CFD Simulation Results vs. Test data from NASA: Onera M6

CFD Simulation Results vs. Test data from NASA: Onera M6

Introduction

The Aerospace industry is one of the most powerful industries worldwide and, as it stands today, supplies 4 basic markets: military aircraft, missiles, space and commercial airliners. Only the commercial aircraft industry, operates more than 20,000 aircrafts at 3,500 airports and is expected to double over the next decade. Considering the global economic state and the more and more strict regulations about flights, aircraft designers have to build more fuel-efficient aircrafts and also make air transportation safer. The only way to accomplish this goal, is by designing planes which generate more lift but produce less drag at the same time. In order to design such aircrafts, it is necessary to have a deep understanding in the aerodynamics of the planes. The most crucial aerodynamic element of an aircraft is the wings. But how do wings actually work?

As an aircraft flies through the sky, the air follows the curvature of the wing surface. Because of this curvature, the air on the top travels faster than the air on the bottom. As a result, the pressure on the top surface is lower (suction surface), and the pressure on the bottom surface is higher (pressure surface). It is this pressure gradient that generates the lift, a force which acts perpendicular to fluid motion, making it possible for aircrafts to fly. Modern wings, are able to generate lift at zero angle of attack, and lift increases as angle of attack increases. The relative motion between air and wing causes friction, and as result a second force acts in a direction which is opposite to the motion of the aircraft. This force is called drag.

FEAC Engineering - External Aerodynamics - Onera - CFD

In order to find more efficient designs and try different modifications of original wing geometries, aerospace industry has turned to CFD packages with which the fluid flow over a wing can be simulated using computers instead of setting experiments. Computational Fluid Dynamics is the analysis of systems involving fluid flow, by means of computer-based simulation. CFD analysis is a dominant key for aerospace industry, in order to design and optimize an aircraft, and this is because it costs less and gives valuable results faster.

Cost

It is much more cost-effective to simulate the flow around an aircraft (or a part of an aircraft such as a wing), in order to get essential engineering data, than using physical experiments. With the rapid development of computers, the cost of simulation is likely to decrease, and with the ability of testing numerous models, and several modifications of the original geometry, the development process of an aircraft can be much more economical.

Speed

CFD simulations can be performed in a “short” period of time (depending on the computer available), especially if it is compared with physical experiments, where, in some cases, only setting the experiment can take months. With CFD analysis several models can be tested on a daily basis, making the designing process of an aircraft a lot faster.

Foresight

CFD analysis is a tool that can actually predict the future. In other words, several “what if” scenarios can be examined and evaluated, judging which design gives the best results, and finally constructing only one prototype, the one with the best performance. By comparing simulation results with experiments, we can be confident that the model represents real physics of the problem, and use it in other cases as well. For instance, the same model can be used, examining different angles of attack and finding the one, which generates the higher lift.

Onera M6 CFD simulation

In this case study, a steady state simulation of the Onera M6 is performed using ANSYS and the results are compared with experimental data obtained from NASA experiment and from a simulation, conducted by NASA. Onera M6 is a well-known wing in aerospace industry, which has been used many times for validating CFD codes. In order to get correct results from the model a mesh with high quality, and the best suitable turbulence model is used. Its simple geometry, can give a deep understanding on how the air flows over a wing, and the pressure distribution on the surfaces.

The experimental data of Pressure Coefficient have been obtained at the seven different measurement positions as it is shown in the picture above. The profile of the wing is symmetrical, which means that a positive angle of attack is necessary in order to generate lift.

FEAC Engineering - External Aerodynamics - Onera post proc locations

The values of interest for this study are the pressure distribution on wing surfaces and calculating the pressure coefficient (Cp). The formula that calculates (Cp)  is:

FEAC Engineering - External Aerodynamics - CFD CP

Pressure Coefficient is a dimensionless number that is used a lot from aerospace industry, and the reason is that different wing shapes and geometries can be compared, regardless of their dimensions.

CFD Results vs. Experimental Data

The main areas of interest when examining wing pressure distribution

The main areas of interest when examining wing pressure distribution.

In the figure above, the key areas of interest when examining wing pressure distribution are highlighted. We note that, as the air flows over the top surface, the pressure is decreasing rapidly. This area of wing contributes to 70% of the total lift generated.  At a point, the pressure becomes minimum and then starts to recover. Note that on the leading edge Cp equals one.

Comparison between simulation results and test data at several cross sections of the wing

Comparison between simulation results and test data at several cross sections of the wing.

An overall good agreement between simulation and experimental data is observed. At y/b=0.99 CFD analysis gives less accurate results due to the wingtip vortex that is created in this region of wing. The rotation of the vortices create strong 3-dimensional effects and this is why it is difficult for the model to predict accurately the pressure coefficients in this region. In addition, the diameter of the wingtip vortex is very small making it difficult to be accurately simulated with the present model.

Simulation Results

The left picture shows the pressure distribution from a CFD simulation done by NASA for Onera M6. We note that our simulation is at good agreement with NASA. Both analyses predict the lower pressure on the suction surface. Also, the distribution of the pressure, and how it recovers along the wing are very similar.

FEAC Engineering - External Aerodynamics - Onera CFD result

From the figure below,we note the corellation between pressure and velocity. On the suction surface where the pressure is low, the air is accelarating at values exceeding Mach=1. We also observe on the leading edge, where air is forced to stop moving, that pressure is maximum.

From the figure above,we note the corellation between pressure and velocity. On the suction surface where the pressure is low, the air is accelarating at values exceeding Mach=1. We also observe on the leading edge, where air is forced to stop moving, that pressure is maximum.From the figure above,we note the corellation between pressure and velocity. On the suction surface where the pressure is low, the air is accelarating at values exceeding Mach=1. We also observe on the leading edge, where air is forced to stop moving, that pressure is maximum.

Streamlines Colored by Mach Number

Streamlines Colored by Mach Number
Streamlines at y/b=0.44

Streamlines at y/b=0.44
Streamlines on the suction surface of the wing

Streamlines on the suction surface of the wing

CONCLUSION

From the last Cp chart (y/b=0.99), we observe the difficulty of the model to predict the pressure coefficient accurately, at the wingtip. In order to get more accurate results, in this region as well, a refinement in this area should be considered.
Generally, a good agreement between experimental data and CFD simulation can be observed. Thus, the air flow over a wing can be simulated with high level of accuracy. From the present analysis we can conclude that, Computational Fluid Dynamics is a tool that can be used with confidence, replacing physical experiments, in order to develop and evaluate new aerodynamics devices, used in aircrafts. Apart from aerospace industry, CFD can be used in other applications as well, such as automotive, hydrodynamics of ships, Internal Combustion Engines, turbomachinery, external and internal environment of buildings: wind loading and heating/ventilation, marine engineering: loads of offshore structures, hydrology and oceanography: flows in rivers and oceans, meteorology: weather prediction…

Written by: Sofoklis Giannaros ([email protected])

Automotive bumper according to IIHS & RCAR

Automotive bumper according to IIHS & RCAR

Low speed collisions are common in areas with traffic congestion and parking occasions. These collisions burden economically the car owners and could have been avoided with suitable design of car bumpers. Bumper beams are one of the most important structures in passenger cars, relative to the safety and the levels of protection of the vehicle chassis. Careful and appropriate design should be considered in order to achieve best impact behavior.

There is no beaten track regarding the bumper beam design, neither its geometry nor the materials used. Consequently, there is a wide range of design and manufacturing philosophies used in modern cars and the research and development in this field is enormous and continuous.

The scope of this project was to design and simulate a light weight automotive bumper according to the full frontal low-speed impact test established by the IIHS (Insurance Institute for Highway Safety) & the RCAR (Research Council for Automobile Repairs). The design includes a prototypal and innovative bumper geometry and the simulation analysis was accomplished for materials that are quite common or will be the state of the art in the near future, like specific aluminum alloys, strengthened thermoplastics and composite materials. Comparisons in terms of weight and impact performance were made. The bumper’s geometry was invariable and the effect of interior additions, like horizontal / vertical composite absorbers or polystyrene foam, on the bumper’s deformation was studied, in order to assess the crashworthiness of each configuration.

The contribution of the advanced Applied Mechanics Laboratory to FEAC, by providing knowledge and technology transfer has been a key factor for the accomplishment of this project, which included:

  •  Parametric CAD modeling, drafting & parameters documentation
  •  APDL input files & macros
  •  Setup of the parametric explicit FE analysis
  •  Optimization of the structure to better fulfill the standards
  •  Procedure & results documentation

Physics Involved

  • Structural analysis
  • Composite materials
  • Optimization

    Tools Used

    • Catia V5
    • MSC Nastran/Patran
    • Ansys Classic
    • APDL Input Files & Macros
    • ETA VPG
    • LS-DYNA
    • LS-Prepost
    11T Superconducting accelerator dipole magnet

    11T Superconducting accelerator dipole magnet

    The LHC (Large Hadron Collider) is planning to use shorter magnets to make room in its tunnel for new instruments that will help narrow the particle beam, protecting the LHC ring from beam losses. But if the magnets must be shorter, they must also be stronger to compensate. To obtain the necessary longitudinal space for the collimators, a solution based on an 11 T dipole as replacement of the 8.33 T LHC main dipoles is being considered.

    In order to increase the magnetic field, the material of the conductor has to change. The superconductor used currently in the accelerator is niobium-titanium but It cannot withstand magnetic field intensity as high as the more expensive (and harder to use) niobium-tin . Niobium-tin is an extremely brittle and difficult-to-manage superconductor therefore the research on methods to withstand the large forces and large temperature changes it will be subjected to in accelerator magnets as they help bend and focus particle beams is ongoing.

    CERN (European Organization for Nuclear Research, Geneva, Switzerland) and FNAL (Fermi National Accelerator Laboratory, Chicago, USA) have started a joint program to demonstrate the feasibility of Nb3Sn technology for this purpose.

    Present FEAC stuff, while working for CERN at the time, were responsible for these services:

    •  Translation of APDL input files to CATIA & ANSYS Workbench files
    •  Parametric CAD modeling, drafting & parameters documentation
    •  APDL input files & macros
    •  Setup of parametric, coupled multiphysics FE analysis
    •  Design space exploration
    •  Shape optimization of components & parameter values to achieve the required results
    •  Comparison between test and FEM results
    •  Procedure & results documentation
    •  Knowledge transfer

    The project is ongoing at CERN & Fermilab. Follow the links to learn more :

    Physics Involved

    • Electro – Magnetic
    • Thermal
    • Structural
    • Optimization

      Tools Used

          • Catia V5
          • CADNexus CAPRI CAE
          • Ansys DesignModeler
          • Ansys Classic
          • APDL Input Files & Macros
          • Ansys EMAG
          • Ansys Maxwell
          • Ansys Structural
          • Ansys DesignXPlorer

      FEAC Engineering joins the SIEMENS PLM partner community

      FEAC Engineering joins the SIEMENS PLM partner community

      FEAC Engineering P.C. has joined the Siemens PLM Software Partner Community to enhance its suite of offerings. As a result, FEAC Engineering is the exclusive authorized reseller of the CAE SIEMENS PLM portfolio to current and future customers, the same Siemens software technology that companies around the world depend on every day to enhance product development decision making and produce better products.

      As part of the partnership, FEAC Engineering is able to offer its customers:

      • Simcenter 3D software, the industry-leading simulation software delivering a unified, scalable, open and extensible environment for 3D CAE
      • Femap software, the industry standard finite element modeling solution
      • NX CAE software, a leading integrated solution for computer-aided engineering (CAE)
      • STAR-CCM+ software, the amazing multi-physics solver
      • HEEDS, the leading software in design exploration and product optimization
      • NX NASTRAN, the world-famous solver for structures

      in Greece, Cyprus & Malta.

      FEAC’s Engineering depth of industry expertise combined with Siemens PLM Software’s industry leading PLM technology provides customers with high quality PLM products and services allowing them to maximize their PLM investment.

      “Siemens PLM Software is committed to using our channel-centric strategy to continually enhance customer access to our industry leading PLM technology,” said Bas van Dijk, Channel Manager Greece, Siemens PLM Software. “This partnership with FEAC Engineering expands our reach and execution capability in Greece, Cyprus & Malta to help customers leverage PLM to capitalize on growing market opportunities.”

      “FEAC Engineering is excited to join Siemens PLM Software’s partner community. The strength of our two organizations working together is expected to deliver significant value to our customers,” said Mr. Sotiris Kokkinos, CEO, FEAC Engineering.

      About FEAC Engineering

      FEAC Engineering is a leading solutions provider in Simulation Driven Engineering. Founded in 2014 and based in Greece, the company applies simulation expertise and operational experience to solve challenging & complex problems. FEAC operates in the global market and collaborates and partners with engineering companies, product manufacturers, research centers and universities. FEAC Engineering P.C. provides state of the art solutions throughout the product development cycle, from concept design to prototype testing. With the use of Advanced Computer Aided Engineering tools (CAE) such as Femap, NX CAE, Simcenter 3D,STAR-CCM+ & HEEDS, FEAC achieves substantial reduction of cost, time and risk while ensuring optimal product performance. FEAC Engineering conducts both Finite Element Method (FEM) & Boundary Element Method (BEM) to offer fast, efficient and highly-accurate results to our partners and clients. Our experienced world-class team has developed unique solutions in a wide range of sectors by optimizing products, systems, entities, phenomena and processes under real-world conditions.

      FEAC Engineering wishes you Merry Christmas & Happy Holidays!!

      FEAC Engineering wishes you Merry Christmas & Happy Holidays!!

      FEAC Engineering wishes you Merry Christmas & Happy holidays, filled with happiness and joy!!! We also wish all our clients, partners, employees as well as friends of our company a very merry Christmas and a happy new year 2019.

      • French: Joyeux Noël
      • German: Frohe Weinachten
      • Spanish: Feliz Navidad
      • Italian: Buon Natale
      • Portuguese: Feliz Natal
      • Dutch: Vrolijk kerstfeest
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      • Czech: Veselé Vánoce

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