LES Informed Data-Driven Modelling of a Spatially Varying Turbulent Diffusivity Coefficient in Film Cooling Flows

2021 ◽  
Author(s):  
Christopher Ellis ◽  
Hao Xia ◽  
Gary Page
Keyword(s):  
Film Cooling ◽  
Data Driven ◽  
Diffusivity Coefficient ◽  
Turbulent Diffusivity ◽  
Cooling Flows ◽  
Spatially Varying

LES Informed Data-Driven Modelling of a Spatially Varying Turbulent Diffusivity Coefficient in Film Cooling Flows

2020 ◽  
Author(s):  
Christopher D. Ellis ◽  
Hao Xia ◽  
Gary J. Page
Keyword(s):  
Random Forests ◽  
Film Cooling ◽  
Turbulent Heat Flux ◽  
Data Driven ◽  
Turbulent Heat ◽  
Diffusivity Coefficient ◽  
Turbulent Diffusivity ◽  
Cooling Flows ◽  
Gradient Diffusion ◽  
Spatially Varying

Abstract A novel data-driven approach is used to describe a spatially varying turbulent diffusivity coefficient for the Higher Order Generalised Gradient Diffusion Hypothesis (HOGGDH) closure of the turbulent heat flux to improve upon RANS cooling predictions in film cooling flows. Machine learning algorithms are trained on two film cooling flows and tested on a case of a different density and blowing ratio. The Random Forests and Neural Network algorithms successfully reproduced the LES described coefficient and the magnitude of the turbulent heat flux vector. The Random Forests model was implemented in a steady RANS solver with a k-ω SST turbulence model and applied to four cases. All cases saw improvements in the predicted Adiabatic Cooling Effectiveness (ACE) over the cooled surface compared to the standard Gradient Diffusion Hypothesis (GDH) approach, but only minor improvements in the centreline and lateral spread are seen compared to a HOGGDH model with a constant cθ of 0.6. Further improvements to cooling predictions are highlighted by extending these data-driven approaches into turbulence modelling to improve flow field predictions.

scholarly journals A Machine Learning Approach for Determining the Turbulent Diffusivity in Film Cooling Flows

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Pedro M. Milani ◽  
Julia Ling ◽  
Gonzalo Saez-Mischlich ◽  
Julien Bodart ◽  
John K. Eaton
Keyword(s):  
Machine Learning ◽  
Film Cooling ◽  
Turbulent Heat Flux ◽  
Navier Stokes ◽  
Data Sets ◽  
Turbulent Heat ◽  
Turbulent Diffusivity ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Novel Approach

In film cooling flows, it is important to know the temperature distribution resulting from the interaction between a hot main flow and a cooler jet. However, current Reynolds-averaged Navier–Stokes (RANS) models yield poor temperature predictions. A novel approach for RANS modeling of the turbulent heat flux is proposed, in which the simple gradient diffusion hypothesis (GDH) is assumed and a machine learning (ML) algorithm is used to infer an improved turbulent diffusivity field. This approach is implemented using three distinct data sets: two are used to train the model and the third is used for validation. The results show that the proposed method produces significant improvement compared to the common RANS closure, especially in the prediction of film cooling effectiveness.

scholarly journals A Machine Learning Approach for Determining the Turbulent Diffusivity in Film Cooling Flows

2017 ◽  
Author(s):  
Pedro M. Milani ◽  
Julia Ling ◽  
Gonzalo Saez-Mischlich ◽  
Julien Bodart ◽  
John K. Eaton
Keyword(s):  
Machine Learning ◽  
Film Cooling ◽  
Learning Algorithm ◽  
Turbulent Heat Flux ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Turbulent Diffusivity ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Novel Approach

In film cooling flows, it is important to know the temperature distribution resulting from the interaction between a hot main flow and a cooler jet. However, current Reynolds-averaged Navier-Stokes (RANS) models yield poor temperature predictions. A novel approach for RANS modeling of the turbulent heat flux is proposed, in which the simple gradient diffusion hypothesis (GDH) is assumed and a machine learning algorithm is used to infer an improved turbulent diffusivity field. This approach is implemented using three distinct data sets: two are used to train the model and the third is used for validation. The results show that the proposed method produces significant improvement compared to the common RANS closure, especially in the prediction of film cooling effectiveness.

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.

Application of a CFD-Based Film Cooling Model to a Gas Turbine Vane Cascade With Cylindrical and Shaped Hole Endwall Film Cooling

2011 ◽  
Author(s):  
Tilman auf dem Kampe ◽  
Stefan Vo¨lker
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Cooling Flows ◽  
Turbine Vane ◽  
Mesh Resolution ◽  
Shaped Hole ◽  
Node Count ◽  
Endwall Film Cooling ◽  
Cooling Model ◽  
Near Wall

This paper presents the application of a CFD-based film cooling model to a gas turbine vane cascade test rig. The experimental investigations feature aerodynamic and endwall film cooling measurements on a first stage gas turbine vane in a linear cascade. An extended version of a previously developed cylindrical hole film cooling model has been employed, which now includes modeling of shaped hole cooling flows. The computational domain extends approximately one axial chord length upstream of the leading edge and downstream of the trailing edge of the vane. Adjacent solid parts are included by means of a conjugate heat transfer analysis to account for conduction effects. A hybrid mesh with resolved boundary layers and high spatial mesh resolution in the near-wall region is being used. This meshing approach ensures that the near-wall mesh resolution requirements of the film cooling model are satisfied, while maintaining a manageable total node count. Results obtained using the film cooling model are compared to surface distributions of film cooling effectiveness from the experimental cascade. Due to the moderate node count (≈ 3.5 × 106), CFD calculations including film cooling flows can be performed at comparatively low computational cost. The film cooling model, which previously had been validated against flat plate measurement data and applied to single cooling hole configurations only, is therefore shown to be a viable tool for the thermal design of gas turbine components with film cooling.

Conjugate heat transfer analysis of film cooling flows

2006 ◽  
Vol 15 (1) ◽  
pp. 85-91 ◽  
Author(s):  
Xiaochen Lu ◽  
Peixue Jiang ◽  
Hideaki Sugishita ◽  
Hideyuki Uechi ◽  
Kiyoshi Suenaga
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Heat Transfer Analysis ◽  
Cooling Flows

scholarly journals The Superposition Approach to Local Heat Transfer Coefficients in High Density Ratio Film Cooling Flows

1999 ◽  
Author(s):  
Michael Gritsch ◽  
Stefan Baldauf ◽  
Moritz Martiny ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Cooling Flows ◽  
Heat Transfer Coefficients ◽  
High Density Ratio ◽  
The Heat Transfer Coefficient

The present paper reports on the use of the superposition approach in high density ratio film cooling flows. It arises from the linearity and homogeneity of the simplified boundary layer differential equations. However, it is widely assumed that the linearity does not hold for variable property flows. Therefore, theoretical considerations and numerical calculations will demonstrate the linearity of the heat transfer coefficient with the dimensionless coolant temperature θ as long as identical flow conditions are applied. This makes it necessary to perform at least two experiments at different θ but with the coolant to main flow temperature ratio kept unchanged. A comprehensive set of experiments is presented to demonstrate the capability of the superposition approach for determining heat transfer coefficients for different film cooling geometries. These comprise coolant injection from two dimensional tangential slots, single holes, and rows of cylindrical holes. Particularly, two dimensional local distributions of the heat transfer coefficient will be addressed.

Turbine Cooling Systems Design: Past, Present and Future

2009 ◽  
Author(s):  
James P. Downs ◽  
Kenneth K. Landis
Keyword(s):  
Research And Development ◽  
Film Cooling ◽  
Gas Turbines ◽  
State Of The Art ◽  
Cooling System ◽  
Systems Design ◽  
Maximum Temperature ◽  
Cooling Systems ◽  
Cooling Flows ◽  
Turbine Cooling

Over a half a century ago, the power and performance of the first gas turbine engines were constrained by material limits on operating temperature. In these machines, the combustor exit temperature could not exceed the capability of the materials used to construct the turbine. Eventually, cooling was introduced into turbine components to enable turbine power and efficiency to be increased. That revolutionary step enabled gas turbines to become competitive with other heat engines for business, particularly in the rapidly expanding aviation and electrical power generation sectors. Although the first cooled turbine components may be considered crude by present standards, the underlying foundation of internal convection cooling remains the backbone for cooled turbine components today. Since its introduction, many improvements and additions to the fundamental basis of turbine component cooling have been developed. The introduction of film cooling is a prominent example. With this past research and development, turbine cooling system designs have progressed to the point where they represent the norm, rather than the exception in today’s gas turbines. Further, the confidence and robustness of these systems has been elevated to the point where the working fluid temperatures can exceed the maximum temperature of the structural materials by wide margins. In this paper, from an engineering perspective, we explore some of the significant accomplishments that have led to the current state-of-the-art in turbine cooling systems design. These systems employ a delicate balance of structural material capabilities with advanced internal and film cooling and the use of thermal barrier coatings to satisfy the goals and objectives of specific applications. At the same time, it is widely recognized that the use of cooling flows in the turbine results in parasitic losses that reduce performance. To that end, we also consider some of the specific challenges that face cooling system designers to reduce cooling flows today. Based on the research and development that has been performed to date, we consider the current status of cooling technology relative to a theoretical peak. Finally, we explore some of the hurdles that must be overcome to effectively raise the bar and realize future advancement of the state-of-the-art. The goal is to measure and separate new technologies that are merely different from those that are superior to past designs. Clearly, the identification of risk and risk reduction will play an important role in the development of future turbine cooling systems.

Investigation of Steady and Unsteady Film-Cooling Using Immersed Mesh Blocks With New Conservative Interface Scheme

2016 ◽  
Author(s):  
Y. Jiang ◽  
L. He ◽  
L. Capone ◽  
E. Romero
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Computational Modelling ◽  
Length Scales ◽  
Cooling Flows ◽  
Cooling Flow ◽  
Mainstream Flow ◽  
Design Analyses ◽  
First Time ◽  
Advanced Development

Advanced development of high pressure turbines requires accurate predictions of film cooling flow. However, the length scales inherent to film cooling flows produce a large disparity compared to those of the mainstream flow field. To address this computational modelling challenge, an immersed mesh block (IMB) methodology has been initiated (Lad and He, 2011) which uses the much refined mesh around cooling holes to be mapped into the base mesh which tends to be much coarser for blade aerodynamic designs. Both the base mesh flow field and that of the IMB are solved simultaneously. By employing a simultaneous two-way coupling, the flow physics in and around cooling holes is able to interact with the mainstream, hence the length scales of both types of flow, as well as their interactions, are appropriately captured and resolved. The present work is aimed to develop a new numerical scheme for enforcing conservation at the interfacing boundary between the immersed cooling block and the base mesh, as well as, carry out a systematic validation and application of the IMB method for some well-established film-cooling experimental configurations (cylindrical and fan-shaped holes) at different blowing ratios. During the validation process, the mesh counts/resolution requirements for consistent cooling predictions for design analyses are established. The method is then applied to a transonic HPT stage. Its steady and unsteady flows are investigated. The results consistently demonstrate the effectiveness and applicability of the conservative IMB method, and indicate, for the first time, some interesting and relevant unsteady film-cooling behaviour.

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