Large Eddy Simulations of a Three-Row Leading Edge Film Cooling Geometry

2008 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Lateral Displacement ◽  
Vortex Pair ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Cylinder Surface ◽  
Stagnation Region ◽  
Single Vortex ◽  
Blowing Ratio ◽  
Large Eddy

A three-row leading edge film cooling geometry is investigated using Large-Eddy Simulations (LES) at a freestream Reynolds number of 32,000 and blowing ratio of 0.5 with lateral injection of 45° to the surface and 90° compound injection. The stagnation jet interacts with the mainstream through the generation of ring vortices which quickly breakdown and convect along the cylinder surface. The coolant penetrates the mainstream both laterally and normal to the surface resulting in increased mixing and turbulence generation. As the coolant loses transverse and lateral momentum it is pushed back to the surface in the stagnation region after which it convects downstream along the blade surface. Surface coverage is uniform but weak with spanwise-averaged effectiveness ranging from 0.1 to 0.3 in the stagnation region. The primary off-stagnation coolant and mainstream interaction is through the generation of a counter-rotating vortex pair in the immediate wake, but which quickly degenerates to a single vortex which entrains free-stream fluid near the surface at the aft-end of the jet. In contrast to the stagnation row, the coolant stays in close proximity to the surface and does not undergo a large lateral displacement along the spanwise pitch. As a consequence it provides good local coverage along its trajectory but barely covers half the lateral pitch. Hence, spanwise-averaged effectiveness is of the same order as at stagnation starting at 0.3 downstream of injection to 0.1 about 6d downstream.

Effect of Blowing Ratio in the Near-Stagnation Region of a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations

2009 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Blowing Ratio ◽  
Large Eddy ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Computational studies are carried out using Large Eddy Simulations (LES) to investigate the effect of coolant to mainstream blowing ratio in a leading edge region of a film cooled vane. The three row leading edge vane geometry is modeled as a symmetric semi-cylinder with a flat afterbody. One row of coolant holes is located along the stagnation line and the other two rows of coolant holes are located at ±21.3° from the stagnation line. The coolant is injected at 45° to the vane surface with 90° compound angle injection. The coolant to mainstream density ratio is set to unity and the freestream Reynolds number based on leading edge diameter is 32000. Blowing ratios (B.R.) of 0.5, 1.0, 1.5, and 2.0 are investigated. It is found that the stagnation cooling jets penetrate much further into the mainstream, both in the normal and lateral directions, than the off-stagnation jets for all blowing ratios. Jet dilution is characterized by turbulent diffusion and entrainment. The strength of both mechanisms increases with blowing ratio. The adiabatic effectiveness in the stagnation region initially increases with blowing ratio but then generally decreases as the blowing ratio increases further. Immediately downstream of off-stagnation injection, the adiabatic effectiveness is highest at B.R. = 0.5. However, further downstream the larger mass of coolant injected at higher blowing ratios, in spite of the larger jet penetration and dilution, increases the effectiveness with blowing ratio.

Effect of Blowing Ratio on Syngas Flyash Particle Deposition on a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations

2009 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Particle Deposition ◽  
Numerical Study ◽  
Leading Edge ◽  
Stagnation Region ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Lagrangian Framework ◽  
Large Eddy ◽  
Turbine Vane

A numerical study is performed to investigate deposition and erosion of Syngas ash in the leading edge region of a turbine vane. The leading edge of the vane is modeled as a symmetric semi-cylinder with a flat after body. Three rows of coolant holes located at stagnation and at ±21.3° from stagnation are simulated at blowing ratios of 0.5, 1.0, 1.5 and 2.0. Large Eddy Simulation (LES) is used to model the flow field of the coolant jet-mainstream interaction and syngas ash particles are modeled using a Lagrangian framework. Ash particle sizes of 5 and 7 micron are considered. Under the conditions of the current simulations, both ash particles have Stokes numbers less than unity of O(1) and hence are strongly affected by the flow and thermal field generated by the coolant interaction with the mainstream. Because of this, the stagnation coolant jets are quite successful in pushing the particles away from the surface and minimizing deposition and erosion in the stagnation region. Overall, about 10% of the 5 μm particles versus 20% of the 7 μm particles are deposited on the surface at B.R. = 0.5. An increase to B.R. = 2, increases deposition of the 5 micron particles to 14% while decreasing deposition of the 7 micron particles to 15%. Erosive ash particles of 5 μm size increase from 5% of the total to 10% as the blowing ratio increases from 0.5 to 2.0, whereas 7 μm erosive particles remain nearly constant at 15%. Overall, for particles of size 5 μm, there is a combined increase in deposition and erosive particles from 16% to 24% as the blowing ratio increases from 0.5 to 2.0. The 7 μm particles, on the other hand decrease from 35% to about 30% as the blowing ratio increases from 0.5 to 2.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2011 ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Large Eddy

Large Eddy Simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported with the jet modeled using a plenum/pipe configuration. This configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
S. Sarkar ◽  
Harish Babu
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Downward Spiral

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using large eddy simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair (CRVP), and downward spiral separation node (DSSN) vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Author(s):  
Harish Babu ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Rotor Stator Interaction

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using Large Eddy Simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair and DSSN vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Effect of Blowing Ratio on Early Stage Deposition of Syngas Ash on a Film-Cooled Vane Leading Edge Using Large Eddy Simulations

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Numerical Study ◽  
Early Stage ◽  
Leading Edge ◽  
Particle Method ◽  
Softening Temperature ◽  
Capture Efficiency ◽  
Particle Sizes ◽  
Stagnation Region ◽  
Blowing Ratio ◽  
Large Eddy

A numerical study is performed to investigate the deposition of Syngas ash in the leading edge region of a turbine vane. The leading edge of the vane is modeled as a symmetric semicylinder with a flat afterbody. Three rows of coolant holes located at stagnation and at ±21.3 deg from stagnation are simulated at blowing ratios of 0.5, 1.0, 1.5, and 2.0. Large eddy simulation (LES) is used to model the flow field of the coolant jet-mainstream interaction and Syngas ash particles are modeled using a discrete particle method. The capture efficiency for eight different ash compositions of particle sizes 5 and 10 microns are investigated. Under the conditions of the current simulations, both ash particles have Stokes numbers less than unity and hence are strongly affected by the flow and thermal field generated by the coolant interaction with the mainstream. Because of this, the coolant jets at stagnation are quite successful in pushing the particles away from the surface and minimizing deposition in the stagnation region. Among all of the ash samples, the ND ash sample shows the highest capture efficiency due to its low softening temperature. For the 5 micron particles, when the blowing ratio increases from 1.5 to 2.0, the percentage of the capture efficiency increases as more numbers of particles are transported to the surface by strong mainstream entrainment by the coolant jets. The deposition results are also estimated using the discrete random walk (DRW) model and are compared to that obtained from the LES calculations. For both particle sizes, the DRW model under-predicts the capture efficiency when compared to the LES calculations and the difference increases with the increasing blowing ratio and decreases with increasing particle size.

Analysis of Flow Physics and Jet-Mainstream Interaction in Leading Edge Filmcooling Using Large Eddy Simulation

2006 ◽  
Author(s):  
Ali Rozati ◽  
Danesh K. Tafti
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Low Frequency ◽  
Vortex Pair ◽  
Leading Edge ◽  
Windward Side ◽  
Stagnation Line ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Counter Rotating Vortex Pair

A numerical investigation is conducted to study leading edge film cooling at a compound angle with Large Eddy Simulation (LES). The domain geometry is adopted from an experimental set-up (Ekkad et al. [14]) where turbine blade leading edge is represented by a semi-cylindrical blunt body. The leading edge has two rows of coolant holes located at ±15° of the stagnation line. Coolant jets are injected into the flow field at 30° (spanwise) and 90° (streamwise). Reynolds number of the mainstream is 100,000 and jet to mainstream velocity and density ratios are 0.4 and 1.0, respectively. The results show the existence of an asymmetric counter-rotating vortex pair in the immediate wake of the coolant jet. In addition to these primary structures, vortex tubes on the windward side of the jet are convected downstream over and to the aft- and fore-side of the counter-rotating vortex pair. All these structures play a role in the mixing of mainstream fluid with the coolant. A turbulent boundary layer forms within 2 jet diameters downstream of the jet. A characteristic low frequency interaction between the jet and the mainstream is identified at a non-dimensional frequency between 0.79 and 0.95 based on jet diameter and velocity. The spanwise averaged adiabatic effectiveness agrees well with the experiments when fully-developed turbulence is used to provide time-dependent boundary conditions at the jet inlet, without which the calculated effectiveness is overpredicted.

Large Eddy Simulation of Leading Edge Film Cooling—Part II: Heat Transfer and Effect of Blowing Ratio

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Ali Rozati ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Large Eddy Simulation ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Adiabatic Effectiveness

Detailed investigation of film cooling for a cylindrical leading edge is carried out using large eddy simulation (LES). The paper focuses on the effects of coolant to mainstream blowing ratio on flow features and, consequently, on the adiabatic effectiveness and heat transfer coefficient. With the advantage of obtaining unique, accurate, and dynamic results from LES, the influential coherent structures in the flow are identified. Describing the mechanism of jet-mainstream interaction, it is shown that as the blowing ratio increases, a more turbulent shear layer and stronger mainstream entrainment occur. The combined effects lead to a lower adiabatic effectiveness and higher heat transfer coefficient. Surface distribution and span-averaged profiles are shown for both adiabatic effectiveness and heat transfer (presented by Frossling number). Results are in good agreement with the experimental data of Ekkad et al. [1998, “Detailed Film Cooling Measurement on a Cylindrical Leading Edge Model: Effect of Free-Steam Turbulence and Coolant Density,” ASME J. Turbomach., 120, pp. 799–807].

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