scholarly journals Controlled Synthetic Freestream Turbulence Intensity Introduced by a Local Volume Force

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 130
Author(s):  
Eike Tangermann ◽  
Markus Klein
Keyword(s):  
Turbulence Structure ◽  
Computational Domain ◽  
Control Loop ◽  
Freestream Turbulence ◽  
High Angle ◽  
Specific Location ◽  
Volume Force ◽  
Turbulent Fluctuations ◽  
Local Volume ◽  
Physical Reasons

Generating freestream turbulence within the computational domain instead of applying it as a boundary condition requires a method to introduce the turbulent fluctuations at a specific location. A method based on applying local volume forces has been adapted and supplemented with a control loop in order to compensate for alterations of the turbulence structure resulting from the numerical treatment and physical reasons. The criteria for the tuning of the controller have been developed and the performance of the approach has been assessed. The capabilities of the method are demonstrated for the flow around an airfoil at high angle of attack and with massive flow separation.

Computational investigation of turbulent jet impinging onto rotating disk

2007 ◽  
Vol 17 (3) ◽  
pp. 284-301 ◽  
Author(s):  
A.C. Benim ◽  
K. Ozkan ◽  
M. Cagan ◽  
D. Gunes
Keyword(s):  
Boundary Conditions ◽  
Isotropic Turbulence ◽  
Domain Size ◽  
Rotating Disk ◽  
Turbulent Jet ◽  
Turbulence Structure ◽  
Computational Domain ◽  
Convergence Criteria ◽  
Computational Investigation ◽  
Content Type

PurposeThe main purpose of the paper is the validation of a broad range of RANS turbulence models, for the prediction of flow and heat transfer, for a broad range of boundary conditions and geometrical configurations, for this class of problems.Design/methodology/approachTwo‐ and three‐dimensional computations are performed using a general‐purpose CFD code based on a finite volume method and a pressure‐correction formulation. Special attention is paid to achieve a high numerical accuracy by applying second order discretization schemes and stringent convergence criteria, as well as performing sensitivity studies with respect to the grid resolution, computational domain size and boundary conditions. Results are assessed by comparing the predictions with the measurements available in the literature.FindingsA rather unsatisfactory performance of the Reynolds stress model is observed, in general, although the contrary has been expected in this rotating flow, exhibiting a predominantly non‐isotropic turbulence structure. The best overall agreement with the experiments is obtained by the k‐ω model, where the SST model is also observed to provide a quite good performance, which is close to that of the k‐ω model, for most of the investigated cases.Originality/valueTo date, computational investigation of turbulent jet impinging on to “rotating” disk has not received much attention. To the best of the authors' knowledge, a thorough numerical analysis of the generic problem comparable with present study has not yet been attempted.

scholarly journals An Improved Synthetic Eddy Method for Generating Inlet Turbulent Boundary Layers

Aerospace ◽  
2022 ◽  
Vol 9 (1) ◽  
pp. 37
Author(s):  
Dapeng Xiong ◽  
Yinxin Yang ◽  
Yanan Wang
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Friction Coefficient ◽  
Skin Friction Coefficient ◽  
Turbulent Boundary Layers ◽  
Computational Domain ◽  
Turbulent Fluctuations ◽  
Dimensionless Velocity ◽  
Simulation Results ◽  
Definition Of

An improved synthetic eddy method (SEM) is proposed in this paper for generating the boundary layer at the inlet of a computational domain via direct numerical simulation. The improved SEM modified the definition of the radius and the velocities of the eddies according to the distance of the eddies from the wall in the synthetic region. The regeneration location of the eddies is also redefined. The simulation results show that the improved SEM generates turbulent fluctuations that closely match the DNS results of the experiments. The skin friction coefficient of the improved SEM recovers much faster and has lower dimensionless velocity at the outer of the boundary layer than that of the traditional SEM.

scholarly journals Wake Turbulence Structure Downstream of a Cambered Airfoil in Transonic Flow: Effects of Surface Roughness and Freestream Turbulence Intensity

2006 ◽  
Vol 2006 ◽  
pp. 1-12 ◽  
Author(s):  
Qiang Zhang ◽  
Phillip M. Ligrani
Keyword(s):  
Surface Roughness ◽  
Turbulence Intensity ◽  
Vortex Shedding ◽  
Transonic Flow ◽  
Streamwise Velocity ◽  
Turbulence Structure ◽  
Freestream Turbulence ◽  
Wake Turbulence ◽  
Vortex Shedding Frequency ◽  
Flow Effects

The wake turbulence structure of a cambered airfoil is studied experimentally, including the effects of surface roughness, at different freestream turbulence levels in a transonic flow. As the level of surface roughness increases, all wake profile quantities broaden significantly and nondimensional vortex shedding frequencies decrease. Freestream turbulence has little effect on the wake velocity profiles, turbulence structure, and vortex shedding frequency, especially downstream of airfoils with rough surfaces. Compared with data from a symmetric airfoil, wake profiles produced by the cambered airfoils also have significant dependence on surface roughness, but are less sensitive to variations of freestream turbulence intensity. The cambered airfoil also produces larger streamwise velocity deficits, and broader wakes compared to the symmetric airfoil.

Direct numerical simulation of hypersonic turbulent boundary layers. Part 1. Initialization and comparison with experiments

2007 ◽  
Vol 570 ◽  
pp. 347-364 ◽  
Author(s):  
M. PINO MARTIN
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Initial Condition ◽  
Experimental Conditions ◽  
Turbulent Fluctuations

A systematic procedure for initializing supersonic and hypersonic turbulent boundary layers at controlled Mach number and Reynolds number conditions is described. The initialization is done by locally transforming a true direct numerical simulation flow field, and results in a nearly realistic initial magnitude of turbulent fluctuations, turbulence structure and energy distribution. The time scales necessary to forget the initial condition are studied. The experimental conditions of previous studies are simulated. The magnitude of velocity and temperature fluctuations, as well as the turbulent shear stresses given by the direct numerical simulations are in agreement with the experimental data.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Microbulldozing and Microchiseling

1969 ◽  
Vol 27 ◽  
pp. 134-135
Author(s):  
J.N. Ramsey ◽  
D.P. Cameron ◽  
F.W. Schneider
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Material Handling ◽  
Microprobe Analysis ◽  
Foreign Matter ◽  
Specific Location ◽  
Potential Problems ◽  
Knoop Indenter ◽  
Scanning Electron ◽  
Microhardness Tester

As computer components become smaller the analytical methods used to examine them and the material handling techniques must become more sensitive, and more sophisticated. We have used microbulldozing and microchiseling in conjunction with scanning electron microscopy, replica electron microscopy, and microprobe analysis for studying actual and potential problems with developmental and pilot line devices. Foreign matter, corrosion, etc, in specific locations are mechanically loosened from their substrates and removed by “extraction replication,” and examined in the appropriate instrument. The mechanical loosening is done in a controlled manner by using a microhardness tester—we use the attachment designed for our Reichert metallograph. The working tool is a pyramid shaped diamond (a Knoop indenter) which can be pushed into the specimen with a controlled pressure and in a specific location.

A High Angle, Double Tilting Cold Stage for the AEI EM7

1974 ◽  
Vol 32 ◽  
pp. 450-451
Author(s):  
P.R. Swann ◽  
A.E. Lloyd
Keyword(s):  
Habit Plane ◽  
Temperature Control ◽  
Tilt Angle ◽  
Cooling System ◽  
Thermal Drift ◽  
High Angle ◽  
Cold Stage ◽  
High Degree ◽  
Better Than

Figure 1 shows the design of a specimen stage used for the in situ observation of phase transformations in the temperature range between ambient and −160°C. The design has the following features a high degree of specimen stability during tilting linear tilt actuation about two orthogonal axes for accurate control of tilt angle read-out high angle tilt range for stereo work and habit plane determination simple, robust construction temperature control of better than ±0.5°C minimum thermal drift and transmission of vibration from the cooling system.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

Determination of the lattice translation across {110} APBs in GaAs

1988 ◽  
Vol 46 ◽  
pp. 600-601
Author(s):  
D.R. Rasmussen ◽  
N.-H. Cho ◽  
C.B. Carter
Keyword(s):  
Grain Boundaries ◽  
Lower Energy ◽  
Antiphase Boundary ◽  
The Other ◽  
Boundary Structure ◽  
Interface Plane ◽  
Inversion Symmetry ◽  
High Angle ◽  
Equilibrium Distance

Domains in GaAs can exist which are related to one another by the inversion symmetry, i.e., the sites of gallium and arsenic in one domain are interchanged in the other domain. The boundary between these two different domains is known as an antiphase boundary [1], In the terminology used to describe grain boundaries, the grains on either side of this boundary can be regarded as being Σ=1-related. For the {110} interface plane, in particular, there are equal numbers of GaGa and As-As anti-site bonds across the interface. The equilibrium distance between two atoms of the same kind crossing the boundary is expected to be different from the length of normal GaAs bonds in the bulk. Therefore, the relative position of each grain on either side of an APB may be translated such that the boundary can have a lower energy situation. This translation does not affect the perfect Σ=1 coincidence site relationship. Such a lattice translation is expected for all high-angle grain boundaries as a way of relaxation of the boundary structure.

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