Blade Coolant Passage Research Articles

가스터빈 블레이드 핀-휜 내부 냉각 유로에 분절핀 설치에 따른 바닥면 유동 및 열전달 특성

가스터빈 블레이드 핀-휜 내부 냉각 유로에 분절핀 설치에 따른 바닥면 유동 및 열전달 특성

Geometric Optimization of a Gas Turbine Blade Cooling Passage using CFD

This work focuses on the rib-turbulated cooling which is a category of impingement cooling and aims at optimizing the geometry of rib-roughened cooling passage of a gas turbine blade. CFD analysis is carried out using Ansys/Fluent to solve the steady RANS equations. Computational domain consists of a long rectangular channel with the length of the channel being 9 times its height. Ratios of rib width, rib height and rib pitch to hydraulic diameter of the channel are taken as 0.1, 0.1 and 1.2, respectively. Numerical simulations are performed to analyze the performance of various rib shapes for Reynolds number, based upon the hydraulic diameter, in a range of 5000 to 50,000. Uniform heat flux of 800 W/m2 is applied to the ribbed wall. Incompressible air is used as the cooling fluid. Turbulent flow conditions are applied to the channel geometry with k-ω turbulence model. The effect of rib cross-section and rib pitch to rib width ratio on the heat transfer and friction factor is observed. The 2D CFD analysis revealed that the presence of ribs has significant effect on thermo-hydraulic performance of the cooling channel. Introducing square ribs in a smooth channel caused the Nusselt number to increase by two-folds. The highest value of Nusselt number was achieved by incorporating right-angle triangular ribs which caused the Nusselt number to increase by further 8%, as compared to the square ribs, and an increase in friction factor of 2.5%. The lowest value of friction factor was observed in semicircular ribs (2.95% less than the square ribs), however, the Nusselt number also decreased by 1.5%, as compared to square ribs. Decreasing rib pitch to rib width ratio increased both the Nusselt number and friction factor for all the cases. For square ribs, decreasing this ratio from 15 to 9 resulted in the rise of Nusselt number by 50% and increase in friction factor by 54%.

Heat Transfer in a Rotating, Blade-Shaped Serpentine Cooling Passage With Discrete Ribbed Walls at High Reynolds Numbers

Abstract This paper experimentally investigates the effect of rotation on heat transfer in a typical turbine blade, three-pass, serpentine coolant channel with discrete ribbed walls at high Reynolds numbers. To achieve the high Reynolds number (Re → 190,000) and low rotation number conditions, pressurized Freon R-134a vapor is utilized as the working fluid. Cooling flow in the first passage is radial outward; after the 180 deg tip turn, the flow is radial inward through the second passage; and after the 180 deg hub turn, the flow is radial outward in the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers as low as 0.07 and Reynolds numbers from 85,000 to 187,000 (based on the first passage geometry and flow conditions). Heat transfer coefficients were measured using thermocouples embedded in copper plates to provide regionally averaged heat transfer coefficients. Heat transfer enhancement due to rotation is observed on the first passage, pressure-side with radially outward flow and the second passage, suction-side with radially inward flow, but a reduction in heat transfer is observed on the third passage pressure-side with radially outward flow. In addition, results from the discrete, broken ribs are compared with those from the same serpentine coolant passage with conventional, angled ribbed walls. A significant increase in the heat transfer due to the discrete ribs is observed in the first passage. These results can be useful for understanding real rotor blade coolant passage heat transfer under high Reynolds number and low rotation number conditions.

Heat Transfer in Rotating Serpentine Coolant Passage With Ribbed Walls at Low Mach Numbers

This paper experimentally investigates the effect of rotation on heat transfer in typical turbine blade serpentine coolant passage with ribbed walls at low Mach numbers. To achieve the low Mach number (around 0.01) condition, pressurized Freon R-134a vapor is utilized as the working fluid. The flow in the first passage is radial outward, after the 180 deg tip turn the flow is radial inward to the second passage, and after the 180 deg hub turn the flow is radial outward to the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers up to 0.6 and Reynolds numbers from 30,000 to 70,000. Heat transfer coefficients were measured using the thermocouples-copper-plate-heater regional average method. Heat transfer results are obtained over a wide range of Reynolds numbers and rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Regional heat transfer coefficients are correlated with Reynolds numbers for nonrotation and with rotation numbers for rotating condition, respectively. The results can be useful for understanding real rotor blade coolant passage heat transfer under low Mach number, medium–high Reynolds number, and high rotation number conditions.

Characterization of Failed First-Stage Turbine Blade Cooling Passage of Gas Turbine Engine

The cooling passages of the first-stage high-pressure turbine blades of gas turbine engines are located and drilled at the manufacturing stage. The external wall thickness is a critical blade strength parameter and has to be inspected accurately and regularly when blades are routed through repair work shops. This paper investigates a case of two blades from two different blade sets that experienced cooling passage failure during repair, after serving less than 20,000 operating hours. The investigation covered material microstructure, hardness condition, and material thickness residual assessment, using an ultrasonic nondestructive technique between the first cooling passage and the external blade surface. It was concluded that the first cooling passage was inappropriately drilled during manufacturing.

Effect of Mesh Topologies on Wall Heat Transfer and Pressure Loss Prediction of a Blade Coolant Passage

This paper studies the effect of mesh topologies such as hybrid and structured meshes on the evaluation of wall heat transfer coefficient (HTC) and pressure loss of a blade cooling passage. An experimental model is chosen; it has five-row of stream wise staggered elliptical pin-fin fitted inside a 10owedge-shape duct and one-row of fillet circular pin-fin in the exit region. Simulations consider two types; i.e. warm test with isothermal wall condition and cold test with adiabatic wall condition respectively, in order to evaluate flow and thermal characteristics such as HTC and pressure loss. Further simulations are carried out by varying Re number, wall surfaces roughness, inlet turbulence intensity and turbulence models. It was found that for unstructured or structured mesh with proper near wall and middle passage grid resolutions, CFD predicted HTC and pressure loss are in good agreement with available experimental data. The wall surface roughness is found to have significant impact on HTC, simulations produce results in better agreement with experimental measurements. Simulation results also confirm that inlet turbulence intensity and turbulence model have insignificant effect of predicting the pin-fin wall and end wall heat transfer coefficient.

Review on Heat Transfer Augmentation Techniques: Application in Gas Turbine Blade Internal Cooling

Gas turbines play a vital role in the today’s industrialized society, and as the demands for power increase, the power output and thermal efficiency of gas turbines must also increase. Modern high-speed aero-engines operate at elevated temperatures about 2000 K to achieve better cycle efficiencies. However, the presently available alloys cannot resist temperatures much higher than 1350 K. Internal cooling techniques for gas turbine blades have been studied for several decades. The internal cooling techniques of the gas turbine blade includes: jet impingement, rib turbulated cooling, and pin-fin cooling which have been developed to maintain the metal temperature of turbine vane and blades within acceptable limits in this harsh environment. The designers need detailed hot gas path heat transfer and temperature distributions along with the detailed flow and heat transfer data to understand the flow physics and to improve the current internal cooling designs. Gas turbine blades are cooled internally by passing the coolant through several artificially roughened serpentine passages to remove heat conducted from the outside surface. The cooling passages located in the middle of the airfoils are often lined with rib turbulators. Near the leading edge of the blade, jet impingement (coupled with film cooling) is commonly used. Pin-fins and dimples can be used in the trailing edge portion of the blades. These techniques have also been combined to further increase the heat transfer from the airfoil walls. For internal cooling, focus is now placed on the effect of rotation on rotor blade coolant passage heat transfer. To better understand the complex three-dimensional flow physics in the complicated blade internal coolant passage geometry, the computational flow and heat transfer results are presented and reviewed at improving the internal cooling of gas-turbine blades.

Turbine Blade Cooling Studies at Texas A&M University: 1980-2004

Gas turbines are used extensively for aircraft propulsion, land-based power generation, and industrial applications. Developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced high-temperature gas turbine engines. Gas turbine blades are cooled internally by passing the coolant through several rib-enhanced serpentine passages to remove heat conducted from the outside surface. External cooling of turbine blades by film cooling is achieved by injecting relatively cooler air from the internal coolant passages out of the blade surface to form a protective layer between the blade surface and hot gas-path flow. The most important research contributions on turbine blade cooling studies at Texas A&M University's Turbine Heat Transfer Laboratory from 1980 to 2004 are summarized. For turbine blade internal cooling, the focus is on the effect of rotation on rotor blade coolant passage heat transfer with rib turbulators, pin fins, dimples, and impinging jets. For turbine blade external cooling, the focus is on unsteady high freestream turbulence effects on film-cooling performance with a special emphasis on turbine blade edge region heat transfer and cooling problems.

Turbine Blade Internal Cooling Passages with Rib Turbulators

Gas turbines are extensively used for aircraft propulsion, land-based power generation, and industrial applications. Developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced gas turbines. Gas turbine blades are cooled internally by passing the coolant through several rib-enhanced serpentine passages to remove heat conducted from the outside surface. For internal cooling, focus is placed on the effect of rotation on rotor blade coolant passage heat transfer with rib turbulators. In particular, the most recent publications are covered that deal with the rotational effects on internal cooling passage heat transfer with low and high aspect ratio channels with various high-performance rib geometries. To better understand the complex three-dimensional flow physics in the complicated blade internal coolant passage geometry, the computational flow and heat transfer results are presented and compared using the Reynolds averaged Navier-Stokes method with various turbulence models such as k-e, and second-moment closure models.

Multidimensional Clustering Interpretation and Its Application to Optimization of Coolant Passages of a Turbine Blade

A data-clustering method can be a useful tool for engineering design that is based on numerical optimization. The clustering method is an effective way of producing representative designs, or clusters, from a large set of potential designs. The results presented here focus on the application of clustering to single-objective optimization results. In the case of single-objective optimization, the method is used to determine the clusters in a set of quasi-optimal feasible solutions generated by an optimizer. A data-clustering procedure based on an evolutionary method is briefly described. The number of clusters is determined automatically and need not be known a priori. The method is demonstrated by application to the results of a turbine blade coolant passage shape-optimization problem. The solutions are transformed to a lower-dimensional space for better understanding of their variance and character. Engineering information, such as the shapes and locations of the internal passages, is supported by the visualization of clustered solutions. The clustering, transformation, and visualization methods presented in this study might be applicable to the increasing interpretation demands of design optimization.

Recent Studies in Turbine Blade Cooling

Gas turbines are used extensively for aircraft propulsion, land‐based power generation, and industrial applications. Developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced gas turbines. Gas turbine blades are cooled internally by passing the coolant through several rib‐enhanced serpentine passages to remove heat conducted from the outside surface. External cooling of turbine blades by film cooling is achieved by injecting relatively cooler air from the internal coolant passages out of the blade surface in order to form a protective layer between the blade surface and hot gas‐path flow. For internal cooling, this presentation focuses on the effect of rotation on rotor blade coolant passage heat transfer with rib turbulators and impinging jets. The computational flow and heat transfer results are also presented and compared to experimental data using the RANS method with various turbulence models such as k‐ε, and second‐moment closure models. This presentation includes unsteady high free‐stream turbulence effects on film cooling performance with a discussion of detailed heat transfer coef‐ ficient and film‐cooling effectiveness distributions for standard and shaped film‐hole geometry using the newly developed transient liquid crystal image method.

Comparisons of High-Reynolds-Number EVM and DSM Models in the Prediction of Heat and Fluid Flow of Turbine Blade Cooling Passages

This paper presents computations of flow and heat transfer through passages relevant to those used to internally cool gas-turbine blades, using high-Reynolds-number models of turbulence. Three types of internal flows are first examined, which between them contain all the main elements found in blade cooling passages; developing flow through a heated straight duct rotating orthogonally, repeating flow and heat transfer through a straight ribbed duct and flow and heat transfer through a round-ended U-bend of strong curvature square and of cross-section. Next, flows influenced by a combination of these elements are computed. The main objective is to establish how reliably, industry-standard high-Reynolds-number models can predict flow and wall-heat transfer in blade-cooling passages. Two high-Reynolds-number models have been used, the standard version of the high-Re k-ε (EVM) model and the basic high-Re model of stress transport (DSM). In all the cases the second-moment closure (DSM) consistently produced flow and thermal predictions that are closer to available measurements than those of the EVM model. Even the high-Re DSM predictions, however, are not in complete agreement with the experimental data. Comparisons with predictions of earlier studies that use low-Re models of turbulence show that at least some of the remaining differences between the current predictions and experimental data are due to the use of the wall-function approach.

An experimental study of a rib-roughened rotating U-bend flow

Abstract In this paper we report an experimental investigation of turbulent flow through a square-sectioned U-bend of strong curvature, in which the inner and outer walls of the upstream and downstream sections are artificially roughened with square ribs, in a staggered arrangement. The U-bend is either stationary or rotates about an axis parallel to that of curvature, with positive rates, i.e. so that the secondary flows provoked by curvature and rotation are in the same sense. The main objective is to provide CFD validation data for flows which contain most of the flow features encountered in blade-cooling passages, but which are numerically easier to compute, while retaining the modelling challenges provided by a real gas-turbine blade. In earlier investigations we showed that the introduction of ribs in the upstream and downstream sections: (a) raises overall turbulence levels; (b) reduces the size of the separation bubble formed along the inner wall of the U-bend and (c) causes the formation of a large separation bubble along the outer wall, as the flow encounters the first outer-wall rib, after the bend exit. Here we: (a) explore how the location of the first outer-wall rib, after the bend exit, affects the development of the downstream flow and (b) focus on the three-dimensional character of these flows, by providing data along a plane close to the top (flat) wall, in addition to data along the duct symmetry plane. We show that, for both stationary and rotating conditions, as the first outer-wall rib is moved further away from the bend exit, the size of the separation bubble along the outer wall is reduced. The separation bubble along the inner wall, however, increases in size but, overall, turbulence levels are reduced. The flow within and immediately downstream of the U-bend is highly three-dimensional, showing strong variations from the symmetry plane to the top wall. Rotation generates the expected secondary motion in the straight sections that, at the duct centre, convects the faster fluid towards the pressure side, and along the top and bottom (flat) walls, has the opposite effect. Within and downstream of the bend, positive rotation reduces the three-dimensionality of the flow.

Recent progress in the computation of flow and heat transfer in internal cooling passages of turbine blades

Abstract This paper describes our efforts to compute convective heat transfer through gas-turbine blade-cooling passages. The influence on the mean and turbulent flow due to surface rib-roughness is the main focus. A number of turbulence models, of effective viscosity (EVM) and second-moment type, are applied to the computation of flow and heat transfer through ribbed-roughened passages. Computations of flow through a rib-roughened U-bend show that second moment closures are necessary in order to correctly reproduce the regions of flow separation. Heat transfer computations through two-and also three-dimensional ribbed passages reveal that low-Re turbulence models are necessary and that a low-Re differential stress closure yields thermal predictions that are superior to those of the low-Re EVM model. A differential version of the Yap length-scale correction term, independent of the wall distance, is introduced to the dissipation rate equation and is found to improve the heat transfer predictions of the low-Re k−ϵ model.

Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib Turbulator

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large-scale structures, and that the dynamics of the large-scale structures, associated with sweep, ejection, and inward and outward interactions, all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important, accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.

Preface

This ninth volume of the serial publication, Annual Review of Heat Transfer, continues the fine tradition of providing improved communication on new, important developments in the general field of heat transfer. As in previous volumes, each chapter in the Annual Review deals with a significant, emerging topic by starting from fundamental physical considerations and then proceeding in a logical fashion to the forefront of recent developments and future challenges. The contributing authors are either young but upcoming, or well-established leaders in these emerging fields. A list of the topics covered in the past two volumes illustrates well this special characteristic of the Annual Review. Volume 7 contained excellent chapters on significant, but wide-ranging heat transfer research and developments in micro- and nano-scale optical and optoelectronic devices, growth of dendritic crystals, polymeric composite processing, active enhancement using electric field, direct-contact transfer with droplets, clean-up of underground toxic wastes, and fluidized beds, while Volume 8 considered such important topics as heat transfer in microelectronics, Rayleigh-Bénard convection, aerodynamics of flame surfaces, radiative transfer in non-isothermal inhomogeneous media, heat pipe analysis and simulation, and high heat flux spray cooling. Continuing with this tradition, the present volume provides informative chapters on bioheat transfer, large scale surface radiative transport, radiative transfer in fibrous media, combustion in porous media, turbine blade coolant passage heat transfer, external flow film boiling, heat transfer in oscillatory flows, and two-dimensional annular flow. The editor is deeply grateful to the participating authors for their excellent contributions, to Begell House for providing invaluable editorial assistance, and to the heat transfer community for its continuing support and input.

LDA Investigation of the Flow Development Through Rotating U-Ducts

This paper reports results from the use of laser-Doppler anemometry (LDA) to measure the mean and fluctuating flow field in a U-bend of strong curvature, Rc/D = 0.65, that is either stationary or rotating in orthogonal mode (the axis of rotation being parallel to the axis of curvature). The data acquisition system enables a stationary optical fiber probe to collect flow data from a rotating U-bend sweeping past it. Three cases have been examined, all concerning a flow Reynolds number of 100,000; a stationary case, a case of positive rotation (the pressure side of the duct coincides with the outer side of the U-bend) at a rotational number (ΩD/Um) of 0.2, and a case of negative rotation at a rotational number of −0.2. Measurements have been obtained along the symmetry plane of the duct and also along a plane near the top wall. The most important influence on the development of the mean and turbulence flow fields is exerted by the streamwise pressure gradients that occur over the entry and exit regions of the U-bend. In the stationary case a three-dimensional separation bubble is formed along the inner wall at the 90 deg location and it extends to about two diameters downstream of the bend, causing the generation of high-turbulence levels. Along the outer side, opposite the separation bubble, turbulence levels are suppressed due to streamwise flow acceleration. For the rotation numbers examined, the Coriolis force also has a significant effect on the flow development. Positive rotation doubles the length of the separation bubble and generally suppresses turbulence levels. Negative rotation causes an extra separation bubble at the bend entry, raises turbulence levels within and downstream of the bend, increases velocity fluctuations in the cross-duct direction within the bend, and generates strong secondary motion after the bend exit. It is hoped that the detailed information produced in this study will assist in the development of turbulence models suitable for the numerical computation of flow and heat transfer inside blade-cooling passages.

Preswirl Blade-Cooling Effectiveness in an Adiabatic Rotor–Stator System

Blade-cooling air for a high-pressure turbine is often supplied from preswirl nozzles attached to a stationary casing. By swirling the cooling air in the direction of rotation of the turbine disk, the temperature of the air relative to the blades can be reduced. The question addressed in this paper is: Knowing the temperatures of the preswirl and disk-cooling flows, what is the temperature of the blade-cooling air? A simple theoretical model, based on the Reynolds analogy applied to an adiabatic rotor–stator system, is used to calculate the preswirl effectiveness (that is, the reduction in the temperature of the blade-cooling air as a result of preswirling the flow). A mixing model is used to account for the “contamination” of the blade coolant with disk-cooling air, and an approximate solution is used to estimate the effect of frictional heating on the disk-cooling air. Experiments were conducted in a rotor–stator rig that had preswirl nozzles in the stator and blade-cooling passages in the rotating disk. A radial outflow or inflow of disk-cooling air was also supplied, and measurements of the temperature difference between the preswirl and blade-cooling air were made for a range of flow rates and for rotational Reynolds numbers up to Reθ = 1.8 × 106. Considering the experimental errors in measuring the small temperature differences, good agreement between theory and experiment was achieved.