Hybrid RANS-LES Modeling of a Normal Jet in Crossflow for Film Cooling Applications

2013 ◽  
Author(s):  
Tej P. Dhakal ◽  
D. Keith Walters
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Mean Flow ◽  
Low Velocity ◽  
Lower Velocity ◽  
Jet In Crossflow ◽  
Wall Structures ◽  
Crossflow Velocity ◽  
Les Model ◽  
Near Wall

Numerical simulation of a normal jet in crossflow has been performed using a recently developed hybrid RANS-LES model. The model form utilizes a solution based parameter that dynamically determines the RANS and LES regions. Numerical simulations using commercially available DDES model and a RANS model have also been performed for comparison purposes. Three jet to crossflow velocity ratios (R = 2, 1, 0.5) have been investigated. Computational results obtained are compared with the experiment of Andreopoulos and Rodi (1984). The results highlight the predictive capabilities of hybrid RANS-LES model to reproduce the important vortical structures of a jet in crossflow case, which play a crucial role in the film cooling. The hybrid RANS-LES model results from the velocity ratio R = 2 case fare well with the experiment in comparison to RANS predictions. For lower velocity ratios, discrepancies in mean flow statistics have been observed at some measurement stations. The near wall statistics from the hybrid model resembles RANS predictions for the case with jet to crossflow velocity ratio R = 0.5. This observation can be attributed to the requirement of higher grid resolution necessary to capture the near wall structures for low velocity ratio cases.

Flow Characteristics of a Low Reynolds Number Jet in Crossflow with an Obstacle Block

2016 ◽  
Vol 9 (1) ◽  
pp. 37-46 ◽  
Author(s):  
Jianlong Chang ◽  
Xudong Shao ◽  
Xiao Hu ◽  
Shuangbiao Zhang
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Vortex Pair ◽  
Lower Velocity ◽  
Eddy Simulation ◽  
Jet In Crossflow ◽  
Crossflow Velocity ◽  
Low Reynolds

The jet in crossflow at very low Reynolds number (Re=100) with and without block is performed by means of large eddy simulation for the jet-to-crossflow velocity ratios (r) ranging from 1 to 3, and the corresponding flow characteristics are compared. The results show that the time-averaged particle trajectories of the jet are slightly changed if a block is presented, and the mixed vortices are weakened. The existence of the block also can accelerate the formation of stable counter-rotating vortex pair. At lower velocity ratio (r=1), the block has little effect on the jet in crossflow with a symmetrically positive and negative kidney shaped vortices. As the velocity ratio increases, the effect of block not only can generate an asymmetry of positive and negative kidney shaped vortices, but also it can reinforce the interaction between the positive and negative vortices in the jet in crossflow. The effect of block on the temperature field is also analyzed in detail.

Transpiration Cooling Using Porous Triple-Laminated Plates

2003 ◽  
Author(s):  
H. L. Wu ◽  
X. F. Peng
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
High Efficiency ◽  
Velocity Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Laminated Plates ◽  
Transpiration Cooling ◽  
Transfer Behavior ◽  
Crossflow Velocity

Transpiration cooling using porous triple-laminated plates was numerically investigated to understand the associated flow mechanism and heat transfer characteristics with/without crossflow. The flow structure and heat transfer behavior are very similar in the two laminate gaps, and crossflow has little influence on them. The cooling performance shows very good uniformity and high efficiency. Violent impingement and turbulent flow inside the plate contribute greatly to local heat transfer intensification. The cooling efficiency might be further improved with enhancement of film cooling effect, by enlarging the discharge holes to decrease the local jet-to-crossflow velocity ratio, or by using inclined discharge holes to increase the film attaching ability.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness: Part II — Compound Angle Shaped Holes

2017 ◽  
Author(s):  
John W. McClintic ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
Zachary D. Webster
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Injection Rate ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Crossflow Velocity ◽  
Film Cooling Holes ◽  
Compound Angle

In gas turbine engines, film cooling holes are commonly fed with an internal crossflow, the magnitude of which has been shown to have a notable effect on film cooling effectiveness. In Part I of this study, as well as in a few previous studies, the magnitude of internal crossflow velocity was shown to have a substantial effect on film cooling effectiveness of axial shaped holes. There is, however, almost no data available in the literature that shows how internal crossflow affects compound angle shaped film cooling holes. In Part II, film cooling effectiveness, heat transfer coefficient augmentation, and discharge coefficients were measured for a single row of compound angle shaped film cooling holes fed by internal crossflow flowing both in-line and counter to the span-wise direction of coolant injection. The crossflow-to-mainstream velocity ratio was varied from 0.2–0.6 and the injection velocity ratio was varied from 0.2–1.7. It was found that increasing the magnitude of the crossflow velocity generally caused degradation of the film cooling effectiveness, especially for in-line crossflow. An analysis of jet characteristic parameters demonstrated the importance of crossflow effects relative to the effect of varying the film cooling injection rate. Heat transfer coefficient augmentation was found to be primarily dependent on injection rate, although for in-line crossflow, increasing crossflow velocity significantly increased augmentation for certain conditions.

Influence of Inlet Velocity Ratio on the Outlet Flow Uniformity of a Fan-Shaped Film Cooling Hole

2009 ◽  
Author(s):  
James S. Porter ◽  
Alan D. Henderson ◽  
Gregory J. Walker
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Velocity Ratio ◽  
Internal Flow ◽  
Experimental Investigations ◽  
Low Velocity ◽  
Inlet Velocity ◽  
Cooling Hole ◽  
Outlet Flow ◽  
Inlet Conditions

Literature regarding the influence of inlet conditions on cooling hole flows is reviewed. A general failure to fully quantify inlet conditions and an inconsistent terminology for describing them is noted. This paper argues for use of an inlet velocity ratio (IVR) defined as the ratio of the coolant passage velocity to the jet velocity, together with additional parameters required to define the velocity distribution in the coolant supply passage. Large scale experimental investigations of the internal flow field for a laterally expanded 50 times scale fan-shaped hole are presented, together with a computational investigation of the flow, for three inlet velocity ratios. Inlet lip separation causes a jetting effect that extends throughout the length of the cooling hole. A low velocity region of separated fluid exists on the downstream wall of the diffuser which deflects the jetting fluid towards the upstream side of the hole. This effect is most pronounced at low IVR values. The exit velocity profiles and turbulence distributions are highly dependent on the IVR.

Computational Study of Jet-in-Crossflow and Film Cooling Using a New Unsteady-Based Turbulence Model

2005 ◽  
Author(s):  
D. Scott Holloway ◽  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Turbulence Model ◽  
Film Cooling ◽  
Computational Study ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Turbulence Models ◽  
Streamwise Velocity ◽  
Pressure Side ◽  
Good Test ◽  
Jet In Crossflow

This paper documents a computational investigation of the unsteady behavior of jet-in-crossflow applications. Improved prediction of fundamental physics is achieved by implementing a new unsteady, RANS-based turbulence model developed by the authors. Two test cases are examined that match experimental efforts previously documented in the open literature. One is the well-documented normal jet-in-crossflow, and the other is film cooling on the pressure side of a turbine blade. All simulations are three-dimensional, fully converged, and grid-independent. High-quality and high-density grids are constructed using multiple topologies and an unstructured, super-block approach to ensure that numerical viscosity is minimized. Computational domains include the passage, film hole, and coolant supply plenum. Results for the normal jet-in-crossflow are for a density ratio of 1 and velocity ratio of 0.5 and include streamwise velocity profiles and injected flow or “coolant” distribution. The Reynolds number based on the average jet exit velocity and jet diameter is 20,500. This represents a good test case since normal injection is known to exaggerate the key flow mechanisms seen in film-cooling applications. Results for the pressure side film-cooling case include coolant distribution and adiabatic effectiveness for a density and blowing ratio of 2. In addition to the in-house model that incorporates new unsteady physics, CFD simulations utilize standard, RANS-based turbulence models, such as the “realizable” k-ε model. The present study demonstrates the importance of unsteady physics in the prediction of jet-in-crossflow interactions and for film cooling flows that exhibit jet liftoff.

Algebraic Anisotropic Eddy-Viscosity Modeling for Application to Turbulent Film Cooling Flows

2011 ◽  
Author(s):  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Eddy Viscosity ◽  
Viscosity Ratio ◽  
Equation Model ◽  
Wall Region ◽  
Mean Flow ◽  
Film Cooling Effectiveness ◽  
Jet In Crossflow ◽  
Comparison Of The Results

Under-predicting the spanwise spreading of film cooling is a big problem in the film cooling computation. This is mainly due to the incorrect simulation of the spanwise transport of the jet in crossflow by conventional isotropic eddy viscosity turbulent models. An improved algebraic anisotropic eddy viscosity method including both the influence of the wall and the strain of the mean flow field to the anisotropic ratio has been raised by the authors in the paper, referred to as Algebraic Anisotropic Eddy Viscosity (AAEV) method. An equation derived from the algebraic Reynolds stress transport equations is applied to compute the anisotropic eddy-viscosity ratio. The variation of the anisotropic eddy-viscosity ratio is a function of both the dimensionless wall distance and the local mean flow field. This method is applied to the two layer k-ε model with a one-equation model in near-wall region to form a new turbulent model- AAEV k-ε model. The new model is tested for the computation of a flat plate film cooling flow with an inclined row of streamwise injected jets. Comparison of the results between the AAEV k-ε model and two-layer k-ε model with the measured adiabatic film-cooling effectiveness distributions indicates that the AAEV k-ε model can correctly predict the spanwise spreading of the film and reduce the strength of the secondary vortices.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness—Part I: Axial Shaped Holes

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
John W. McClintic ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
Zachary D. Webster
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Turbine Blades ◽  
Lateral Spreading ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Crossflow Velocity ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Injection Rates

The effect of feeding shaped film cooling holes with an internal crossflow is not well understood. Previous studies have shown that internal crossflow reduces film cooling effectiveness from axial shaped holes, but little is known about the mechanisms governing this effect. It was recently shown that the crossflow-to-mainstream velocity ratio is important, but only a few of these crossflow velocity ratios have been studied. This effect is of concern because gas turbine blades typically feature internal passages that feed film cooling holes in this manner. In this study, film cooling effectiveness was measured for a single row of axial shaped cooling holes fed by an internal crossflow with crossflow-to-mainstream velocity ratio varying from 0.2 to 0.6 and jet-to-mainstream velocity ratios varying from 0.3 to 1.7. Experiments were conducted in a low speed flat plate facility at coolant-to-mainstream density ratios of 1.2 and 1.8. It was found that film cooling effectiveness was highly sensitive to crossflow velocity at higher injection rates while it was much less sensitive at lower injection rates. Analysis of the jet shape and lateral spreading found that certain jet characteristic parameters scale well with the crossflow-to-coolant jet velocity ratio, demonstrating that the crossflow effect is governed by how coolant enters the film cooling holes.

Cavitation about a jet in crossflow

2015 ◽  
Vol 768 ◽  
pp. 141-174 ◽  
Author(s):  
P. A. Brandner ◽  
B. W. Pearce ◽  
K. L. de Graaf
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
High Speed ◽  
Velocity Ratio ◽  
Cavitation Number ◽  
Variable Pressure ◽  
Lower Velocity ◽  
Freestream Velocity ◽  
Jet In Crossflow ◽  
Cavity Closure

Cavitation occurrence about a jet in crossflow is investigated experimentally in a variable-pressure water tunnel using still and high-speed photography. The 0.012 m diameter jet is injected on the centreplane of a 0.6 m square test section at jet to freestream velocity ratios ranging from 0.2 to 1.6, corresponding to jet-velocity-based Reynolds numbers of $25\times 10^{3}$ to $160\times 10^{3}$ respectively. Measurements were made at a fixed freestream-based Reynolds number, for which the ratio of the undisturbed boundary layer thickness to jet diameter is 1.18. The cavitation number was varied from inception (up to about 10) down to 0.1. Inception is investigated acoustically for bounding cases of high and low susceptibility to phase change. The influence of velocity ratio and cavitation number on cavity topology and geometry are quantified from the photography. High-speed photographic recordings made at 6 kHz provide insight into cavity dynamics, and derived time series of spatially averaged pixel intensities enable frequency analysis of coherent phenomena. Cavitation inception was found to occur in the high-shear regions either side of the exiting jet and to be of an intermittent nature, increasing in occurrence and duration from 0 to 100 % probability with decreasing cavitation number or increasing jet to freestream velocity ratio. The frequency and duration of individual events strongly depends on the cavitation nuclei supply within the approaching boundary layer. Macroscopic cavitation develops downstream of the jet with reduction of the cavitation number beyond inception, the length of which has a power-law dependence on the cavitation number and a linear dependence on the jet to freestream velocity ratio. The cavity closure develops a re-entrant jet with increase in length forming a standing wave within the cavity. For sufficiently low cavitation numbers the projection of the re-entrant jet fluid no longer reaches the cavity leading edge, analogous to supercavitation forming about solid cavitators. Hairpin-shaped vortices are coherently shed from the cavity closure via mechanisms of shear-layer roll-up similar to those shed from protuberances and jets in crossflow in single-phase flows. These vortices are shed at an apparently constant frequency, independent of the jet to freestream velocity ratio but decreasing in frequency with reducing cavitation number and cavity volume growth. Highly coherent cavitating vortices form along the leading part of the cavity due to instability of the jet upstream shear layer for jet to freestream velocity ratios greater than about 0.8. These vortices are cancelled and condense as they approach the trailing edge in the shear layer of opposing vorticity associated with the cavity closure and the hairpin vortex formation. For lower velocity ratios, where there is decreased jet penetration, the jet upstream shear velocity gradient reverses and vortices of the opposite sense form, randomly modulated by boundary layer turbulence.

scholarly journals Experiments on a jet in a crossflow in the low-velocity-ratio regime

2019 ◽  
Vol 863 ◽  
pp. 386-406 ◽  
Author(s):  
L. Klotz ◽  
K. Gumowski ◽  
J. E. Wesfreid
Keyword(s):  
Spatial Dependence ◽  
Velocity Ratio ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Threshold Values ◽  
Low Velocity ◽  
Landau Model ◽  
Global Behaviour ◽  
Crossflow Velocity ◽  
Ratio Range

The hairpin instability of a jet in a crossflow (JICF) for a low jet-to-crossflow velocity ratio is investigated experimentally for a velocity ratio range of $R\in (0.14,0.75)$ and crossflow Reynolds numbers $Re_{D}\in (260,640)$. From spectral analysis we characterize the Strouhal number and amplitude of the hairpin instability as a function of $R$ and $Re_{D}$. We demonstrate that the dynamics of the hairpins is well described by the Landau model, and, hence, that the instability occurs through Hopf bifurcation, similarly to other hydrodynamical oscillators such as wake behind different bluff bodies. Using the Landau model, we determine the precise threshold values of hairpin shedding. We also study the spatial dependence of this hydrodynamical instability, which shows a global behaviour.

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