Sunil Patil

Experimental and Numerical Investigation of Convective Heat Transfer in a Gas Turbine Can Combustor

Experiments and numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under cold flow conditions in a Reynolds number range between 50,000 and 500,000 with a characteristic swirl number of 0.7. It is observed that the flow field in the combustor is characterized by an expanding swirling flow, which impinges on the liner wall close to the inlet of the combustor. The impinging shear layer is responsible for the peak location of heat transfer augmentation. It is observed that as Reynolds number increases from 50,000 to 500,000, the peak heat transfer augmentation ratio (compared with fully developed pipe flow) reduces from 10.5 to 2.75. This is attributed to the reduction in normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.7 with Reynolds number. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change.

Wall modeled large eddy simulation of flow over a backward facing step with synthetic inlet turbulence

Application of Large Eddy Simulations (LES) to complex high Reynolds number problems has been limited by the computational cost. This paper uses wall layer modeling to mitigate near wall grid resolution requirements and the specification of inlet turbulence to reduce the cost of LES simulations. The wall model uses the two layer approach which is generalized for complex geometries and the synthetic eddy method (SEM) for the generation of inlet boundary conditions. Three different problems are considered, fully developed turbulent channel flow up to a Reynolds number of 2x10 6 , developing channel flow, and flow over a backward facing step at Re=40,000. Predictions with wall modeled LES are compared with available DNS and experimental data. Good agreement of the predicted mean flow velocity field and turbulent statistics with data indicates that the formulated wall modeled LES and the synthetic eddy method can be used effectively to predict high Reynolds number separated flows at a cost at least an order of magnitude less than wall resolved LES.

Two-Layer Wall Model for Large-Eddy Simulations of Flow over Rough Surfaces

Two-layer zonal near-wall treatment for flow over rough surfaces is proposed in a generalized coordinate largeeddy simulation framework. Rotta’s [Rotta, J. C., “Turbulent Boundary Layers in Incompressible Flow,” Progress in Aeronautical Sciences, Vol. 2, 1962, pp. 1–220.] approach to amplify the mixing length near the wall is used to model the eddy viscosity in the inner layer. Calculations are performed in a rod-roughened channel at high flow Reynolds numbers in the range of 6000 to 56,000 and in the fully rough regime. An equivalent sand-grain roughness is used to correlate the amplification in the wall shear stress with the roughness geometry. The roughness wall model predicts the skin-friction coefficient and the mean velocity profile, in close agreement with experiments. Turbulence statistics are also predicted with good accuracy. For the lowest Reynolds number investigated in the current study, the spatial resolution required bywall-modeled large-eddy simulation is three orders ofmagnitude smaller thanwith a direct simulation on the same geometry that resolves the roughness elements. This results in large savings in computational cost.

Large Eddy Simulation of Flow and Convective Heat Transfer in a Gas Turbine Can Combustor With Synthetic Inlet Turbulence

Large eddy simulations of swirling flow and the associated convective heat transfer in a gas turbine can combustor under cold flow conditions for Reynolds numbers of 50,000 and 80,000 with characteristic Swirl number of 0.7 are carried out. A precursor Reynolds Averaged Navier-Stokes (RANS) simulation is used to provide the inlet boundary conditions to the large-eddy simulation (LES) computational domain, which includes only the can combustor. A stochastic procedure based on the classical view of the turbulence as superposition of the coherent structures is used to simulate the turbulence at the inlet plane of the computational domain using the mean flow velocity and Reynolds stress data from the precursor RANS simulation. To further reduce the overall computational resource requirement and the total computational time, the near wall region is modeled using zonal two layer model. A novel formulation in generalized co-ordinate system is used for solution of effective tangential velocity and temperature in the inner layer virtual mesh. LES predictions are compared with the experimental data of Patil et al. [1] for the local heat transfer distribution on the combustor liner wall obtained using robust infrared thermography technique. The heat transfer coefficient distribution on the liner wall predicted from LES is in good agreement with experimental values. The location and the magnitude of the peak heat transfer are predicted in very close agreement with the experiments.© 2011 ASME

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the LES framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of Rau et al. [1], and Han et al. [2], and wall resolved LES data of Tafti [3]. Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.Copyright