Large Eddy Simulation of Turbulent Flows

Large Eddy Simulation (LES) of Turbulent Flows

Ingredients of the method development:

  1. Discretization of The unsteady Navier-Stokes equations using the Space-Time Conservation Element and Solution Element (CE/SE) scheme. The scheme treats the both time and space frames in a unified manner. The numerical results have consistently demonstrated that this 2nd order scheme, possesses very useful properties of high resolution, low dissipation, and non-oscillatory behaviour around shock waves.
  2. Large Eddy Simulations (LES) is implemented, so that the unsteady NS solver will be able to resolve the transient large scale turbulence structures, whilst only those small scale which can not be resolved at the level of the mesh grid spacing, will be modelled  by the Smagorinsky subgrid scale  model (SGS).

Large Eddy Simulation of Mixing Layer

Instantaneous vorcity contours

Instantaneous vorcity contours

 Normalized Reynolds normal stress

 

Normalized Reynolds normal stress

Automobile Cavity Noise

Automobile Cavity Noise

 

Automobile Cavity Noise

Computation of Screech Tones

The jet is assumed to be supplied by convergent nozzle with a designed Mach number equal to 1. The free stream flow condition is assumed at rest and free stream pressure (P∞) and temperature (T∞) are equal to 105 Pa and 288 K, respectively. Reservoir temperature (Tr) is taken equal to the free stream temperature and an elevated pressure is imposed at the nozzle exit Pe /P∞ = 2.09. Designed nozzle velocity (Ue) is 310 m/s.

Whole domain and symmetric computations are carried out. For whole domain, computational domain is divided into 64 subdomains and for the symmetric one 32 subdomains are used.

Jet fighter

Screech tones 

Screech tones generated by under-expanded

Computed Instantaneous density-gradient

Computed Instantaneous density-gradient

Aircraft Weapon Bay Cavity Flow

Three-dimensional large eddy simulation is carried out for subsonic cavity flow. Numerical results are compared with experimental data. The length-to-depth ratio L/D = 5. Flow conditions and geometry details of the cavity can be seen from Table 3. Computational domain is decomposed into 64 subdomains and mesh density is 3.744×106. (250×80×30) cells inside the cavity and (400×130×60) cells above the cavity.

lgeddy8

 

 

lgeddy9

 

 

lgeddy10

 

lgeddy11lgeddy12

 

Reference:

- O. Abay and L. He, “Time Conservative Finite Volume Method for Large Eddy Simulation of Turbulence”, Proc, the 2007 International Conference in Engineering Mechanics, London, July, 2007.

-O. Aybay, L. He, “Developemnet of High-Resolution Time-Conservative Finite Volume Method for Large Eddy Simulation”, Enghineering Letters, Vol.16. No1, pp96-103, 2008.

 

Large Eddy Simulation for Turbine Blades

     LES for high pressure turbine blade passages presents a significant challenge chiefly due to the local high Reynolds number. The appeal on the other hand is considerable as the level of inflow turbulence (exit from the combustor) tends to be very high. A further complication is the non-negligible amount of heat transfer, thus leading to the issue of the wall boundary condition for the unsteady energy equation.  Recently, some new effort has been made in this area with a particular emphasis on the unsteady fluid-solid conjugate heat transfer interfacing  & inflow synthetic turbulence generation (He, 2013).

LES_turbine1.png

References:

- L  He, “Fourier Spectral Method for Multi-Scale Aerothermal Analysis”,  International Journal of  Computational Fluid Dynamics, Vol.27, No2, 2013, pp118-129.