The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Paul A. Durbin - One of the best experts on this subject based on the ideXlab platform.
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Direct numerical simulations of transition in a compressor cascade: the influence of Free-Stream turbulence
Journal of Fluid Mechanics, 2010Co-Authors: Tamer A. Zaki, Jan G. Wissink, Wolfgang Rodi, Paul A. DurbinAbstract:The flow through a compressor passage without and with incoming Free-Stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of Free-Stream disturbances. When exposed to Free-Stream forcing, the boundary layer remains attached due to transition to turbulence upstream of the laminar separation point. Three types of breakdowns are observed; they combine characteristics of natural and bypass transition. In particular, instability waves, which trace back to discrete modes of the base flow, can be observed, but their development is not independent of the Klebanoff distortions that are caused by Free-Stream turbulent forcing. At a higher turbulence intensity, the transition mechanism shifts to a purely bypass scenario. Unlike the pressure side, the suction surface boundary layer separates independent of the Free-Stream Condition, be it laminar or a moderate Free-Stream turbulence of intensity T u ~ 3%. Upstream of the separation, the amplification of the Klebanoff distortions is suppressed in the favourable pressure gradient (FPG) region. This suppression is in agreement with simulations of constant pressure gradient boundary layers. FPG is normally stabilizing with respect to bypass transition to turbulence, but is, thereby, unfavourable with respect to separation. Downstream of the FPG section, a strong adverse pressure gradient (APG) on the suction surface of the blade causes the laminar boundary layer to separate. The separation surface is modulated in the instantaneous fields of the Klebanoff distortion inside the shear layer, which consists of forward and backward jet-like perturbations. Separation is followed by breakdown to turbulence and reattachment. As the Free-Stream turbulence intensity is increased, T u ~ 6.5 %, transitional turbulent patches are initiated, and interact with the downstream separated flow, causing local attachment. The calming effect, or delayed re-establishment of the boundary layer separation, is observed in the wake of the turbulent events.
Tamer A. Zaki - One of the best experts on this subject based on the ideXlab platform.
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Direct numerical simulations of transition in a compressor cascade: the influence of Free-Stream turbulence
Journal of Fluid Mechanics, 2010Co-Authors: Tamer A. Zaki, Jan G. Wissink, Wolfgang Rodi, Paul A. DurbinAbstract:The flow through a compressor passage without and with incoming Free-Stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of Free-Stream disturbances. When exposed to Free-Stream forcing, the boundary layer remains attached due to transition to turbulence upstream of the laminar separation point. Three types of breakdowns are observed; they combine characteristics of natural and bypass transition. In particular, instability waves, which trace back to discrete modes of the base flow, can be observed, but their development is not independent of the Klebanoff distortions that are caused by Free-Stream turbulent forcing. At a higher turbulence intensity, the transition mechanism shifts to a purely bypass scenario. Unlike the pressure side, the suction surface boundary layer separates independent of the Free-Stream Condition, be it laminar or a moderate Free-Stream turbulence of intensity T u ~ 3%. Upstream of the separation, the amplification of the Klebanoff distortions is suppressed in the favourable pressure gradient (FPG) region. This suppression is in agreement with simulations of constant pressure gradient boundary layers. FPG is normally stabilizing with respect to bypass transition to turbulence, but is, thereby, unfavourable with respect to separation. Downstream of the FPG section, a strong adverse pressure gradient (APG) on the suction surface of the blade causes the laminar boundary layer to separate. The separation surface is modulated in the instantaneous fields of the Klebanoff distortion inside the shear layer, which consists of forward and backward jet-like perturbations. Separation is followed by breakdown to turbulence and reattachment. As the Free-Stream turbulence intensity is increased, T u ~ 6.5 %, transitional turbulent patches are initiated, and interact with the downstream separated flow, causing local attachment. The calming effect, or delayed re-establishment of the boundary layer separation, is observed in the wake of the turbulent events.
Jan G. Wissink - One of the best experts on this subject based on the ideXlab platform.
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Direct numerical simulations of transition in a compressor cascade: the influence of Free-Stream turbulence
Journal of Fluid Mechanics, 2010Co-Authors: Tamer A. Zaki, Jan G. Wissink, Wolfgang Rodi, Paul A. DurbinAbstract:The flow through a compressor passage without and with incoming Free-Stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of Free-Stream disturbances. When exposed to Free-Stream forcing, the boundary layer remains attached due to transition to turbulence upstream of the laminar separation point. Three types of breakdowns are observed; they combine characteristics of natural and bypass transition. In particular, instability waves, which trace back to discrete modes of the base flow, can be observed, but their development is not independent of the Klebanoff distortions that are caused by Free-Stream turbulent forcing. At a higher turbulence intensity, the transition mechanism shifts to a purely bypass scenario. Unlike the pressure side, the suction surface boundary layer separates independent of the Free-Stream Condition, be it laminar or a moderate Free-Stream turbulence of intensity T u ~ 3%. Upstream of the separation, the amplification of the Klebanoff distortions is suppressed in the favourable pressure gradient (FPG) region. This suppression is in agreement with simulations of constant pressure gradient boundary layers. FPG is normally stabilizing with respect to bypass transition to turbulence, but is, thereby, unfavourable with respect to separation. Downstream of the FPG section, a strong adverse pressure gradient (APG) on the suction surface of the blade causes the laminar boundary layer to separate. The separation surface is modulated in the instantaneous fields of the Klebanoff distortion inside the shear layer, which consists of forward and backward jet-like perturbations. Separation is followed by breakdown to turbulence and reattachment. As the Free-Stream turbulence intensity is increased, T u ~ 6.5 %, transitional turbulent patches are initiated, and interact with the downstream separated flow, causing local attachment. The calming effect, or delayed re-establishment of the boundary layer separation, is observed in the wake of the turbulent events.
Wolfgang Rodi - One of the best experts on this subject based on the ideXlab platform.
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Direct numerical simulations of transition in a compressor cascade: the influence of Free-Stream turbulence
Journal of Fluid Mechanics, 2010Co-Authors: Tamer A. Zaki, Jan G. Wissink, Wolfgang Rodi, Paul A. DurbinAbstract:The flow through a compressor passage without and with incoming Free-Stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of Free-Stream disturbances. When exposed to Free-Stream forcing, the boundary layer remains attached due to transition to turbulence upstream of the laminar separation point. Three types of breakdowns are observed; they combine characteristics of natural and bypass transition. In particular, instability waves, which trace back to discrete modes of the base flow, can be observed, but their development is not independent of the Klebanoff distortions that are caused by Free-Stream turbulent forcing. At a higher turbulence intensity, the transition mechanism shifts to a purely bypass scenario. Unlike the pressure side, the suction surface boundary layer separates independent of the Free-Stream Condition, be it laminar or a moderate Free-Stream turbulence of intensity T u ~ 3%. Upstream of the separation, the amplification of the Klebanoff distortions is suppressed in the favourable pressure gradient (FPG) region. This suppression is in agreement with simulations of constant pressure gradient boundary layers. FPG is normally stabilizing with respect to bypass transition to turbulence, but is, thereby, unfavourable with respect to separation. Downstream of the FPG section, a strong adverse pressure gradient (APG) on the suction surface of the blade causes the laminar boundary layer to separate. The separation surface is modulated in the instantaneous fields of the Klebanoff distortion inside the shear layer, which consists of forward and backward jet-like perturbations. Separation is followed by breakdown to turbulence and reattachment. As the Free-Stream turbulence intensity is increased, T u ~ 6.5 %, transitional turbulent patches are initiated, and interact with the downstream separated flow, causing local attachment. The calming effect, or delayed re-establishment of the boundary layer separation, is observed in the wake of the turbulent events.
Masashi Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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Performance of a scramjet nozzle in hypersonic flight Conditions
31st Joint Propulsion Conference and Exhibit, 1995Co-Authors: Tetsuo Hiraiwa, Sadatake Tomioka, Muneo Izumikawa, Tohru Mitani, Masashi MatsumotoAbstract:Performance of a scramjet nozzle (Singlc Expanded Ramp Nozzle) was estimated in relation to exteinal Conditions along a corridor having flight paths with a constant dynamic pressure. The flow Conditions in an airlramc-intcgratcd scramjet engine were calculated with a quasi-one-dimensional calculation mcthod. Thc cxpansion ratio of the nozzle was set at 5. The back pressure of the nozzle was assumed to be that behind the shock wave generated at the nose of the vehicle. The results show that thc flight Conditions of the nozzle along each path did not differ significantly from each other. The nozzle worked in underexpanded Conditions but suffered from overexpansion loss along the corridor. Nomenclature A Cf = thrust coefficient C* = characteristic velocity Isp 2) MOC = method of characteristic NPR = nozzle pressure ratio Pb = back pressure of SERN Ps = static pressure of the free strcam and outer surface of a vehicle Po = total pressure of nozzle flow Pw = static(wal1) pressure in scramjet cnginc and SERN 9 = dynamic pressure of the frce stream SERN = single expanded ramp nozzle Vei = exhaust velocity of isentropic expansion = area of the scramjet engine and SERN = specific impulse (x-componcnt i n Figurc nozzle TDK = two-dimensional kinetic codc E = nozzle expansion ratio Y = specific heat ratio Subscripts ideal = isentropic expansion nozzlc 0 2 nose of vehicle 5 engine of the inlct of SERN = free stream Condition , = behind the shock wave gencratcd at thc = exit of the internal nozzle of sclaiiijct ?Researcher, Ramjet Combustion Laboratory. $Head, Ramjet Combustion Laboratory. $Research Engineer, Fluid Dynamics and Combustion Dcpartmcnt, Rcscarch Institute(Toyosu). Copyfight
