Active and Adaptive Control of Supersonic Impinging Jets

Abstract

The behavior of supersonic impinging jets is dominated by a feedback loop due to the coupling between the fluid and acoustic fields. This leads to many adverse effects when such flows occur in short takeoff and vertical landing aircraft, such as a significant increase in the noise level, very high unsteady loads on the nearby structures, and an appreciable loss in lifting during hover. In earlier studies, it was demonstrated that by using supersonic microjets one could disrupt the feedback loop that leads to substantial reductions in the aforementioned adverse effects. However, the effectiveness of control was found to be strongly dependent on the ground plane distances and the jet-operating conditions. The effect of various microjet control parameters are investigated in some detail to identify their influence on control efficiency and additional insight is provided on the physical mechanism behind this control method. Parameters studied include microjet angle, microjet pressure, and the use of microtabs instead of microjets. These results indicate that by choosing appropriate control parameters it should be possible to devise a control strategy that produces optimal control for the entire operating range of conditions of the supersonic impinging jet. Moreover, the experimental results provide convincing evidence of the generation of significant streamwise vorticity by the activation microjets. It is postulated that the generation of streamwise vorticity and its evolution in the jet flow might be one of the main physical phenomena responsible for the reduction of flow unsteadiness in impinging jets.

Large-eddy simulation of twin impinging jets in cross-flow

“…Although there was no crossflow in Cabrita et al's (9) twin-jet experiment, its high speed visualisation still gives important information on the unsteady fountain and jet shear layer variations. Active and passive control of supersonic impinging single jet and twin jets have been studied by Alkislar et al (10) and Lou et al (11) using microjets. Nearfield microphone spectra suggested that, for the non-controlled case, there were dominant frequencies in the jet shear-layer or close to the ground plate.…”

Torch Design Modification Using Micro-jets to Suppress Fluid Dynamic Instabilities in Plasma Arc Cutting

“…Micro-jets have been used in short takeoff and vertical landing (STOVL) aircraft to control the jet shear layer and to reduce unsteadiness [8][9][10][11][12][13]. Lou et al [13] took pictures of the instantaneous shadowgraph images for the normal STOVL jet and the jet with micro-jets.…”

“…Lou et al [13] took pictures of the instantaneous shadowgraph images for the normal STOVL jet and the jet with micro-jets. 16 micro-jets with a diameter of 400 lm were placed around the nozzle exit and the microjet angle was set to 20°towards the center of the jet.…”

“…Micro-jets have been used to control and stabilize gas jets with high turbulence in combustion systems. A great deal of the research work has been done on the use of micro-jets to control the jet shear layer and to reduce unsteadiness in supersonic impinging jets for short takeoff and vertical landing (STOVL) aircraft [8][9][10][11][12][13]. In this research, the authors utilized flow visualization technologies such as shadowgraph imaging, stereoscopic particle image velocimetry (PIV) and planar laser scattering (PLS).…”

An optimal local active noise control method based on stochastic finite element models

“…Since then, ANC techniques have been of a considerable research interest. There have been plenty of ANC studies in aircraft [6][7][8][9] and car cabin applications [10][11][12][13][14][15][16][17][18][19]. Aircraft propeller and car engine are typical low frequency noise sources that are considered relatively easy to control by ANC techniques, as engine rotation can be used as a reference signal to the system that controls secondary source actuators.…”