scholarly journals Adjoint-Based Aerodynamic Design of Complex Aerospace Configurations

2016 ◽  
Author(s):  
Eric J. Nielsen
Keyword(s):  
Large Scale ◽  
Design Research ◽  
Design Parameters ◽  
Aerodynamic Design ◽  
Cfd Simulations ◽  
Sensitivity Derivatives ◽  
Computational Fluid Dynamics Cfd ◽  
Langley Research Center ◽  
The Cost ◽  
Derivatives Of

An overview of twenty years of adjoint-based aerodynamic design research at NASA Langley Research Center is presented. Adjoint-based algorithms provide a powerful tool for efficient sensitivity analysis of complex large-scale computational fluid dynamics (CFD) simulations. Unlike alternative approaches for which computational expense generally scales with the number of design parameters, adjoint techniques yield sensitivity derivatives of a simulation output with respect to all input parameters at the cost of a single additional simulation. With modern large-scale CFD applications often requiring millions of compute hours for a single analysis, the efficiency afforded by adjoint methods is critical in realizing a computationally tractable design optimization capability for such applications.

Numerical Investigation of the Effect of Balancing-Hole on the Axial Force of a Partial Emission Pump

2014 ◽  
Author(s):  
Zhang Lisheng ◽  
Jiang Jin ◽  
Xiao Zhihuai ◽  
Li Yanhui
Keyword(s):  
Axial Force ◽  
Stokes Equations ◽  
Dominant Role ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Design Parameters ◽  
Navier Stokes Equations ◽  
Computational Fluid Dynamics Cfd ◽  
The Cost

In this paper numerical simulations were conducted to analyze the effects of design parameters and distribution of balancing-hole on the axial-force of a partial emission pump. The studied pump is a single stage pump with a Barske style impeller. Based on the original impeller, we designed 7 pumps with different balancing-hole diameters and the partial emission pump equipped with different impellers were simulated employing the commercial computational fluid dynamics (CFD) software Fluent 12.1 to solve the Navier-Stokes equations for three-dimensional steady flow. A sensitivity analysis of the numerical model was performed with the purpose of balancing the contradiction of numerical accuracy and the cost of calculation. The results showed that, with increasing of the capacity, the axial force varies little. The diameter of the inner balancing-hole plays a dominant role of reducing axial-force of partial emission pump, the axial-force decreases with increasing of inner balancing-hole diameter on the whole range of operation, the axial-force of impeller without inner balancing-hole is approximately 3 times larger than that of impeller with inner balancing-hole. While the diameter of outer balancing-hole has a reverse effects compared with that of inner balancing-hole. With increasing of outer balancing-hole, the axial force increases accordingly.

An Immersive and Interactive Visualization System for Large-Scale CFD

2003 ◽  
Author(s):  
Yuichi Matsuo
Keyword(s):  
Large Scale ◽  
Interactive Visualization ◽  
Cfd Simulations ◽  
Output Data ◽  
Visualization System ◽  
Aerospace Research ◽  
Projection Screen ◽  
Computational Fluid Dynamics Cfd ◽  
Collaboration And Communication ◽  
Rear Projection Screen

We have been long involved in large-scale computational fluid dynamics (CFD) simulations in aerospace research. These days, as the computer power grows, output data from the simulations becomes larger and larger, and we feel that the current visualization methodology has its limitation in understanding. Thus, with the target concepts of reality, collaboration, and communication, we has built an immersive and interactive visualization system with a large-sized wall-type display. The system, which has been in operation since April 2001, is driven by a SGI Onyx 3400 server with 32 CPUs, 64Gbytes memory, and 6 IR3 graphics pipelines, and comprises a 4.6×1.5-meter (15×5-foot) rear projection screen with 3 high-resolution CRT projectors, supporting stereoscopic viewing, easy color/luminosity matching, and accurate edge-blending. The system is mainly used for visualization of large-scale CFD simulations. This paper will describe the new visualization system introduced at the National Aerospace Laboratory of Japan, and the features of the system are discussed while illustrating some typical visualized examples.

Multiphase Computation of Cavitation Breakdown in Model and Prototype Scale Francis Turbines

2015 ◽  
Author(s):  
Daniel J. Leonard ◽  
Jules W. Lindau
Keyword(s):  
Large Scale ◽  
Scale Model ◽  
Cfd Model ◽  
Cfd Simulations ◽  
Qualitative And Quantitative ◽  
Machine Performance ◽  
Computational Fluid Dynamics Cfd ◽  
Stage Analysis ◽  
Reduced Scale ◽  
Francis Hydroturbine

Steady-periodic multiphase Computational Fluid Dynamics (CFD) simulations were conducted to capture cavitation breakdown in a Francis hydroturbine due to large-scale vaporous structures. A reduced-scale model and a full-scale prototype were investigated to display differences in vapor content and machine performance caused by lack of Reynolds and Froude similarity. The model scale efficiencies compared favorably (within 3%) to the experimental cavitation tests. The CFD model and prototype displayed distinct qualitative and quantitative differences as σ was reduced. A stage-by-stage analysis was conducted to assess the effect of cavitation on loss distribution throughout the machine. Furthermore, a formal mesh refinement study was conducted on efficiency and volume of vapor, with three mesh levels and Richardson extrapolation, to ensure convergence.

Approach for uncertainty propagation and design in Saint Venant equations via automatic sensitive derivatives applied to Saar river

2009 ◽  
Vol 36 (7) ◽  
pp. 1144-1154 ◽  
Author(s):  
Otmane Souhar ◽  
Jean-Baptiste Faure
Keyword(s):  
Automatic Differentiation ◽  
Divided Difference ◽  
Uncertainty Propagation ◽  
Free Surface Flows ◽  
Cfd Simulations ◽  
Surface Flows ◽  
One Dimensional ◽  
Saint Venant Equations ◽  
Computational Fluid Dynamics Cfd ◽  
Derivatives Of

This paper describes the assessment of uncertainties of computational fluid dynamics (CFD) for modelling free surface flows. A series of CFD simulations, using MAillé GEnéralisé (MAGE), are employed to compute the flood extent resulting from the overflow of rivers. These simulated outputs are affected by uncertainties in the empiric roughness coefficients. Uncertainty propagation in MAGE outputs is difficult to evaluate because of the complexity and the nonlinearity of models. Assessment of uncertainties may be carried out by computing derivatives of the output results with respect to the inputs. Recently, automatic differentiation (AD) has become an efficient numerical method for sensitivity analysis and assessment of uncertainties. In this paper, AD is used to transform mechanically a given one-dimensional hydraulic model, MAGE, into a new program capable of computing the original simulation and the desired derivatives. Specifically, derivatives of the flood extent and the water width with respect to the roughness coefficients are computed. Numerical experiments of derivatives obtained from AD and divided difference (DD) approximations are compared, validating derivatives obtained by AD. Results can serve to evaluate existing flood models.

Evaluation of a Practical Approach for Numerical Propulsion Tests

2019 ◽  
Author(s):  
Andreas Giannoulis ◽  
Karl H. Halse
Keyword(s):  
Numerical Simulation ◽  
Model Tests ◽  
Full Scale ◽  
Practical Approach ◽  
Computational Time ◽  
Cfd Simulations ◽  
Numerical Accuracy ◽  
Ship Model Test ◽  
Computational Fluid Dynamics Cfd ◽  
The Cost

Abstract Prediction of resistance and propulsion characteristics for a ship is among the most important steps in a ship design process. Traditionally, model tests are used for these predictions and the results are extrapolated to the full-scale ship. Model test techniques can provide reasonably accurate results, but the cost and time they require — and the unavoidable scaling issues — have lead Naval Architects to look for other alternatives. With the increasing computer power and the increasing experience with numerical simulation of fluid flow, Computational Fluid Dynamics (CFD) have become an appealing alternative to model tests. Numerical computations will always be a trade-off between computational efforts and numerical accuracy. Typically, increased accuracy requirements will cause the mesh to be very fine, and hence the computational time will increase. At a Workshop on numerical simulation of full-scale ships in Southampton in November 2016, a practical approach for predicting the propulsion characteristics of a full-scale ship was introduced by participants from Becker Marine Systems. The pragmatic CFD approach reduced the computational efforts without scarifying the level of accuracy! In the present work, the alternative practical CFD approach is evaluated in a model scale case to study its benefits and possible short-comings compared to conventional CFD simulations of the self-propulsion case.

Application of Simple Gradient-Based Method and Multi-Section Blade Parameterization Technique to Aerodynamic Design Optimization of a 3D Transonic Single Rotor Compressor

2009 ◽  
Author(s):  
N. X. Chen ◽  
H. W. Zhang ◽  
Q. Xu ◽  
W. G. Huang
Keyword(s):  
Design Optimization ◽  
Optimal Parameter ◽  
Iteration Process ◽  
Design Parameters ◽  
Optimization Strategy ◽  
Aerodynamic Design ◽  
Blade Optimization ◽  
Gradient Based ◽  
Turbomachinery Blades ◽  
The Cost

A 3D blade optimization strategy for improving turbomachinery performance is proposed mainly based on simple gradient-based method and multi-section blade parameterization technique (MS-BPT) in the present paper. The blade rebuilding method (BRM), the 3D grid generation method (RAPID3DGRID) and the N. S. solver are also used. By using the blade rebuilding method the coordinates of arbitrary blade profile (2D) of each section can be transformed into a set of blade design parameters. For all sections (i.e. in the 3D case) the number of the total design parameters to be searched is increased. But, it can be reduced by designers’ experiences. Since these design parameters, which are obtained by the present blade parameterization method, are independent each from other, this feature allows us to use a simple gradient-based method (SGBM) to search the optimum of the cost function, i.e. with changing any one of the parameters and using grid generator and N. S. solver the optimal design parameters can be obtained in each single optimal parameter searching. And then, instead the old one the new obtained parameter joins the other parameter optimum-searching process in an iteration turn. By repeating the iteration process the convergence of whole optimization process can be reached. The NASA single rotor compressor served as a computation example. The adiabatic efficiency was increased nearly by three percentages. The converged results can be obtained only by a few iterations turns. It is shown that the present method is efficient and can be applied as one of the optimization tools to the design optimization of turbomachinery blades.

CFD Simulations of Aerosol Particles Deposition in a Venturi Meter Used in Smoke Sampling Devices

2016 ◽  
Author(s):  
Omar A. Melhem
Keyword(s):  
Ultrafine Particles ◽  
Particle Deposition ◽  
Aerosol Particles ◽  
Design Parameters ◽  
Brownian Diffusion ◽  
Cfd Simulations ◽  
Flow Meter ◽  
Flow Paths ◽  
Micron Size ◽  
Computational Fluid Dynamics Cfd

Smoke sampling devices are used in several fields to study dynamics of smoke aerosols. An important criterion in designing smoke sampling devices is that flow paths leading to where the sample is characterized are constructed such that deposition of aerosol particles along the paths is minimized. Sampling devices often include a Venturi flow meter installed downstream of the smoke source, which may significantly alter the composition of the aerosol reaching the sample analyzer. The current work employs Computational Fluid Dynamics (CFD) to model particle deposition within the flow meter and to examine the effects of different design parameters. This study focuses on particles with sizes ranging from 0.01 to 100 microns, for which three main mechanisms for deposition can be identified: inertial impaction, gravitational sedimentation, and Brownian diffusion. It has been shown that inertial deposition is negligible for ultrafine particles (5–560 nm) and it becomes noticeable for particles in the micron size range. Also, deposition fractions increase with increasing particle sizes. Moreover, inertial particle deposition increases with increasing volume flow rates.

CFD Modelling of Reverse Osmosis Channels with Potential Applications to the Desalination Industry

2011 ◽  
Vol 6 (2) ◽  
Author(s):  
S. Wardeh ◽  
Herve P. Morvan
Keyword(s):  
Reverse Osmosis ◽  
Large Scale ◽  
Middle Eastern ◽  
Membrane System ◽  
Design Parameters ◽  
Cfd Modelling ◽  
The United Kingdom ◽  
Through Flow ◽  
Potential Applications ◽  
The Cost

Desalination by reverse osmosis is receiving increasing attention due to recent improvements in membrane technology in particular. This technique is now used for small to very large scale applications, and has been identified as a key contributor to water treatment and provision not only in Middle Eastern countries but also closer to home in the United Kingdom for example. Computational Fluid Dynamics (CFD) is increasingly used for complex modelling applications in the chemical process and water industries. Previous work by the writers and others for spacer-filled desalination channels have yielded very good results in terms of modelling the flow and salt characteristics and history in the channels, as well as the overall performance of the membrane system. However, transient features imply that such simulations can be very costly and, if they can approximate experimental layouts with horizontal membranes, the investigation of a full desalination performance and operation remains a very distant prospect. CFD would therefore appear to be unsuited to industrial design at the present time. It is necessary to reduce the cost of the numerical simulations whilst maintaining high fidelity in key design parameters such as pressure loss, shear stress and salt concentration on the membrane, and through flow across the membrane for the method to be useful in design. A momentum loss approach based on a porous medium model is presented to this effect and benchmarked against detailed CFD results with success. It is shown to be capable of meeting key design parameters at a fraction of the full CFD cost.

Cost- und Monitoring-Projekt: Zwei neue forstliche Meinungsumfragen im Vergleich | The Cost- and Monitoring-Projects: A Comparison of Two New Forestry Opinion Polls

2000 ◽  
Vol 151 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Stephan Wild-Eck ◽  
Willi Zimmermann
Keyword(s):  
Large Scale ◽  
Forest Policy ◽  
Forest Economics ◽  
Positive Attitudes ◽  
Federal Institute ◽  
Swiss Confederation ◽  
Institute Of Technology ◽  
The Cost ◽  
Near Future ◽  
Opinion Polls

Two large-scale surveys looking at attitudes towards forests, forestry and forest policy in the second half ofthe nineties have been carried out. This work was done on behalf of the Swiss Confederation by the Chair of Forest Policy and Forest Economics of the Federal Institute of Technology (ETH) in Zurich. Not only did the two studies use very different methods, but the results also varied greatly as far as infrastructure and basic conditions were concerned. One of the main differences between the two studies was the fact that the first dealt only with mountainous areas, whereas the second was carried out on the whole Swiss population. The results of the studies reflect these differences:each produced its own specific findings. Where the same (or similar) questions were asked, the answers highlight not only how the attitudes of those questioned differ, but also views that they hold in common. Both surveys showed positive attitudes towards forests in general, as well as a deep-seated appreciation ofthe forest as a recreational area, and a positive approach to tending. Detailed results of the two surveys will be available in the near future.

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