Mixing Enhancement Induced by a Delta Wing in Supersonic Flows

2016 ◽  
Author(s):  
Wei Huang ◽  
Shi-bin Li ◽  
Li Yan ◽  
Jun Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Delta Wing ◽  
Pressure Ratio ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Efficient Operation ◽  
Injection Flow ◽  
Transverse Injection

The maximization of rapid fuel-air mixing is one of the essential issues for the efficient operation of scramjet engines. A delta wing with its height being 6mm is located ahead of the injector to enhance the mixing process between the injectant and air in the supersonic flow with the freestream Mach number being 3.75, and the influence of the distance between the delta wing and the injector on the mixing efficiency is evaluated numerically, as well as the effect of the jet-to-crossflow pressure ratio. At the same time, the predicted results obtained in the three-dimensional transverse injection flow field are compared with the available experimental data in the open literature, and the grid independency analysis is conducted as well. The obtained results show that the mixing efficiency increases with the decrease of the jet-to-crossflow pressure ratio, and this conclusion is consistent with that obtained in the transverse injection flow field. The predicted wall static pressure distributions show reasonable agreement with the experimental data, and the grid scale has only a slight impact on the predicted results. Further, it is observed that the mixing efficiency increase with the decrease of the distance between the delta wing and the injector, and the hydrogen penetrates deeper into the core flow when the distance is smaller. Accordingly, the plume area is larger. This illustrates that the transverse jet flow field is affected by the vortex generated by the delta wing, and the mixing process is enhanced. The maximum mixing efficiency at x = −350mm is nearly 0.84 in the range considered in this paper.

Control of Flow Field, Mass Transfer and Mixing Enhancement in T-Shaped Microchannels

2016 ◽  
Vol 33 (3) ◽  
pp. 387-394
Author(s):  
Y. Bazargan-Lari ◽  
S. Movahed ◽  
M. Mashhoodi
Keyword(s):  
Flow Field ◽  
Applied Voltage ◽  
Electroosmotic Flow ◽  
Microfluidic Devices ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Field Mass ◽  
Control Of Flow ◽  
Micro Mixer ◽  
Two Fluid

AbstractA T-shaped microfluidic micro-mixer was designed to mix desired concentrations of two fluid streams and to prepare their homogenous mixture solution. A hydrostatic pressure gradient was induced in one of the branches of the system (mixing channel) by applying external electric field and generating electroosmotic flow in the two other branches of the system. The flow field and transferred mass into the mixing channel can be regulated by controlling the applied voltage of the system. In order to prepare more homogenous mixture solution, some obstacles were added to the mixing channel to induce perturbation in the flow field and enhance the mixing efficiency of the system. Numerical simulations were performed to show the correctness of the proposed mixing strategy and to investigate the influences of the applied voltage on the mixing efficiency and induced pressure flow in the mixing channel. A proposed design can be used as a guideline to control and enhance mixing efficiency, and consequently functionality, of different microfluidic devices.

Study on the Flow Characteristics of Transverse Injection in Cavity

2013 ◽  
Vol 291-294 ◽  
pp. 1940-1944
Author(s):  
Hai Jun Sun ◽  
Zhuo Xiong Zeng ◽  
Yi Hua Xu
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Flow Characteristics ◽  
Mass Diffusion ◽  
Mixing Efficiency ◽  
Flame Stability ◽  
Fuel Distribution ◽  
Turbulence Flow ◽  
Transverse Injection

The combination of transverse injection and cavity flame stabilizer is a good way to improve the mixing efficiency and flame stability. In order to study the influence of transverse injection on the flow field of cavity in advanced vortex combustor, the turbulence flow and the fuel distribution under the influence of different assignments of jet holes were simulated numerically. The results show that the different assignments of jet holes have a bigger impact on the geometry and center of vortex, but lesser on the total pressure of combustor. The content of fuel reduces quickly in the jet direction, injection can improve the mixing of fuel and air. The phenomenon of mass diffusion and transport is obvious, it is in favor of flame stability.

Numerical validation and back-pressure effect on internal compression flows of typical supersonic inlet

2015 ◽  
Vol 119 (1215) ◽  
pp. 631-645 ◽  
Author(s):  
F. Ding ◽  
C.-B. Shen ◽  
W. Huang ◽  
J. Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Stokes Equations ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Wave Pattern ◽  
Back Pressure ◽  
Freestream Turbulence ◽  
Supersonic Inlet

AbstractA numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNGk-ε, realisablek-ε, standardk-ε, and SSTk-ω turbulence models. The RNGk-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.

Flow Analysis of a High Flowrate Centrifugal Compressor Stage and Comparison With Test Rig Data

2016 ◽  
Author(s):  
Anton Weber ◽  
Christian Morsbach ◽  
Edmund Kügeler ◽  
Christoph Rube ◽  
Matthias Wedeking
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Test Rig ◽  
Total Pressure Ratio

The flow field inside a single-stage centrifugal compressor characterized by a high flowrate of Φ = 0.15 and a design total pressure ratio of approximately 1.4 is analysed numerically. The stage geometry consists of a radially oriented inlet duct with uniform inflow without swirl, a 90 deg inlet bend in front of the impeller, the shrouded impeller itself followed by a large radial vaneless diffuser, a 180 deg U-turn, a radially oriented turning vane, a subsequent 90 deg bend, and as the last item a long axial exit duct. The impeller blades have large fillets at hub and tip and thick blunt trailing edges. Due to the rotating shroud, a labyrinth seal is placed above the impeller with 5 seal tips. The complete leakage region is also included in the CFD analysis. The blade numbers for the impeller and vane are 15 and 14, respectively. The test rig has recently been built at the Institute of Propulsion and Turbomachinery at RWTH Aachen University (Germany). The first part of the CFD work presented was carried out before the first experimental data were available. Using the k-ω turbulence model of Wilcox (1988), a number of principal steady RANS calculations were performed to investigate the following: Impact of near wall grid resolution and turbulence model wall boundary condition treatment, impact of impeller fillets, and the influence of leakage flow. This part is completed by a comparison of steady RANS simulations with the time-mean results of unsteady RANS analyses of one blade passage. For the calculations presented in the second part, experimental data are available at the inflow and outflow planes. At these planes overall mean values were deduced. Additionally, 3- and 5-hole probe data are available at spanwise traverse planes located at the zenith of the U-turn and in the exit plane. For part two a finer grid with y+ values of approximately unity for all solid walls was used. In addition to the Wilcox k-ω model and the Menter SST k-ω model, two higher level turbulence models — the explicit algebraic Reynolds stress model Hellsten EARSM k-ω and the differential Reynolds stress model SSG/LRR-ω — have been tested and compared with the experiments. The agreement in terms of overall performance (total pressure ratio, isentropic efficiency) is satisfactory for all turbulence models used, but there are some differences: the k-ω model is shown to be the most stable one towards stall. On the other hand, it is shown that details of the flow field in terms of the two spanwise traverses can be better represented by the more advanced turbulence models. All CFD simulations have been performed at 100% shaft speed.

Application of Delayed Detached Eddy Simulation and RANS to Compressor Cascade Flow

2008 ◽  
Author(s):  
Chunwei Gu ◽  
Meilan Chen ◽  
Xuesong Li ◽  
Fan Feng
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Mixing Process ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Eddy Simulation ◽  
Cascade Flow ◽  
Delayed Detached Eddy Simulation ◽  
Comparison Results ◽  
Instantaneous Flow Field

Spalart-Allmaras (S-A) model based Delayed Detached Eddy Simulation (DDES) is performed to investigate the flow field in a compressor cascade (NACA64A-905) with experimental data for calibration. The value of the modeling coefficient CDES in DDES is open for revision and depends heavily on the numerical schemes. The effects of CDES on the DDES results are studied and an optimal CDES value is estimated for the specific case, with MUSCL reconstructed Roe scheme incorporated in in-house CFD codes. CDES value of 0.2 is turned out reliable concerning both accuracy and convergence. S-A model is also performed for comparison. Results from different methods indicate that the time-averaged results by DDES with CDES of 0.2 are more consistent with the experimental results than those by S-A model. The instantaneous flow field predictions show that DDES is well capable of capturing the unsteady features of the cascade flow, especially the wake mixing process.

scholarly journals Influence of Seal Cavity Leakage Flow on Compressor Performance Investigated with a Circumferentially Averaged Method

2021 ◽  
Vol 11 (2) ◽  
pp. 780
Author(s):  
Dong Liang ◽  
Xingmin Gui ◽  
Donghai Jin
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Interaction Mechanism ◽  
Main Flow ◽  
Leakage Flow ◽  
Destructive Effect ◽  
Through Flow ◽  
Compressor Performance ◽  
Overall Performance ◽  
Flow Blockage

In order to investigate the effect of seal cavity leakage flow on a compressor’s performance and the interaction mechanism between the leakage flow and the main flow, a one-stage compressor with a cavity under the shrouded stator was numerically simulated using an inhouse circumferentially averaged through flow program. The leakage flow from the shrouded stator cavity was calculated simultaneously with main flow in an integrated manner. The results indicate that the seal cavity leakage flow has a significant impact on the overall performance of the compressor. For a leakage of 0.2% of incoming flow, the decrease in the total pressure ratio was 2% and the reduction of efficiency was 1.9 points. Spanwise distribution of the flow field variables of the shrouded stator shows that the leakage flow leads to an increased flow blockage near the hub, resulting in drop of stator performance, as well as a certain destructive effect on the flow field of the main passage.

Nanoparticle Precipitation in a T-Mixer: Coupling Experimental and Numerical Investigations of the Fluid Dynamics With the Solid Formation Processes

2006 ◽  
Author(s):  
Johannes Gradl ◽  
Florian Schwertfirm ◽  
Hans-Christoph Schwarzer ◽  
Hans-Joachim Schmid ◽  
Michael Manhart ◽  
...  
Keyword(s):  
Flow Field ◽  
Fluid Dynamic ◽  
Concentration Field ◽  
Population Balance ◽  
Mixing Process ◽  
Image Velocimetry ◽  
Modeling Material ◽  
Field Information ◽  
Set Up ◽  
3D Information

Mixing and consequently fluid dynamic is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. Due to fast and intensive mixing a static T-mixer configuration is capable for synthesizing continuously nanoparticles. The flow and concentration field of the applied mixer is investigated experimentally at different flow rates by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). Due to the PIV measurements the flow field in the mixer was characterized qualitatively and the mixing process itself is quantified by the subsequent LIF-measurements. A special feature of the LIF set up is to detect structures in the flow field, which are smaller than the Batchelor length. Thereby a detailed insight into the mixing process in a static T-Mixer is given. In this study a CFD-based approach using Direct Numerical Simulation (DNS) in combination with the solid formation kinetics solving population balance equations (PBE) is applied, using barium sulfate as modeling material. A Lagrangian Particle Tracking strategy is used to couple the flow field information with a micro mixing model and with the classical theory of nucleation. We found that the DNS-PBE approach including macro and micro mixing, combined with the population balance is capable of predicting the full PSD in nanoparticle precipitation for different operating parameters. Additionally to the resulting PSD, this approach delivers a 3D-information about all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which is visualized for different process variables.

Mixing Enhancement of Two Gases in a Microchannel Using DSMC

2013 ◽  
Vol 307 ◽  
pp. 166-169 ◽  
Author(s):  
Masoud Darbandi ◽  
Elyas Lakzian
Keyword(s):  
Gas Flow ◽  
Flow Analysis ◽  
Direct Simulation Monte Carlo ◽  
Equilibrium Composition ◽  
Mass Composition ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Result Section ◽  
Flow Through ◽  
Simulation Monte Carlo

Microgas flow analysis may not be performed accurately using the classical CFD methods because of encountering high Knudsen number regimes. Alternatively, the gas flow through micro-geometries can be investigated reliably using the direct simulation Monte Carlo (DSMC) method. Our concern in this paper is to use DSMC to study the mixing of two gases in a microchannel. The mixing process is assumed to be complete when the mass composition of each species deviates by no more than ±1% from its equilibrium composition. To enhance the mixing process, we focus on the effects of inlet-outlet pressure difference and the pressure ratios of the incoming CO and N2 streams on the mixing enhancement. The outcome of this study is suitably discussed in the result section.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

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