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Impinging jets are encountered in many industrial applications. Previous studies have considered different parameters that affect the flow and enhance mass and energy transfer of these flows, such as Reynolds number, nozzle geometry, nozzle-to-plate distance, wall material and angle, and the flow regime at the jet exit. Furthermore, the dynamics of these jets could be a source of a high level of noise when the transfer of energy is optimized between the aerodynamic and acoustic fields. This can lead to a resonant jet producing self-sustained tones. Self-sustained tones are related to aero-acoustic coupling and occur in impinging jets when a feedback loop is present between the jet exit and the impinged plate. Few studies that deal with the heat transfer of an impinging jet in the presence of an acoustic resonance have been conducted. This state of the art review and discussion will focus on the heat transfer and flow dynamics in such noisy and resonant configurations. Such investigation will allow us to understand how a similar regime characterized by acoustic instabilities could be useful in enhancing heat transfer at the wall. [ABSTRACT FROM AUTHOR]

Heat exchangers are widely studied in energy and production processes. There are various techniques available to enhance the performance of heat exchangers, but in recent years, vortex generators have gained significant attention. Vortex generators (VGs) is a passive control method that can improve heat transfer if properly designed. Vortex generators achieve heat exchange enhancement by creating transverse, longitudinal, or normal twiddle flows, disrupting the flow field, and improving transport phenomena. The improvement in convective heat transfer coefficient is achieved by increasing fluid mixing, breaking down the thermal boundary layer, and improving mean velocity and temperature gradient. In this paper, a coaxial counter-flow heat exchanger was considered. Prism shape vortex generators were installed on the outer surface of the inner tube of the heat exchanger and resulting performance was compared to that of the same heat exchanger without vortex generators. RANS CFD study (SST k-ω turbulence model was used) demonstrated a 13% improvement in heat transfer rate when using a heat exchanger with vortex generators as compared to the case without VGs. [ABSTRACT FROM AUTHOR]

Passive control of the flow over a deep cavity at low subsonic velocity is considered in the present paper. The cavity length-to-depth aspect ratio is L/H = 0.2. particle image velocimetry (PIV) measurements characterized the flow over the cavity and show the influence of the control method on the cavity shear layer development. It is found that both the 'cylinder' and the 'shaped cylinder', placed upstream from the cavity leading edge, result in the suppression of the aero-acoustic coupling and highly reduce the cavity noise. It should be noted that the vortical structures impinge at almost the same location near the cavity downstream corner with and without passive control. The present study allows to identify an innovative passive flow control method of cavity resonance. Indeed, the use of a 'shaped cylinder' presents similar suppression of the cavity resonance as with the 'cylinder' but with less impact on the cavity flow. The 'shaped cylinder' results in a smaller shear layer growth than the cylinder. Velocity deficiency and turbulence levels are less pronounced using the 'shaped cylinder'. The 'cylinder' tends to diffuse the vorticity in the cavity shear layer and thus the location of the maximum vorticity is more affected as compared to the 'shaped cylinder' control. The fact that the 'shaped cylinder' is capable of suppressing the cavity resonance, despite the vortex shedding and the high frequency forcing being suppressed, is of high interest from fundamental and applied points of view. Key words: cavity flow, PIV, flow control, shear layer, shear layer growth. Nous prenons ici en consideration le controle passif d'un ecoulement a faible vitesse subsonique sur une cavite. Le rapport longueur a profondeur de la cavite est L/H = 0.2. Les mesures de velocimetrie par image de particule caracterisent l'ecoulement au dessus de la cavite et montrent l'influence de la methode de controle sur le developpement de la couche de cisaillement de la cavite. Nous trouvons que le placement d'un cylindre ou d'un cylindre profile place en amont du bord d'attaque de la cavite, resulte en la suppression du couplage aeroacoustique et reduit fortement le bruit de cavite. Il faut noter que la structure tourbillonnante s'impose a pratiquement la meme localisation pres du coin aval de la cavite et sans controle passif. L'etude actuelle permet d'identifier une methode innovante et passive pour controler la resonnance de cavite. En effet, l'utilisation d'un cylindre profile presente des suppressions similaires a celles du cylindre, mais avec un impact plus faible sur l'ecoulement de cavite. Les deficits de vitesse et les niveaux de turbulence sont moins prononces avec le cylindre profile. Le cylindre tend a diffuser la vorticite dans la couche de cisaillement de la cavite et ainsi la localisation du maximum de vorticite est plus affectee qu'avec le controle par le cylindre profile. Le fait que le cylindre profile soit capable de supprimer la resonance de la cavite, malgre que les structures tourbillonnaires et le forcage de haute frequence soient amenuises, est tres interessant d'un point de vue fondamental et applique. [Traduit par la Redaction] Mots-cles: ecoulement sur cavite, controle d'ecoulement, couche de cisaillement, croissance de la couche de cisaillement., 1. Introduction The flow-induced cavity resonance leads to a high acoustic level, which in many industrial applications is problematic and needs to be strongly reduced or suppressed. Active and passive [...]