DNS 1-6 Description: Difference between revisions

From KBwiki
Jump to navigation Jump to search
No edit summary
 
(33 intermediate revisions by 3 users not shown)
Line 1: Line 1:
 
=Wing-body junction=
{{DNSHeaderLib
{{DNSHeader
|area=1
|area=1
|number=6
|number=6
Line 7: Line 7:
= Introduction =
= Introduction =


This test case features wing mounted on a flat plate, which is representative of the wing-body junction flow problems encountered in applications of aeronautical interest.
This test case considers the flow around a wing mounted on a flat plate, which is representative of the wing-body junction flow problems encountered in applications of aeronautical interest.
The flow features the interaction between the incipient turbulent boundary layer and the mounted airfoil and the main physical phenomenon of interest is the horseshoe vortex developing at the junction and the corner separation. This flow is also highly 3D and anisotropic regarding the turbulent stresses. Establishing a DNS database of this flow is of crucial interest since it has been shown that RANS models (both Boussinesq and Reynolds stresses-based models) display strong difficulties in recovering data from the available experiments. Such a database allows for a more thorough availability of the flow field with respect to the experiments and gives the possibility of using Machine Learning or data-assimilation techniques to improve standard RANS models.
The flow features the interaction between the incipient turbulent boundary layer and the mounted airfoil, and the main physical phenomenon of interest is the horseshoe vortex developing at the junction and the corner separation. This flow is also highly 3D and anisotropic regarding the turbulent stresses. Establishing a DNS database of this flow is of crucial interest since it has been shown that RANS models (both Boussinesq and Reynolds stresses-based models) display strong difficulties in recovering data from the available experiments. Such a database allows for a more thorough availability of the flow field with respect to the experiments and gives the possibility of using Machine Learning or data-assimilation techniques to improve standard RANS models.


= Review of previous studies and choice of test case=
= Review of previous studies and choice of test case=


A thorough listing of existing experimental and numerical studies regarding wing-body junction flows can be found in [[lib:DNS_1-6_description#2|Gand  ''et al.'' (2010)]]. The present DNS is based on the configuration considered in the simulations by [[lib:DNS_1-6_description#1|Apsley & Leschziner (2001)]], who were based themselves on the experimental studies by [[lib:DNS_1-6_description#3|Devenport and Simpson (1990)]] and [[lib:DNS_1-6_description#4|Fleming  ''et al.'' (1995)]]. The Reynolds number based on the airfoil thickness is similar to the experiment and its value is 115,000 and the flow is almost incompressible with a Mach number based on the freestream velocity of 0.078. The uDNS setup reproduces the experimental conditions but with half the experimental impacting boundary layer thickness. Therefore a direct comparison with the experimental results is not possible for the present uDNS.
A thorough listing of existing experimental and numerical studies regarding wing-body junction flows can be found in [[DNS_1-6_description#2|Gand  ''et&nbsp;al.'' (2010)]]. The present uDNS is based on the configuration considered in the simulations by [[DNS_1-6_description#1|Apsley and Leschziner (2001)]], who were based themselves on the experimental studies by [[DNS_1-6_description#3|Devenport and Simpson (1990)]] and [[DNS_1-6_description#4|Fleming  ''et&nbsp;al.'' (1995)]]. The Reynolds number based on the airfoil thickness is similar to the experiment and its value is <math>115,000</math>. The flow is almost incompressible with a Mach number based on the freestream velocity of <math>0.078</math>. The uDNS setup reproduces the experimental conditions but with half the experimental impacting boundary layer thickness. Therefore a direct comparison with the experimental results is not possible for the present uDNS.


= Description of the test case =
= Description of the test case =
==Geometry and flow parameters==
==Geometry and flow parameters==


[[lib:DNS_1-6_description#figure2|Fig. 2]] displays a view of the computational domain and flow configuration geometry. The reference length scale is the wing thickness <math>T</math>, and the corresponding Reynolds number <math>Re_T=115,000</math>. The computational domain size is <math>62.75T</math> in the stream direction, <math>8T</math> in the span direction and <math>3T</math> in the wall-normal direction. The coordinates origin is located at the root leading edge of the airfoil. The is no flow incidence relatively to the wing, corresponding to an angle of attack of <math>0</math> degrees.
[[DNS_1-6_description#figure2|Fig. 2]] displays the flow geometry, i.e. the wing body mounted on a flat plate, and the computional domain. The wing is formed by a 3:2 semi-elliptic nose with a NACA0020 tail profile, see [[DNS_1-6_description#figure3|Fig. 3]], and has a thickness <math>T=71.7\,\text{mm}</math>, which serves as reference lengthscale. The Reynolds number based on this is <math>Re=115\,000</math> and the chord-to-thickness ratio is <math>4.254</math>.
The computational domain size is <math>62.75T</math> in the streamwise direction, <math>8T</math> in the spanwise direction and <math>3T</math> in the wall-normal direction, see  [[DNS_1-6_description#figure2|Fig. 2]]. The coordinate origin is located at the root leading edge of the airfoil. There is no flow incidence relatively to the wing, corresponding to an angle of attack of <math>0</math> degrees.
Parameters of the flow (air with <math>\gamma=1.4</math>, <math>MM=28.96\,\text{kg/kmol}</math>, <math>\mu=1.716\cdot10^{-5}\,\text{Pa s}</math>) are reported in [[DNS_1-6_description#table1|Tab. 1]].


<div id="figure2"></div>
<div id="figure2"></div>
{|align="center" border="0" width="500"
{|align="center" border="0" width="800"
|[[Image:DNS TC04 setup.png|800px]]
|align="center"|[[Image:DNS TC04 setup.png|800px]]
|-
|-
!align="center"|Figure 2: Wing-body junction. Domain for the DNS simulation
|align="center"|'''Figure 2:''' Wing-body junction. Flow geometry and domain for the DNS simulation
|}
|}
<br/>
<br/>


==Boundary conditions | TO UPDATE !!!==
<div id="figure3"></div>
{|align="center" border="0" width="1000"
|align="center"|[[Image:DNS1-6 Wing-body junction wing thickness.png|1000px]]
|-
|align="center"|'''Figure 3:''' Wing-body junction. Wing geometry, thickness and location of boundary layer tripping superimposed by the instantaneous wall shear stress on the flat plate
|}
<br/>


Although for DNS the inflow boundary conditions are different than RANS, to allow a valid comparison they must guarantee the same boundary layer properties at a given point, hereinafter referred to as checkpoint, upstream of the rounded step, i.e., <math>{x_{ckp}/H = -3.5}</math>.
<div id="table1"></div>
At this position <math>{x_{ckp}}</math>, the properties to be matched are the Reynolds number based on the momentum thickness <math>{Re_{\theta} = 1,780}</math>, the Reynolds number based on the friction velocity <math>{Re_{\tau} = 700}</math> and the boundary layer thickness <math>\delta_{99}/H=0.241</math>.
{|align="center" border="1" cellpadding="10"
As a technique to promote the laminar-turbulent transition of the boundary layer and reduce the upstream length of the domain, a local tripping term inspired by the work of [[lib:DNS_1-5_description#5|Housseini ''et&nbsp;al.'' (2016)]] and [[lib:DNS_1-5_description#6|Schlatter and Örlü (2012)]] is used.
|-
To define the mesh density and the computational domain size that ensure the target boundary layer integral parameters at <math>{x_{chp}}</math>, a precursory computational campaign for the turbulent flow over a flat plate was performed.
|align="center"|<math>{Ma}</math>||align="center"|<math>{Re}</math>||align="center"|<math>{T_{ref}}</math>||align="center"|<math>{u_{ref}}</math>||align="center"|<math>{\rho_{ref}}</math>||align="center"|<math>{p_{ref}}</math>
According to the outcomes of this campaign, the inlet boundary is located at <math>{x/H = -12.7}</math>, where the Blasius laminar velocity profile computed at <math>{Re_x=650,000}</math>, the uniform static pressure <math>{P_{s,ref}}</math> and the uniform total temperature <math>{T_{t,inflow}}</math> are imposed, see [[Lib:UFR_3-36_Test_Case#table2|UFR 3-36: Table 2]] for dimensional values of each quantity. At location <math>{x/H = -12.1}</math>, within the laminar boundary layer region, the tripping source term is activated to promote the transition to turbulence, see [[Lib:DNS_1-5_description#figure2|Fig. 2]].
|-
At the outlet boundary, placed at <math> x/H=24.0 </math>, the static pressure <math>{P_{s,ref}}</math> is imposed with an exit-pressure outflow boundary condition. To mitigate spurious perturbations possibly originating at the outlet boundary, the mesh is coarsened in the streamwise direction for <math>{x/H > 13.82}</math>. The upper boundary is a permeable far-field Riemann boundary condition located <math>180.0 H</math> from the no-slip adiabatic wall downstream the smooth step and computed via the exact Riemann solver. Finally, side planes are considered as periodic with a distance from each other of <math>{\Delta z = 3 H}</math>.
|align="center"|<math>{0.078}</math>||align="center"|<math>{115\,000}</math>||align="center"|<math>{298.15\,\text{K}}</math>||align="center"|<math>{27.00\,\text{m/s}}</math>||align="center"|<math>{1.019\,\text{kg/m}^{3}}</math>||align="center"|<math>{87251\,\text{Pa}}</math>
|}
<center>'''Table 1:''' Wing-body junction. Flow parameters </center>
<br/>


==Boundary conditions==


For this particular flow configuration, we aim at simulating a transitional boundary layer in order to replicate the flow conditions of the experiment. To do so, a Blasius velocity profile is imposed at the inlet corresponding to <math>Re_x=900,000</math> with a uniform temperature. A laminar boundary layer is then established, and a flow perturbation is introduced at <math>Re_x=950,000</math> with amplitude <math>A_T=\frac{\rho_{ref} U_{ref}^2}{T}</math> to trigger transition to turbulence. The total length of the boundary layer was determined such that the turbulent boundary layer thickness upwind the airfoil reaches half of the experimental value. Symmetry conditions are imposed at the lateral boundary conditions (<math>z=\pm 4T</math>). The bottom boundary is a no-slip adiabatic wall type for <math>xz</math> planes at <math>y=0</math> between <math>x=-12.75T</math> and <math>x=17T</math>, and symmetry type between <math>x=17T</math> and <math>x=67T</math>. The outlet is located away from the profile at <math>x=67T</math>, and the zone between <math>x=17T</math> and <math>x=67T</math> acts as a sponge layer, featuring increasingly coarse elements such that a constant flow field is recovered when reaching the outlet.
The computational set-up aims at replicating the flow conditions of the experiment but with a halved incoming boundary layer thickness. To enforce these conditions in an efficient and accurate manner a Blasius velocity profile corresponding to <math>Re_x=900\,000</math> and free stream velocity <math>u_{\infty}=u_{ref}</math> is imposed at the inlet together with uniform static pressure <math>p_{inflow}=p_{ref}</math>. and total temperature <math>T_{t,inflow}=T_{ref}\left[1+0.5\left(\gamma-1\right){Ma}^{2}\right]</math>.
A laminar boundary layer is then established, and a flow perturbation is applied at <math>Re_x=950\,000</math> to trigger transition to turbulence following the idea of [[DNS_1-6_description#5|Housseini ''et&nbsp;al.'' (2016)]] and [[DNS_1-6_description#6|Schlatter and Örlü (2012)]].
The distance of the inlet boundary from the wing-body junction is defined such that the incoming turbulent boundary layer reaches a thickness <math>\delta_{99.5}/T=0.25</math> (half of the experimental value) at a given point, hereinafter referred as checkpoint, upstream the airfoil leading edge, i.e., at <math>x_{ckp}/T=-2.15</math>.
To define such distance, a precursory computational campaign for the turbulent flow over a flat plate was performed.
According to the outcomes of this campaign, the inlet boundary is positioned at <math>x/T=-12.75</math>.
The tripping term promoting the boundary layer transition is then located at <math>x/T=-12.3</math>, see [[DNS_1-6_description#figure3|Fig. 3]].
At the outlet boundary, placed at <math>x/T=50</math>, the static pressure <math>{p_{outflow}=p_{ref}}</math> is imposed with an exit-pressure outflow boundary condition.
The bottom boundary is an adiabatic solid wall type (no slip) for <math>-12.75\leq x/T\leq 17</math> and symmetry type for <math>x/T>17</math>.
This choice aims to mitigate spurious perturbations possibly originating at the outlet boundary.
Symmetry conditions are imposed at the lateral (<math>z/T=\pm 4</math>) and top (<math>y/T=3</math>) boundaries.
An adiabatic solid wall(no slip) condition is finally imposed on the wing surface.


=References=
=References=
Line 46: Line 68:
#<div id="4">'''Fleming, J.L., Simpson, R.L., Cowling, J.E. and Devenport, W.J. (1993)''': An experimental study of wing-body junction and wake flow. '''Exp. Fluids''' Vol. 14, pp. 366–378</div>
#<div id="4">'''Fleming, J.L., Simpson, R.L., Cowling, J.E. and Devenport, W.J. (1993)''': An experimental study of wing-body junction and wake flow. '''Exp. Fluids''' Vol. 14, pp. 366–378</div>
# <div id="5">'''S. Hosseini, R. Vinuesa, P. Schlatter, A. Hanifia and D. Henningson (2016):''' Direct numerical simulation of the flow around a wing section at moderate Reynolds number, ''International Journal of Heat and Fluid Flow,''&nbsp;61:117&ndash;128</div>
# <div id="5">'''S. Hosseini, R. Vinuesa, P. Schlatter, A. Hanifia and D. Henningson (2016):''' Direct numerical simulation of the flow around a wing section at moderate Reynolds number, ''International Journal of Heat and Fluid Flow,''&nbsp;61:117&ndash;128</div>
# <div id="6">'''Schlatter, P. and &Ouml;rl&uuml;, R. (2012):''' Turbulent boundary layers at moderate Reynolds numbers: inflow length and tripping effects,''Journal of Fluid Mechanics,''&nbsp;710:5&ndash;34</div>
# <div id="6">'''Schlatter, P. and &Ouml;rl&uuml;, R. (2012):''' Turbulent boundary layers at moderate Reynolds numbers: inflow length and tripping effects, ''Journal of Fluid Mechanics,''&nbsp;710:5&ndash;34</div>
<br/>
<br/>
----
----
Line 53: Line 75:
| organisation=University of Bergamo (UNIBG), ICL (Imperial College London), ONERA
| organisation=University of Bergamo (UNIBG), ICL (Imperial College London), ONERA
}}
}}
{{DNSHeaderLib
{{DNSHeader
|area=1
|area=1
|number=6
|number=6

Latest revision as of 11:38, 27 February 2023

Wing-body junction

Front Page

Description

Computational Details

Quantification of Resolution

Statistical Data

Instantaneous Data

Storage Format

Introduction

This test case considers the flow around a wing mounted on a flat plate, which is representative of the wing-body junction flow problems encountered in applications of aeronautical interest. The flow features the interaction between the incipient turbulent boundary layer and the mounted airfoil, and the main physical phenomenon of interest is the horseshoe vortex developing at the junction and the corner separation. This flow is also highly 3D and anisotropic regarding the turbulent stresses. Establishing a DNS database of this flow is of crucial interest since it has been shown that RANS models (both Boussinesq and Reynolds stresses-based models) display strong difficulties in recovering data from the available experiments. Such a database allows for a more thorough availability of the flow field with respect to the experiments and gives the possibility of using Machine Learning or data-assimilation techniques to improve standard RANS models.

Review of previous studies and choice of test case

A thorough listing of existing experimental and numerical studies regarding wing-body junction flows can be found in Gand et al. (2010). The present uDNS is based on the configuration considered in the simulations by Apsley and Leschziner (2001), who were based themselves on the experimental studies by Devenport and Simpson (1990) and Fleming et al. (1995). The Reynolds number based on the airfoil thickness is similar to the experiment and its value is . The flow is almost incompressible with a Mach number based on the freestream velocity of . The uDNS setup reproduces the experimental conditions but with half the experimental impacting boundary layer thickness. Therefore a direct comparison with the experimental results is not possible for the present uDNS.

Description of the test case

Geometry and flow parameters

Fig. 2 displays the flow geometry, i.e. the wing body mounted on a flat plate, and the computional domain. The wing is formed by a 3:2 semi-elliptic nose with a NACA0020 tail profile, see Fig. 3, and has a thickness , which serves as reference lengthscale. The Reynolds number based on this is and the chord-to-thickness ratio is . The computational domain size is in the streamwise direction, in the spanwise direction and in the wall-normal direction, see Fig. 2. The coordinate origin is located at the root leading edge of the airfoil. There is no flow incidence relatively to the wing, corresponding to an angle of attack of degrees. Parameters of the flow (air with , , ) are reported in Tab. 1.

DNS TC04 setup.png
Figure 2: Wing-body junction. Flow geometry and domain for the DNS simulation


DNS1-6 Wing-body junction wing thickness.png
Figure 3: Wing-body junction. Wing geometry, thickness and location of boundary layer tripping superimposed by the instantaneous wall shear stress on the flat plate


Table 1: Wing-body junction. Flow parameters


Boundary conditions

The computational set-up aims at replicating the flow conditions of the experiment but with a halved incoming boundary layer thickness. To enforce these conditions in an efficient and accurate manner a Blasius velocity profile corresponding to and free stream velocity is imposed at the inlet together with uniform static pressure . and total temperature . A laminar boundary layer is then established, and a flow perturbation is applied at to trigger transition to turbulence following the idea of Housseini et al. (2016) and Schlatter and Örlü (2012). The distance of the inlet boundary from the wing-body junction is defined such that the incoming turbulent boundary layer reaches a thickness (half of the experimental value) at a given point, hereinafter referred as checkpoint, upstream the airfoil leading edge, i.e., at . To define such distance, a precursory computational campaign for the turbulent flow over a flat plate was performed. According to the outcomes of this campaign, the inlet boundary is positioned at . The tripping term promoting the boundary layer transition is then located at , see Fig. 3. At the outlet boundary, placed at , the static pressure is imposed with an exit-pressure outflow boundary condition. The bottom boundary is an adiabatic solid wall type (no slip) for and symmetry type for . This choice aims to mitigate spurious perturbations possibly originating at the outlet boundary. Symmetry conditions are imposed at the lateral () and top () boundaries. An adiabatic solid wall(no slip) condition is finally imposed on the wing surface.

References

  1. Apsley, D.D. and Leschziner, M. (2001): Investigation of Advanced Turbulence Models for the Flow in a Generic Wing-Body Junction. Flow, Turbulence and Combustion, Vol. 67, pp. 25–55
  2. Gand, F., Deck, S., Brunet, V., and Sagaut, P. (2010): Flow dynamics past a simplified wing body junction. Physics of Fluids, Vol. 22, 115111
  3. Devenport W.J. and Simpson R.L. (1990): Time-dependent and time-averaged turbulence structure near the nose of a wing-body junction. Journal Fluid Mechanics, Vol. 67, pp. 23–55
  4. Fleming, J.L., Simpson, R.L., Cowling, J.E. and Devenport, W.J. (1993): An experimental study of wing-body junction and wake flow. Exp. Fluids Vol. 14, pp. 366–378
  5. S. Hosseini, R. Vinuesa, P. Schlatter, A. Hanifia and D. Henningson (2016): Direct numerical simulation of the flow around a wing section at moderate Reynolds number, International Journal of Heat and Fluid Flow, 61:117–128
  6. Schlatter, P. and Örlü, R. (2012): Turbulent boundary layers at moderate Reynolds numbers: inflow length and tripping effects, Journal of Fluid Mechanics, 710:5–34




Contributed by: Francesco Bassi (UNIBG), Alessandro Colombo (UNIBG), Francesco Carlo Massa (UNIBG), Michael Leschziner (ICL/ERCOFTAC), Jean-Baptiste Chapelier (ONERA) — University of Bergamo (UNIBG), ICL (Imperial College London), ONERA

Front Page

Description

Computational Details

Quantification of Resolution

Statistical Data

Instantaneous Data

Storage Format


© copyright ERCOFTAC 2024