Separated-Reattaching Flow Over a Backstep With Uniform Normal Mass Bleed (Data Bank Contribution)

Yang, Jing‐Tang; Tsai, Bor-Bin; Tsai, Go-Long

doi:10.1115/1.2910236

Cited by 41 publications

(30 citation statements)

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“…2-3b). The shift in the reattachment location has been observed previously with inert mass injection [23] and heat release [35]. The large-scale BrownRoshko vortices [5] are visible in the inert shear-layer (Fig.…”

Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 56%

“…For the highest injection case, the recirculation zone extends past the measurement rake and reverse flow velocities on the order of 20% of U 1 are estimated, in accord with previous studies [31,37]. While several previous studies investigated inert mass injection behind rearward-facing step flows [23,24], injection rates were typically quite small and injection is from the bottom wall, making even qualitative comparisons to the current geometry difficult. Nevertheless, the observed acceleration of the upper portion of the profile and increased reverse flow in the lower portion of the profile with increasing injection are qualitatively similar to that seen for uniform mass bleed behind rearward-facing steps [24].…”

Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 58%

“…Increased injection will push reattachment downstream, increasing the length of the recirculation zone and changing the pressure coefficient at a given downstream location [23]. Reattachment location and pressure coefficient can also be controlled by varying the amount of heat release via exothermic chemical reactions [10,35].…”

Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 99%

“…Rearward-facing steps have been utilized to provide the benefits of recirculating flow for flame stabilization [20][21][22]. Injection into the recirculating flow can be accomplished using transverse-jet/-slot injectors [21,22], a uniform normal mass bleed [23,24], or a combination. This work investigates mixing in an expansion-ramp geometry, which is similar to a rearward-facing step flow with uniform mass injection.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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The mixing and flowfield of a complex geometry, similar to a rearwardfacing step flow but with injection, is studied. A subsonic top-stream is expanded over a perforated ramp at an angle of 30 • , through which a secondary stream is injected. The mass flux of the second stream is chosen to be insufficient to provide the entrainment requirements of the shear layer, which, as a consequence, attaches to the lower guidewall. Part of the flow is directed upstream forming a re-entrant jet within the recirculation zone that enhances mixing and flameholding. A control-volume model of the flow is found to be in good agreement with the variation of the overall pressure coefficient of the device with variable mass injection. The flowfield response to changing levels of heat release is also quantified. While increased heat release acts somewhat analogously to increased mass injection, fundamental differences in the flow behaviour are observed. The hypergolic hydrogen-fluorine chemical reaction employed allows the level of molecular mixing in the flow to be inferred. The amount of mixing is found to be higher in the expansion-ramp geometry than in classical freeshear layers. As in free-shear layers, the level of mixing is found to decrease with increasing top-stream velocity. Results for a similar configuration with supersonic flow in the top stream are reported in Part II of this two-part series.

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Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 56%

Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 58%

Section: Flowfield For Inert and Reacting Injectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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show abstract

“…The reattachment location is near the perforated plate and the recirculating fluid reaches all the way up to the intersection of the ramp with the lower guidewall. As the injection velocity is increased, the shear layer is deflected upwards, a larger fraction of the shear-layer entrainment requirements are provided, and reattachment occurs further downstream [31]. The recirculation becomes less pronounced with increased injection, but remains evident at all injection velocities.…”

Section: Flowfield Effects With Inert Mass Injectionmentioning

confidence: 91%

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part II: Supersonic Flow

Bonanos

Bergthorson

Dimotakis

2009

Flow Turbulence Combust

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Fundamental aspects of mixing between two gaseous streams in a complex geometry are studied and discussed. In the present paper, a supersonic top-stream is expanded over a 30 • ramp, through which a secondary lower-stream is injected. The mass flux through the secondary stream is purposely insufficient to provide the entrainment requirements of the resulting shear layer, causing it to attach to the lower guidewall. Part of the shear layer fluid is directed upstream forming a recirculation zone, with enhanced mixing characteristics. The pressure coefficient of the device is quantified as a function of velocity ratio. The effect of heat release on the pressure coefficient is also reported. Molecular mixing was measured employing "flip" experiments based on the hypergolic hydrogen-fluorine chemical reaction. The amount of mixing for the expansion-ramp geometry is found to be higher than in classical free shear layers. However, as in free shear layers, the level of mixing decreases with increasing top-stream velocity. Results for a similar configuration with subsonic/transonic flow in the top stream are reported in Part I of this two-part series.

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On the performance of sudden‐expansion pipe without/with cross‐flow injection: experimental and numerical studies

El‐Askary

El-Mayet

Balabel

2011

Numerical Methods in Fluids

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SUMMARY The paper explores the possibilities that different turbulence closures offer, for in‐depth analysis of a complex flow. The case under investigation is steady, turbulent flow in a pipe with sudden expansion without/with normal‐to‐wall injection through jets. This is a typical geometry where generation of turbulence energy takes place, due to sudden change in boundary conditions. This study is aimed at investigating the capability of a developed computational program by the present authors with three different turbulence models to calculate the mean flow variables. Three two‐equation models are implemented, namely the standard linear k − ε model, the low Reynolds number k − ε model and the cubic nonlinear eddy viscosity (NLEV) k − ε model. The performance of the chosen turbulence models is investigated with regard to the available data in the literature including velocity profiles, turbulent kinetic energy and reattachment position in a pipe expansion. In order to further assess the reliability of the turbulence models, an experimental program was conducted by the present authors also at the fluid mechanics laboratory of Menoufiya University. Preliminary measurements, including the surface pressure along the two walls of the expansion pipe and the pressure drop without and with the presence of different arrangements of wall jets produced by symmetrical or asymmetrical fluid cross‐flow injection, are introduced. The results of the present studies demonstrate the superiority of the cubic NLEV k − ε model in predicting the flow characteristics over the entire domain. The simple low Reynolds number k − ε model also gives good prediction, especially when the reattachment point is concerned. The evaluation of the reattachment point and the pressure‐loss coefficient is numerically addressed in the paper using the cubic NLEV k − ε model. The results show that the injection location can control the performance of the pipe‐expansion system. It is concluded that the introduction of flow injection can increase the energy loss in the pipe expansion. The near‐field turbulence structure is also considered in the present study and it is noticed that the turbulence level is strongly affected by the cross‐flow injection and the jet location. Copyright © 2011 John Wiley & Sons, Ltd.

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Separated-Reattaching Flow Over a Backstep With Uniform Normal Mass Bleed (Data Bank Contribution)

Cited by 41 publications

References 0 publications

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part II: Supersonic Flow

On the performance of sudden‐expansion pipe without/with cross‐flow injection: experimental and numerical studies

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