A numerical study on the mixing of air and hydrogen in a scramjet combustor

2005 ◽  
Vol 109 (1097) ◽  
pp. 325-335
Author(s):  
M. Ali ◽  
T. Fujiwara
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Side Wall ◽  
Recirculation Region ◽  
Mixing Efficiency ◽  
Main Stream ◽  
Two Dimensional ◽  
Injection Angle ◽  
Scramjet Combustor ◽  
Flow Field Characteristics

Abstract A numerical study on mixing of air and hydrogen is performed by solving two-dimensional full Navier-Stokes equations. The main stream is air of Mach 5 entering through the configured inlet of the combustor and gaseous hydrogen is injected from the configured jet on the side wall. Supersonic mixing and diffusion mechanisms of a transverse hydrogen jet in two-dimensional finite air streams have been analyzed and discussed. The computed results are compared with the experimental data and show good agreement. For an otherwise fixed combustor geometry, the air inlet width and injection angle are varied to study the physics of mixing and flow field characteristics. On the effect of inlet width variation, two competing phenomena have been observed: (i) upstream of injector the strength of recirculation is higher for wider inlet and consequently the mixing increases, and (ii) downstream, the diffusion of hydrogen decreases with the increase of inlet width and eventually mixing decreases. As a result, in far downstream the mixing efficiency increases up to certain inlet width and then decreases for further increment of inlet width. For the variation of injection angle results show that upstream of injector the mixing is dominated by recirculation and downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.

A Numerical Study of Unsteady Natural Convection in a Rectangular Enclosure: The Effect of Compressibility

2004 ◽  
Author(s):  
K. M. Akyuzlu ◽  
Y. Pavri ◽  
A. Antoniou
Keyword(s):  
Mathematical Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Vertical Wall ◽  
Ideal Gas ◽  
Working Fluid ◽  
Two Dimensional ◽  
Algebraic Equations ◽  
Rectangular Enclosure ◽  
Circulation Patterns

A two-dimensional, mathematical model is adopted to investigate the development of buoyancy driven circulation patterns and temperature contours inside a rectangular enclosure filled with a compressible fluid (Pr=1.0). One of the vertical walls of the enclosure is kept at a higher temperature then the opposing vertical wall. The top and the bottom of the enclosure are assumed insulated. The physics based mathematical model for this problem consists of conservation of mass, momentum (two-dimensional Navier-Stokes equations) and energy equations for the enclosed fluid subjected to appropriate boundary conditions. The working fluid is assumed to be compressible through a simple ideal gas relation. The governing equations are discretized using second order accurate central differencing for spatial derivatives and first order forward finite differencing for time derivatives where the computation domain is represented by a uniform orthogonal mesh. The resulting nonlinear equations are then linearized using Newton’s linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns (primitive variables) of the problem. A numerical experiment is carried out for a benchmark case (driven cavity flow) to verify the accuracy of the proposed solution procedure. Numerical experiments are then carried out using the proposed compressible flow model to simulate the development of the buoyancy driven circulation patterns for Rayleigh numbers between 103 and 105. Finally, an attempt is made to determine the effect of compressibility of the working fluid by comparing the results of the proposed model to that of models that use incompressible flow assumptions together with Boussinesq approximation.

scholarly journals Numerical Study on the Solid Fuel Rocket Scramjet Combustor with Cavity

Energies ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1235 ◽  
Author(s):  
Chaolong Li ◽  
Zhixun Xia ◽  
Likun Ma ◽  
Xiang Zhao ◽  
Binbin Chen
Keyword(s):  
Solid Fuel ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Combustion Efficiency ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Particle Combustion ◽  
Scramjet Combustor ◽  
Cavity Configuration

Scramjet based on solid propellant is a good supplement for the power device of future hypersonic vehicles. A new scramjet combustor configuration using solid fuel, namely, the solid fuel rocket scramjet (SFRSCRJ) combustor is proposed. The numerical study was conducted to simulate a flight environment of Mach 6 at a 25 km altitude. Three-dimensional Reynolds-averaged Navier–Stokes equations coupled with shear stress transport (SST) k − ω turbulence model are used to analyze the effects of the cavity and its position on the combustor. The feasibility of the SFRSCRJ combustor with cavity is demonstrated based on the validation of the numerical method. Results show that the scramjet combustor configuration with a backward-facing step can resist high pressure generated by the combustion in the supersonic combustor. The total combustion efficiency of the SFRSCRJ combustor mainly depends on the combustion of particles in the fuel-rich gas. A proper combustion organization can promote particle combustion and improve the total combustion efficiency. Among the four configurations considered, the combustion efficiency of the mid-cavity configuration is the highest, up to about 70%. Therefore, the cavity can effectively increase the combustion efficiency of the SFRSCRJ combustor.

Power Generation Using Kites in a GroundGen Airborne Wind Energy System: A Numerical Study

2019 ◽  
Vol 142 (6) ◽  
Author(s):  
Alireza Mahdavi Nejad ◽  
Gretar Tryggvason
Keyword(s):  
Wind Energy ◽  
High Speed ◽  
Stokes Equations ◽  
Numerical Study ◽  
Energy System ◽  
Staggered Grid ◽  
Immersed Boundary ◽  
Uniform Mesh ◽  
Two Dimensional ◽  
Time Step

Abstract A computational model of a massless kite that produces power in an airborne wind energy (AWE) system is presented. AWE systems use tethered kites at high altitudes to extract energy from the wind and are being considered as an alternative to wind turbines since the kites can move in high-speed cross-wind motions over large swept areas to increase power production. In our model, the kite completes successive power-retraction cycles where the kite angle of attack is altered as required to vary the resultant aerodynamic forces on the kite. The flow field is found in a two-dimensional domain near the flexible kite by solving the full Navier–Stokes equations using an Eulerian grid together with a Lagrangian representation of the kite. The flow solver is a finite volume projection method using a non-uniform mesh on a staggered grid and corrector–predictor technique to ensure a second-order accuracy in time. The two-dimensional kite shape is modeled as a slightly cambered immersed boundary that moves with the flow. The flexible kite is modeled with a set of linear springs following Hooke’s law. The unstretched length of each elastic tether at a given time step is controlled using periodic triangular wave shapes to achieve the required power-retraction phases. A study was conducted in which the wave shape amplitude, frequency, and phase (between two tethers) were adjusted to achieve a suitably high net power output. The results are in good agreement with predictions for Loyd’s simple kite in two-dimensional motion. Aerodynamic coefficients for the kite, tether tensions, tether reel-out and reel-in speeds, and the vorticity fields in the kite wake are also determined.

The Influence of Non-Axisymmetric End Wall in a High-Load Compressor Stage With Tandem Stator

2019 ◽  
Author(s):  
Xiangjun Li ◽  
Wuli Chu
Keyword(s):  
Optimization Design ◽  
Numerical Study ◽  
Suction Side ◽  
High Load ◽  
Recirculation Region ◽  
Wall Region ◽  
Two Dimensional ◽  
Corner Separation ◽  
Positive Effects ◽  
End Wall

Abstract The application of tandem blade in compressors has been study for decades. According to the open literature, using tandem blade can effectively extend the working range of the compressor under high incidence. Many earlier researches focused on the two-dimensional influence of tandem blade, and revealed that a proper arrangement on the positions of the front and the rear blade would allow the boundary layer on the suction side to develop in a more favourable way to control the two-dimensional separation. However, because of the serious corner separation and higher loss in the end wall region of high-load compressors. Some recent researches started to focus on the three-dimensional flow for further understanding the effect of the tandem setup. As an effective way to influence the end wall flow, the profiled end wall can be applied to both turbines and compressors to reduce the end wall loss. However, the co-work of tandem blade and profiled end wall was seldom reported. In this paper, a numerical research was carried out based on a single-stage high-load compressor with a tandem stator. After a numerical study for the hub separation. A series of optimization design were carried out for the hub end wall of the rotor, stator and the stage to improve the overall efficiency. The discussion revealed the positive effects of the optimum profiled end wall on the tandem stator were on one hand to limit the extension of the recirculation region of the front passage and on another hand to suppress the suction side corner separation in the rear passage. The efficiency of the upstream rotor was also reduced in small value because the variation of the through flow. After that, the indirect influence of the rotor profiled end wall on the stator and the stage profiling case were also analysed. The optimum stage hub profiling did not equal to the simple combination of the optimum stator and the rotor hub end wall. It is found that in the stage profiling case, the variation of loss in stator and rotor are very well adjusted and balanced by the optimization algorithm. The improvement of efficiency therefore achieved the highest value.

Calculation of Laminar Separated Flow in Symmetric Two-Dimensional Diffusers

1995 ◽  
Vol 117 (4) ◽  
pp. 612-616 ◽  
Author(s):  
Yeng-Yung Tsui ◽  
Chia-Kang Wang
Keyword(s):  
Reynolds Number ◽  
Side Wall ◽  
Separated Flow ◽  
Expansion Ratio ◽  
Pressure Recovery ◽  
Recirculation Region ◽  
Two Dimensional ◽  
Symmetric Flow ◽  
Small Diffusion ◽  
Recirculating Flow

This study is concerned with numerical analysis of laminar separated flow in symmetric, two-dimensional, straight-walled diffusers. With Reynolds numbers Re = 56 and 114 and expansion ratios ER = 3 and 4, totally, there are four cases considered. At the low Reynolds number and the low expansion ratio the flow in the diffuser is nearly symmetric to the center line, irrespective of the diffusion angle. As Reynolds number or expansion ratio increases, a large recirculation region forms at one side wall and a small one at the other side. For the case with Re = 114 and ER = 4 the small recirculating flow disappears at small diffusion angles and a third recirculating flow appear in the same side of the small main recirculation region for large diffusion angles. The pressure recovery reaches its peak value somewhere downstream of the reattachment point of the large recirculating flow. The effectiveness of the diffuser deteriorates as the diffusion angle increases, apart from that at Re = 56 the effectiveness increases from θ = 15 to 30 deg. Symmetric flow solutions can be obtained by incorporating a symmetric relaxation method. The pressure recovery is higher for the symmetric flow than that for the asymmetric flow owing to the weaker recirculating strength in the former.

NUMERICAL STUDY ON NATURAL CONVECTION OF A GROWING CRYSTAL IN SOLUTION LAYER CAVITY

2009 ◽  
Vol 09 (03) ◽  
pp. 273-281
Author(s):  
SHUICHI TORII ◽  
WEN-JEI YANG
Keyword(s):  
Numerical Study ◽  
Side Wall ◽  
Circulation Pattern ◽  
Two Dimensional ◽  
Governing Equations ◽  
Vertical Side ◽  
Finite Difference Technique ◽  
Flow Transport ◽  
Solution Layer ◽  
Thermal Fluid Flow

Numerical study is performed on the thermal fluid-flow transport phenomena in a disk-shape cavity. Consideration is given to the movement and growth of the crystal in solution layer. Here the lysozyme is employed as the crystal. The mechanism is numerically investigated by solving the two-dimensional governing equations through discretization by means of a finite-difference technique and simultaneously the crystal movement is predicted by the Basset–Boussinesq–Oseen (BBO) equation. It is found that (i) the crystal circulates in the cavity with fluid current and shows the circulation pattern of a donut shape, like the flow in a typical Benard cell, (ii) when the particle makes the second circulation with a larger loop, it falls on to the bottom near the vertical side-wall, and (iii) the size of the falling particle becomes larger as the Rayleigh number, i.e. the temperature difference between the heat sink and the vertical side-wall is increased.

2D Numerical Study of a Micromixer Based on Blowing and Vortex Shedding Mechanisms

2019 ◽  
pp. 79-113
Author(s):  
Maria Sanchez-Claros ◽  
Joaquin Ortega-Casanova ◽  
Francisco Jose Galindo-Rosales
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Fluid Flows ◽  
Input Power ◽  
Mixing Efficiency ◽  
Injection Angle ◽  
Two Fluids ◽  
Optimum Configuration ◽  
Intensity Ratios

In this chapter, a numerical study and assessment of the mixing efficiency of a novel microfluidic device for mixing two fluids are presented. The device under study consists of a two-dimensional straight microchannel with a square pillar centered across the channel. The main fluid flows through the microchannel from the main inlet to the outlet, while the second fluid is injected through the pillar as two small jets at its upstream corners. For different values of the Reynolds number, intensity ratio between the jets and the main channel stream and jets injection angle, the authors have conducted several numerical simulations to characterize both the mixing efficiency and the required input power to make the fluids flow. The optimum configuration has been revealed for high values of the Reynolds number, low intensity ratios, and high injection angles. Thanks to vortex shedding and the corresponding downstream oscillations, a mixing efficiency of around 90% can be reached. The worst mixing efficiency is obtained for a configuration without vortex shedding, having a mixing efficiency of only around 2%.

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