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Aero-acoustic coupling inside large deep cavities at low-subsonic speeds / Mouhammad El Hassan in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 1 (Janvier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 10 p. Titre : Aero-acoustic coupling inside large deep cavities at low-subsonic speeds Type de document : texte imprimé Auteurs : Mouhammad El Hassan, Auteur ; Keirsbulck, Laurent, Auteur ; Labraga, Larbi, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Aero-acoustic  coupling;  deep  cavity;  hydrodynamic  mode Résumé : Aero-acoustic coupling inside a deep cavity is present in many industrial processes. This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios (L/H=0.2 and 0.41), as a function of freestream velocities of a 2×2m2 wind tunnel. Convection velocity of instabilities was measured along the shear layer, using velocity cross-correlations. Experiments have shown that in deep cavity for low Mach numbers, oscillations of discrete frequencies can be produced. These oscillations appear when the freestream velocity becomes higher than a minimum value. Oscillations start at L/θ0=10 and 21 for L/H=0.2 and 0.41, respectively. The highest sound pressure level inside a deep cavity is localized at the cavity floor. A quite different behavior of the convection velocity was observed between oscillating and nonoscillating shear-layer modes. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model (1964, “ Wind Tunnel Experiments on the Flow Over Rectangular Cavities at Subsonic and Transonic Speeds,” Aeronautical Research Council Reports and Memo No. 3438) when measured convection velocity is used and the empirical time delay is neglected. For L/H=0.2, only the first Rossiter mode is present. For L/H=0.41, both the first and the second modes are detected with the second mode being the strongest. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Aero-acoustic coupling inside large deep cavities at low-subsonic speeds [texte imprimé] / Mouhammad El Hassan, Auteur ; Keirsbulck, Laurent, Auteur ; Labraga, Larbi, Auteur . - 2009 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 10 p. Mots-clés : Aero-acoustic  coupling;  deep  cavity;  hydrodynamic  mode Résumé : Aero-acoustic coupling inside a deep cavity is present in many industrial processes. This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios (L/H=0.2 and 0.41), as a function of freestream velocities of a 2×2m2 wind tunnel. Convection velocity of instabilities was measured along the shear layer, using velocity cross-correlations. Experiments have shown that in deep cavity for low Mach numbers, oscillations of discrete frequencies can be produced. These oscillations appear when the freestream velocity becomes higher than a minimum value. Oscillations start at L/θ0=10 and 21 for L/H=0.2 and 0.41, respectively. The highest sound pressure level inside a deep cavity is localized at the cavity floor. A quite different behavior of the convection velocity was observed between oscillating and nonoscillating shear-layer modes. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model (1964, “ Wind Tunnel Experiments on the Flow Over Rectangular Cavities at Subsonic and Transonic Speeds,” Aeronautical Research Council Reports and Memo No. 3438) when measured convection velocity is used and the empirical time delay is neglected. For L/H=0.2, only the first Rossiter mode is present. For L/H=0.41, both the first and the second modes are detected with the second mode being the strongest. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Flow bistability downstream of three-dimensional double backward facing steps at zero-degree sideslip / Herry, Benjamin B. in Transactions of the ASME . Journal of fluids engineering, Vol. 133 N° 5 (Mai 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 5 (Mai 2011) . - 04 p. Titre : Flow bistability downstream of three-dimensional double backward facing steps at zero-degree sideslip Type de document : texte imprimé Auteurs : Herry, Benjamin B., Auteur ; Keirsbulck, Laurent, Auteur ; Labraga, Larbi, Auteur Année de publication : 2011 Article en page(s) : 04 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  control  Flow  instability  Flow  visualisation  Turbulence  Two-phase  flow Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The flow downstream of a three-dimensional double backward facing step (3D DBWFS) is investigated for Reynolds number Reh ranging from 5×103 to 8×104 (based on the first step height h). The flow is studied both qualitatively by means of laser tomoscopy and oil-flow visualizations and quantitatively by means of particle image velocimetry (PIV) measurements. In particular, the results show a mean flow asymmetry. A sensitivity study around zero degree sideslip has shown that the flow is bistable for this geometry. This bistability has been observed in two different wind tunnels for very different upstream conditions. As a main consequence, the zero degree drift angle could be a relevant validation case of unstable flow computation. More tests are carried out to understand and control this particular flow feature. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...] [article] Flow bistability downstream of three-dimensional double backward facing steps at zero-degree sideslip [texte imprimé] / Herry, Benjamin B., Auteur ; Keirsbulck, Laurent, Auteur ; Labraga, Larbi, Auteur . - 2011 . - 04 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 5 (Mai 2011) . - 04 p. Mots-clés : Flow  control  Flow  instability  Flow  visualisation  Turbulence  Two-phase  flow Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The flow downstream of a three-dimensional double backward facing step (3D DBWFS) is investigated for Reynolds number Reh ranging from 5×103 to 8×104 (based on the first step height h). The flow is studied both qualitatively by means of laser tomoscopy and oil-flow visualizations and quantitatively by means of particle image velocimetry (PIV) measurements. In particular, the results show a mean flow asymmetry. A sensitivity study around zero degree sideslip has shown that the flow is bistable for this geometry. This bistability has been observed in two different wind tunnels for very different upstream conditions. As a main consequence, the zero degree drift angle could be a relevant validation case of unstable flow computation. More tests are carried out to understand and control this particular flow feature. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...]

Unsteady wall shear stress in transient flow using electrochemical method / H. Zidouh in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Titre : Unsteady wall shear stress in transient flow using electrochemical method Type de document : texte imprimé Auteurs : H. Zidouh, Auteur ; Labraga, Larbi, Auteur ; M. William-Louis, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  stress;  shear  (mechanics);  pipes;  valves Résumé : Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Unsteady wall shear stress in transient flow using electrochemical method [texte imprimé] / H. Zidouh, Auteur ; Labraga, Larbi, Auteur ; M. William-Louis, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Mots-clés : pressure;  flow  (dynamics);  stress;  shear  (mechanics);  pipes;  valves Résumé : Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]