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Effect of Physical Parameters on Thermal Behavior of Microcombustor

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2012年第2期26卷 300-304页

作者： Li, Yanxia Liu, Zhongliang Feng, Liang Beijing Univ Technol Coll Environm & Energy Engn Educ Minist Key Lab Enhanced Heat Transfer & Energy Conservat Beijing 100124 Peoples R China

A numerical study on methane/air combustion inside a microchannel was undertaken to investigate the effects of inlet velocity, equivalence ratio, and convective heat transfer coefficient on combustion characteristics. The simulation results show that the inlet velocity has a strong influence on the reaction zone, and the flame front shifts downstream as the inlet velocity increases. The influence of inlet velocity on convection heat transfer between mixture and walls is significant and the temperature difference between mixture and walls in the inlet section increases with the inlet velocity first to a certain value and then decreases. The equivalence ratio is a key parameter that affects the combustion characteristics. The highest flame temperature is obtained if the equivalence ratio is set at 1.0. The reaction rate of the equivalence ratio equal to 0.8 is larger than that of the equivalence ratio equal to 1.0 and 1.2. The steady flame cannot be obtained with a 0.6 equivalence ratio and 0.5 m/s inlet velocity. However, when the inlet velocity is increased to 0.7 m/s, a steady flame is observed. The convective heat transfer coefficient shows a very strong influence on combustion characteristics. With the increase of heat transfer coefficient on external walls, the wall temperature and downstream fluid temperature decrease. However, the influence is weakened at the inlet section. No oscillatory behavior is observed when the heat transfer coefficient is less than 50 W/(m(2) . K) and the steady flame cannot be obtained if the heat transfer coefficient is set at 100 W/(m(2) . K).

关键词： Convection Heat Transfer Coefficient Catalytic Combustion Thermal Resistance Combustors computational fluid dynamics simulation Thermal Conductivity Microelectromechanical Systems Energy Density Specific Heat Velocity Profiles

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Compressible Modeling of the Internal Flow in a Gas-Centered Swirl-Coaxial Fuel Injector

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JOURNAL OF PROPULSION AND POWER 2012年第4期28卷 685-693页

作者： Trask, Nathaniel Schmidt, David P. Lightfoot, Malissa Danczyk, Stephen Univ Massachusetts Dept Mech Engn Amherst MA 01002 USA USAF Res Lab RZSA Edwards AFB CA 93524 USA

Predicting the liquid film dynamics inside the injector cup of gas-centered swirl-coaxial fuel injectors requires a general two-phase approach that is appropriate for all liquid-volume fractions, high Mach and Weber numbers, and complex geometries. A Eulerian two-phase model is implemented to represent the liquid and gas interactions in the injector as well as the atomization processes occurring at the rough interface. Previous work using an incompressible formulation encountered difficulty in matching film profiles at large mass flow rates. The current work is an enhanced approach that includes compressibility effects. The improvement gained by implementing a compressible formulation is attributed to a sudden expansion occurring following the injector lip. Two-dimensional results are compared to high-speed photographs of the liquid film within the injector cup. Applications of closures for the turbulent liquid flux commonly used in the literature are presented and are shown to substantially overpredict the atomization rate. By limiting the rate at which entrainment occurs via the Schmidt number, the film profile is accurately predicted over a wide range of momentum flux ratios, highlighting the stabilizing effect the swirl has upon the atomization process. The applicability of this modeling approach and an assessment of the necessity for investigating Reynolds stress closures in future work are assessed.

关键词： Fuel Injection Reynolds Averaged Navier Stokes Hydrostatic Pressure Mass Flow Rate Compressibility Effect Velocity Profiles computational fluid dynamics simulation Axisymmetric Flow Mach Numbers Continuity Equation

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Design Criteria for Oilfield Separators Improved by computational fluid dynamics

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CHEMICAL ENGINEERING & TECHNOLOGY 2012年第2期35卷 323-333页

作者： Laleh, Ali Pourahmadi Svrcek, William Y. Monnery, Wayne D. Univ Calgary Dept Chem & Petr Engn Calgary AB T2N 1N4 Canada Chem Pet Proc Tech Ltd Calgary AB Canada

Oilfield separator data ranging from light-oil conditions to heavy-oil conditions were incorporated into suitable two-phase and three-phase computational fluid dynamics (CFD) models to provide improved design criteria for separator design methods. The CFD simulation results revealed that the most important affecting parameters are vapor density and oil viscosity. In contrast with the classic design methods, noticeable residence times were required for liquid droplets to penetrate through the fluid interfaces. Moreover, it was indicated that the Abraham equation should be used instead of the Stokes' law in the liquid-liquid separation calculations. The velocity constraints caused by re-entrainment in horizontal separators were also studied and led to novel correlations.

关键词： computational fluid dynamics simulation Multiphase flows Oilfield separator Phase separation

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Implementation of Menter's Transition Model on an Isolated Natural Laminar Flow Nacelle

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AIAA JOURNAL 2011年第4期49卷 824-835页

作者： Lin, Yujing Robinson, Theresa Early, Juliana Riordan, David Tweedie, James Magee, Liam Queens Univ Belfast Dept Mech & Aerosp Engn Belfast BT7 1NN Antrim North Ireland Queens Univ Belfast Dept Mech & Aerosp Engn Belfast BT9 5AH Antrim North Ireland Bombardier Tech Engn Belfast BT3 9DZ Antrim North Ireland Bombardier Powerplant & Syst Dept Bombardier Aerosp Belfast BT3 9DZ Antrim North Ireland

This study evaluates the implementation of Menter's gamma-Re-theta Transition Model within the CFX12 solver for turbulent transition prediction on a natural laminar flow nacelle. Some challenges associated with this type of modeling have been identified. The computational fluid dynamics transitional flow simulation results are presented for a series of cruise cases with freestream Mach numbers ranging from 0.8 to 0.88, angles of attack from 2 to 0 degrees, and mass flow ratios from 0.60 to 0.75. These were validated with a series of wind-tunnel tests on the nacelle by comparing the predicted and experimental surface pressure distributions and transition locations. A selection of the validation cases are presented in this paper. In all cases, computational fluid dynamics simulations agreed reasonably well with the experiments. The results indicate that Menter's gamma-Re-theta Transition Model is capable of predicting laminar boundary-layer transition to turbulence on a nacelle. Nonetheless, some limitations exist in both the Menter's gamma-Re-theta Transition Model and in the implementation of the computational fluid dynamics model. The implementation of a more comprehensive experimental correlation in Menter's gamma-Re-theta Transition Model, preferably the ones from nacelle experiments, including the effects of compressibility and streamline curvature, is necessary for an accurate transitional flow simulation on a nacelle. In addition, improvements to the computational fluid dynamics model are also suggested, including the consideration of varying distributed surface roughness and an appropriate empirical correction derived from nacelle experimental transition location data.

关键词： Natural Laminar Flow Airframes computational fluid dynamics simulation Hybrid Laminar Flow Control Laminar Turbulent Transition Transonic Wind Tunnel Angle of Attack Mass Flow Rate Velocity Profiles Surface Roughness

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Natural Convection in an Enclosed Cavity with Conjugate Effects Using Fuzzy Logic

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2011年第3期25卷 393-400页

作者： Jain, Abhishek Kaminski, Deborah A. Intel Corp Chandler AZ 85226 USA Rensselaer Polytech Inst Dept Mech Engn Troy NY 12180 USA

A controller algorithm using a predefined set of fuzzy rules is implemented for fast convergence of a computational fluid dynamics simulation in an enclosed cavity. Relaxation factors are adjusted using the rule set to heuristically guide the iterative scheme towards convergence. The model problem of natural convection in an inclined rectangular cavity is analyzed using this scheme. To test the efficacy of the fuzzy logic guidance method, finite thickness walls with conjugate heat transfer are imposed. Governing equations of continuity, momentum, and energy in laminar flow are solved using a finite difference method. The performance of the controller is compared with that of the simulation with constant relaxation factors. Overall, the number of iterations required for the controller algorithm using fuzzy logic is comparable to the number of iterations obtained using constant relaxation factors. However, six cases of high Grashof number and high tilt angle, which do not converge with any fixed relaxation factor, can be solved using the fuzzy controller. The probability of convergence with the controller is higher than it is when using a fixed relaxation factor.

关键词： Fuzzy Control Natural Convection Conjugate Heat Transfer computational fluid dynamics simulation Buoyancy Force Flow Conditions Finite Difference Method Conduction Velocity Profiles Thermal Conductivity

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computational Study of Microflaps with Application to Vibration Reduction in Helicopter Rotors

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AIAA JOURNAL 2011年第7期49卷 1450-1465页

作者： Liu, Li Padthe, Ashwani K. Friedmann, Peretz P. Univ Michigan Dept Aerosp Engn Ann Arbor MI 48109 USA

A comprehensive study on unsteady effects of oscillating Gurney flaps, or microflaps, has been conducted. Two-dimensional unsteady airloads for lift, moment, and drag due to an oscillating microflap were computed using a compressible Reynolds-averaged Navier-Stokes flow solver. The computational fluid dynamics results were generated with an overset-mesh approach that captures oscillatory microflap motion. Three microflap configurations were examined to determine the type most suitable in terms of actuation efficiency and practical implementation. Furthermore, a reduced-order model for the unsteady microflaps was developed based on computational fluid dynamics simulations, using the rational function approximation approach. The resulting rational function approximation model is a state-space time-domain aerodynamic model that accounts for unsteadiness, compressibility, and time-varying freestream effect. The agreement between the reduced-order model and direct computational fluid dynamics calculations was found to be excellent for a wide range of flow conditions examined. The approximate model is suitable for incorporation in a comprehensive code, from which the potential of microflaps for active control of vibrations in rotors can be determined. Open-loop control studies indicated that the microflap produces substantial vibration reduction (80% reduction in vertical shear), whereas closed-loop control using combined harmonic inputs consisting of a sum of four harmonics (2-5/rev) reduced the vibration objective by 92%, on a hingeless rotor configuration resembling the Messerschmitt-Bolkow-Blohm BO-105. These results confirmed the control authority and effectiveness of the microflap for vibration reduction in rotorcraft.

关键词： Helicopter Rotor Modeling Aerodynamic Response computational fluid dynamics simulation Trailing Edge Flap Rotorcraft simulations State Space Representation Reynolds Averaged Navier Stokes Compressible Flow Messerschmitt Bolkow Blohm Flow Characteristics

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Flow and Heat Transfer in Hydraulic Reservoir of Thrust Vector Control System

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2011年第1期25卷 147-154页

作者： Frate, D. T. Pham, N. T. Christie, R. J. Mcquillen, J. B. Motil, B. J. Chao, D. F. Zhang, N. NASA John H Glenn Res Ctr Lewis Field Launch Syst Project Off Cleveland OH 44135 USA NASA John H Glenn Res Ctr Lewis Field Thermal Syst Branch Cleveland OH 44135 USA NASA John H Glenn Res Ctr Lewis Field Fluid Phys & Transport Branch Cleveland OH 44135 USA

Launch vehicle thrust vector control provides vehicle steering functions during powered flight starting from liftoff until engine cutoff. The thrust vector control on the first stage of Ares 1 provides steering during the first 133 s of ascent, while the thrust vector control on the upper stage provides steering for the next 465 s. Heat absorption by the hydraulic reservoir is a key factor in the performance of the upper stage thrust vector control system. A computational fluid dynamics simulation of the fluid flow and heat transfer in the hydraulic reservoir in the Ares 1 upper stage thrust vector control has been performed with the corresponding operating conditions and environmental conditions. The reservoir was set at 75% full of working fluid. Two steady-state cases, for fluid inlet temperatures of 294.3 and 394.3 K, and one transient case for the fluid inlet temperature ramping from 294.3 to 352.2 K over a 4.63 min period were simulated. The temperature, velocity, and pressure fields, as well as the absorbed heat for each case, were obtained, which have improved the understanding of the thermal dynamics of the thrust vector control subsystem.

关键词： Calculated Heat Transfer Coefficients Thrust Vector Control Inlet Temperature computational fluid dynamics simulation fluid Flow Heat Absorption Launch Vehicles Flow Patterns Natural Convection Thermal Conductivity

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Efficient Uncertainty Quantification Approach for Reentry Flows with Mixed Uncertainties

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2011年第4期25卷 523-535页

作者： Bettis, Benjamin R. Hosder, Serhat Missouri Univ Sci & Technol Rolla MO 65409 USA

The primary focus of this paper is to present and demonstrate an efficient approach for propagating mixed input uncertainties, aleatory and epistemic, through a complex simulation code. In particular, the approach is applied to the uncertainty quantification of surface heat flux to the spherical nonablating heat-shield of a generic reentry vehicle due to epistemic and aleatory uncertainties that may exist in various parameters used in the numerical solution of hypersonic, viscous, laminar blunt-body flows with thermochemical nonequilibrium. Two main uncertainty sources were treated in the computational fluid dynamics simulations: 1) aleatory uncertainty in the freestream velocity and 2) epistemic uncertainty in the recombination efficiency for a partially catalytic wall boundary condition. The second-order uncertainty quantification using a stochastic response surface obtained with point-collocation nonintrusive polynomial chaos was used for the propagation of mixed (aleatory and epistemic) uncertainties. The uncertainty quantification approach was thoroughly tested on a stochastic model problem with mixed uncertainties for the prediction of stagnation-point heat transfer with Fay-Riddell relation, which included the comparison with direct Monte Carlo sampling results. In the stochastic computational fluid dynamics problem, the uncertainty in surface heat transfer was obtained in terms of intervals at different probability levels at various locations, including the stagnation point and the shoulder region. The mixed uncertainty results were compared with the results obtained with a purely aleatory uncertainty analysis to show the difference between two uncertainty quantification approaches. A global sensitivity analysis indicated that the velocity has a stronger contribution to the overall uncertainty in the stagnation-point heat transfer.

关键词： Stagnation Temperature Surface Heat Transfer Freestream Conditions computational fluid dynamics simulation Cumulative Distribution Function Coefficient of Viscosity Reentry Vehicles Nonequilibrium Flows Thermal Protection System Angle of Attack

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computational fluid dynamics Modeling of an Inverted Frusto-conical Shaking Bioreactor for Mammalian Cell Suspension Culture

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BIOTECHNOLOGY AND BIOPROCESS ENGINEERING 2011年第3期16卷 567-575页

作者： Hang, Haifeng Guo, Yuanxin Liu, Jian Bai, Li Xia, Jianye Guo, Meijin Hui, Matthew E China Univ Sci & Technol State Key Lab Bioreactor Engn Shanghai 200237 Peoples R China Chinese Acad Sci Inst Proc Engn Natl Key Lab Biochem Engn Beijing 100190 Peoples R China

We previously developed an inverted frusto-conical shaking bioreactor (IFSB) which had high mammalian cell culture performance when compared with a mechanically stirred tank reactor (STR) or a flat-bottom shaking bioreactor (FBSB). Here, we determined the mixing time (t) and volumetric oxygen transfer coefficient (k(L)a) of this IFSB at various speeds, and simulated the fluid hydrodynamics, including the shear stress and specific surface area, by computational fluid dynamics. The shortest mixing time was observed in a STR. The maximum k(L)a value of 12/h was achieved in the IFSB at an aeration rate of 4 L/h, demonstrating that our IFSB has enhanced oxygen transfer capabilities needed to meet the demands of mammalian cells. simulation studies revealed a 3% greater specific surface area and a 21% lower shear strain in the IFSB compared to an FBSB under the same conditions. Additionally, the conical angle of the vessel, which significantly affected cell growth and recombinant protein production, was tested here. We conclude that, compared to the STR and FBSB, the IFSB has an increased liquid surface area for oxygen uptake and exhaust CO2 stripping, an enhanced k(L)a for cell robust growth to a high cell density, and a lower shear stress to alleviate cell damage.

关键词： inverted frusto-conical shaking bioreactor mammalian cell suspension culture mixing time volumetric oxygen transfer coefficient computational fluid dynamics simulation

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Numerical analysis of airflow alteration in central airways following tracheobronchial stent placement

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EXPERIMENTAL HEMATOLOGY & ONCOLOGY 2012年第2012期1卷 23-23页

作者： Ho, Chien-Yi Liao, Hsiu-Mei Tu, Chih-Yen Huang, Chih-Yang Shih, Chuen-Ming Su, Min-Ying Lydia Chen, Jeon-Hor Shih, Tzu-Ching China Med Univ Sch Chinese Med Grad Inst Chinese Med Taichung Taiwan China Med Univ Hosp Dept Family Med Taichung Taiwan China Med Univ Grad Inst Basic Med Sci Taichung Taiwan China Med Univ Hosp Dept Internal Med Div Chest Med Taichung 40402 Taiwan Natl Chung Hsing Univ Dept Life Sci Taichung Taiwan China Med Univ Dept Resp Therapy Taichung Taiwan China Med Univ Hosp Prevent Med Ctr Taichung Taiwan Univ Calif Irvine Dept Radiol Sci Tu & Yuen Ctr Funct Onco Imaging Irvine CA 92697 USA China Med Univ Hosp Dept Radiol Taichung Taiwan China Med Univ Coll Hlth Care Dept Biomed Imaging & Radiol Sci Taichung 40402 Taiwan

The computational fluid dynamics method, which provides an estimation of the pressure drop in the airway before and after the stent implantation, is proposed in this study. This method is based on the finite volume model. The pressure field was solved by the Navier-Stokes equations. The proposed methodology was evaluated in seven health people (control group) and in fourteen patients who were assigned in two groups, in which one was tracheal stenosis and the other was bronchial stenosis. The results showed that the pressure drop after tracheal stent implantation became significantly smaller. For bronchial stent implantation cases, the airway resistance improved insignificantly.

关键词： Pressure Drop computational fluid dynamics Stent Placement Stent Implantation computational fluid dynamics simulation

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