scholarly journals Experiments on a three-dimensional turbulent boundary layer over a ridge. 1st report. Mean flow field at yaw angle 30.DEG..

1988 ◽  
Vol 54 (500) ◽  
pp. 823-832
Author(s):  
Shintaro YAMASHITA ◽  
Ikuo NAKAMURA ◽  
Kazuro NAGASE ◽  
Hiroya YAMADA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Three Dimensional ◽  
Mean Flow ◽  
Yaw Angle

Subsonic Turbulent Flow Past a Planar Fence

1979 ◽  
Vol 101 (3) ◽  
pp. 373-375
Author(s):  
M. L. Agarwal ◽  
P. K. Pande ◽  
Rajendra Prakash
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Boundary Conditions ◽  
Mean Flow ◽  
Governing Equations ◽  
Flow Past ◽  
Entire Flow ◽  
The Mean ◽  
Shape And Size

The mean flow past a fence submerged in a turbulent boundary layer is numerically simulated. The governing equations have been simplified by neglecting the convective effects of turbulence and solved numerically using experimental boundary conditions. The information obtained includes the shape and size of the upstream and downstream separation bubbles and the streamline pattern in the entire flow field. General agreement between the simulated and the experimental flow field was found.

scholarly journals DNS of a turbulent boundary layer using inflow conditions derived from 4D-PTV data

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Jason Appelbaum ◽  
Duncan Ohno ◽  
Ulrich Rist ◽  
Christoph Wenzel
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Nearest Neighbor ◽  
Tracer Particle ◽  
Flow Analysis ◽  
Mean Flow ◽  
Experimental Field ◽  
Inlet Region

AbstractUnsteady, 3D particle tracking velocimetry (PTV) data are applied as an inlet boundary condition in a direct numerical simulation (DNS). The considered flow case is a zero pressure gradient (ZPG) turbulent boundary layer (TBL) flow over a flat plate. The study investigates the agreement between the experimentally measured flow field and its simulated counterpart with a hybrid 3D inlet region. The DNS field inherits a diminishing contribution from the experimental field within the 3D inlet region, after which it is free to spatially evolve. Since the measurement does not necessarily provide a spectrally complete description of the turbulent field, the spectral recovery of the flow field is analyzed as the TBL evolves. The study summarizes the pre-processing methodology used to bring the experimental data into a form usable by the DNS as well as the numerical method used for simulation. Spectral and mean flow analysis of the DNS results show that turbulent structures with a characteristic length on the order of one average tracer particle nearest neighbor radius $${\bar{r}}_{\text {NN}}$$ r ¯ NN or greater are well reproduced and stay correlated to the experimental field downstream of the hybrid inlet. For turbulent scales smaller than $${\bar{r}}_{\text {NN}}$$ r ¯ NN , where experimental data are sparse, a relatively quick redevelopment of previously unresolved turbulent energy is seen. The results of the study indicate applicability of the approach to future DNS studies in which specific upstream or far field boundary conditions (BCs) are required and may provide the utility of decreasing high initialization costs associated with conventional inlet BCs. Graphic abstract

Large-eddy simulation of a three-dimensional shear-driven turbulent boundary layer

2000 ◽  
Vol 423 ◽  
pp. 175-203 ◽  
Author(s):  
CHANDRASEKHAR KANNEPALLI ◽  
UGO PIOMELLI
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Quasi Equilibrium ◽  
Mean Flow ◽  
Curvature Effects ◽  
Large Eddy

A three-dimensional shear-driven turbulent boundary layer over a flat plate generated by moving a section of the wall in the transverse direction is studied using large-eddy simulations. The configuration is analogous to shear-driven boundary layer experiments on spinning cylinders, except for the absence of curvature effects. The data presented include the time-averaged mean flow, the Reynolds stresses and their budgets, and instantaneous flow visualizations. The near-wall behaviour of the flow, which was not accessible to previous experimental studies, is investigated in detail. The transverse mean velocity profile develops like a Stokes layer, only weakly coupled to the streamwise flow, and is self-similar when scaled with the transverse wall velocity, Ws. The axial skin friction and the turbulent kinetic energy, K, are significantly reduced after the imposition of the transverse shear, due to the disruption of the streaky structures and of the outer-layer vortical structures. The turbulent kinetic energy budget reveals that the decrease in production is responsible for the reduction of K. The flow then adjusts to the perturbation, reaching a quasi-equilibrium three-dimensional collateral state. Following the cessation of the transverse motion, similar phenomena take place again. The flow eventually relaxes back to a two-dimensional equilibrium boundary layer.

Measurement of the Reynolds stresses and the mean-flow field in a three-dimensional pressure-driven boundary layer

1982 ◽  
Vol 119 ◽  
pp. 121-153 ◽  
Author(s):  
Udo R. Müller
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Field ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Acceleration ◽  
The Mean

An experimental study of a steady, incompressible, three-dimensional turbulent boundary layer approaching separation is reported. The flow field external to the boundary layer was deflected laterally by turning vanes so that streamwise flow deceleration occurred simultaneous with cross-flow acceleration. At 21 stations profiles of the mean-velocity components and of the six Reynolds stresses were measured with single- and X-hot-wire probes, which were rotatable around their longitudinal axes. The calibration of the hot wires with respect to magnitude and direction of the velocity vector as well as the method of evaluating the Reynolds stresses from the measured data are described in a separate paper (Müller 1982, hereinafter referred to as II). At each measuring station the wall shear stress was inferred from a Preston-tube measurement as well as from a Clauser chart. With the measured profiles of the mean velocities and of the Reynolds stresses several assumptions used for turbulence modelling were checked for their validity in this flow. For example, eddy viscosities for both tangential directions and the corresponding mixing lengths as well as the ratio of resultant turbulent shear stress to turbulent kinetic energy were derived from the data.

Numerical Study of Vortical Separation From a Three-Dimensional Hill Using Eddy-Viscosity Models

2015 ◽  
Author(s):  
Varun Chitta ◽  
Tausif Jamal ◽  
Keith Walters
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Eddy Viscosity ◽  
Three Dimensional ◽  
Flow Transition ◽  
Mean Flow ◽  
New Model ◽  
Streamline Curvature ◽  
Viscosity Models ◽  
Rans Models

Turbulent flow over an axisymmetric hill is highly three-dimensional (3D) due to the presence of both streamwise and spanwise pressure gradients. Complex vortical separations and reattachments of the turbulent boundary layer are observed on the lee side, accurate prediction of which presents a demanding task for linear eddy-viscosity models (EVMs) when compared to attached boundary layer flows. In this study, an axisymmetric hill is investigated using three Reynolds-averaged Navier-Stokes (RANS) models — fully turbulent model (SST k-ω), transition-sensitive model (k-kL-ω), and a new four-equation model (k-kL-ω-v2). The new model is designed to exhibit physically correct responses to flow transition, streamline curvature, and system rotation effects. The test case includes a hill mounted in a channel with hill height H = 2δ, where δ is the approach turbulent boundary layer thickness. The flow Reynolds number (Re) based on the hill height is ReH = 1.3 × 105. Computational fluid dynamics (CFD) simulation results obtained using the new model are compared with the other two RANS models and with experimental data. Improved mean flow statistics are obtained using the new model that match well with the experiments. The results from this study highlight the need for a model that is able to resolve both flow transition and streamline curvature effects over blunt/curved bodies with reasonable engineering accuracy and computational cost.

Experimental investigation of coherent structures of a three-dimensional separated turbulent boundary layer

2018 ◽  
Vol 859 ◽  
pp. 1-32 ◽  
Author(s):  
Mohammad Elyasi ◽  
Sina Ghaemi
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Boundary Layer ◽  
Saddle Point ◽  
Turbulent Kinetic Energy ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Spanwise Direction ◽  
Mean Flow ◽  
Elliptical Cross

Coherent structures of a three-dimensional (3D) separation due to an adverse pressure gradient are investigated experimentally. The flow set-up consists of a flat plate to develop a turbulent boundary layer upstream of an asymmetric two-dimensional diffuser with one diverging surface. The diffuser surface has an initial mild curvature followed by a flat section where flow separation occurs. The top and the two sidewalls of the diffuser are not equipped with any flow control mechanism to form a 3D separation. Planar particle image velocimetry (PIV) using four side-by-side cameras is applied to characterize the flow with high spatial resolution over a large streamwise-wall-normal field of view (FOV). Tomographic PIV (tomo-PIV) is also applied for volumetric measurement in a domain flush with the flat surface of the diffuser. The mean flow obtained from averaging instantaneous velocity fields of this intermittent unsteady flow appears as a vortex with an elliptical cross-section. The major axis of the ellipse is tilted with respect to the streamwise direction. As a result, the average velocity in the mid-span of the diffuser has an upstream forward flow and a downstream backward flow, separated by a point of zero wall shear stress. Sweep motions mainly carry out transport of turbulent kinetic energy upstream of this point, while ejections dominate at the downstream region. In the instantaneous flow fields, forward and backward flows have equivalent strength, and the separation front is extended in the spanwise direction. The conditional average of the separation instants forms a saddle-point structure with streamlines converging in the spanwise direction. Proper orthogonal decomposition (POD) of the tomo-PIV data demonstrates that about 42 % of the turbulent kinetic energy is present in the first pair of modes, with a strong spanwise component. The spatial modes of POD also show focus, node and saddle-point structures. The average of the coefficients of the dominant POD modes during the separation events is used to develop a reduced-order model (ROM). Based on the ROM, the instantaneous 3D separation over the diffuser is a saddle-point structure interacting with focus-type structures.

Wall region of a relaxing three-dimensional incompressible turbulent boundary layer

1978 ◽  
Vol 85 (1) ◽  
pp. 33-56 ◽  
Author(s):  
K. S. Hebbar ◽  
W. L. Melnik
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Cross Flow ◽  
Wall Region ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Angle ◽  
The Mean

An experimental investigation was conducted at selected locations in the wall region of a three-dimensional turbulent boundary layer relaxing in a nominally zero external pressure gradient behind a transverse hump (in the form of a 30° swept, 5 ft chord, wing-type model) faired into the side wall of a low-speed wind tunnel. The boundary layer (approximately 3·5 in. thick near the first survey station, where the length Reynolds number was 5·5 × 106) had a maximum cross-flow velocity ratio of 0·145 and a maximum cross-flow angle of 21·9° close to the wall. The hot-wire data indicated that the apparent dimensionless velocity profiles in the viscous sublayer are universal and that the wall influence on the hot wire is negligible beyond y+= 5. The existence of wall similarity in the relaxing flow field was confirmed in the form of a log law based on the resultant mean velocity and resultant friction velocity (obtained from the measured skin friction).The smallest collateral region extended from the point nearest to the wall (y+≈ 1) up to y+= 9·7, corresponding to a resultant mean velocity ratio (local to free-stream) of 0·187. The unusual feature of these profiles was the presence of a narrow region of slightly decreasing cross-flow angle (1° or less) that extended from the point of maximum cross-flow angle down to the outer limit of the collateral region. A sublayer analysis of the flow field using the measured local transverse pressure gradient slightly overestimated the decrease in cross-flow angle. It is concluded that, in the absence of these gradients, the skewing of the flow could have been much more pronounced practically down to the wall (limited only by the resolution of the sensor), implying a near-wallnon-collateralflow field consistent with the equations of motion in the neighbourhood of the wall.The streamwise relaxation of the mean flow field based on the decay of the cross-flow angle was much faster in the inner layer than in the outer layer. Over the stream-wise distance covered, the mean flow in the inner layer and the wall shear-stress vector relaxed to a two-dimensional state in approximately 10 boundary-layer thicknesses whereas the relaxation of the turbulence was slower and was not complete over the same distance.

Characterization of Thermals in a Heated Turbulent Boundary Layer

2019 ◽  
Author(s):  
Kadeem Dennis ◽  
Kamran Siddiqui
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Mean Flow ◽  
Buoyant Force ◽  
Viscous Shear ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Abstract The hydrodynamic boundary layer encountered in many practical engineering systems is turbulent in nature and known to play a significant role in governing the induced friction drag and species transport. In turbulent boundary layer flows, heat transfer is often involved which increases flow complexity due to the influence of buoyancy. When the buoyant force is sufficiently large in magnitude, thermals carrying heated fluid are known to detach and rise from the wall. Literature review shows that in mixed convection, thermals have been primarily identified through qualitative flow visualizations and there is a scarcity of their quantitative assessment. Furthermore, the evolution of thermals in the boundary layer with respect to flow inertia and viscous shear is not well-understood. Hence, there is a need for a better understanding of the dynamics of thermals in mixed convection turbulent boundary layer flow. The objective of this study is to experimentally investigate the three-dimensional nature of thermals rising from a turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop low-disturbance wind tunnel with a test section featuring a 1 m long heated bottom wall. The multi-plane particle image velocimetry (PIV) technique was used to capture images in multiple planes with respect to the turbulent boundary layer mean flow direction for three-dimensional characterization. The measurements were conducted at Richardson numbers (Ri) of 0.3, 1.0, and 2.0. Flow visualization images are used to describe the nature of thermals and the dynamical processes involved during their interaction with bulk boundary layer flow. An image processing algorithm to detect thermals is then detailed and applied to experimental images. The performance of the new algorithm is then assessed in its ability to detect thermals.

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