UFR 2-10 Test Case: Difference between revisions

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== Brief Description of the Study Test Case ==
== Brief Description of the Study Test Case ==
The case considered is the flow past a finite-height circular cylinder mounted on a flat plate
The case considered is the flow past a finite-height circular cylinder mounted on a flat plate
for two height-to-diameter ratios ''h/D'' = 2.5 and 5.0. The parameters of the study and the
for two height-to-diameter ratios ''h/D'' = 2.5 and 5.0. The parameters of the study and the dimensions of the cylinder are given in [[UFR_2-10_Test_Case#table1|Table 1]].
dimensions of the cylinder are given in Table 1. The cylinder was placed in a water tunnel and
The cylinder was placed in a water tunnel and
the measurement section dimensions are provided in Fig. 2. The thickness of the approach-
the measurement section dimensions are provided in
[[UFR_2-10_Test_Case#fig2|Fig. 2]]. The thickness of the approach-
flow boundary layer was about 0.1 = ''h''
flow boundary layer was about 0.1 = ''h''
and the free-stream turbulence level was ''Tu'' ≈ 2%.
and the free-stream turbulence level was ''Tu'' ≈ 2%.




[[Image:UFR2-10_figure_2.gif|centre|thumb|500px|Figure 2. Experimental configuration for flow visualization and LDV measurements, from Palau-Salvador ''et al'' (2010)]]
<div id="table1">
{|border="1" align="center" cellpadding="6" cellspacing="0"
!''D'' (mm)||''h'' (mm)||''h/D''||''U''<sub>&infin;</sub> (m/s)||''Re = U<sub>&infin;</sub> D / &nu;''
|-
|80||200||2.5||0.54||4.3&times;10<sup>4</sup>
|-
|40||200||5.0||0.54||2.2&times;10<sup>4</sup>
|}
 
 
<center>'''Table 1.''' Parameters in the experimental study</center>
</div>
 
 
 
 
<div id="fig2">
<center>
{|
|[[Image:UFR2-10_figure_2.png|600px]]
|-
|align="center"|'''Figure 2.''' Experimental configuration for flow visualization and LDV measurements, from Palau-Salvador&nbsp;''et al''&nbsp;(2010)
|}
</center>
</div>


== Test Case Experiments ==
== Test Case Experiments ==
The experiments were carried out by Kappler&nbsp;(2002) in the closed high pressure water tunnel
The experiments were carried out by [[UFR_2-10_References#kappler|Kappler&nbsp;(2002)]]
in the closed high pressure water tunnel
of the Institute for Hydromechanics at the University of Karlsruhe. The experiments are
of the Institute for Hydromechanics at the University of Karlsruhe. The experiments are
described in detail in Kappler&nbsp;(2002) and a link to the actual data is given in the reference. A
described in detail in [[UFR_2-10_References#kappler|Kappler&nbsp;(2002)]]
short description is provided in Palau-Salvador&nbsp;''et al''&nbsp;(2010).
and a link to the actual data is given in the reference. A
short description is provided in
[[UFR_2-10_References#palau|Palau-Salvador&nbsp;''et al''&nbsp;(2010)]].
The measurement section and the
The measurement section and the
cylinder placed in it are shown in Fig. 2. Measurements of all three components of mean and
cylinder placed in it are shown in
[[UFR_2-10_Test_Case#fig2|Fig. 2]]. Measurements of all three components of mean and
fluctuating velocities were carried out with a 2D LDV in two consecutive steps. In the first
fluctuating velocities were carried out with a 2D LDV in two consecutive steps. In the first
step, the optical axis was oriented in the vertical direction, thus allowing determination of the
step, the optical axis was oriented in the vertical direction, thus allowing determination of the
velocity components ''u'' and ''v''. In the second step, the optical system was reconfigured to point
velocity components ''u'' and ''v''. In the second step, the optical system was reconfigured to point
horizontally for simultaneous measurements of ''u'' and ''w'' (see also Fig. 2). The uncertainty in
horizontally for simultaneous measurements of ''u'' and ''w'' (see also
[[UFR_2-10_Test_Case#fig2|Fig. 2]]). The uncertainty in
the velocity measurements was judged to be less than 5% of the inlet velocity for the mean
the velocity measurements was judged to be less than 5% of the inlet velocity for the mean
and fluctuation values, with somewhat higher possible errors for the turbulent shear stress.
and fluctuation values, with somewhat higher possible errors for the turbulent shear stress.
Reference LDV measurements were performed without the cylinder in place in order to
Reference LDV measurements were performed without the cylinder in place in order to
determine the boundary layer characteristics at different streamwise positions and the results
determine the boundary layer characteristics at different streamwise positions and the results
are included in Kappler&nbsp;(2002). Prior to the LDV measurements, extensive flow visualizations
are included in
[[UFR_2-10_References#kappler|Kappler&nbsp;(2002)]].
Prior to the LDV measurements, extensive flow visualizations
were carried out for four cylinder configurations in the range
were carried out for four cylinder configurations in the range
''h/D''&nbsp;=&nbsp;2.0&nbsp;–&nbsp;5.0. The results can
''h/D''&nbsp;=&nbsp;2.0&nbsp;–&nbsp;5.0. The results can
also be found in Kappler&nbsp;(2002).
also be found in [[UFR_2-10_References#kappler|Kappler&nbsp;(2002)]].




Line 46: Line 78:
''h/D''&nbsp;=&nbsp;2.
''h/D''&nbsp;=&nbsp;2.
Some of these results and the original references are included in
Some of these results and the original references are included in
Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010).
[[UFR_2-10_References#palau|Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010)]].


== CFD Methods ==
== CFD Methods ==
The test cases considered here were only calculated by
The test cases considered here were only calculated by
Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010) with LES
[[UFR_2-10_References#palau|Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010)]] with LES
and these calculations are described in detail in this paper. The LES employed the dynamic
and these calculations are described in detail in this paper. The LES employed the dynamic
approach of Germano&nbsp;''et&nbsp;al''&nbsp;(1991) as modified by Lilly&nbsp;(1992)
approach of
[[UFR_2-10_References#germano|Germano&nbsp;''et&nbsp;al''&nbsp;(1991)]] as modified by [[UFR_2-10_References#lilly|Lilly&nbsp;(1992)]]
to model the subgrid-scale
to model the subgrid-scale
stresses. The model parameter ''c'' was regularized by averaging over the surrounding grid cells
stresses. The model parameter ''c'' was regularized by averaging over the surrounding grid cells
and imposing the subgrid-scale eddy viscosity to be larger than zero
and imposing the subgrid-scale eddy viscosity to be larger than zero
(Zang&nbsp;''et&nbsp;al''&nbsp;1993). The
[[UFR_2-10_References#zang|(Zang&nbsp;''et&nbsp;al''&nbsp;1993)]]. The
contribution of the subgrid-scale stress is rather small in the simulations. The LES code
contribution of the subgrid-scale stress is rather small in the simulations. The LES code
MGLET originally developed at the Institute for Fluid Mechanics at the Technical University
MGLET originally developed at the Institute for Fluid Mechanics at the Technical University
of Munich (Tremblay ''et al'' 2001) was employed to perform the large eddy simulations. This
of Munich
finite volume code uses a Cartesian grid and an immersed boundary method (Verzicco ''et al''
[[UFR_2-10_References#tremblay|(Tremblay ''et al'' 2001)]]
2000) to represent the circular cylinder on this grid. The computational domain is sketched in
was employed to perform the large eddy simulations. This
Fig. 3 for the two cases considered; the height of the cylinder is constant and it is the diameter
finite volume code uses a Cartesian grid and an immersed boundary method
[[UFR_2-10_References#verzicco|(Verzicco ''et al'' 2000)]]
to represent the circular cylinder on this grid. The computational domain is sketched in
[[UFR_2-10_Test_Case#fig3|Fig. 3]]
for the two cases considered; the height of the cylinder is constant and it is the diameter
which varies giving different ''h/D'' ratios. 580&nbsp;&times;&nbsp;380&nbsp;&times;&nbsp;204
which varies giving different ''h/D'' ratios. 580&nbsp;&times;&nbsp;380&nbsp;&times;&nbsp;204
grid points were used for the
grid points were used for the
Line 70: Line 107:
vertical directions respectively, yielding a total of 45 million grid points for the first case and
vertical directions respectively, yielding a total of 45 million grid points for the first case and
27 million grid points for the second one respectively. Around the cylinder, uniform
27 million grid points for the second one respectively. Around the cylinder, uniform
distribution of grid cells was used in lateral and streamwise direction. Fig. 4 shows the grid in
distribution of grid cells was used in lateral and streamwise direction.
[[UFR_2-10_Test_Case#fig4|Fig. 4]] shows the grid in
a horizontal and in a vertical plane indicating the refinement of the grid towards the cylinder
a horizontal and in a vertical plane indicating the refinement of the grid towards the cylinder
and the ground plate. The mesh spacings around the cylinder in streamwise and lateral
and the ground plate. The mesh spacings around the cylinder in streamwise and lateral
Line 87: Line 125:
reasonably good agreement was found
reasonably good agreement was found
even though in the LES fully realistic turbulence had not yet developed in the boundary layer
even though in the LES fully realistic turbulence had not yet developed in the boundary layer
(Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;2010).
[[UFR_2-10_References#palau|(Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;2010)]].
 
 
<div id="fig3">
<center>
{|
|[[Image:UFR2-10_figure_3.png|center|600px]]
|-
|align="center"|'''Figure 3.''' Sketch of the computational domain, from Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010)
|}
</center>
</div>
 
 


<div id="fig4">
<center>
{|
|[[Image:UFR2-10_figure_4.png|center|600px]]
|-
|align="center"|'''Figure 4.''' Details of the numerical grid for the case ''h/D''=5 showing every 5th grid line, from Palau-Salvador&nbsp;''et&nbsp;al''&nbsp;(2010)
|}
</center>
</div>
<br>
<br>
<br>
<br>

Latest revision as of 11:39, 12 February 2017

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References


Test Case

Brief Description of the Study Test Case

The case considered is the flow past a finite-height circular cylinder mounted on a flat plate for two height-to-diameter ratios h/D = 2.5 and 5.0. The parameters of the study and the dimensions of the cylinder are given in Table 1. The cylinder was placed in a water tunnel and the measurement section dimensions are provided in Fig. 2. The thickness of the approach- flow boundary layer was about 0.1 = h and the free-stream turbulence level was Tu ≈ 2%.


D (mm) h (mm) h/D U (m/s) Re = U D / ν
80 200 2.5 0.54 4.3×104
40 200 5.0 0.54 2.2×104


Table 1. Parameters in the experimental study



UFR2-10 figure 2.png
Figure 2. Experimental configuration for flow visualization and LDV measurements, from Palau-Salvador et al (2010)

Test Case Experiments

The experiments were carried out by Kappler (2002) in the closed high pressure water tunnel of the Institute for Hydromechanics at the University of Karlsruhe. The experiments are described in detail in Kappler (2002) and a link to the actual data is given in the reference. A short description is provided in Palau-Salvador et al (2010). The measurement section and the cylinder placed in it are shown in Fig. 2. Measurements of all three components of mean and fluctuating velocities were carried out with a 2D LDV in two consecutive steps. In the first step, the optical axis was oriented in the vertical direction, thus allowing determination of the velocity components u and v. In the second step, the optical system was reconfigured to point horizontally for simultaneous measurements of u and w (see also Fig. 2). The uncertainty in the velocity measurements was judged to be less than 5% of the inlet velocity for the mean and fluctuation values, with somewhat higher possible errors for the turbulent shear stress. Reference LDV measurements were performed without the cylinder in place in order to determine the boundary layer characteristics at different streamwise positions and the results are included in Kappler (2002). Prior to the LDV measurements, extensive flow visualizations were carried out for four cylinder configurations in the range h/D = 2.0 – 5.0. The results can also be found in Kappler (2002).


In addition to the components of mean and fluctuating velocities measured in various vertical and horizontal planes, and the visualizations of Kappler with dye-injection, some oil flow pictures showing the streamlines of the flow near the ground, along the cylinder walls and also the complex flow at the top of the cylinder are available from other studies at h/D = 2. Some of these results and the original references are included in Palau-Salvador et al (2010).

CFD Methods

The test cases considered here were only calculated by Palau-Salvador et al (2010) with LES and these calculations are described in detail in this paper. The LES employed the dynamic approach of Germano et al (1991) as modified by Lilly (1992) to model the subgrid-scale stresses. The model parameter c was regularized by averaging over the surrounding grid cells and imposing the subgrid-scale eddy viscosity to be larger than zero (Zang et al 1993). The contribution of the subgrid-scale stress is rather small in the simulations. The LES code MGLET originally developed at the Institute for Fluid Mechanics at the Technical University of Munich (Tremblay et al 2001) was employed to perform the large eddy simulations. This finite volume code uses a Cartesian grid and an immersed boundary method (Verzicco et al 2000) to represent the circular cylinder on this grid. The computational domain is sketched in Fig. 3 for the two cases considered; the height of the cylinder is constant and it is the diameter which varies giving different h/D ratios. 580 × 380 × 204 grid points were used for the h/D = 2.5 case and 516 × 252 × 204 grid points for the h/D = 5 case in streamwise, lateral and vertical directions respectively, yielding a total of 45 million grid points for the first case and 27 million grid points for the second one respectively. Around the cylinder, uniform distribution of grid cells was used in lateral and streamwise direction. Fig. 4 shows the grid in a horizontal and in a vertical plane indicating the refinement of the grid towards the cylinder and the ground plate. The mesh spacings around the cylinder in streamwise and lateral direction in wall units are in the range 2 – 6 while the vertical mesh sizes in wall units near the free end are around 1 – 3 and near the ground plate 2 – 5 in the vicinity of the cylinder. The time steps were such that the maximum CFL number was 0.83. At the outflow a convective condition was applied. At the ground plate and the cylinder walls the no-slip condition was used. The top wall and the side walls were treated as frictionless rigid lid so that the free slip condition was applied. At the inflow (x/h = −1.6) a u-velocity profile taken from the measurements was specified, v and w were set to zero and no fluctuations were imposed. Profiles of the u-velocity and the u-fluctuations in front of the cylinder were compared with measurements without the cylinder being present and reasonably good agreement was found even though in the LES fully realistic turbulence had not yet developed in the boundary layer (Palau-Salvador et al 2010).


UFR2-10 figure 3.png
Figure 3. Sketch of the computational domain, from Palau-Salvador et al (2010)


UFR2-10 figure 4.png
Figure 4. Details of the numerical grid for the case h/D=5 showing every 5th grid line, from Palau-Salvador et al (2010)





Contributed by: Guillermo Palau-Salvador, Wolfgang Rodi, — Universidad Politecnica de Valencia, Karlsruhe Institute of Technology


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