scholarly journals A computational study of turbulent separated flow over a wall-mounted cube at two different Reynolds numbers and incoming velocity profiles

2021 ◽  
Author(s):  
S. Haering ◽  
R. Balakrishnan ◽  
R. Kotamarthi
Keyword(s):  
Computational Study ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Turbulent Separated Flow

Experiments on Backward-Facing Step Flows Preceding a Filter

2007 ◽  
Author(s):  
S. Yao ◽  
C. Krishnamoorthy ◽  
F. W. Chambers
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Step Height ◽  
Reattachment Point ◽  
Backward Facing Step ◽  
Air Filters ◽  
Air Filter

The resistance of automotive air filters alters upstream pressure gradients and thereby affects flow separation, the velocity distributions over the filter, and the performance of the filter. Air filters provide a resistance sufficient to alter flows, but not enough to make face velocities uniform. The backward-facing step flow is an archetype with a separation that resembles those found in automotive air filter housings. To gain insight to the problem of separation and filters, experiments were conducted measuring velocity fields for air flows in a 10:1 aspect ratio rectangular duct with a backward-facing step with and without the resistance of an air filter mounted downstream. The expansion ratio for the step was 1:2. The filter was mounted 4.25 and 6.75 step heights downstream of the step; locations both upstream and downstream of the nominal 6 step-height no-filter reattachment point. Experiments were performed at four Reynolds numbers between 2000 and 10,000. The Reynolds numbers were based on step height and inlet maximum velocity. The inlet velocity profiles at the step were developed. A Laser Doppler Anemometer (LDA) was used to measure velocity profiles and map separated regions between the step and the filter. The results indicate that the filter tends to decrease the streamwise velocity on the non-separated side of the channel and increase it on the separated, step, side compared to the no-filter flow. Non-separated flow tends to separate due to the deceleration and separated flow reattaches before the filter, whether the filter is placed at 4.25 or 6.75 step heights. The literature shows that without a filter the reattachment location depends on the Reynolds number in the laminar and transitional regimes, but is constant for turbulent flow. However, the area of the reversed flow may vary with Reynolds number for turbulent flow. With the filter at 4.25 step heights, the area of reversing flow is reduced significantly, and the Reynolds number has little effect on the main properties of the flow. With the filter at 6.75 step heights, the reversing flow area decreases as the Reynolds number increases though the reattachment point is fixed just upstream of the filter.

Turbulent Transport in Pin Fin Arrays: Experimental Data and Predictions

2005 ◽  
Author(s):  
F. E. Ames ◽  
L. A. Dvorak
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Boundary Layers ◽  
Fluid Dynamic ◽  
Turbulent Transport ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Pin Fin ◽  
Pin Fin Arrays

The objective of this research has been to experimentally investigate the fluid dynamics of pin fin arrays in order to clarify the physics of heat transfer enhancement and uncover problems in conventional turbulence models. The fluid dynamics of a staggered pin fin array have been studied using hot wire anemometry with both single and x-wire probes at array Reynolds numbers of 3000; 10,000; and 30,000. Velocity distributions off the endwall and pin surface have been acquired and analyzed to investigate turbulent transport in pin fin arrays. Well resolved 3-D calculations have been performed using a commercial code with conventional two-equation turbulence models. Predictive comparisons have been made with fluid dynamic data. In early rows where turbulence is low, the strength of shedding increases dramatically with increasing in Reynolds numbers. The laminar velocity profiles off the surface of pins show evidence of unsteady separation in early rows. In row three and beyond laminar boundary layers off pins are quite similar. Velocity profiles off endwalls are strongly affected by the proximity of pins and turbulent transport. At the low Reynolds numbers, the turbulent transport and acceleration keep boundary layers thin. Endwall boundary layers at higher Reynolds numbers exhibit very high levels of skin friction enhancement. Well resolved 3-D steady calculations were made with several two-equation turbulence models and compared with experimental fluid mechanic and heat transfer data. The quality of the predictive comparison was substantially affected by the turbulence model and near wall methodology.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

The Effect of Four Part Gap Geometry Configurations for Variable Stator Vanes in a Compressor Cascade

2012 ◽  
Author(s):  
Marcel Gottschall ◽  
Konrad Vogeler ◽  
Ronald Mailach
Keyword(s):  
Flow Field ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Compressor Cascade ◽  
Field Development ◽  
Operating Range ◽  
Rear Part ◽  
Axis Position ◽  
Stagger Angle ◽  
Variable Stator

The article describes numerical investigations on the influence of four different endwall clearance topologies for variable stator vanes to secondary flow field development and the performance of high pressure compressors. The aim of this work is to quantify the characteristics of different clearance configurations depending on the penny-axis position and the penny diameter for a typical operating range. All clearance configurations were implemented to a linear cascade of modern stator profiles. The analysis was introduced using a relative clearance size of 1.3% chord at three stagger angles and two characteristic Reynolds numbers to model the operating range on aircraft engines. 3D numerical calculations were carried out to gain information about the flow field inside the cascade. They were compared with measurements of a 5-hole-probe as well as pressure tappings on the airfoil and the endwall. The CFD shows the clearance characteristics in good agreement with the measurements for the lower and the nominal stagger angle. Small gaps in the rear part of the vane have a beneficial effect on the flow field. In contrast, a clearance in the higher loaded front part of the vane always resulted in increased losses. Otherwise, the significant enhanced performance of a rear part gap, which was measured at the higher stagger angle, was not reflected by the CFD. The reduced mixing losses and the higher averaged flow turning even compared to a configuration without a clearance are not verified with the calculations. Large flow separations at the high stagger angle result in a two to four times higher underturning of the CFD in comparison to the experiments. The clearance effects to the characteristic radial loss distribution up to 40 % bladeheight also deviate from the measurements due to heavy mixing of clearance and reversed separated flow.

A Computational Study on Airfoils at a Low Reynolds Number

2000 ◽  
Author(s):  
Ajit Pal Singh ◽  
S. H. Winoto ◽  
D. A. Shah ◽  
K. G. Lim ◽  
Robert E. K. Goh
Keyword(s):  
Reynolds Number ◽  
Computational Analysis ◽  
Computational Study ◽  
Low Reynolds Number ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Reynolds Numbers ◽  
Study Results ◽  
Low Reynolds

Abstract Performance characteristics of some low Reynolds number airfoils for the use in micro air vehicles (MAVs) are computationally studied using XFOIL at a Reynolds number of 80,000. XFOIL, which is based on linear-vorticity stream function panel method coupled with a viscous integral formulation, is used for the analysis. In the first part of the study, results obtained from the XFOIL have been compared with available experimental data at low Reynolds numbers. XFOIL is then used to study relative aerodynamic performance of nine different airfoils. The computational analysis has shown that the S1223 airfoil has a relatively better performance than other airfoils considered for the analysis.

scholarly journals LOCAL VELOCITY PROFILES MEASURED BY PIV IN AN VESSEL AGITATED BY RUSHTON TURBINE

2014 ◽  
Vol 54 (6) ◽  
pp. 430-438 ◽  
Author(s):  
Radek Šulc ◽  
Vít Pešava ◽  
Pavel Ditl
Keyword(s):  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Radial Component ◽  
Flat Bottom ◽  
Local Isotropy ◽  
Time Resolved ◽  
Rushton Turbine ◽  
Fully Developed Turbulent Flow ◽  
High Turbulence

<p>The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 300 mm in inner diameter. The tank was agitated by a Rushton turbine 100 mm in diameter. The velocity fields were measured for three impeller rotation speeds 300 rpm, 450 rpm and 600 rpm and the corresponding Reynolds numbers in the range 50 000 &lt; Re &lt; 100 000, which means that the fully-developed turbulent flow was reached. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller rotational speed. The velocity profiles were averaged, and were expressed by Chebyshev polynomials of the 1<sup>st</sup> order. Although the experimentally investigated area was relatively far from the impeller, and it was located in upward flow to the impeller, no state of local isotropy was found. The ratio of the axial rms fluctuation velocity to the radial component was found to be in the range from 0.523 to 0.768. The axial turbulence intensity was found to be in the range from 0.293 to 0.667, which corresponds to a high turbulence intensity.</p>

An Investigation of Flow Fields Over Multi-Element Aerofoils

2001 ◽  
Vol 124 (1) ◽  
pp. 154-165 ◽  
Author(s):  
S. R. Maddah ◽  
H. H. Bruun
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Separated Flow ◽  
Mean Flow ◽  
Model Configuration ◽  
Attached Flow ◽  
The Mean ◽  
Flap Deflection ◽  
Comparative Results ◽  
Lift And Drag

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.

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