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AIAA SciTech Forum

作者： Cocirla, Gianluca Grossi, Marco Migliorino, Mario Tindaro Bianchi, Daniele Nasuti, Francesco Sapienza Univ Rome Dept Mech & Aerosp Engn Via Eudossiana 18 I-00184 Rome Italy

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

Modern high performance liquid rocket engines are characterized by elevated hot gas temperatures and combustion chamber pressures leading to high wall heat fluxes, which must be correctly predicted and managed to guarantee safe operation. In these severe operating conditions, active cooling systems such as regenerative cooling might not be enough to counteract such high thermal loads. In such cases, cooling capabilities can be enhanced with the addition of a further cooling strategy, such as film cooling. The prediction of wall heat flux in such thrust chambers is of paramount importance during the design phase both for sizing and safety purposes. Despite the complexity of the phenomenon, computational fluid dynamics simulations represent a valuable solution in the convective wall heat flux prediction with respect to more expensive procedures such as hot-firing tests. In any case, the presence of experimental data is necessary in order to validate and evaluate the predictive capacity of a numerical model. In this framework, this paper aims at investigating different operating conditions of the single injector thrust chamber burning gaseous oxygen and kerosene of the Technical University of Munich (TUM) test case with and without the injection of film cooling in order to validate an in-house Reynolds-averaged Navier-Stokes solver.

关键词： Regenerative Cooling Kerosene Rocket Thrust Chamber Heat Flux Combustion Chambers Reynolds Averaged Navier Stokes Roe Approximate Riemann Solver computational fluid dynamics simulation Liquid Rocket Engine Combustion Products

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CFD Predictions of Fluctuating Pressure Environments on NASA's SLS Ascent Unsteady Aerodynamics Wind Tunnel Test

CFD Predictions of Fluctuating Pressure Environments on NASA...

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AIAA SciTech Forum

作者： Boustani, Jonathan Hall, Leslie Steva, Thomas B. Mclaurin Aerosp Jacobs Space Explorat Grp Huntsville AL 35802 USA NASA Marshall Space Flight Ctr Aerosci Branch Huntsville AL 35808 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

This paper details work that is being conducted on predicting fluctuating pressure environments on NASA launch vehicles using computational fluid dynamics (CFD). The accurate characterization of these aeroacoustic environments is necessary in the analysis of vehicle structural capability and development of sub-component vibration design. High-fidelity simulations of the unsteady flow over NASA's SLS Ascent Unsteady Aerodynamics wind tunnel Test (AUAT) using the hybrid Reynolds-averaged Navier-Stokes (RANS)large eddy simulations (LES) methodologies in Mississippi States' Loci/CHEM solver are presented. The two available methods, Nelson-Nichols and dynamic hybrid RANS-LES (DHRL), are compared head-to-head on identical grids at twoMach numbers. At the high-subsonic Mach number, locally supersonic flow expanding over a shoulder induces a separation-reattachment system that is predicted poorly by the Nelson-Nichols method due to an under-prediction in unsteady content. The DHRL solution predicts the spatial extent and frequency domain response of this system well but under-predicts the peak noise levels due to a delay in the RANS-to-LES transition. At the low-supersonic Mach number, compression corner dynamics dominate the unsteady flow. While the Nelson-Nichols solution captures this phenomenon well, another solution on a refined grid indicates that some model stress depletion is occurring. The DHRL solution again performs well at this Mach number and matches the wind tunnel data fairly closely, but perhaps most impressively, is fairly agnostic to increasing grid resolution. The findings in this paper are expected to be generally applicable and will be used to guide the prediction of aeroacoustic environments of other NASA launch vehicles.

关键词： Unsteady Aerodynamics Unitary Plan Wind Tunnel computational fluid dynamics simulation Reynolds Averaged Navier Stokes Flow Instabilities Freestream Conditions Frequency Domain Launch Vehicles NASA Overall Sound Pressure Level

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computational fluid dynamics modelling approaches of gas explosion in the chemical process industry: A review

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PROCESS SAFETY AND ENVIRONMENTAL PROTECTION 2023年 170卷 112-138页

作者： Shamsuddin, Dyg Siti Nurzailyn Abg Fekeri, Ahmad Faris Mohd Muchtar, Andanastuti Khan, Faisal Khor, Bee Chin Lim, Bee Huah Rosli, Masli Irwan Takriff, Mohd Sobri Univ Kebangsaan Malaysia Dept Chem & Proc Engn Fac Engn & Built Environm Bangi 43600 Malaysia Univ Kebangsaan Malaysia Fuel Cell Inst Bangi 43600 Malaysia Univ Kebangsaan Malaysia Fac Engn & Built Environm Dept Mech Mfg Engn Bangi Malaysia Texas A&M Univ Artie McFerrin Dept Chem Engn 400 Bizzell St College Stn TX 77843 USA Technol Innovat Sect Indah Water Konsortium Sdn Bhd Kuala Lumpur Malaysia Univ Sharjah Chem & Water Desalinat Program Sharjah 27272 U Arab Emirates

Previous studies have revealed that major accidents in Chemical Process Industry (CPI) are most commonly due to explosions. Thus, analytical studies of explosion-related risk assessments are performed to predict the consequences of potential explosions. As physical experiments on explosions are very expensive, modelling and simulation techniques using theoretical models are becoming increasingly popular, allowing researchers to replicate the potential explosion scenarios. In this regard, computational fluid dynamics (CFD) models are more than appropriate. Although CFD simulations are widely applied, they have several weaknesses such as high computational costs as well as potential simulation inaccuracies due to inaccurate modelling steps. The weaknesses can be overcome with appropriate techniques such as model simplification, defining the appropriate method, grid design and boundary conditions. Many studies have reported different aspects and perspectives of explosion modelling and simulation techniques, but few evaluate the techniques across every different type of explosion. This subject is critical, as modelling steps and techniques directly affect the accuracy of simulation results. Hence, a review of the assumptions and simulation techniques that are used to reduce the computational costs associated with gas explosion modelling for each of the different explosion types is presented.

关键词： Chemical process industry Explosion computational fluid dynamics simulation Risk assessment FLACS Fluent

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Model Error Quantification in Non-Equilibrium Flows

Model Error Quantification in Non-Equilibrium Flows

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AIAA SciTech Forum

作者： Kuppa, Mridula Singh, Narendra Ghanem, R. Panesi, Marco Univ Illinois Dept Aerosp Engn 302 ETalbot Lab104 S Wright St Urbana IL 61801 USA Univ Southern Calif Dept Civil & Environm Engn Dept Aerosp & Mech Engn KAP 210 Los Angeles CA 90089 USA Univ Illinois Dept Aerosp Engn 306 Talbot Lab104 S Wright St Urbana IL 61801 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

In computational fluid dynamics simulations for reentry space vehicles, reduced-order models for thermochemical nonequilibrium are commonly employed due to their computational efficiency. However, it is crucial to assess the inadequacies of these models, as their predictions directly impact the design of the thermal protection system. In this study, we enhance the multi-temperature model, obtained through a coarse-graining strategy, by introducing stochastic model error terms to account for inaccuracies arising in simulations of reentry flow over a blunt body. The Lagrangian approach is employed to solve for the evolution of species mole fractions across various realizations of the stochastic model error terms. Utilizing Karhunen-Loeve Expansion and Polynomial Chaos Expansions, we create an efficient surrogate from the obtained realizations. This surrogate is then applied in Bayesian inference to determine the posteriors of the stochastic model error terms. When these posteriors are forward propagated through the model, they yield probabilistic predictions of the low-fidelity model that effectively capture the high-fidelity model output, which was used as data in the calibration procedure.

关键词： Uncertainty Quantification Blunt Bodies computational fluid dynamics simulation Thermal Protection System Karhunen Loeve Expansion Reentry Space Vehicle Chemical Kinetics Nonequilibrium Flows Reynolds Averaged Navier Stokes Binding Energy

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FPGA Based Hardware Accelerator for Euler Equations with Finite Volume Method

FPGA Based Hardware Accelerator for Euler Equations with Fin...

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AIAA SciTech Forum

作者： Yigit, Emine Elif Yeniceri, Ramazan Istanbul Tech Univ Aerosp Res Ctr Dept Def Technol TR-34467 Istanbul Turkiye Istanbul Tech Univ Aerosp Res Ctr Dept Aeronaut Engn TR-34467 Istanbul Turkiye

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

computational fluid Dynamic (CFD) is of great importance in the design and analysis of aircraft. The utilization of CFD enables the improvement of aircraft design, cost reduction, enhanced energy efficiency, and optimization of aircraft performance. By conducting realistic CFD simulations prior to production, the performance of the designed aircraft can be thoroughly tested. CFD solves complex equations numerically to analyze fluid flow, hence requiring substantial computational power and time. Presently, high-core-count computers are available to facilitate these calculations. However, the cost of such computers is considerably high. Therefore, we propose the development of an Field Programmable Gate Array (FPGA) based CFD accelerator to reduce computation time and cost. The focus is on designing an FPGA based Euler Equations solver for high-speed flow simulations. The two-dimensional Euler Equations are derived and discretized using the Finite Volume Method (FVM). MATLAB scripts are developed for the solver, resulting in the generation of core script files that created intial model. A MATLAB simulator is developed using these files. The simulator's performance is validated against ANSYS Fluent analysis. Once validated, the initial model are transferred to the MATLAB HDLcoder environment. In HDLcoder, hardware design is performed for a single finite volume, utilizing information from the simulation logger stored in the idea step. The model undergoes elaboration and high-level synthesis. The resulting HDLcoder model generates synthesizable HDL (Hardware Description Language) code for FPGA implementation. Verification and evaluation are conducted using the simulation logger results. FPGA resource utilization was analyzed and the speed of the accelerator was compared with the Central Process Unit (CPU).

关键词： Continuity Equation Field Programmable Gate Array Finite Volume Method computational fluid dynamics simulation Simulink ANSYS Central Processing Unit Energy Consumption fluid Flow Aircraft Design

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Flashback Studies of High-hydrogen Flames using High-speed OH Planar Laser-induced Fluorescence

Flashback Studies of High-hydrogen Flames using High-speed O...

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AIAA SciTech Forum

作者： Parajuli, Pradeep Strakey, Peter Natl Energy Technol Lab 3610 Collins Ferry Rd Morgantown WV 26505 USA NETL Res & Innovat Ctr 3610 Collins Ferry Rd Morgantown WV 26505 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

Flame flashback is a crucial challenge during the application of high-hydrogen fuels for the development of next-generation lean premixed combustors. The fundamentals of stable flame configuration, flashback phenomena, and spatiotemporal information of flame dynamics in a premixed, swirl-stabilized burner are investigated experimentally at atmospheric pressure conditions using high-repetition-rate nanosecond (ns)-duration hydroxyl radical planar laser-induced fluorescence (OH-PLIF) measurements. The inlet conditions are varied systematically with respect to equivalence ratio (phi), hydrogen content (X-H2) for 50%-90% (H-2, by mole) hydrogen-methane mixture and pre-mixer velocities (V). The experiments are performed on a burner modified to provide optical access to the premixing section. Signal interferences such as saturation effects, background chemiluminescence, and laser non-uniformity issues were minimized or corrected during data acquisition and subsequent data processing steps. A stable flame characterization was performed at 20 kHz-repetition-rate for varied V, X-H2 and phi in the reactant mixture. The investigation of flame lift-off length (L) above the burner rim showed dependence on each of these parameters. Flame dynamics such as flame flashback events, flashback-to-flame holding transition, local ignition, local extinction, flame curvature as well as the main reaction zone of the combustion mechanism are well characterized. Flashback.. showed an expected linearly increasing trend with increasing V and decreasing X-H2 and the conclusions drawn aligned well with detailed L investigations. Such spatially and temporally resolved kilohertz (kHz)-rate OH-PLIF is a promising technique to observe rapidly occurring flashback dynamics and can further validate turbulence-chemistry interaction models of swirling flames.

关键词： Planar Laser Induced Fluorescence Adiabatic Flame Temperature Chemiluminescence Hydrogen Fuels Lean Premixed Combustor Data Acquisition Data Processing Natural Gas Laser Powder Bed Fusion computational fluid dynamics simulation

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Trajectory-Informed Sampling for Efficient Construction of Multi-Fidelity Surrogate Models for Hypersonic Vehicles

Trajectory-Informed Sampling for Efficient Construction of M...

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AIAA SciTech Forum

作者： Needels, Jacob T. Alonso, Juan J. Stanford Univ Dept Aeronaut & Astronaut Stanford CA 94305 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

This paper studies the use of multi-fidelity surrogate modeling for analysis of hypersonic vehicles with a focus on the computation of trajectory sensitivities to inform sampling policy. A multi-fidelity aerodynamic database is generated for a hypersonic glide vehicle and surrogate accuracy is assessed for different numbers of high-fidelity samples. A methodology for computing sensitivities of trajectory quantities of interest to surrogate-modeled aerodynamic parameters is applied to hypersonic glide vehicle dynamics. The necessary adjoint equations are derived to compute sensitivities to aerodynamic parameters, which are then used to inform high-fidelity sampling. Of several strategies assessed, sensitivity-based sampling is found to give the best performance for fixed computational cost. Extensions of this methodology are discussed in the context of future work, including the use of sensitivities to allocate simulations among several disciplines in multidisciplinary design problems.

关键词： Hypersonic Vehicles Uncertainty Quantification Hypersonic Glide Vehicle Computing Technology Aerodynamic Coefficients Aerodynamic Performance computational fluid dynamics simulation Lift to Drag Ratio Gaussian Process Gaussian Process Regression

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Surrogate Models for Hypersonic Aerothermodynamics and Aerodynamics using Gaussian Process Regression

Surrogate Models for Hypersonic Aerothermodynamics and Aerod...

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AIAA SciTech Forum

作者： Rataczak, Jens A. Boyd, Iain D. McMahon, Jay W. Univ Colorado Boulder Dept Aerosp Engn Sci Boulder CO 80302 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

This work presents a method for generating efficient surrogate models for hypersonic aerothermodynamics and aerodynamics using Gaussian process regression (GPR). Three surrogate models are developed. The first is trained to simultaneously predict the stagnation-point heat flux and axial-force coefficient. It is shown that the trained model is able to predict the two quantities of interest with a high level, and the chemical kinetic uncertainty in the underlying CFD data is naturally incorporated into the Gaussian process's (GP) predictions of the stagnation-point convective heat flux. A second model is trained to predict entire distributions of convective heat flux on the vehicle surface. Excellent predictive capabilities at inputs that are both included and excluded in the training data is demonstrated, emphasizing ability of GPR to generalize well to new data. Finally, a model is designed to predict the vehicle lift and drag coefficient considering variations in angle of attack. It is shown that, as the training data set grows in size, the trained GP is able to produce excellent out-of-distribution predictions - a characteristic that is not typically observed when using GPR. This single-fidelity model GP is compared to a multi-fidelity GP that uses computationally efficient axisymmetric CFD simulations as low-fidelity data and computationally expensive 3D-CFD simulations as high-fidelity data. The multi-fidelity model produces more accurate predictions when compared to the single-fidelity model, such that the multi-fidelity model requires only half of the high-fidelity data that the single-fidelity model does. Finally, the developed models are implemented within a trajectory simulation framework to demonstrate the advantage of using probabilistic aerodatabases compared to heritage lookup table aerodatabases.

关键词： Hypersonic Aerothermodynamics Numerical Stability Aerodynamic Characteristics Gaussian Process Regression Stagnation Region Lift Coefficient Heat Flux Distribution computational fluid dynamics simulation Gaussian Process Thermal Protection System

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computational fluid dynamics simulation OF AIRFLOW PATTERNS AND PARTICLE DEPOSITION CHARACTERISTICS IN CHILDREN UPPER RESPIRATORY TRACTS

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ENGINEERING APPLICATIONS OF computational fluid MECHANICS 2012年第4期6卷 556-571页

作者： Liu, Zhijian Li, Angui Xu, Xiaoxia Gao, Ran Xian Univ Architecture & Technol Sch Environm & Municipal Engn Xian 710055 Shanxi Peoples R China

As findings from studies of airflow patterns and particle deposition in the upper respiratory tracts (URTs) of adults may not be readily extrapolated to studies of the URTs of children, due to the differences in airway anatomy and breathing conditions, the effects of pediatric, physiological features on airflow patterns and particle deposition have been investigated utilizing an idealized model of the URTs of children. Particle deposition characteristics in a 0.01-10 mm spectrum were assessed employing a well-verified, Lagrangian tracking method for different inhalation flow rates, consistent with sedentary (3.5 L/min), light (7.0 L/min) and high (10.5 L/min) activity levels. The main results are: (1) airflow patterns during inhalation and exhalation modes are very different, while airflow patterns are similar during each inhalation or exhalation mode, while subject to three different airflow rates;(2) higher Stokes and impaction numbers are observed in the model for a 3 year old child, when compared to adults under comparably scaled activity levels;and (3) breathing airflow rates, particle diameters and particle densities are three key factors influencing particle deposition rates, with higher deposition rates for children observed when compared to adults under comparable activity levels. For identical impaction parameters, all deposition rates for children are also higher. The localized particle deposition rates in the mouth cavity are similar for children and adults, while those in the larynx, pharynx, trachea and bronchi are higher for children than for adults. Results of this study demonstrate that differences do exist between children and adults in both airflow distribution and aerosol deposition characteristics. These differences should be taken into account in the determination of children's risk exposure levels for airborne toxicants.

关键词： children upper respiratory tract airflow patterns particle deposition rates Stokes number computational fluid dynamics simulation

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Flow Field Analysis of Vortex Interactions on Multi-Swept Wing Configurations

Flow Field Analysis of Vortex Interactions on Multi-Swept Wi...

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AIAA SciTech Forum

作者： Presas, Christian Park, Austin M. McCollum, Joeseph L. Avelar, Jacob A. Fagley, Casey Ghoreyshi, Mehdi Seide, Jurgen US Air Force Acad Dept Aeronaut Aeronaut Engn Usaf Acad CO 80840 USA US Air Force Acad Dept Aeronaut Usaf Acad CO 80840 USA US Air Force Acad High Performance Comp Res Ctr Aeronaut Engn Usaf Acad CO 80840 USA US Air Force Acad High Performance Comp Res Ctr Usaf Acad CO 80840 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

The underlying flow physics of vortex breakdown and vortex-vortex interactions at moderate to high angles of attack is not well understood. This lack of understanding is a challenge to the development of optimized wing designs for fighter aircraft. The goal of this study is to gain insight into the breakdown of vortices on multi-swept wing configurations. Two generic models were considered, one with a gradual vortex breakdown and one with a rapid (abrupt) breakdown. Aerodynamic forces were calculated from the US Air Force Academy (USAFA) subsonic wind tunnel to validate the experimental setup using computational fluid dynamics (CFD) and previous work. Stereoscopic particle imaging velocimetry (SPIV) was used to visualize vortex-vortex interactions, measure vortex strengths, and identify vortex breakdown locations. The measured lift and drag forces showed flow physics that agreed with previous experiments and CFD, supporting the validity of the new experimental setup. Analysis of SPIV and CFD data improved our understanding of the different types of vortex interactions observed for both models. The only difference between the models was the location of the secondary sweep angle on the chord. The C4L80 model, with a secondary sweep angle at 40% of the root chord, had a large shear layer along the leading edge, which led to vortex merging and gradual vortex breakdown at lower angles of attack than its counterpart. The C6L80 model, with a secondary sweep angle at 60% of the root chord, had no such shear layer and instead developed strong, isolated vortices that were characterized by vortex braiding and abrupt breakdown at high angles of attack. These vortices were entrained into the main vortex at the leading edge of the strake (inboard vortex), creating a balanced vortex system that enhanced lift and delayed the onset of gradual vortex breakdown seen in the C4L80 model.

关键词： Delta Wing Configuration Vortex Breakdown Critical Angle of Attack Mean Aerodynamic Chord computational fluid dynamics simulation Stereoscopic Particle Image Velocimetry Aerodynamic Coefficients Wind Tunnels Boundary Layer Thickness Fuselages

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