief review of a selected number of these efforts follows next.…”