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Multiple Injector Model for Primary Breakup of a Liquid Jet in Crossflow

AIAA JOURNAL 2011年第11期49卷 2407-2420页

作者： Mashayek, A. Behzad, M. Ashgriz, N. Univ Toronto Dept Mech & Ind Engn Toronto ON M5S 3G8 Canada Univ Toronto Dept Phys Toronto ON M5S 1A7 Canada Univ Toronto Dept Civil Engn Toronto ON M5S 1A4 Canada

A model for the atomization of a turbulent liquid jet injected into a subsonic gaseous crossflow is provided. The trajectory of the jet before its breakup is predicted theoretically. The stripping of droplets from the jet is modeled by defining multiple injectors along the predicted jet trajectory. The properties of the stripping droplets are prescribed using empirical correlations specifically derived for jets in crossflow. The secondary breakup of the product droplets and their subsequent motion in the gas flow are predicted using a Lagrangian-Eulerian numerical scheme. Experiments are carried out to investigate the capability of the model in predicting spray penetration and droplet size, and velocity distributions downstream of the nozzle.

关键词： Aerodynamic Force Particle Image Velocimetry Sauter Mean Diameter Velocity Profiles Weber Numbers Flow Conditions Numerical Modeling computational fluid dynamics simulation Vortices Arbitrary Lagrangian Eulerian

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Analysis of Interference Drag for Strut-Strut Interaction in Transonic Flow

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AIAA JOURNAL 2011年第3期49卷 449-462页

作者： Duggirala, Ravi K. Roy, Christopher J. Schetz, Joseph A. Virginia Polytech Inst & State Univ Dept Aerosp & Ocean Engn Blacksburg VA 24061 USA

computational fluid dynamics simulations were performed to predict the interference drag produced by two streamlined struts intersecting at various angles in transonic flow because no relevant experimental data are available for use in design studies. The one-equation Spalart-Allmaras turbulence model was employed in a Reynolds-averaged Navier-Stokes formulation assuming fully turbulent flow. Selected cases were run using the two-equation k-omega shear stress transport turbulence model for comparison. NACA 64A series airfoils with thickness ratios of 5 and 7.5% were studied at Mach 0.8 and 0.85 for intersection angles between 45 and 90 deg at an altitude of 12.2 km (chord-based Reynolds numbers of approximately 5 million). The commercial computational fluid dynamics code FLUENT was used for the analysis. To better understand the flow behavior, contours of surface pressure and velocity near the interaction region were examined. It is observed that the flowfield is disturbed due to shock-induced separation only near the interaction region. There is little effect on viscous drag due to the strut-strut interaction, but changes in the pressure drag result in net interference drag. It is noted that there is an unexpected rise in the interference drag when the struts intersects at 90 deg due to significant shock-induced flow separation on both sides of the intersecting strut, whereas smaller intersection angles show flow separation only on the side with the acute angle. A response surface for the interference drag coefficient as a function of Mach number, thickness ratio, and intersection angle was generated using the numerical simulations for use in the Multidisciplinary Design Optimization studies where efficient means of estimating the interference drag are needed.

关键词： Flow Conditions Fuselages Interference Drag Freestream Mach Number computational fluid dynamics simulation Spalart Allmaras Turbulence Model Reynolds Averaged Navier Stokes Turbulent Boundary Layer MDO Thickness to Chord Ratio

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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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Aerodynamic Evaluation of Miniature Trailing-Edge Effectors for Active Rotor Control

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JOURNAL OF AIRCRAFT 2011年第3期48卷 995-1004页

作者： Matalanis, Claude G. Wake, Brian E. Opoku, Daniel Min, Byung-Young Yeshala, Nandita Sankar, Lakshmi United Technol Res Ctr E Hartford CT 06108 USA Georgia Inst Technol Atlanta GA 30332 USA

This work presents progress on a detailed aerodynamic evaluation of miniature trailing-edge effectors for active rotor control. We begin with a two-dimensional computational fluid dynamics study focused on establishing the dependency of miniature trailing-edge effector effectiveness and performance upon basic geometric parameters of a VR-12 airfoil. The computational fluid dynamics study demonstrated that a miniature trailing-edge effector placed at 10% chord upstream of the trailing-edge and sized at approximately 1% chord is capable of delivering moment coefficient increments of approximately +/- 0.03, or the same moment authority as a 20% chord conventional flap moving +/- 2.3 degrees. Wind-tunnel experiments were performed on a model blade section equipped with an operational miniature trailing-edge effector in order to validate the steady computational fluid dynamics results, and reasonable agreement was shown. Finally, a small set of three-dimensional unsteady computational fluid dynamics simulations with the prescribed blade motion of a rotor equipped with miniature trailing-edge effectors were performed. Under high-thrust moderate speed conditions, miniature trailing-edge effectors deployed sinusoidally at 4/rev frequency were capable of reducing 4/rev integrated aerodynamic loads in the vertical direction by approximately 80%.

关键词： Trailing Edges computational fluid dynamics simulation Thin Airfoil Aerodynamic Characteristics Low Speed Wind Tunnel Aerodynamic Performance Aspect Ratio Trailing Edge Flap Rotorcrafts Spalart Allmaras Turbulence Model

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Behavior of Detached-Eddy simulations for Mild Airfoil Trailing-Edge Separation

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JOURNAL OF AIRCRAFT 2011年第1期48卷 193-202页

作者： Durrani, Naveed Qin, Ning Univ Sheffield Dept Mech Engn Sheffield S1 3JD S Yorkshire England

The flow around the A-airfoil at the maximum lift condition (alpha = 13.3 degrees) with a chord Reynolds number of 2 x 10(6) is simulated using unsteady Reynolds-averaged Navier-Stokes solution, detached-eddy simulation, and delayed- detached eddy simulation. This case features a relatively thick boundary layer with a mild trailing-edge separation. Detailed comparisons of the modeled Reynolds stresses are carried out with the available experimental data at different locations on the suction side of the airfoil and in the wake region. The impact of the delayed switching on modeled Reynolds stresses from delayed-detached-eddy simulation as compared with the original detached-eddy simulation is studied. On the suction side of the airfoil, the modeled turbulent Reynolds stresses computed through the detached-eddy simulation are generally lower than the unsteady Reynolds-averaged Navier-Stokes solutions, whereas the delayed-detached-eddy simulation gives comparable values with the unsteady Reynolds-averaged Navier-Stokes solutions results. None of them give consistent comparison with the experimental Reynolds stresses. It is observed that for the cases with the mild separation, the original detached-eddy simulation may perform better than the delayed-detached-eddy simulation, due to its relatively lower turbulent dissipation levels. The detached-eddy simulation Reynolds stresses in the wake region show better results, in comparison with the experimental data.

关键词： computational fluid dynamics simulation Trailing Edges Airfoil Reynolds Averaged Navier Stokes Spalart Allmaras Turbulence Model Mach Number Vortex Shedding Skin Friction Coefficient Velocity Profiles Angle of Attack

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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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Estimation of Captive Flight Loads Using Grid-Free Euler Solver

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JOURNAL OF AIRCRAFT 2011年第4期48卷 1273-1279页

作者： Shah, Vaibhav More, Rohit R. Raju, S. Srinivasa Anandhanarayanan, K. Krishnamurthy, R. Chakraborty, Debasis Def Res & Dev Lab Computat Fluid Dynam Div Directorate Computat Dynam Hyderabad 500258 Andhra Pradesh India

The structural integrity of a store and its attachments to a fighter aircraft has to be verified at various aircraft maneuvering conditions in its flight envelope for the clearance of the store to integrate with aircraft. The captive loads of a flight vehicle mounted on a fighter aircraft have been estimated at various Mach numbers, angles of attack, and sideslip angles using an indigenously developed 3-D grid-free Euler. solver. The point distributions required to apply grid-free solver are obtained using chimera cloud technique, and the connectivity required for the solver is obtained using gradient search method. Forces and moments acting on the fighter aircraft with launchers and flight vehicles have been estimated using computational fluid dynamics simulations at different flow conditions, and load distributions on flight vehicle have been obtained. The aerodynamic loads obtained from computational fluid dynamics calculations form the basis of the flight testing.

关键词： Flight Vehicle Angle of Attack Fighter Aircraft Aerodynamic Characteristics Flow Conditions computational fluid dynamics simulation Mean Aerodynamic Chord Sideslip Structural Integrity Flight Testing

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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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Micro-particle deposition and lobar distribution of mass flow in human upper respiratory tract model

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Science Bulletin 2011年第Z1期 380-385页

作者： HUANG JianHua1 & ZHANG LianZhong1,2 1 School of Physics,Nankai University,Tianjin 300071,China 2 State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710075,China

A representative human upper respiratory tract model consisting of oropharyngeal and asymmetric tracheobronchial(TB) airways from the trachea(G0) to the main lobar bronchi(G2) was constructed. Laminar-to-turbulent airflow for typical inhalation modes as well as micro-particle transportation,wall deposition and mass flow to lobes was simulated using the CFX10.0 software from Ansys Inc. The numerical particle deposition efficiency of the oropharynx region and two generations(G1 and G2) of TB airways shows great agreement with the experimental data obtained from realistic casts. The particle deposition pattern indicates that inertial impaction is the primary mechanism in the human upper airway,and turbulence dispersion performs crescent influence especially for small particles. The initial positions of particles with different fates are confined to specifically concentrated zones. The particle mass distributions of five lobes are close to airflow distributions. The upper lobes receive fewer particles than lower lobes and the right middle lobe receives the least.

关键词： upper respiratory tract asymmetric tracheobronchial airways transportation and deposition lobar differences computational fluid dynamics simulation

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