Flow Separation Research Papers - Academia.edu (original) (raw)

... School of Engineering Springfield, Massachussetts Drag Reduction and Wake Minimization on Marine Vehicles ,,P. ,3 1991 By: , Craig A. Hunter Pasquale Delore Walter M. Presz, Jr. Final Report Office of Naval Research Grant... more

- by Walter Presz
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- Control, Fluid Dynamics, Mixing, Models
- by Majid Ghassemi
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- Engineering, Magnetohydrodynamics, Finite Volume Methods, Energy
- by max platzer
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- Mechanical Engineering, Robotics, Aerospace Engineering, Aerodynamics
- by Garth Hobson
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- Mechanical Engineering, Aerospace Engineering, Turbulence, Flow Visualization
- by Hassan Hemida
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- Mechanical Engineering, Applied Mathematics, Computational Fluid Dynamics, Modeling
- by Sven Schmitz
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- Mechanical Engineering, Applied Mathematics, Computational Fluid Dynamics, Modeling

In the case of high overexpansion, the exhaust jet of the supersonic nozzle of rocket engines separates from nozzle wall because of the large adverse pressure gradient. Correspondingly, to match the pressure of the separated flow region, an oblique shock is generated which evolves through the supersonic jet starting approximately at the separation point. This shock reflects on the nozzle axis with a Mach reflection. Thus, a peculiar Mach reflection takes place whose features depend on the upstream flow conditions, which are usually not uniform. The expected features of Mach reflection may become much difficult to predict, depending on the nozzle shape and the position of the separation point along the divergent section of the nozzle.

- by Marcello Onofri
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- Shock Waves, Classical Physics, Flow Separation, Pressure Gradient
- by Mansour Ziyaeifar
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- Engineering, Modeling, Physical sciences, Sound and Vibration
- by James Coder
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- Engineering, Turbulence, Methodology, Laminar Flow
- by Jim Best
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- Turbulence, Complexity, Morphology, Topology
- by Luis Bernal
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- Mechanical Engineering, Aerospace Engineering, Mesh generation, Aerodynamics
- by Sanjeev Sanghi
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- Mechanical Engineering, Applied Mathematics, Mesh generation, Comparative Study
- by Sara Bagheri
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- Engineering, Technology, Fluid Mechanics, Interaction
- by Michael Breuer
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- Engineering, STEP, Laminar Flow, Pipe Flow
- by Wim Uijttewaal
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- Geology, Morphology, Text, Laboratory
- by max platzer
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- Numerical Analysis, Coding, Propulsion Systems, Flight

Since the dawn of the space age, flow separation issue in rocket nozzles has been an unwanted phenomenon for the engineers. So, naturally, this became a task for the engineers which is to be brought under control. But it turned out to be a daunting task; even though many were able to explain the physics behind this phenomenon, it is not fully understood even to the present day. So, there are not many methods, which explains how to control or suppress this phenomenon. This paper aims to study about two of those few methods which affectively are able to suppress flow separation in rocket nozzles.

- by Jainul Abedin
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- Aerospace Engineering, Heat Transfer, Rocket nozzles, Flow Separation

This paper primarily presents velocities, Reynolds stresses and turbulence intensities of flow over a series of two-dimensional asymmetric sharp-crested, gravel bedforms. The bedforms have a mean wavelength of 0.96 m, a mean height of 0.08 m, and a width of 0.4 m (equal to the flume width) and a lee slope of 28°. The results show that extrapolating spat ial ly-averaged log-law veloc ity profiles provided the best estimate of bed shear stress for bedforms . Maximum values of the root-mean-squared velocity over the sharp-crested gravel bedforms were located farther away from the bed when compared to those for sand dunes. The Reynolds stresses were zero or negative near the water surface over sand dunes, whi ls t they were positive over sharp-crested gravel bedforms. The length of the separation zone of gravel dunes was less than that for sand dunes, showing a faster reattachment over a gravel bed in comparison to that of a sand bed. Quadrant analysis showed that near the bed the contr...

- by Jacques Gallichand and +1
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- Turbulence, Hydraulic Engineering, Flow Separation
- by ismail Celik
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- Engineering, Computational Fluid Dynamics, Mesh generation, Standard Deviation

This paper reports velocity measurement data in the interaction region between the impeller and vaned diffuser and the results of numerical flow simulation of the whole machine (impeller, vaned diffuser and volute) of a single stage centrifugal fan. Two-dimensional instantaneous velocity measurement is done using particle image velocimetry (PIV). Numerical simulation of impeller-diffuser-volute interaction is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady calculation and a rotor-stator simulation model is used for the unsteady calculation using the steady results as an initial guess. The simulation results show that the separated flow regime near the diffuser hub extends to the volute. Comparison between the unsteady computation and those of measurement indicates that the rotor/stator model employed in the simulation predicts essential characteristics of unsteady flow in the centrifugal fan. However, quantitative agreement remain...

- by tarek Meakhail
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- Mechanical Engineering, Aerospace Engineering, Modeling, Interaction

Turbulent flow separation in over-expanded rocket nozzles is investigated numerically in a sub-scale parabolic nozzle fed with cold nitrogen. Depending upon the feeding to ambient pressure ratio either a free shock separation or a restricted shock separation is computed, with a significant hysteresis between these two flow regimes. This hysteresis was also found in experimental tests with the same nozzle geometry. The present study is mainly focused on the transition between the two shock separation patterns. The analysis of the numerical solutions aims to provide clues for the explanation of the hysteresis cycle.

- by Emanuele Martelli
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- Shock Waves, Hysteresis, Classical Physics, Nitrogen

We consider a combined experimental (based on flow visualization, direct force measurement and phaseaveraged 2D particle image velocimetry in a water tunnel), computational (2D Reynolds-averaged Navier-Stokes) and theoretical (Theodorsen's formula) approach to study the fluid physics of rigid-airfoil pitch-plunge in nominally two-dimensional conditions. Shallow-stall (combined pitch-plunge) and deep-stall (pure-plunge) are compared at a reduced frequency commensurate with flapping-flight in cruise in nature. Objectives include assessment of how well attached-flow theory can predict lift coefficient even in the presence of significant separation, and how well 2D velocimetry and 2D computation can mutually validate one another. The shallow-stall case shows promising agreement between computation and experiment, while in the deepstall case, the computation's prediction of flow separation lags that of the experiment, but eventually evinces qualitatively similar leading edge vortex size. Dye injection was found to give good qualitative match with particle image velocimetry in describing leading edge vortex formation and return to flow reattachment, and also gave evidence of strong spanwise growth of flow separation after leadingedge vortex formation. Reynolds number effects, in the range of 10,000-60,000, were found to influence the size of laminar separation in those phases of motion where instantaneous angle of attack was well below stall, but have limited effect on post-stall flowfield behavior. Discrepancy in lift coefficient time history between experiment, theory and computation was mutually comparable, with no clear failure of Theodorsen's formula. This is surprising and encouraging, especially for the deep-stall case, because the theory's assumptions are clearly violated, while its prediction of lift coefficient remains useful for capturing general trends.

- by Luis Bernal
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- Mechanical Engineering, Aerospace Engineering, Mesh generation, Aerodynamics
- by Zhiyin Yang
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- Mechanical Engineering, Aerospace Engineering, Boundary Layers, Large Eddy Simulation
- by Alessandro Armellini
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- Engineering, Water, Heat Transfer, Particle Image Velocimetry
- by Ali Belghith
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- Mechanical Engineering, Applied Mathematics, Turbulence, Large Eddy Simulation
- by Patrick McGah and +1
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- Mechanical Engineering, Biomechanical Engineering, Surgery, Biomedical Engineering
- by hossein R hamdani
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- Engineering, Computational Fluid Dynamics, Mesh generation, Aerodynamics
- by max platzer
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- Turbulence, Numerical Analysis, Geometry, Dynamics
- by Martin Skote
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- Engineering, Fluid Mechanics, Boundary Layers, Direct Numerical Simulation

Abstract- Flow separation at the vehicle’s rear end is the major cause of an aerodynamic drag in a car. In order to delay the flow separation at the rear, bump-shaped vortex generators at the roof end of a car are tested in this paper for two different types of car models Sedan and Hatchback. The aerodynamic analysis is carried out using GAMBIT and FLUENT for Sedan and Hatchback models. Vortex Generators are found to be not very sensitive for the designing parameters. CFD analysis confirms that the use of Vortex Generators reduces both the drag and lift coefficients.

- by shashank chheniya
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- Aerodynamics, Drag, Lift, Flow Separation
- by Laurent Cordier
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- Distributed Computing, Flow Control, Actuators, Calibration
- by Patrick Legentilhomme and +1
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- Mechanical Engineering, Aerospace Engineering, Instrumentation, Low Frequency
- by parviz moin
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- Computational Fluid Dynamics, Turbulence, Convergence, Finite Element Analysis
- by Jean-Christophe Robinet and +1
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- Mechanical Engineering, Applied Mathematics, Stability, Spectral method
- by Fabián López
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- Environmental Engineering, Civil Engineering, Water resources, Applied Economics
- by Peter Johnston
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- Applied Mathematics, Computational Fluid Dynamics, Modeling, Mesh generation
- by md.ashraful alam
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- Two Phase Flow, Pattern Formation, Boundary Layers, Numerical Analysis
- by Sebastien Poncet
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- Boundary Layers, Analytical Model, Flow Separation, Boundary Layer
- by Marcello Onofri
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- Shock Waves, Hysteresis, Classical Physics, Nitrogen
- by Alexander Zheltovodov
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- Compression, Flow Separation, Compressible Flow, Reynolds Number
- by Pietro Catalano
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- Computational Fluid Dynamics, Fluid Mechanics, Numerical Analysis, Turbulent Flow

Further development of large-eddy simulation (LES) faces as major obstacles the strong coupling between subgrid-scale (SGS) modeling and the truncation error of the numerical discretization. One can exploit this link by developing discretization methods where the truncation error itself functions as an implicit SGS model. The adaptive local deconvolution method (ALDM) is an approach to LES of turbulent ﬂows that represents a full coupling of SGS model and discretization scheme. To provide evidence for the validity of this new SGS model, well resolved large-eddy simulations of a fully turbulent ﬂat-plate boundarylayer ﬂow subjected to a constant adverse pressure gradient are conducted. Flow parameters are adapted to an available experiment. The Reynolds number based on the local free-stream velocity and momentum thickness is 670 at the inﬂow and 5100 at the separation point. Clauser’s pressure-gradient parameter
increases monotonically from 0 up to approximately 100 since a constant pressure gradient is prescribed. The adverse pressure gradient leads to a highly unsteady and massive separation of the boundary layer. The numerical predictions agree well with theory and experimental data.

- by Stefan Hickel
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- Turbulence, Boundary Layer Meteorology, Large Eddy Simulation, Turbulent Flows
- by Tomas Bohr
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- Engineering, Physics, Fluid Mechanics, Pattern Formation