Huntsville, AL, United States


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Zhao X.,Alabama A&M University | Meganathan A.,ESI CFD Inc. | Zhang S.,ESI CFD Inc.
Journal of Thermophysics and Heat Transfer | Year: 2017

In this paper, a coupling methodology was proposed to solve simultaneously the external flowfield of a hypersonic reentry vehicle/capsule and the resultant heating on the vehicle's structure and internal components with buoyancydriven very low-speed flows resulting from conjugate heat transfer through the thermal protection system of the vehicle/capsule. Two flow solvers were employed to solve the hypersonic flowfield and the very low-speed flowfield, respectively. The coupling was done through the exchange of appropriate interface data between the two solvers. One of them was a density-based solver, and the other was a pressure-based solver. Validations of the individual solvers were done with two benchmark cases. The proposed coupling method was proved through simulating two conjugate heat transfer problems. Finally, an aerothermal-man-machine system exposed in a hypersonic flow was computed using the proposed coupling method. Copyright © 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Zhao X.,Alabama A&M University | Zhu Y.,Beihang University | Zhu Y.,Aviation Industry Corporation of China AVIC | Zhang S.,ESI CFD Inc.
Computers and Fluids | Year: 2012

This paper presents transonic wing flutter predictions by coupling Euler/Navier-Stokes equations and structural modal equations. This coupling between Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) is achieved through a Multi-Disciplinary Computing Environment (MDICE), which allows several computer codes or 'modules' to communicate in a highly efficient fashion. The present approach offers the advantage of utilizing well-established single-disciplinary codes in a multi-disciplinary framework. The flow solver is density-based for modeling compressible, turbulent flow problems using structured and/or unstructured grids. A modal approach is employed for the structural response. Flutter predictions performed on an AGARD 445.6 wing at different Mach numbers are presented and compared with experimental data. © 2012 Elsevier Ltd.

Zhao X.,Alabama A&M University | Bayyuk S.,ESI CFD Inc. | Zhang S.,ESI CFD Inc.
Computers and Fluids | Year: 2013

The aeroelastic response of rocket nozzles subjected to combined axial thrust and side loads is investigated using a particular computational technique. The technique uses two-way " loose" coupling between an accurate flow solver and an accurate structural-dynamics solver to accurately capture the behavior of the internal flow, the behavior of the nozzle wall, and the interactions between the fluid-dynamic and structural-dynamic phenomena. It is shown that the technique captures the fluid-dynamic phenomena that are known to contribute to nozzle side loads, including the asymmetry in the propagation of the initial blast wave, the asymmetry in the separation lines, the pressure pulsations at the separation lines, the transition of separated flow patterns, and various flow instabilities. It is also shown that the computational technique couples the fluid-dynamic and the structural-dynamic solutions with an accuracy and a resolution that are sufficient for accurate prediction of the aeroelastic response modes in the system. The fluid-dynamics solver is validated for shock-induced flow separations in a sub-scale J-2S nozzle, while the structural-dynamic solver is validated for a typical dynamic response in a rocket nozzle. The two-way loose coupling methodology is validated for the flutter of a flat plate in supersonic flow, and the validation results are discussed and assessed with respect to the fitness of the computational technique for the prediction of the aeroelastic response of typical actual nozzle configurations. Finally, the side loads are computed for a J-2S nozzle with rigid walls and with flexible walls, and the results for the two types of walls are analyzed and compared. It is found that allowing aeroelastic coupling significantly affects the response of the nozzle and the predicted side loads. It is speculated that the computational technique investigated in this work combines all the elements required to accurately predict and simulate the aeroelastic response of a rocket nozzle to non-symmetric thrust, and that such a technique can be used to study and investigate side load phenomena in rocket nozzles in detail and also as a design tool for rocket nozzles. The technique is also speculated to be effective and appropriate for other fluid-structure interaction problems within an appropriate range of aeroelastic regimes. © 2013 Elsevier Ltd.

Zhao X.,Alabama A&M University | Montgomery T.,Alabama A&M University | Zhang S.,ESI CFD Inc.
Annals of Nuclear Energy | Year: 2015

This paper presents a numerical study of the stationary and moving pebbles in a pebble bed reactor (PBR) by means of discrete element method (DEM). The packing structure of stationary pebbles is simulated by a filling process that terminates with the settling of the pebbles into a PBR. The packing structural properties are obtained and analyzed. Subsequently, when the outlet of the PBR is opened during the operation of the PBR, the stationary pebbles start to flow downward and are removed at the bottom of the PBR. The dynamic behavior of pebbles is predicted and discussed. Our results indicate the DEM can offer both macroscopic and microscopic information for PBR design calculations and safety assessment. © 2015 Elsevier Ltd. All rights reserved.

Guan H.,Aviation Industry Corporation of China AVIC | Zhu Y.,Aviation Industry Corporation of China AVIC | Zhang S.J.,ESI CFD Inc.
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013 | Year: 2013

This paper presents computational studies of ejection seat and occupant aerodynamics. The overset Chimera grid to deal moving bodies in CFD-FASTRAN is employed to study the dynamic behaviors of ejection seat and occupant. Two benchmark cases were in investigated in this work. The first case is about an advanced concept ejection seat (ACES), in which the full scale of ACES II was simulated. In the second case, the aerodynamic characteristics of the seat/occupant system for Mach number 0.9 at angles of attack from -30 to 60 degrees and the angles of sideslip from 0 to 60 degrees are considered. The results are presented in the form of force and moment coefficients and compared to wind tunnel test data. Surface contours are illustrated to highlight the details of the flow field. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Zhao X.,Alabama A&M University | Montgomery T.,Alabama A&M University | Zhang S.,ESI CFD Inc.
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2013

The nuclear thermal rocket is one of the candidate propulsion systems for future space exploration including traveling to Mars and other planets of the solar system. Nuclear thermal propulsion can provide a much higher specific impulse than the best chemical propulsion available today. A basic nuclear propulsion system consists of one or several nuclear reactors that heat hydrogen propellant to high temperatures and then allow the heated hydrogen and its reacting product to flow through a nozzle to produce thrust. This paper presents computational study on a single flow element in a nuclear thermal rocket. The computational results provide both detailed and global thermo-fluid environments of a single flow element for thermal stress estimation and insight for possible occurrence of mid-section corrosion. Copyright © 2013 by ASME.

Zhang S.J.,ESI CFD Inc. | Zhu Y.,Aviation Industry Corporation of China AVIC
10th AIAA/ASME Joint Thermophysics and Heat Transfer Conference | Year: 2010

Thermal protection systems (TPS) have to withstand very large heat loads. Whereas the TPS "absorbs" a large portion of the aerodynamic heating during re-entry conditions for example, heat is still conducted to the inside of the aircraft. This study is dedicated to investigating the heat loads and cooling possibilities for the payload in the capsule. The primary task in this work was to develop a fully coupled simulation tool that would allow the external hypersonic flow field to be predicted as well as to take the heat conduction into the capsule volume. This paper will focus on the coupling and the results obtained within the scope of a feasibility study. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Zhao X.,Alabama A&M University | Montgomery T.,Alabama A&M University | Zhang S.,ESI CFD Inc.
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2013

This paper presents a review on the research activities conducted at AAMU (Alabama A&M University) in the last five years. The researchers in College of Engineering, Technology and Physical Sciences of AAMU have been receiving financial support from the U.S. Department of Energy under Massie Chair Excellence Program in Nuclear Engineering from 2008. The main objectives of this project were to improve the capability of understanding the static, dynamic behavior of pebbles and gas flows/heat transfer in a pebble bed reactor (PBR), which is the key to the design, optimization and safe operation of the reactors. Copyright © 2013 by ASME.

Zhang S.,ESI CFD Inc. | Zhao X.,Alabama A&M University | Bayyuk S.,ESI CFD Inc.
Journal of Computational Physics | Year: 2014

In this paper, generalized formulations for the Rhie-Chow interpolation for co-located-grid discretizations are derived. These generalized formulations eliminate the major known defects in the standard Rhie-Chow interpolation, including the following: dependence of the converged solution on the value of the under-relaxation factor, saw-tooth pressure oscillations in transient problems with small time steps, and incorrect or non-converged solutions for problems with discontinuities. The generalized formulations are also shown to be applicable to a wider range of flow conditions than the standard Rhie-Chow interpolation. The derivation of the Rhie-Chow interpolation is first recalled and its numerical errors are analyzed. Then, the generalized formulations are presented and explained, and the way in which they eliminate or counter some of the known defects of the standard Rhie-Chow interpolation are outlined. The generalized formulations are then verified and validated with numerical experiments, including experiments with flow in porous media and in a packed bed. It is then concluded that the generalized formulations presented in this work represent an advance over the standard Rhie-Chow interpolation with a negligible increase in computational cost. © 2013 Elsevier Inc.

Zhang S.,ESI CFD Inc. | Shotorban B.,University of Alabama in Huntsville | Pohly J.,University of Alabama in Huntsville | Zhang J.A.,Bob Jones High School
22nd AIAA Computational Fluid Dynamics Conference | Year: 2015

Lateral nozzle forces are known to cause severe structural damage to any new rocket engine in development during test. While three-dimensional, transient, turbulent, chemically reacting computational fluid dynamics methodology has been demonstrated to capture major side load physics with rigid nozzles, hot-fire tests often show nozzle structure deformation during major side load events. Such deformation leads to structural damages if appropriate structural strengthening measures are not taken. The modeling picture is incomplete without the aeroelastic coupling to address the two-way responses between the structure and fluid. The present work takes into account the aeroelastic coupling for side loads predictions. A loosely coupled method for fluid structural interaction is employed to study the role of the coupling. Two side load cases were computed and are comparatively analyzed for the J-2S nozzle, one case with flexible walls and the other with rigid walls. It is found that aeroelastic coupling has significant effects on the side loads in the nozzle. © 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

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