LargeEddy Simulation & DetachedEddy Simulations
How to use an inHouse Fortran source code
The traditional method for CFD in industry and universities is ReynoldsAveraged NavierStokes (RANS). It is a fast method and
mostly rather accurate. However, in flows involving large separation regions, wakes and transition it is inaccurate. The reason
is that all turbulence is modeled with a turbulence model. For predicting aeroacoustic, RANS is even more unreliable.
For these flow, LargeEddy Simulation (LES) and DetachedEddy Simulations (DES) is a suitable option although it is much more
expensive. Still, in many industries (automotive, aerospace, gas turbines, nuclear reactors, wind power) DES is used as an alternative to RANS.
In universities, extensive research has been carried out during the last decade(s) on LES and DES.
Unfortunately, most engineers and many researchers have limited knowledge of what a LES/DES CFD code is doing. The object of this
online course is to close that knowledge gap. During the course, the participants will learn and work with an inhouse LES/DES code called CALCLES, written by the
lecturer. It is a finite volume code written in Fortran 77. It includes two zeroequation SGS models (Smagorinsky and WALE) and one
twoequation model (the PANS model).
The convective terms in the momentum equations are discretized using
central differencing.
Hybrid central/upwind is used for the k and eps equations. The CrankNicolson scheme is used for time discretization of all equations.
The numerical procedure is based on an implicit, fractional step technique with a
multigrid pressure Poisson solver [1] and a nonstaggered grid arrangement.
CALCLES is a singleblock structured code. It is not
parallelized. However, it is very fast. The hump flow (see below), it
requires less than 14 seconds/time step on a standard PC. For a converged solutions,
7500+7500 timesteps are sufficient. The number of cells is 648x108x64.
THE ONLINE COURSE
The course includes lectures (12 hours) and workshops (12 hours) learning and using CALCLES. The
course is given 22, 24, 26 June 2020.
The lectures will be given online (Live) using Zoom. During the workshops, the participants will get
supervision in a joint Zoom room which will enable participants to learn from each others questions. Part of the supervision
may also be given in individual breakout Zoom rooms.
Zoom
In the lectures we will address:
 finite volume discretization
 central differencing scheme
 hybrid central/upwind scheme
 Smagorinsky model
 WALE model
 the keps DES model
 twoequation PANS model (k and epsilon)
 wall and periodic boundary conditions
 TDMA (tridiagonalmatrixalgorithm) solver
 how to prescribe turbulent inlet boundary conditions
 how to generate inlet anisotropic synthetic turbulent fluctuations
In the workshops, the participants will use CALCLES.
The participants will get the source code and install it on their laptop or desktop.
It is recommended that the participants use Linux with the
GNU, Intel's or PGI compiler
and have a simple plotting program such as
Python,
Matlab or
Octave
installed. If participants use Windows or Mac, no support will be given for installing
the code (it is most likely easy to install the code also on Windows and Mac).
Four test cases are provided in the CALCLES code:
 DNS and LES of fully developed channel flow [25]. Periodic boundary conditions in streamwise and
spanwise directions.
 LES of atmospheric boundary layer over a forest relevant to windpower engineering [10,11]. Periodic boundary conditions in streamwise and
spanwise directions. The figure show instantanoues streamwise velocity. The height of the forest (20m) is indicted by the green line.
A 384x192x96 mesh is used. The CPU time for one timestep on a standard desktop PC is 15 seconds.
 LES of the hill flow [6]. Periodic boundary conditions in streamwise and
spanwise directions.
 DES of the hump flow [6]. Synthetic inlet fluctuations at the inlet [79].
Periodic boundary conditions spanwise direction. On a 624x108x64 mesh the CPU time is 20 seconds per time step on a standard PC [14].
Python and Matlab/Octave files
OBJECT
The object is that the participants should learn how a CFD code for LES/DES works. It will give them
increased knowledge, confidence and knowhow when using commercial CFD codes.
PARTiCiPANTS
The participants are expected to hold a MSC degree or PhD degree related to fluid mechanics. They are expected
to have at least a basic knowledge in LES and DES. Programming skills is also useful. The course is expected to be valuable also for researchers
with extensive knowledge in LES and/or DES. The participants may continue to use CALCLES after the course, in their daily work and/or research. However, no support
will be given.
LECTURER
The lecturer at the course (both during lectures and workshops) will be Prof. Lars Davidson,
Chalmers University of Technology.
homepage
COURSE MATERiAL
COURSE LANGUAGE
The course material is in English and the lectures will be given in English.
DATE & LOCATiON
The course will be held 22, 24, 26 June 2020 online at Zoom
Zoom
REGiSTRATiON
Registration form should be submitted no later than May 20, 2020.
The price is 14,700 SEK (excl. VAT). No refunding after May 21.
The number of participants is limited to 16.
registration form
PROGRAM
DAY 1, Monday, 8 hours
 General structure of CALCLES
 Discretization in CALCLES
 Compute geometrical quantities
 Studying Test Case 1 (channel flow)
 Studying Test Case 2 (atmospheric boundary layer)
 WORKSHOP, see Section workshop in
CALCLES: A Fortran Code for LES and Hybrid LESRANS
 Fullydeveloped channel flow simulations using PANS
 Channel flow simulations with inletoutlet using PANS
 Investigation of different synthetic fluctuating inlet fluctuations. For example, change the prescribed
integral length scale, the integral time scale, the anisotropy ...
Tueday (no teaching). Participants can work on CALCLES
DAY 2, Wednesday, 8 hours
 Implicit RhieChow interpolation in CALCLES
 TDMA solver
 Implementation of Zero equation models
 Implementation of the PANS model in CALCLES
 Studying Test Case 3 (hill flow)
 WORKSHOP, see Section workshop in
CALCLES: A Fortran Code for LES and Hybrid LESRANS
 Implementing a oneequation hybrid LESRANS model
 Implementing a DES model (keps and/or komega)
 Implementing a DDES model (keps and/or komega)
Thursday (no teaching). Participants can work on CALCLES
DAY 3, Friday, 8 hours
 How to implement a new turbulence model in CALCLES
 Implementation of synthetic turbulence in CALCLES
 How to generate anisotropic turbulent fluctuations in CALCLES
 how to implement a keps DES model
 Precursor RANS (using a 1D solver written in Python and Matlab/Octave)
as input to synthetic turbulence generator
 Studying Test Case 4 (hump flow)
 WORKSHOP, see Section workshop in pdf
 Implementing an IDDES model (keps and/or komega)
 Implementing the SAS model (komega)
 Making heat transfer simulations in a channel with inletoutlet boundary conditions
Above, we give above examples on what turbulence models to implement in the workshops. Students may of course propose
to implement other turbulence models.
QUESTiONS & FURTHER iNFORMATiON
Please contact
 Lars Davidson
 tel. +46 (0) 730791 161
 Email: lada@flowsim.se, lada@chalmers.se
REFERENCES
 P. Emvin, The Full Multigrid Method Applied to Turbulent Flow in Ventilated
Enclosures Using Structured and Unstructured Grids. PhD thesis, Dept. of
Thermo and Fluid Dynamics, Chalmers University of Technology, Göteborg,
1997.
 L. Davidson, Large eddy simulations: how to evaluate resolution. International Journal of Heat and Fluid Flow, 30(5):10161025, 2009.
 L. Davidson, The PANS kε model in a zonal hybrid RANSLES formulation. International Journal of Heat and Fluid Flow, 46:112126, 2014.
 L. Davidson, Zonal PANS: evaluation of different treatments of the RANSLES interface. Journal of Turbulence, 17(3):274307, 2016.
 A. Altintas and L. Davidson, Direct numerical simulation analysis of spanwise oscillating lorentz force in turbulent channel flow at low Reynolds number. Acta Mechanica, pages 118, 2016.
 J. Ma, S.H. Peng, L. Davidson, and F. Wang, A low Reynolds number variant of PartiallyAveraged NavierStokes model for turbulence. International Journal of Heat and Fluid Flow, 32(3):652669, 2011.10.1016/j.ijheatfluidflow.2011.02.001.
 L. Davidson, Using isotropic synthetic fluctuations as inlet boundary conditions for unsteady simulations. Advances and Applications in Fluid Mechanics, 1(1):135, 2007.
 L. Davidson and S.H. Peng, Embedded largeeddy simulation using the partially averaged NavierStokes model. AIAA Journal, 51(5):10661079, 2013.
 L. Davidson, Twoequation hybrid RANSLES models: A novel way to treat k and ω at inlets and at embedded interfaces. Journal of Turbulence, 18(4):291315, 2017.
 B. Nebenfuhr, L. Davidson, LargeEddy Simulation Study of Thermally Stratified Canopy Flow, BoundaryLayer Meteorology, Vol. 156, number 2 , pp. 253276, 2015
 B. Nebenfuhr, L. Davidson, Prediction of windturbine fatigue loads in forest regions based on turbulent LES inflow fields, Volume 20, Issue 6 pp. 10031015, Wind Energy, 2017.
 L. Davidson and C. Friess,
The PANS and PITM model: a new formulation of f_k,
Proceedings of 12th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements (ETMM12), Montpelier,
France 2628 September, 2018
 L. Davidson, Zonal Detached Eddy Simulation coupled with steady RANS in the wall region,
ECCOMAS MSF 2019 Thematic Conference, 1820 September 2019, Sarajevo, BosniaHerzegovina
 L. Davidson, inlet boundary conditions.
 L. Davidson, "NonZonal Detached Eddy Simulation coupled with a steady RANS solver in the wall region",
ERCOFTAC Bullentin 120, Special Issue on Current trends in
RANSbased scaleresolving simulation methods, pp 4348, 2019.
