Computational analysis of the flow field structure of a non-reacting hypersonic flow over forward-facing steps

2014 ◽  
Vol 763 ◽  
pp. 460-499 ◽  
Author(s):  
P. H. M. Leite ◽  
W. F. N. Santos
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Field Structure ◽  
Recirculation Region ◽  
Transition Flow ◽  
Face Surface ◽  
Face Height ◽  
Flow Past ◽  
Forward Facing Step

AbstractThis work is a computational study of a rarefied non-reacting hypersonic flow past a forward-facing step at zero-degree angle of attack in thermal non-equilibrium. Effects on the flow field structure and on the aerodynamic surface quantities due to changes in step frontal-face height are investigated by employing the direct simulation Monte Carlo method. The work focuses the attention of designers of hypersonic configurations on the fundamental parameter of surface discontinuity, which can have an important impact on even initial design. The results presented highlight the sensitivity of the primary flow field properties, velocity, density, pressure and temperature, to changes in the step frontal-face height. In addition, the behaviour of heat transfer, pressure and skin friction coefficients with variation of the step frontal-face height is detailed. The analysis shows that hypersonic flow past a forward-facing step in the transition flow regime is characterized by a strong compression ahead of the frontal face, which influences the aerodynamic surface properties upstream and adjacent to the frontal face. The analysis also shows that the extension of the upstream disturbance depends on the step frontal-face height. It was found that the recirculation region ahead of the step is also a function of the frontal-face height. A sequence of Moffatt eddies of decreasing size and intensity is observed in the concave step corner. Locally high heating and pressure loads were observed at three locations along the surface, i.e. on the lower surface, on the frontal face and on the upper surface. The results showed that both loads rely on the frontal-face height. The peak values for the heat transfer coefficient on the frontal-face surface were at least one order of magnitude larger than the maximum value observed for a smooth surface, i.e. a flat plate without a step. A comparison of the present simulation results with numerical and experimental data showed close agreement concerning the wall pressure acting on the step surface.

Numerical Simulation of Fractal Tree-Shaped Flow Field Structures in PEMFC

2012 ◽  
Vol 151 ◽  
pp. 32-35 ◽  
Author(s):  
Jin Hua Dong ◽  
Shun Fang Liu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Mass Transfer ◽  
Flow Field ◽  
Proton Exchange Membrane ◽  
Plant Root ◽  
Fractal Theory ◽  
Bipolar Plate ◽  
Field Structure ◽  
Proton Exchange

The fractal tree-shaped structure such as tree, plant root, leaves, animal lung and so on is universal and unique in nature. These structures possess the symmetric micro-channel distributions and the efficient transport characteristics. They are considered to be an optimal network channel of mass transfer and heat transfer. The mass transfer and heat transfer feature of bipolar plate in proton exchange membrane fuel cell (PEMFC) is similar with animal lungs and leaves. In this paper, fractal theory is used to study tree-shaped flow field structure of bipolar plate in PEMFC. It is demonstrated by numerical simulation that fractal tree-shaped flow field structure can provide substantially flow-field distribution, current density and heat transfer compared to the traditional flow field structure.

A uniformly valid solution for the hypersonic flow past blunted bodies

1968 ◽  
Vol 31 (2) ◽  
pp. 397-415 ◽  
Author(s):  
W. Schneider
Keyword(s):  
Flow Field ◽  
Hypersonic Flow ◽  
Local Thermodynamic Equilibrium ◽  
Density Ratio ◽  
Intersection Point ◽  
The Body ◽  
Boundary Values ◽  
Stagnation Region ◽  
Flow Past ◽  
Valid Solution

The plane and axisymmetric hypersonic flow past blunted bodies is investigated as an inverse problem (shock shape given). The fluid may behave as a real gas in local thermodynamic equilibrium. Viscosity and heat conduction are neglected. An analytical solution uniformly valid in the whole flow field (from the stagnation region up to large distances from the body nose) is given. The solution is based on two main assumptions: (i) the density ratio ε across the shock is very small, (ii) the pressure at a pointPof the disturbed flow field isnotvery small compared with the pressure immediately behind the shock in the intersection point of the shock surface with its normal throughP.TermsO(ε) are neglected in comparison with 1, but it is not necessary for the shock layer to be thin. The change of velocity along streamlines is taken into account. In order to calculate the flow quantities one has to evaluate only two integrals (equations (49) and (53) together with the boundary values (5) and (10)). The application of the solution is illustrated and the accuracy is tested in some examples.

Density and velocity fields in collisionless flow past a diffusely reflecting cone

1970 ◽  
Vol 48 (13) ◽  
pp. 1628-1631
Author(s):  
James Parker Elliott
Keyword(s):  
Flow Field ◽  
Free Stream ◽  
Angle Of Attack ◽  
Velocity Fields ◽  
Circular Cone ◽  
Two Dimensional ◽  
Transition Flow ◽  
Flow Past ◽  
Monatomic Gas

Results of flow field calculations for the collisionless flow of a neutral, monatomic gas past a diffusely reflecting right circular cone at zero angle of attack with the free stream are presented. Singularities at the vertex and at the shoulder of the base are illustrated and discussed. Comparison is made with similar results for spheres and two-dimensional polygonal bodies and with results for transition flow past sharp cones. Methods for improving the analysis are suggested.

Numerical analysis of exhaust jet secondary combustion in hypersonic flow field

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840045
Author(s):  
Tian-Peng Yang ◽  
Jiang-Feng Wang ◽  
Fa-Ming Zhao ◽  
Xiao-Feng Fan ◽  
Yu-Han Wang
Keyword(s):  
Flow Field ◽  
Hypersonic Flow ◽  
Flight Control ◽  
Stokes Equations ◽  
Field Structure ◽  
Control Surface ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Secondary Combustion ◽  
Exhaust Jet

The interaction effect between jet and control surface in supersonic and hypersonic flow is one of the key problems for advanced flight control system. The flow properties of exhaust jet secondary combustion in a hypersonic compression ramp flow field were studied numerically by solving the Navier–Stokes equations with multi-species and combustion reaction effects. The analysis was focused on the flow field structure and the force amplification factor under different jet conditions. Numerical results show that a series of different secondary combustion makes the flow field structure change regularly, and the temperature increases rapidly near the jet exit.

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
H. A. Mohammed ◽  
Omar A. Hussein
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Recirculation Region ◽  
Fluid Temperature ◽  
Laminar Mixed Convection ◽  
Forward Facing Step

Numerical simulations of two-dimensional (2D) laminar mixed convection heat transfer and nanofluids flows over forward facing step (FFS) in a vertical channel are numerically carried out. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The wall downstream of the step was maintained at a uniform wall heat flux, while the straight wall that forms the other side of the channel was maintained at constant temperature equivalent to the inlet fluid temperature. The upstream walls for the FFS were considered as adiabatic surfaces. The buoyancy assisting and buoyancy opposing flow conditions are investigated. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes' fractions in the range of 1–4% and different nanoparticle diameters in the range of 25–80 nm, are dispersed in the base fluid (water) are used. In this study, several parameters, such as different Reynolds numbers in the range of 100 < Re < 900, and different heat fluxes in the range of 500 ≤ qw ≤ 4500 W/m2, and different step heights in the range of 3 ≤ S ≤ 5.8 mm, are investigated to identify their effects on the heat transfer and fluid flow characteristics. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase, and it decreases as the nanoparticle diameter increases. This study has revealed that the assisting flow has higher Nusselt number than opposing flow.

Effect of Slot Injection and Effusion Array on the Liner Heat Transfer Coefficient of a Scaled Lean Burn Combustor With Representative Swirling Flow

2015 ◽  
Author(s):  
Antonio Andreini ◽  
Riccardo Becchi ◽  
Bruno Facchini ◽  
Alessio Picchi ◽  
Fabio Turrini
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Flame Stabilization ◽  
Recirculation Region ◽  
Flow Conditions ◽  
Lean Burn ◽  
Cooling Flows ◽  
The Impact

International standards regarding polluting emissions from civil aircraft engines are becoming gradually even more stringent. Nowadays, the most prominent way to meet the target of reducing NOx emissions in modern aero-engine combustors is represented by lean burn technology. Swirl injectors are usually employed to provide the dominant flame stabilization mechanism coupled to high efficiency fuel atomization solutions. These systems generate very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that affect the distribution and therefore the estimation of heat loads on the gas side of the liner as well as the interaction with the cooling system flows. The main purpose of the present work is to provide detailed measurements of Heat Transfer Coefficient (HTC) on the gas side of a scaled combustor liner highlighting the impact of the cooling flows injected through a slot system and an effusion array. Furthermore, for a deeper understanding of the interaction phenomena between gas and cooling flows, a standard 2D PIV (Particle Image Velocimetry) technique has been employed to characterize the combustor flow field. The experimental arrangement has been developed within EU project LEMCOTEC and consists of a non-reactive three sectors planar rig installed in an open loop wind tunnel. Three swirlers, replicating the real geometry of a GE Avio PERM (Partially Evaporated and Rapid Mixing) injector technology, are used to achieve representative swirled flow conditions in the test section. The effusion geometry is composed by a staggered array of 1236 circular holes with an inclination of 30deg, while the slot exit has a constant height of 5mm. The experimental campaign has been carried out using a TLC (Thermochromic Liquid Crystals) steady state technique with a thin Inconel heating foil and imposing several cooling flow conditions in terms of slot coolant consumption and effusion pressure drop. A data reduction procedure has been developed to take into account the non-uniform heat generation and the heat loss across the liner plate. Results, in terms of 2D maps and averaged distributions of HTC have been supported by flow field measurements with 2D PIV technique focussed on the corner recirculation region.

Surface pressure and heat transfer measurements in the unsteady separated hypersonic flow field over double cones

Shock Waves ◽  
2005 ◽  
pp. 389-394
Author(s):  
B. Vasudevan ◽  
S. P. Srikanth ◽  
H. U. Shashidhar ◽  
G. Jagadeesh
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Surface Pressure
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