10 results on '"Transonic"'
Search Results
2. A spacetime framework for aerodynamics of complex motions
- Author
-
Flamarique Ederra, Imanol, Rendall, Thomas, and Gaitonde, Ann
- Subjects
629.1 ,Spacetime ,Aerodynamics ,CFD modelling ,Unsteady ,Time-accurate ,Finite-volume ,Navier-Stokes ,Euler ,Spalart-Allmaras ,Central-difference ,Upwind ,Stability analysis ,Alternative to ALE ,Complex motions ,Topological geometry change ,Relative motions ,Explicit Runge-Kutta ,2D landing case ,Slat and flap ,Spoiler ,Transonic ,Supersonic ,Subsonic ,RANS ,Stencil ,Boundary conditions ,Cell-centered ,CFL condition ,Negative Spalart-Allmaras ,Rotor-stator ,Sock-tube problem ,Isentropic Euler vortex ,NACA 0012 ,Adverse lift ,Pitching motion - Abstract
A two-dimensional spacetime framework is presented to solve unsteady aerodynamics problems as an alternative to conventional approaches for complex unsteady problems involving large deformations or topological change. Some examples of problems that the spacetime method can cope with seamlessly are store separation, slat and flap deployment, spoiler deflection or rotor-stator configurations. It avoids methods such as Chimera or overset grids, or even re-meshing, by the use of a finite-volume approach both in space and time. The simulation of unsteady problems of dimension N is effectively done as the simulation of steady problems of dimension N+1. Hence, both the geometry and its motion are defined by a spacetime mesh in an N+1 dimensional space. The use of an arbitrary Lagrangian-Eulerian formulation along with a geometric conservation law are also avoided by the spacetime formulation. Moreover, it is a conservative method both in space and time. Therefore, it is very suitable for the solution of time-periodic problems. The finite-difference approach used for the time integration in conventional methods based on an ALE formulation uses directionally biased schemes since the solution is only know at previous time levels. In contrast with this, the use of a central-difference scheme in spacetime yields non-physical transient solutions as a consequence of pressure waves travelling backwards in time. The search for a more realistic time stencil has led to the formulation of one hybrid (central-difference in space, upwind in time) and two upwind stencils. Initially, most of the work has been done based on an Euler solver. Then, a RANS formulation has also been implemented with the Spalart-Allmaras one-equation turbulence model. Several two-dimensional unsteady aerodynamics problems have been computed with the different formulations and compared with the central-difference scheme. In particular, the following problems are presented in this work: a one-dimensional periodic piston problem and one with a rapid change of direction; the shock tube problem; a two-dimensional isentropic Euler vortex transport problem; a periodic pitching NACA-0012 aerofoil at different flight conditions; a simple flap deflection; a slat and slotted flap deployment; a spoiler deployment; an investigation of adverse lift due to rapidly deploying spoiler; a full landing case with a combination of slat, flap and spoiler deployments along with ground effect; a case where aerofoils fly in opposite directions at subsonic and supersonic speeds; and a rotor-stator configuration with infinite relative motions. Moreover, some of the spacetime solutions have been correlated with a couple of analytical solutions and some empirical data. It has been demonstrated that the use of a central-difference stencil leads to non-physical solutions as a consequence of pressure waves travelling backwards in physical-time, as expected. It has also been proved that upwind (e.g. Van Leer, Roe) and hybrid (CSUT = central-difference in space, upwind in time) stencils yield more representative physical solutions and improve the rate of convergence. The benefits derived from the use of an upwind stencil as opposed to a central-difference one are more noticeable in the case of non-periodic problems, especially in fast transients. Unfortunately, upwind stencils are more dissipative and, as implied by the results of the isentropic Euler vortex transport problem, they did not seem to achieve as high a temporal accuracy as the central-difference counterpart. The potential for very efficient time-accurate simulations through the spacetime method has been demonstrated by the use of a variable time-step size across the spatial domain. It is possible to use small time-steps in the neighbourhood of the geometry, where big gradients occur, whilst retaining very large time-steps far away in the farfield, where the solution remains almost constant throughout the whole simulation. The versatility and broad applicability of the spacetime method to almost any kind of unsteady problems have been shown by the simulation of a wide range of problems involving complex boundary motions. Large relative motions or topological changes in the geometry are simulated with ease by the use of a spacetime formulation, which avoids the use of an arbitrary Lagrangian-Eulerian (ALE) formulation in combination with a geometric conservation law (GCL). The solver did not need any modifications to cope with any of the problems presented here which proves its potential for highly automated CFD simulations. This could, in turn, speed up the design cycle of industrial applications.
- Published
- 2019
3. New Aerodynamic Studies of an Adaptive Winglet Application on the Regional Jet CRJ700
- Author
-
Ruxandra Mihaela Botez, Marine Segui, Alessandro Ceruti, Frederico R. Abel, Marine Segui, Federico R. Abel, Ruxandra M. Botez, and Alessandro Ceruti
- Subjects
Technology ,Drag coefficient ,longitudinal ,Computer science ,winglet ,Biomedical Engineering ,Bioengineering ,Biochemistry ,aerodynamic ,transonic ,Article ,Biomaterials ,Wingtip device ,Aerospace engineering ,Navier–Stokes equations ,Jet (fluid) ,subsonic ,business.industry ,adaptive ,Aerodynamics ,morphing ,Molecular Medicine ,Climb ,OpenFoam ,Pitching moment ,business ,Transonic ,optimization ,Biotechnology - Abstract
This study aims to evaluates how an adaptive winglet during flight can improve aircraft aerodynamic characteristics of the CRJ700. The aircraft geometry was slightly modified to integrate a one-rotation axis adaptive winglet. Aerodynamic characteristics of the new adaptive design were computed using a validated high-fidelity aerodynamic model developed with the open-source code OpenFoam. The aerodynamic model successively uses the two solvers simpleFoam and rhoSimpleFoam based on Reynold Averaged Navier Stokes equations. Characteristics of the adaptive winglet design were studied for 16 flight conditions, representative of climb and cruise usually considered by the CRJ700. The adaptive winglet can increase the lift-to-drag ratio by up to 6.10% and reduce the drag coefficient by up to 2.65%. This study also compared the aerodynamic polar and pitching moment coefficients variations of the Bombardier CRJ700 equipped with an adaptive versus a fixed winglet.
- Published
- 2021
4. Constrained pseudo-transient continuation.
- Author
-
Ceze, Marco and Fidkowski, Krzysztof J.
- Subjects
NONLINEAR dynamical systems ,MATHEMATICAL models of aerodynamics ,PARTIAL differential equations ,NEWTON-Raphson method ,DISCONTINUOUS functions ,DISCRETIZATION methods ,SUBSONIC flow - Abstract
This paper addresses the problem of finding a stationary point of a nonlinear dynamical system whose state variables are under inequality constraints. Systems of this type often arise from the discretization of PDEs that model physical phenomena (e.g., fluid dynamics) in which the state variables are under realizability constraints (e.g., positive pressure and density). We start from the popular pseudo-transient continuation method and augment it with nonlinear inequality constraints. The constraint handling technique does not help in situations where no steady-state solution exists, for example, because of an under-resolved discretization of PDEs. However, an often overlooked situation is one in which the steady-state solution exists but cannot be reached by the solver, which typically fails because of the violation of constraints, that is, a non-physical state error during state iterations. This is the shortcoming that we address by incorporating physical realizability constraints into the solution path from the initial condition to steady state. Although we focus on the DG method applied to fluid dynamics, our technique relies only on implicit time marching and hence can be extended to other spatial discretizations and other physics problems. We analyze the sensitivity of the method to a range of input parameters and present results for compressible turbulent flows that show that the constrained method is significantly more robust than a standard unconstrained method while on par in terms of cost. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
5. Cavity Tones by Computational Aeroacoustics.
- Author
-
Takeda, K. and Shieh, C. M.
- Subjects
- *
AERODYNAMICS , *ENGINEERING , *FLUID dynamics , *AERONAUTICS , *FREQUENCY response , *PERFORMANCE - Abstract
The flow past open cavities is a problem that is encountered in many engineering applications and can result in intense acoustic tones. The flow physics and acoustics of cavity configurations are complex and computational simulation techniques provide an opportunity to gain further understanding and provide a tool to predict not only cavity tone frequencies but their amplitude. In this paper, we describe the available techniques for performing computational aeroacoustic simulations of cavity flows, and review recent applications for the prediction and control of cavity tones in subsonic, transonic and supersonic regimes. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
6. Compressor Blade Leading Edges in Subsonic Compressible Flow.
- Author
-
Tain, L and Cumpsty, N A
- Subjects
COMPRESSOR blades ,AERODYNAMICS ,FLOW meters - Abstract
The flow around the leading edge of a compressor blade is interesting and important because there is such a strong interaction between the viscous boundary layer flow and the inviscid flow around it. As the velocity of the inviscid flow just outside the boundary layer is increased from subsonic to supersonic, the type of viscous--inviscid interaction changes; this has important effects on the boundary layer downstream and thus on the performance of the aerofoil or blade. An investigation has been undertaken of the flow in the immediate vicinity of a simulated compressor blade leading edge for a range of inlet Mach numbers from 0.6 to 0.95. The two-dimensional aerofoil used has a circular leading edge on the front of a flat aerofoil. The incidence, Reynolds number and level of free-stream turbulence have been varied. Measurements include the static pressure around the leading edge and downstream and the boundary layer profile far enough downstream for the leading edge bubble to have reattached. Schlieren pictures were also obtained. The flow around the leading edge becomes supersonic when the inlet Mach number is 0.7 for the zero-incidence case; for an inlet Mach number of 0.95 the peak Mach number was approximately 1.7. The pattern of flow around the leading edge alters as the Mach number is increased, and at the highest Mach number tested here the laminar separation bubble is removed. Positive incidence, raised free-stream turbulence or increased Reynolds number at intermediate inlet Mach numbers tended to promote flow patterns similar to those seen at the highest inlet Mach number. Both increased free-stream turbulence and increased Reynolds number, for the same Mach number and incidence, produced thinner shear layers including a thinner boundary layer well downstream. The measurements were supported by calculations using the MSES code (the single aerofoil version of the MISES code); the calculations were helpful in interpreting the measured results and were demonstrated to be accurate enough to be used for design purposes. [ABSTRACT FROM AUTHOR]
- Published
- 2000
- Full Text
- View/download PDF
7. Experimental Study of ExoMars Sub- and Transonic Aerodynamics and Heat Shield Separation in HST
- Author
-
Neeb, Dominik, Gülhan, Ali, and Augenstein, Edgar
- Subjects
Transonic ,Aerodynamics ,HST ,Heat shield separation ,Static stability ,Subsonic ,Capsule ,ExoMars - Published
- 2011
8. Calibration of a Four-Hole Mini Probe in Sub-, Trans- and Supersonic Flow
- Author
-
Ren, Celine
- Subjects
Transonic ,Pneumatic Probe ,Aerodynamics ,Error Propagation ,Subsonic ,Supersonic Flow ,Turbine - Published
- 2010
9. Aerodynamic Design of an Ariane 5 Liquid Fly-Back Booster
- Author
-
Thino Eggers
- Subjects
subsonic ,Engineering ,Booster (rocketry) ,business.industry ,Technology research ,super- and hypersonic ,Hypersonic flow ,Mechanical engineering ,Area of interest ,Aerodynamics ,ASTRA ,transonic ,aerodynamic design ,Staging procedure ,Aerospace engineering ,flight mechanics ,business ,aerodynamics ,Transonic - Abstract
Within the German future space launcher technology research program ASTRA two reusable first stage designs are under investigation. The one dedicated for near term application with an existing expendable core stage is called a winged liquid fly-back booster (LFBB). The main goal of the present study is the refinement of an existing LFBB design. The regarded partially reusable space tranportation system consists of two booster stages, which are attached to the expendable Ariane 5 core stage at an upgraded future technology level. The area of interest discussed here is the descent after the staging procedure which dominates the aerodynamic design of the LFBB. The aerodynamic parameter studies pointed out that a LFBB may not be trimmed or stabilised without the introduction of canards as control surface. By introduction of canards a more robust configurations is obtained.
- Published
- 2004
10. Aerodynamic Design and Analysis of an ARIANE 5 Liquid Fly-Back Booster
- Author
-
Eggers, T. and Bozic, O.
- Subjects
subsonic ,super- and hypersonic ,flight mechanics ,transonic ,aerodynamics ,aerodynamic design - Published
- 2002
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.