UFR 3-32 Description: Difference between revisions

From KBwiki
Jump to navigation Jump to search
m (Dave.Ellacott moved page SilverP:UFR 3-32 Description to UFR 3-32 Description)
 
(37 intermediate revisions by the same user not shown)
Line 29: Line 29:
of magnitude? Several possibilities have been examined in recent years. A
of magnitude? Several possibilities have been examined in recent years. A
first one assumes that the superstructures of the incoming layer (hairpin
first one assumes that the superstructures of the incoming layer (hairpin
packets of length about 20 /?/ or  more)  make  the  shock  wave  and  the
packets of length about 20''δ'' or  more)  make  the  shock  wave  and  the
separated zone move (Ganapathisubramani et al, 2007, 2009). A second  one
separated zone move
(Piponniau et al. 2009) considers that the low frequencies  are  produced
([[UFR_3-32_References#8|Ganapathisubramani ''et al,'' 2007, 2009]]).
A second  one
([[UFR_3-32_References#13|Piponniau ''et al '' 2009]])
considers that the low frequencies  are  produced
by a process of emptying/filling of the  separation  bubble.  Because  of
by a process of emptying/filling of the  separation  bubble.  Because  of
fluid entrainment, the air of the separation zone is drained by the large
fluid entrainment, the air of the separation zone is drained by the large
Line 43: Line 46:
therefore  cannot  be  reduced  by  some  simple  similarity  to  the
therefore  cannot  be  reduced  by  some  simple  similarity  to  the
characteristics of the boundary layer. This latter point is reinforced by
characteristics of the boundary layer. This latter point is reinforced by
a third approach (Touber & Sandham, 2011), based on a simplified momentum
a third approach ([[UFR_3-32_References#17|Touber & Sandham, 2011]]),
based on a simplified momentum
integral analysis, which shows how the low  frequency  can  develop  from
integral analysis, which shows how the low  frequency  can  develop  from
uncorrelated broadband stochastic forcing of a separating boundary layer.
uncorrelated broadband stochastic forcing of a separating boundary layer.
Line 92: Line 96:
in  pioneering  work  performed  at  Princeton  University  and  at  the
in  pioneering  work  performed  at  Princeton  University  and  at  the
University of Austin, some aspects of  the  unsteadiness  of  SWBLI  were
University of Austin, some aspects of  the  unsteadiness  of  SWBLI  were
examined (see for example Dolling 2001 and  Smits & Dussauge 2006  for
examined (see for example [[UFR_3-32_References#3|Dolling (2001)]]
and  [[UFR_3-32_References#14|Smits & Dussauge (2006)]] for
reviews). Many cases were investigated, such as corner flows, blunt  body
reviews). Many cases were investigated, such as corner flows, blunt  body
interactions  and  3D  interactions;  they  provided  in  many  cases
interactions  and  3D  interactions;  they  provided  in  many  cases
Line 112: Line 117:
flow field (mean and fluctuating) and a characterization of  unsteadiness
flow field (mean and fluctuating) and a characterization of  unsteadiness
by the measurements of spectra. Details of the experiments can  be  found
by the measurements of spectra. Details of the experiments can  be  found
in Doerffer (2009) Numerical simulations within  UFAST  include  a  large
in [[UFR_3-32_References#1|Doerffer (2009)]].
Numerical simulations within  UFAST  include  a  large
number of turbulence  modelling  approaches,  together  with  2D  and  3D
number of turbulence  modelling  approaches,  together  with  2D  and  3D
computations. The simulations were performed by  NUMECA  (Brussels),  IMF
computations. The simulations were performed by  NUMECA  (Brussels),  IMF
Toulouse,  UAN  (Karkhov),  SOTON  (University  of  Southampton),  and
Toulouse,  UAN  (Karkhov),  SOTON  (University  of  Southampton),  and
ONERA/DAAP. Table 1, taken from Garnier (Chapter 10 in  Doerffer et al.
ONERA/DAAP. [[UFR_3-32_Description#table1|Table 1]],
2010), sums up the different attempts by the different groups.
taken from Garnier (Chapter 10 in  [[UFR_3-32_References#2|Doerffer ''et al.'' 2010]]),
sums up the different attempts by the different groups.


As reported in Doerffer (2009) and in Doerffer et al. (2010),  it  is
As reported in [[UFR_3-32_References#1|Doerffer (2009)]] and in
[[UFR_3-32_References#2|Doerffer ''et al.'' (2010)]],  it  is
interesting to focus on the IUSTI  experiments,  both  because  they  are
interesting to focus on the IUSTI  experiments,  both  because  they  are
extensively documented, including  some  three-dimensional  aspects,  and
extensively documented, including  some  three-dimensional  aspects,  and
Line 135: Line 143:
although we make some reference to RANS simulations.
although we make some reference to RANS simulations.


{|align="center" border="1"
 
<div id="table1"></div>
{|align="center" border="1" cellpadding="5"
! !!Temporal Scheme!!Spatial Scheme!!Modelling!!Remark
! !!Temporal Scheme!!Spatial Scheme!!Modelling!!Remark
|-
|-
|NUMECA||Runge-Kutta + IRS||Jameson||''RANS:'' SA, k-&epsilon;, SST, v2-f||Multigrid
|align="center"|NUMECA||align="center"|Runge-Kutta + IRS||align="center"|Jameson
|align="center"|''RANS:'' SA, ''k-&epsilon;'', SST, v2-f
''Hybrid:'' DES-SA
|align="center"|Multigrid
|-
|align="center"|IMFT||align="center"|DTA||align="center"|Roe (Van Leer limiter)
|align="center"|''RANS:'' SA
''Hybrid:'' DES, OES
|align="center"|&nbsp;
|-
|align="center"|UAN||align="center"|Implicit ''O''(2)||align="center"|ENO Godunov ''O''(2)
|align="center"|''RANS:'' ''k-&omega;'', SST
|align="center"|Realisabilty cond. in turb. model
|-
|align="center"|SOTON||align="center"|RK3||align="center"|Centred ''O''(4) + TV model
|align="center"|''LES:'' MTS, DYN
|align="center"|Digital filter for inf. cond.
|-
|align="center"|ONERA||align="center"|Implicit ''O''(2)||align="center"|Roe ''O''(2) + TVD filter
|align="center"|''RANS:'' MSM, SA
''Hybrid:'' DDES SA based, SDES SA based
|align="cenetr"|Synthetic Eddy Method (SEM) inflow conditions
|}
|}
<center>'''Table 1:''' Brief description of the codes from [[UFR_3-32_References#2|Garnier (2010)]]</center>
<br/>
<br/>
----
----
{{ACContribs
{{ACContribs
| authors=Jean-Paul Dussauge
|authors=Jean-Paul Dussauge (*), P. Dupont (*) , N. Sandham (**), E. Garnier (***)
| organisation=Orange
|organisation= (*)&nbsp;Aix-Marseille Université, and Centre National de la Recherche Scientifique UM 7343, (**)&nbsp;University of Southampton, (***)&nbsp;ONERA/DAAP, Meudon, France
}}
}}
{{UFRHeader
{{UFRHeader

Latest revision as of 13:45, 12 February 2017

Planar shock-wave boundary-layer interaction

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References

Semi-confined Flows

Underlying Flow Regime 3-32

Description

Introduction

The problem of the unsteadiness in shock wave/boundary layer interactions (SWBLI) is challenging in many respects. A more general question is related to the unsteadiness or "breathing" of separated flows, whatever the regime, subsonic or supersonic. This is a problem that is important for both applications and basic research. In many aeronautical applications, such as aircraft profiles, air intakes, turbines or compressors, shock waves are formed and generally lead to separation. The resulting separation bubbles are unsteady, in the sense that they produce frequencies much lower (by at least two orders of magnitude) than the identified frequencies of the turbulent flow. Another difficulty arises if high-speed flows are considered, in which case the unsteadiness is also dependent on Mach number.

A first point is the understanding of the origin of these low frequencies: how is it possible to produce, from the turbulent fluctuations of the boundary layer, very low frequencies, involving scales differing from the turbulent layer itself generally by two orders of magnitude? Several possibilities have been examined in recent years. A first one assumes that the superstructures of the incoming layer (hairpin packets of length about 20δ or more) make the shock wave and the separated zone move (Ganapathisubramani et al, 2007, 2009). A second one (Piponniau et al  2009) considers that the low frequencies are produced by a process of emptying/filling of the separation bubble. Because of fluid entrainment, the air of the separation zone is drained by the large structures, Kelvin-Helmholtz-like, formed at the edge of the recirculating zone, and is progressively emptied, until it is filled again by air incoming in the reverse direction. The second scenario seems more appropriate, since it is able to reproduce the dominant frequencies in shock reflections, while the first one fails for this flow case. A point which can be underlined is that the scales involved in the unsteadiness are not directly related to the incoming boundary layer, and therefore cannot be reduced by some simple similarity to the characteristics of the boundary layer. This latter point is reinforced by a third approach (Touber & Sandham, 2011), based on a simplified momentum integral analysis, which shows how the low frequency can develop from uncorrelated broadband stochastic forcing of a separating boundary layer.

From the CFD point of view, such flows remain challenging. Many attempts have been made to compute SWBLI, to determine the mean and turbulent fields or the unsteadiness. The few attempts of applying compressibility flow corrections in turbulence modelling have demonstrated an insufficient predictive capability of unsteady flows with strong compressibility effects and attempts to 'extrapolate' turbulence modelling from incompressible flows have also proven insufficient for the accurate prediction of the buffeting phenomenon and of transonic-dip flutter (examples: research program ETMA, Vieweg, Vol. 65 and European research program UNSI, final report edited by Springer, Vol. 81), concerning the simulation of buffeting phenomenon and of shock unsteady motion. A difficulty for RANS methods comes probably from their tuning to simple, self-similar equilibrium situations, and hence cannot cope with the new scales which are typically out of equilibrium, having a particular dynamics. More recently the hybrid approach DES (Detached Eddy Simulation), that is an inherently 3D approach, has been applied to the transonic flows around airfoils, indicating the crucial need for improvement of flow-physics knowledge concerning the modification of the turbulence scales due to the unsteadiness and compressibility.

It seems that methods like LES do not suffer from the same limitations as RANS; a consequence is that hybrid methods like the different versions of DES may represent an interesting compromise by combining the flexibility of LES and the economy in computational resources of RANS. On the numerical side, such flows represent some challenging aspects: there are the usual requirements on meshes, since in LES computations the mesh size acts as a filter and therefore is part of the modelling, and there are other difficulties since unsteady shocks should be adequately represented by the computations, without being confused with turbulence.

For the present application to shock-wave/boundary-layer interaction, experiments provide detailed descriptions of the flow, for the mean and turbulent fields, and for the characterization of the unsteadiness. The data are compared to the results of computations, using LES, several types of DES, and URANS and RANS methods based on Spalart-Allmaras modelling. The discussions will also lead to the assessment of the importance of taking in account the 3D effects for predicting correctly the separated zone and in turn, the interaction unsteadiness.

Review of UFR studies and choice of test case

Shock-wave/boundary-layer interactions (SWBLI) remain challenging for the physical understanding and for numerical simulations, in particular when they lead to flow separation, which is in general unsteady. In the past, in pioneering work performed at Princeton University and at the University of Austin, some aspects of the unsteadiness of SWBLI were examined (see for example Dolling (2001) and Smits & Dussauge (2006) for reviews). Many cases were investigated, such as corner flows, blunt body interactions and 3D interactions; they provided in many cases measurements of wall pressure fluctuations, and led to first understanding of shock unsteadiness and separated flow breathing. The European program UFAST organised considerable effort to study and document this question. Among all the possible interactions, particular attention was paid to the case of oblique shock reflection, which imposes severe compression to boundary layers. Moreover, this occurs in many particular situations, such as air intakes, compressors, turbines etc., and can be very detrimental for the structures. It was felt that there was a need for experiments at moderate Reynolds numbers to serve as test cases for advanced turbulence modelling like LES or DES. Several cases were studied experimentally at Mach numbers of 1.7, 2.0 and 2.25 respectively at Delft University of Technology (TU Delft), at the Institute of Theoretical and Applied Mechanics (ITAM) Novosibirsk and at the Institut Universitaire des Systèmes Thermiques Industriels (IUSTI) Marseille. All the experiments include statistical measurements of the flow field (mean and fluctuating) and a characterization of unsteadiness by the measurements of spectra. Details of the experiments can be found in Doerffer (2009). Numerical simulations within UFAST include a large number of turbulence modelling approaches, together with 2D and 3D computations. The simulations were performed by NUMECA (Brussels), IMF Toulouse, UAN (Karkhov), SOTON (University of Southampton), and ONERA/DAAP. Table 1, taken from Garnier (Chapter 10 in Doerffer et al. 2010), sums up the different attempts by the different groups.

As reported in Doerffer (2009) and in Doerffer et al. (2010), it is interesting to focus on the IUSTI experiments, both because they are extensively documented, including some three-dimensional aspects, and because the associated computations have led to comparisons between RANS, URANS, hybrid methods like DES, and LES. RANS methods by principle cannot catch the unsteadiness. They can however give some indications, provided they can predict the size of the interactions. In some analyses, this size is related to the characteristic frequency of the shock motion, so that it can indirectly provide indications on its time dependent behaviour. However, the conclusions show of course the potential of LES and DES to determine unsteadiness. The results have also underlined the importance of 3D effects in nozzles of finite span, which contribute to the organization of the separated zone. The present document is based on the numerical simulations of ONERA/DAAP (DES and LES) and SOTON (LES), although we make some reference to RANS simulations.


Temporal Scheme Spatial Scheme Modelling Remark
NUMECA Runge-Kutta + IRS Jameson RANS: SA, k-ε, SST, v2-f

Hybrid: DES-SA

Multigrid
IMFT DTA Roe (Van Leer limiter) RANS: SA

Hybrid: DES, OES

 
UAN Implicit O(2) ENO Godunov O(2) RANS: k-ω, SST Realisabilty cond. in turb. model
SOTON RK3 Centred O(4) + TV model LES: MTS, DYN Digital filter for inf. cond.
ONERA Implicit O(2) Roe O(2) + TVD filter RANS: MSM, SA

Hybrid: DDES SA based, SDES SA based

Synthetic Eddy Method (SEM) inflow conditions


Table 1: Brief description of the codes from Garnier (2010)




Contributed by: Jean-Paul Dussauge (*), P. Dupont (*) , N. Sandham (**), E. Garnier (***) — (*) Aix-Marseille Université, and Centre National de la Recherche Scientifique UM 7343, (**) University of Southampton, (***) ONERA/DAAP, Meudon, France

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References


© copyright ERCOFTAC 2024