Numerical study of extreme mechanical force exerted by a turbulent flow on a bluff body by direct and rare-event sampling techniques

In this paper, a numerical study has been carried out to investigate the effects of inlet turbulent intensity and angle of attack on the chemically reacting turbulent flow and thermal fields in a channel with an inclined bluff body V-gutter flame holder. With a basic geometry used in a previous experimental study, the inlet turbulent intensity was varied from 2% to 100%, while the angle of attack of the V-gutter was varied from 0 deg to 30 deg. The turbulent flow was modeled with a realizable k-ε two-equation turbulence model. The chemical reaction was premixed propane-air combustion with an equivalence ratio of 0.6. The chemistry-turbulence interaction was simulated with an eddy-dissipation model. Numerical results indicated that increasing the inlet turbulent intensity and V-gutter angle of attack resulted in an increase not only in the size, but also in the magnitude of the downstream high turbulence areas with shedding vortexes. The recirculation flow behind the flame holder tended to maintain the rear wall at constant temperature, except at the edges of the wall. The friction factor of the flow channel was more sensitive to the change in inlet turbulence intensity at smaller angle of attack of the V-gutter.

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Numerical study of the flow over the modified simple frigate shape

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020977752 ◽

2020 ◽

pp. 095441002097775

Author(s):

Tong Li ◽

Yibin Wang ◽

Ning Zhao

Keyword(s):

Bluff Body ◽

Recirculation Zone ◽

Numerical Study ◽

Reference Value ◽

Flow Fields ◽

Navier Stokes ◽

Detached Eddy Simulation ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation ◽

Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

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Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

10.12681/eadd/48856 ◽

2020 ◽

Author(s):

Γεώργιος Πατεράκης

Keyword(s):

Experimental Investigation ◽

Turbulent Flow ◽

Bluff Body ◽

Operating Conditions ◽

Reacting Flow ◽

Wide Range ◽

Flow Features ◽

Air Mixing ◽

The Impact ◽

Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

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A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall

Volume 5A: Heat Transfer ◽

10.1115/gt2018-75929 ◽

2018 ◽

Cited By ~ 1

Author(s):

Peng Zhang ◽

Yu Rao ◽

Yanlin Li

Keyword(s):

Heat Transfer ◽

Turbulent Flow ◽

Numerical Simulations ◽

Numerical Study ◽

Reynolds Numbers ◽

Hybrid Structure ◽

Transfer Enhancement ◽

Nusselt Numbers ◽

Flow And Heat Transfer ◽

Flow Mixing

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.

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Effect of Prandtl number on heat transfer characteristics in an axisymmetric sudden expansion: A numerical study

Thermal Science ◽

10.2298/tsci0704171a ◽

2007 ◽

Vol 11 (4) ◽

pp. 171-178

Author(s):

Khalid Alammar

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Prandtl Number ◽

Turbulent Flow ◽

Turbulence Model ◽

Numerical Study ◽

Sudden Expansion ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Simulated Effect

Using the standard k-e turbulence model, an incompressible, axisymmetric turbulent flow with a sudden expansion was simulated. Effect of Prandtl number on heat transfer characteristics downstream of the expansion was investigated. The simulation revealed circulation downstream of the expansion. A secondary circulation (corner eddy) was also predicted. Reattachment was predicted at approximately 10 step heights. Corresponding to Prandtl number of 7.0, a peak Nusselt number 13 times the fully-developed value was predicted. The ratio of peak to fully-developed Nusselt number was shown to decrease with decreasing Prandtl number. Location of maximum Nusselt number was insensitive to Prandtl number.

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