# Fluid dynamics in starting and terminating transients of zero-secondary flow ejector

TL;DR: In this article, the starting transient and plume blowback at diffuser breakdown of a straight cylindrical supersonic exhaust diffuser with no externally supplied secondary flow are numerically investigated.

About: This article is published in International Journal of Heat and Fluid Flow.The article was published on 2008-02-01. It has received 36 citations till now. The article focuses on the topics: Diffuser (thermodynamics) & Shock (fluid dynamics).

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TL;DR: In this paper, a numerical method has been implemented to evaluate the formation of droplets due to condensation in a convergent-divergent nozzle and the verified numerical scheme has been applied to internal flow of the thermo-compressor.

32 citations

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TL;DR: In this article, a low area ratio rectangular supersonic gaseous ejector is subjected to parametric evaluation to calculate the performance parameters like stagnation pressure ratio, compression ratio, entrainment ratio and the mixing parameter known as non-mixed length.

28 citations

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TL;DR: In this paper, an experimental investigation was conducted to study the Reynolds number influence on dual-bell transition behavior for tests inside a high-altitude simulation chamber, where the authors found that the width of the inflection region decreases with an increase in the nozzle Reynolds number.

Abstract: An experimental investigation was conducted to study the Reynolds number influence on dual-bell transition behavior for tests inside a high-altitude simulation chamber. For the range of nozzle supply pressures tested, the nozzle Reynolds number is seen to gradually decrease from a relatively high value (of the order of 107 for tests in sea-level atmospheric conditions) toward the transitional range (lower side of 106 for tests inside the high-altitude chamber). This influences the width of the inflection region, which is seen to decrease with an increase in nozzle Reynolds number. Because of the smaller negative pressure gradient experienced during sneak transition with a decrease in nozzle Reynolds number, the separation point is seen to move into the region of wall inflection much earlier and tends to stay in the region of wall inflection for a relatively longer time. Although the time duration of final transition remains more or less constant for different nozzle supply pressure values, the time durati...

24 citations

### Cites methods from "Fluid dynamics in starting and term..."

...Such a high-altitude test facility primarily includes an ejector nozzle to evacuate the altitude chamber, either singly or in combination with other simulation methods [23–27] and provides a platform for conducting subscale cold gas tests on topics of basic and cost-effective research....

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TL;DR: In this paper, the effects of essential performance parameters on the starting transient of a straight cylindrical supersonic exhaust diffuser (SED) are numerically investigated in terms of SED length and pre-evacuation configuration.

24 citations

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01 Jul 2010

TL;DR: In this article, the authors analyzed the transient flow through the vacuum ejector system with the help of a computational fluid dynamics method and showed that the one and only condition in which a continuous mass entrainment can be possible in such types of ejectors is the generation of a recirculation zone near the primary nozzle exit.

Abstract: The objective of the present study is to analyse the transient flow through the vacuum ejector system with the help of a computational fluid dynamics method. An attempt is made to investigate the interesting and conflicting phenomenon of the continuous entrainment into the primary stream with limited mass supply from the secondary chamber. The results obtained show that the one and only condition in which a continuous mass entrainment can be possible in such types of ejectors is the generation of a recirculation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium of pressure at the onset of the recirculation zone. A steady flow assumption in such ejector systems is valid only after the dynamic equilibrium state.

22 citations

##### References

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TL;DR: In this paper, a review of the fundamental characteristics of the shock train and pseudo-shock is presented, and some simple predictions are made to simulate these very complicated phenomena, and control methods of the pseudo-shocks are also described.

478 citations

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TL;DR: In this paper, the performance of six well-known turbulence models for the study of supersonic ejectors was evaluated and the results showed that the k-omega-sst model agrees best with experiments.

323 citations

01 Sep 1992

TL;DR: In this article, a k-epsilon model for wall bonded turbulent flows is proposed and the damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+).

Abstract: A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+). Hence, the model could be used for flows with separation. The model constants used are the same as in the high Reynolds number standard k-epsilon model. Thus, the proposed model will be also suitable for flows far from the wall. Turbulent channel flows at different Reynolds numbers and turbulent boundary layer flows with and without pressure gradient are calculated. Results show that the model predictions are in good agreement with direct numerical simulation and experimental data.

320 citations

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TL;DR: In this paper, a k-epsilon model for wall bonded turbulent flows is proposed and the damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+).

Abstract: A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+). Hence, the model could be used for flows with separation. The model constants used are the same as in the high Reynolds number standard k-epsilon model. Thus, the proposed model will be also suitable for flows far from the wall. Turbulent channel flows at different Reynolds numbers and turbulent boundary layer flows with and without pressure gradient are calculated. Results show that the model predictions are in good agreement with direct numerical simulation and experimental data.

285 citations

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TL;DR: In this article, wall static and in-stream phot pressure distributions are presented for confined, nonreacting, supersonic flows in cylindrical sections wherein a shock structure has been stabilized.

Abstract: Wall static and in-stream phot pressure distributions are presented for confined, nonreacting, supersonic flows in cylindrical sections wherein a shock structure has been stabilized. Based on an analysis of these measurements, the character of the wave structure is shown to be oblique rather than normal, with the flow remaining primarily supersonic downstream of the shock system. When additional cylindrical sections are either added or deleted the shock structure is, with the exception of slight changes due to the different initial conditions, independent of location in the duct. The parameters which govern the distance st, over which the pressure rise is spread, viz., Mach number, momentum thickness Reynolds number, duct diameter, and the momentum thickness of the upstream boundary layer, were varied as follows: 1.53 ^ Ma ^ 2.72, 5 x 10 ^ Ree ^ 6 x 10, 1.0 D 6.1 in., and 0.007 ^ 6 ^ 0.036 in. In each test the wave structure was generated by either lowering the pressure in the air supply system so that the cylindrical duct was, in effect, overexpanded when discharging to ambient conditions, or by throttling the flow leaving the duct. For a given pressure ratio across the disturbance, Pf/pa, st varies approximately directly with the product 0D and inversely with (Ma — l)Re0. A simple quadratic expression is presented which adequately represents this corespondence for the complete range of conditions tested and for data from the cited reference.

280 citations