Bulletin of the American Physical Society, Nov 21, 2016
Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies depend... more Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies dependent on the geometry of the cavity and the properties and flow conditions of the fluid. Numerical studies of this kind, Computational Aeroacoustics (CAA), pose a grave challenge to the accuracy and efficiency of numerical methods. This project examines the Space-Time Conservation Element Solution Element (CESE) method developed by Dr. S.C. Chang at NASA GRC and compares numerical results of two-dimensional flow to previous experimental data found in literature. The conclusion the project reached is that the test data agrees well with one of the modes of the predicted frequencies, and that further testing is needed to be able to match experimental results.
Complexities of liquid rocket engine heat transfer which involve the injector faceplate and regen... more Complexities of liquid rocket engine heat transfer which involve the injector faceplate and regeneratively and film cooled walls are being investigated by computational analysis. A conjugate heat transfer analysis will be used to describe localized heating phenomena associated with particular injector configurations and coolant channels and film coolant dumps. These components are being analyzed, and the analyses verified with appropriate test data. Finally, the component analyses will be synthesized into an overall flowfield/heat transfer model. The FDNS code is being used to make the component analyses. Particular attention is being given to the representation of the thermodynamic properties of the fluid streams and to the method of combining the detailed models to represent overall heating. Unit flow models of specific coaxial injector elements have been developed and will be described. Since test data from the NLS development program are not available, new validation heat transfer data have been sought. Suitable data were obtained from a Rocketdyne test program on a model hydrocarbon/oxygen engine. Simulations of these test data will be presented. Recent interest in the hybrid motor have established the need for analyses of ablating solid fuels in the combustion chamber. Analysis of a simplified hybrid motor will also be presented.
41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Jul 10, 2005
In this paper, we rigorously validate and verify the recently developed Space-Time Conservation E... more In this paper, we rigorously validate and verify the recently developed Space-Time Conservation Element/Solution Element (CE/SE) based Courant Number Insensitive transient viscous flow solver. Although, the CE/SE framework in two spatial dimension was ...
33rd Joint Propulsion Conference and Exhibit, Jul 6, 1997
The understanding and predictions of spray combustion characteristics are essential to the design... more The understanding and predictions of spray combustion characteristics are essential to the design of liquid and hybrid rocket engines. Flow distributions, such as local mixture ratio and state of the propellants and combustion products, near the injector face have a profound effect on both the performance and the hardware integrity of the rocket engine. In order to provide a simple and practical spray combustion analysis, several submodels were developed and incorporated into a computational fluid dynamics (CFD) code. These submodels include a real-fluid property module which is employed to account for the effect of the phase change, a pressure-correction model for the real-fluid flow, and combustion kinetics/equilibrium chemistry models. Several gas/gas and gas/liquid injector flows were simulated to demonstrate the capability and validity of the proposed CFD spray combustion model.
The flow features near the injector of liquid rocket engines are extremely complicated; for examp... more The flow features near the injector of liquid rocket engines are extremely complicated; for example, supercritical-pressure spray, turbulent mixing, and chemical reactions are present. A spray combustion model was developed to account for the real fluid effect such that ...
46th AIAA Aerospace Sciences Meeting and Exhibit, Jan 7, 2008
... 저자, Balaji Shankar Venkatachari (Department of Mechanical Engineering, University of Alabama ... more ... 저자, Balaji Shankar Venkatachari (Department of Mechanical Engineering, University of Alabama at Birmingham) , Gary C.Cheng (Department of Mechanical Engineering, University of Alabama at Birmingham) , Roy P.Koomullil (Department of Mechanical ... KARI 지식정보시스템.
International Journal of Heat and Mass Transfer, Oct 1, 2013
Radiative heat transfer is an important physical phenomenon, especially in the high speed and hig... more Radiative heat transfer is an important physical phenomenon, especially in the high speed and high temperature flow regimes, making its application important in space exploration vehicles. This paper presents the development and validation of computational tools for modeling the radiative heat transfer that can be either employed by itself or coupled with a computational fluid dynamics solver to analyze aerothermodynamics environments. A generalized mesh is used for discretization of the spatial domain and a finite volume method is used for solving the radiative heat transfer equation. Solution of the radiative heat transfer equation in an angular domain is carried out in a parallel environment. This numerical approach is validated with different benchmark test cases for gray gas radiation in various geometries. To enable the simulation of non-gray gas radiation, the full spectrum correlated-k model is implemented into the radiation solver. A grid sensitivity study is conducted to analyze the dependency of mesh resolution in spatial and angular domains on solution accuracy. The results of the validation studies, grid sensitivity studies, and parallel performance of the implementation are presented in this paper.
A technique for improving the numerical predictions of turbulent flows with the effect of streaml... more A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flow fields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity μt incorporating the k–ε turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal (where axial velocities change signs) of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the longitudinal velocity and the static pressure in an S-bend duct and in 180 deg turn-around ducts. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.
Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the inc... more Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the incoming freestream have been studied to determine the effects of the jet in reducing the drag and the heat loads on the rocket. The effects are comparatively evaluated for different jet exit Mach numbers from ideally expanded nozzles, designed using the method of characteristics, operating at a total temperature of 500 K and at total pressures with predetermined ratios of the freestream total pressure. Axisymmetric computations were conducted with the generic rocket flying at a Mach number of 6.0 and 40,000 ft altitude with zero-degree angle of attack. Results indicate that a jet generated by the Mach 1.5 nozzle, operating at a total pressure corresponding to 1/4th of the freestream total pressure, resulted in the best combined overall drag and temperature reduction. The area-averaged surface temperature and drag were reduced by 52%, and 22%, respectively, in comparison to the body without the flow control.
Abstract Effects of a jet emanating from the nose of a generic rocket in the opposite direction o... more Abstract Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the incoming freestream have been studied to determine the effects of the jet in reducing the drag and the heat loads on the rocket. The effects are comparatively evaluated for different jet exit Mach numbers from ideally expanded nozzles, designed using the method of characteristics, operating at a total temperature of 500 K and at total pressures with predetermined ratios of the freestream total pressure. Axisymmetric computations were conducted with the generic rocket flying at a Mach number of 6.0 and 40,000 ft altitude with zero-degree angle of attack. Results indicate that a jet generated by the Mach 1.5 nozzle, operating at a total pressure corresponding to 1/4th of the freestream total pressure, resulted in the best combined overall drag and temperature reduction. The area-averaged surface temperature and drag were reduced by 52%, and 22%, respectively, in comparison to the body without the flow control.
The flow over a rocket may result in plume induced flow separation (PIFS) depending on flight con... more The flow over a rocket may result in plume induced flow separation (PIFS) depending on flight conditions and nozzle-to-ambient pressure ratios. In the current study, the flow structure over a generic rocket model has been investigated to determine the conditions that would results in PIFS over the rocket body. The rocket used in the current study has a tangent-ogive nose with a length of 25.4 cm (nose length/diameter ~ 4.0), followed by a 57.2-cm long cylindrical rocket body (overall length/diameter ~ 13.0). A 45° conical nozzle with an exit Mach number of 2.7 (nozzle expansion ratio, ε ~1.786) was used to simulate the plume. The total temperature and the total pressure in the combustion chamber were kept as 3589 K (6000 °F), and 5.86 MPa abs (850 psia). The flow conditions investigated including flight Mach numbers from 0.7 to 2.0, at five different altitudes; 0, 3.05, 6.10, 9.14 and 12.2 km (0, 10,000, 20,000, 30,000 and 40,000 feet). Based on the validation study using various eddy-viscosity turbulence models, the k-ϵ RNG turbulence model was selected for the parametric study. PIFS is not observed at Mach numbers less than 1.0 up to altitudes including 9.1 km (30,000 ft), and occurs only between Mach 1.0 and 2.0. The Mach number range where PIFS is observed increases with increasing altitude. However at 12.2 km (40,000 ft) PIFS is observed at every Mach number considered, including subsonic range.
An improved parallelized hybrid DSMC‐NS algorithm presented and verified. In previous work [1], i... more An improved parallelized hybrid DSMC‐NS algorithm presented and verified. In previous work [1], it showed the slow convergence of coupling between two numerical solvers if the normal velocities across the breakdown interfaces are very low. By detailed kinetic velocity ...
The objective of this effort is to develop an efficient and accurate computational methodology to... more The objective of this effort is to develop an efficient and accurate computational methodology to predict both detailed thermo-fluid environments and global characteristics of the internal ballistics for a hypothetical solid-core nuclear thermal thrust chamber assembly (NTTCA). Several numerical and multi-physics thermofluid models, such as real fluid, chemically reacting, turbulence, conjugate heat transfer, porosity, and power generation, were incorporated into an unstructuredgrid, pressure-based computational fluid dynamics solver as the underlying computational methodology. The numerical simulations of detailed thermo-fluid environment of a single flow element provide a mechanism to estimate the thermal stress and possible occurrence of the mid-section corrosion of the solid core. In addition, the numerical results of the detailed simulation were employed to fine tune the porosity model mimic the pressure drop and thermal load of the coolant flow through a single flow element. The use of the tuned porosity model enables an efficient simulation of the entire NTTCA system, and evaluating its performance during the design cycle.
Bulletin of the American Physical Society, Nov 21, 2016
Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies depend... more Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies dependent on the geometry of the cavity and the properties and flow conditions of the fluid. Numerical studies of this kind, Computational Aeroacoustics (CAA), pose a grave challenge to the accuracy and efficiency of numerical methods. This project examines the Space-Time Conservation Element Solution Element (CESE) method developed by Dr. S.C. Chang at NASA GRC and compares numerical results of two-dimensional flow to previous experimental data found in literature. The conclusion the project reached is that the test data agrees well with one of the modes of the predicted frequencies, and that further testing is needed to be able to match experimental results.
Complexities of liquid rocket engine heat transfer which involve the injector faceplate and regen... more Complexities of liquid rocket engine heat transfer which involve the injector faceplate and regeneratively and film cooled walls are being investigated by computational analysis. A conjugate heat transfer analysis will be used to describe localized heating phenomena associated with particular injector configurations and coolant channels and film coolant dumps. These components are being analyzed, and the analyses verified with appropriate test data. Finally, the component analyses will be synthesized into an overall flowfield/heat transfer model. The FDNS code is being used to make the component analyses. Particular attention is being given to the representation of the thermodynamic properties of the fluid streams and to the method of combining the detailed models to represent overall heating. Unit flow models of specific coaxial injector elements have been developed and will be described. Since test data from the NLS development program are not available, new validation heat transfer data have been sought. Suitable data were obtained from a Rocketdyne test program on a model hydrocarbon/oxygen engine. Simulations of these test data will be presented. Recent interest in the hybrid motor have established the need for analyses of ablating solid fuels in the combustion chamber. Analysis of a simplified hybrid motor will also be presented.
41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Jul 10, 2005
In this paper, we rigorously validate and verify the recently developed Space-Time Conservation E... more In this paper, we rigorously validate and verify the recently developed Space-Time Conservation Element/Solution Element (CE/SE) based Courant Number Insensitive transient viscous flow solver. Although, the CE/SE framework in two spatial dimension was ...
33rd Joint Propulsion Conference and Exhibit, Jul 6, 1997
The understanding and predictions of spray combustion characteristics are essential to the design... more The understanding and predictions of spray combustion characteristics are essential to the design of liquid and hybrid rocket engines. Flow distributions, such as local mixture ratio and state of the propellants and combustion products, near the injector face have a profound effect on both the performance and the hardware integrity of the rocket engine. In order to provide a simple and practical spray combustion analysis, several submodels were developed and incorporated into a computational fluid dynamics (CFD) code. These submodels include a real-fluid property module which is employed to account for the effect of the phase change, a pressure-correction model for the real-fluid flow, and combustion kinetics/equilibrium chemistry models. Several gas/gas and gas/liquid injector flows were simulated to demonstrate the capability and validity of the proposed CFD spray combustion model.
The flow features near the injector of liquid rocket engines are extremely complicated; for examp... more The flow features near the injector of liquid rocket engines are extremely complicated; for example, supercritical-pressure spray, turbulent mixing, and chemical reactions are present. A spray combustion model was developed to account for the real fluid effect such that ...
46th AIAA Aerospace Sciences Meeting and Exhibit, Jan 7, 2008
... 저자, Balaji Shankar Venkatachari (Department of Mechanical Engineering, University of Alabama ... more ... 저자, Balaji Shankar Venkatachari (Department of Mechanical Engineering, University of Alabama at Birmingham) , Gary C.Cheng (Department of Mechanical Engineering, University of Alabama at Birmingham) , Roy P.Koomullil (Department of Mechanical ... KARI 지식정보시스템.
International Journal of Heat and Mass Transfer, Oct 1, 2013
Radiative heat transfer is an important physical phenomenon, especially in the high speed and hig... more Radiative heat transfer is an important physical phenomenon, especially in the high speed and high temperature flow regimes, making its application important in space exploration vehicles. This paper presents the development and validation of computational tools for modeling the radiative heat transfer that can be either employed by itself or coupled with a computational fluid dynamics solver to analyze aerothermodynamics environments. A generalized mesh is used for discretization of the spatial domain and a finite volume method is used for solving the radiative heat transfer equation. Solution of the radiative heat transfer equation in an angular domain is carried out in a parallel environment. This numerical approach is validated with different benchmark test cases for gray gas radiation in various geometries. To enable the simulation of non-gray gas radiation, the full spectrum correlated-k model is implemented into the radiation solver. A grid sensitivity study is conducted to analyze the dependency of mesh resolution in spatial and angular domains on solution accuracy. The results of the validation studies, grid sensitivity studies, and parallel performance of the implementation are presented in this paper.
A technique for improving the numerical predictions of turbulent flows with the effect of streaml... more A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flow fields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity μt incorporating the k–ε turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal (where axial velocities change signs) of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the longitudinal velocity and the static pressure in an S-bend duct and in 180 deg turn-around ducts. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.
Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the inc... more Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the incoming freestream have been studied to determine the effects of the jet in reducing the drag and the heat loads on the rocket. The effects are comparatively evaluated for different jet exit Mach numbers from ideally expanded nozzles, designed using the method of characteristics, operating at a total temperature of 500 K and at total pressures with predetermined ratios of the freestream total pressure. Axisymmetric computations were conducted with the generic rocket flying at a Mach number of 6.0 and 40,000 ft altitude with zero-degree angle of attack. Results indicate that a jet generated by the Mach 1.5 nozzle, operating at a total pressure corresponding to 1/4th of the freestream total pressure, resulted in the best combined overall drag and temperature reduction. The area-averaged surface temperature and drag were reduced by 52%, and 22%, respectively, in comparison to the body without the flow control.
Abstract Effects of a jet emanating from the nose of a generic rocket in the opposite direction o... more Abstract Effects of a jet emanating from the nose of a generic rocket in the opposite direction of the incoming freestream have been studied to determine the effects of the jet in reducing the drag and the heat loads on the rocket. The effects are comparatively evaluated for different jet exit Mach numbers from ideally expanded nozzles, designed using the method of characteristics, operating at a total temperature of 500 K and at total pressures with predetermined ratios of the freestream total pressure. Axisymmetric computations were conducted with the generic rocket flying at a Mach number of 6.0 and 40,000 ft altitude with zero-degree angle of attack. Results indicate that a jet generated by the Mach 1.5 nozzle, operating at a total pressure corresponding to 1/4th of the freestream total pressure, resulted in the best combined overall drag and temperature reduction. The area-averaged surface temperature and drag were reduced by 52%, and 22%, respectively, in comparison to the body without the flow control.
The flow over a rocket may result in plume induced flow separation (PIFS) depending on flight con... more The flow over a rocket may result in plume induced flow separation (PIFS) depending on flight conditions and nozzle-to-ambient pressure ratios. In the current study, the flow structure over a generic rocket model has been investigated to determine the conditions that would results in PIFS over the rocket body. The rocket used in the current study has a tangent-ogive nose with a length of 25.4 cm (nose length/diameter ~ 4.0), followed by a 57.2-cm long cylindrical rocket body (overall length/diameter ~ 13.0). A 45° conical nozzle with an exit Mach number of 2.7 (nozzle expansion ratio, ε ~1.786) was used to simulate the plume. The total temperature and the total pressure in the combustion chamber were kept as 3589 K (6000 °F), and 5.86 MPa abs (850 psia). The flow conditions investigated including flight Mach numbers from 0.7 to 2.0, at five different altitudes; 0, 3.05, 6.10, 9.14 and 12.2 km (0, 10,000, 20,000, 30,000 and 40,000 feet). Based on the validation study using various eddy-viscosity turbulence models, the k-ϵ RNG turbulence model was selected for the parametric study. PIFS is not observed at Mach numbers less than 1.0 up to altitudes including 9.1 km (30,000 ft), and occurs only between Mach 1.0 and 2.0. The Mach number range where PIFS is observed increases with increasing altitude. However at 12.2 km (40,000 ft) PIFS is observed at every Mach number considered, including subsonic range.
An improved parallelized hybrid DSMC‐NS algorithm presented and verified. In previous work [1], i... more An improved parallelized hybrid DSMC‐NS algorithm presented and verified. In previous work [1], it showed the slow convergence of coupling between two numerical solvers if the normal velocities across the breakdown interfaces are very low. By detailed kinetic velocity ...
The objective of this effort is to develop an efficient and accurate computational methodology to... more The objective of this effort is to develop an efficient and accurate computational methodology to predict both detailed thermo-fluid environments and global characteristics of the internal ballistics for a hypothetical solid-core nuclear thermal thrust chamber assembly (NTTCA). Several numerical and multi-physics thermofluid models, such as real fluid, chemically reacting, turbulence, conjugate heat transfer, porosity, and power generation, were incorporated into an unstructuredgrid, pressure-based computational fluid dynamics solver as the underlying computational methodology. The numerical simulations of detailed thermo-fluid environment of a single flow element provide a mechanism to estimate the thermal stress and possible occurrence of the mid-section corrosion of the solid core. In addition, the numerical results of the detailed simulation were employed to fine tune the porosity model mimic the pressure drop and thermal load of the coolant flow through a single flow element. The use of the tuned porosity model enables an efficient simulation of the entire NTTCA system, and evaluating its performance during the design cycle.
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