scholarly journals MODELLING OF SHEAR AND SHEARLESS FLOW WITH PERIODIC VELOCITY NONSTATIONARITY

2018 ◽  
Vol 40 (2) ◽  
pp. 72-77
Author(s):  
T.T. Suprun
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Physical Modelling ◽  
Transport Processes ◽  
Experimental Investigations ◽  
Bypass Transition ◽  
Flat Plates ◽  
Flow Core ◽  
Squirrel Cage ◽  
External Conditions

The results of experimental modeling of shear and shearless flow with periodic velocity nonstationarity, organized using a generator of periodic wakes such as the "squirrel" cage, are presented. The purpose of this paper is to compare the structure of the flow behind the "squirrel" cages, as well as the analysis of the characteristics of the transition boundary layer for two different ways of locating the working surfaces: in the zone of the shearless core and shear periphery zone. The physical modelling of turbulized flow with velocity periodic nonstationarity is carried out in two experimental installations. It is shown that behind rotating “squirrel” cages there are two regions in the distributions of mean time velocities: the shearless flow core located in the center of “squirrel” cage and peripheral shear part. The aim of this paper is to compare the flow structure behind “squirrel” cages as well as to analyze the features of transient boundary layer for two different installations of working surfaces. The latter were flat plates installed on the different distances from the center of the “squirrel” cages: in the shearless flow core and in shear zone. Total longitudinal fluctuations are characterized by peaks reason of which is intersections of wakes. Behind the “squirrel” cages the levels of fluctuations decrease along the plates at x~100-600 mm from ~12 to 4,5% (II) and from ~6 to 3,5% (I). Despite the development of boundary layer happens under different external conditions (in uniform (I) and shear (II) flows), wake-induced transition takes place in both installations. Transformation of velocity profiles from pseudolaminar to turbulent is similar to one taking place in bypass transition. Distributions of total longitudinal fluctuations across the boundary layer differ by quantity of peaks and their intensity.  Today the physical modeling is one of the most perspective methods for studying transport processes under complex conditions. That is why the experimental investigations of periodic external flow structure are necessary for the further optimization of different equipment and their reliability enhancement.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

Heat Transfer Committee and Turbomachinery Committee Best Paper of 1996 Award: The Path to Predicting Bypass Transition

1997 ◽  
Vol 119 (3) ◽  
pp. 405-411 ◽  
Author(s):  
R. E. Mayle ◽  
A. Schulz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Energy Equation ◽  
Free Stream ◽  
Bypass Transition ◽  
Turbulence Level ◽  
Free Stream Turbulence ◽  
Energy Profiles ◽  
Computer Codes ◽  
Good Agreement

A theory is presented for calculating the fluctuations in a laminar boundary layer when the free stream is turbulent. The kinetic energy equation for these fluctuations is derived and a new mechanism is revealed for their production. A methodology is presented for solving the equation using standard boundary layer computer codes. Solutions of the equation show that the fluctuations grow at first almost linearly with distance and then more slowly as viscous dissipation becomes important. Comparisons of calculated growth rates and kinetic energy profiles with data show good agreement. In addition, a hypothesis is advanced for the effective forcing frequency and free-stream turbulence level that produce these fluctuations. Finally, a method to calculate the onset of transition is examined and the results compared to data.

scholarly journals Boundary layer turbulence and flow structure over a fringing coral reef

2006 ◽  
Vol 51 (5) ◽  
pp. 1956-1968 ◽  
Author(s):  
Matthew A. Reidenbach ◽  
Stephen G. Monismith ◽  
Jeffrey R. Koseff ◽  
Gitai Yahel ◽  
Amatzia Genin
Keyword(s):  
Boundary Layer ◽  
Coral Reef ◽  
Flow Structure ◽  
Boundary Layer Turbulence

Oval Flow Mode Between Two Corotating Disks With Stationary Shroud

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Ching Min Hsu ◽  
Jia-Kun Chen ◽  
Min Kai Hsieh ◽  
Rong Fung Huang
Keyword(s):  
Flow Structure ◽  
Solid Body ◽  
Circumferential Velocity ◽  
Body Rotation ◽  
Flow Core ◽  
Core Flow ◽  
Node Point ◽  
Solid Body Rotation ◽  
Characteristic Flow ◽  
Buffer Region

The characteristic flow behavior, time-averaged velocity distributions, phase-resolved ensemble-averaged velocity profiles, and turbulence properties of the flow in the interdisk midplane between shrouded two corotating disks at the interdisk spacing to disk radius aspect ratio 0.2 and rotation Reynolds number 3.01 × 105 were experimentally studied by flow visualization method and particle image velocimetry (PIV). An oval core flow structure rotating at a frequency 60% of the disks rotating frequency was observed. Based on the analysis of relative velocities, the flow in the region outside the oval core flow structure consisted of two large vortex rings, which move circumferentially with the rotation motion of the oval flow core. Four characteristic flow regions—solid-body-rotation-like region, buffer region, vortex region, and shroud-influenced region—were identified in the flow field. The solid-body-rotation-like region, which was featured by its linear distribution of circumferential velocity and negligibly small radial velocity, was located within the inscribing radius of the oval flow core. The vortex region was located outside the circumscribing radius of the oval flow core. The buffer region existed between the solid-body-rotation-like region and the vortex region. In the buffer region, there existed a “node” point that the propagating circumferential velocity waves diminished. The circumferential random fluctuation intensity presented minimum values at the node point and high values in the solid-body-rotation-like region and shroud-influenced region due to the shear effect induced by the wall.

Effects of Roughness Strip and Acoustic Sensor Height on Subsonic Boundary Layer by Experiment

2013 ◽  
Vol 421 ◽  
pp. 459-463
Author(s):  
Ning Zong ◽  
Guang Jun Yang ◽  
Jing Sun
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Dynamic Test ◽  
Acoustic Sensor ◽  
Body Type ◽  
Test Plate ◽  
Spectrum Measurement ◽  
Layer Flow ◽  
Analysis System ◽  
Wind Speed Measurement

According to the measurement requirements of acoustic fatigue load on aft fuselage structure and the external installation restriction of the acoustic sensor on aircraft surface, an acoustic sensor is installed on the silencing jet test plate with reference to body type of the real aircraft. A dynamic test and analysis system combined hot wire wind speed measurement and acoustic spectrum measurement is built up for the combined experiments with different acoustic sensor height and various boundary layer flow structure at subsonic flow condition. Turbulence development of different boundary layer is analyzed. The test result can be coordinated with the local measurement to aircraft flow structure so as to estimate the effect of acoustic sensor on the flow field.

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