Local flow structure beyond bubbly flow in large diameter channels

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]

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Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/99-gt-164 ◽

1999 ◽

Cited By ~ 4

Author(s):

C. R. Hedlund ◽

P. M. Ligrani

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Flow Structure ◽

Flow Behavior ◽

Turbine Blades ◽

Reynolds Numbers ◽

Local Flow ◽

Flux Boundary Condition ◽

Nusselt Numbers ◽

Swirl Chamber

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall beat flux boundary condition) using infrared thermography, in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20000. Bulk helical flow is produced in each chamber by two inlets which ore tangent to the swirl chamber circumference. Important changes to local and globally-averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally-averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tiad to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Görtler vnrtex pair trajectories greater skewness as they are advected downstream of each inlet.

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Modeling of Flow Structure, Bubble Distribution, and Heat Transfer in Polydispersed Turbulent Bubbly Flow Using the Method of Delta Function Approximation

Journal of Engineering Thermophysics ◽

10.1134/s1810232819040015 ◽

2019 ◽

Vol 28 (4) ◽

pp. 453-471 ◽

Cited By ~ 2

Author(s):

M. A. Pakhomov ◽

V. I. Terekhov

Keyword(s):

Heat Transfer ◽

Flow Structure ◽

Function Approximation ◽

Bubbly Flow ◽

Delta Function ◽

Bubble Distribution

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Experimental Investigation of Ignition and LBO Characteristics of SPP Injector: The Effect of Pilot Stage Air Split Ratio

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-76282 ◽

2018 ◽

Author(s):

Jinhu Yang ◽

Cunxi Liu ◽

Haowei Wu ◽

Fuqiang Liu ◽

Yong Mu ◽

...

Keyword(s):

Pressure Drop ◽

Flow Structure ◽

Research Work ◽

Combustion Stability ◽

Meridian Plane ◽

Flame Stability ◽

Local Flow ◽

Fuel Distribution ◽

Split Ratio ◽

Pilot Fuel

The influence of PASR (Pilot stage Air Split Ratio) on the ignition and LBO (Lean Blow Out) performances is experimentally investigated for an SPP (Stratified Partially Premixed) injector in this paper. The pilot stage of the SPP injector comprises two axial air swirlers as well as an air blast prefilm atomizer for pilot fuel preparation. It is believed that the variation of the air split ratio between the outer swirler and the inner swirler of the pilot stage will transform the flow structure and fuel distribution of the local flame anchoring zone, and consequently improves or deteriorates the stability of the pilot flame. The ignition and LBO characteristics were measured for PASR = 8:2, 7:3 and 6:4, and several inexplicable but interesting results are observed. In order to make out the underlying reasons for the differences of the obtained ignition and LBO data, the velocity field and spray concentration at the meridian plane were acquired experimentally with the help of optical diagnostics at isothermal conditions. It it concluded that two dominant mechanisms of flame stability exist depending on the range of the injector pressure drop (Δ Psw/P3t). At low pressure drop of the injector, the flame stability is mainly affected by the fuel distribution, however, the flow structure will play a more important role at high Δ Psw/P3t in that it can transform the local flow structures around the pilot flame root. The inherent correlations between the combustion stability and the flow structure as well as the fuel distribution are disscussed and conclusions are drawn for this research work in the end of this paper.

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Nusselt Numbers and Flow Structure on and Above a Shallow Dimpled Surface Within a Channel Including Effects of Inlet Turbulence Intensity Level

Journal of Turbomachinery ◽

10.1115/1.1861913 ◽

2004 ◽

Vol 127 (2) ◽

pp. 321-330 ◽

Cited By ~ 40

Author(s):

P. M. Ligrani ◽

N. K. Burgess ◽

S. Y. Won

Keyword(s):

Nusselt Number ◽

Flow Structure ◽

Turbulence Intensity ◽

Local Nusselt Number ◽

Channel Height ◽

Intensity Level ◽

Stagnation Temperature ◽

Channel Inlet ◽

Local Flow ◽

Nusselt Numbers

Experimental results from a channel with shallow dimples placed on one wall are given for Reynolds numbers based on channel height from 3,700 to 20,000, levels of longitudinal turbulence intensity from 3% to 11% (at the entrance of the channel test section), and a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94. The ratio of dimple depth to dimple print diameter δ∕D is 0.1, and the ratio of channel height to dimple print diameter H∕D is 1.00. The data presented include friction factors, local Nusselt numbers, spatially averaged Nusselt numbers, a number of time-averaged flow structural characteristics, flow visualization results, and spectra of longitudinal velocity fluctuations which, at a Reynolds number of 20,000, show a primary vortex shedding frequency of 8.0Hz and a dimple edge vortex pair oscillation frequency of approximately 6.5Hz. The local flow structure shows some qualitative similarity to characteristics measured with deeper dimples (δ∕D of 0.2 and 0.3), with smaller quantitative changes from the dimples as δ∕D decreases. A similar conclusion is reached regarding qualitative and quantitative variations of local Nusselt number ratio data, which show that the highest local values are present within the downstream portions of dimples, as well as near dimple spanwise and downstream edges. Local and spatially averaged Nusselt number ratios sometimes change by small amounts as the channel inlet turbulence intensity level is altered, whereas friction factor ratios increase somewhat at the channel inlet turbulence intensity level increases. These changes to local Nusselt number data (with changing turbulence intensity level) are present at the same locations where the vortex pairs appear to originate, where they have the greatest influences on local flow and heat transfer behavior.

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Analysis of Local Flow Structure and Global Compressor Performance During Rotating Stall

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-53816 ◽

2004 ◽

Author(s):

Chiara Palomba

Keyword(s):

Flow Field ◽

Flow Structure ◽

Rotational Speed ◽

Axial Flow ◽

Rotating Stall ◽

Performance Parameters ◽

Flow Conditions ◽

Local Flow ◽

Flow Parameters ◽

Compressor Performance

Rotating stall is an instability phenomenon that arises in axial flow compressors when the flow is reduced at constant rotational speed. It is characterised by the onset of rotating perturbations in the flow field accompanied by either an abrupt or gradual decrease of performances. Although the flow field is unsteady and non axisymmetric, the global operating point is stable and a stalled branch of performance curve may be experimentally determined. The number, rotational speed, circumferential extension of the rotating perturbed flow regions named rotating cells may vary from one compressor to another and may depend on the throttle position. The present work focuses on the interaction between local flow parameters and global compressor performance parameters with the aim of reaching a better understanding of the phenomenon. Starting from the Day, Greitzer and Cumpsty [1] model the detailed flow conditions during rotating stall are studied and related to the global performance parameters. This is done both to verify if the compressor under examination fits to the model and if the detailed flow structure may highlight the physics that in the simple model may hide behind the correlation’s used.

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