Coolant Flow Passage Research Articles

CFD Simulation of Heat Transfer Characteristics in a Rectangular Duct with Trapezoidal Turbulence Promoters

The heat transfer rate from the hot surface to the coolant flow increases by placing the ribs on the surface of the coolant flow passage. The effect of turbulence promoters with different angle of attack and with a fixed tapered angle on the heat transfer characteristics in a rectangular stationary duct is considered for this study. Here turbulence promoters increase the heat transfer in the duct. The examination has been conducted on the rectangular smooth duct and rectangular duct with inverted V-shaped ribs of a different angle of attack. The rib angle attack of 45º, 60º, 90º and tapered angle 20º (fixed) on the top surface of the rib are considered. The rib blockage ratio and pitch ratio are 0.0553 and 10 respectively. The heat transfer characteristics are compared with Reynolds number of 6000. The heat transfer and computational flow analysis are conducted by k-epsilon turbulence model in ANSYS FLUENT. The tapered angled cross-sectional inverted V-shaped ribs of 60º shown high average heat transfer coefficients among the 45º, 60º and 90º smooth duct.

Flow Non-Uniformity and Secondary Flow Characteristics Within a Serpentine Cooling Channel of a Realistic Gas Turbine Blade

Abstract Unlike the ideal conditions considered in most previous studies, the actual cooling flow passage inside gas turbine blades is extremely complex. This complexity is due to the geometrical restrictions resulting from the external cooling holes and blade shape, which change the secondary flow and flow non-uniformity of the internal cooling flow. This study conducted an experimental and numerical analysis to characterize the secondary flow and flow non-uniformity in a realistic internal cooling serpentine passage. Magnetic resonance velocimetry was utilized to measure the average three-dimensional–three-components of the mean velocity. By integrating the flow field, parameters indicating the flow non-uniformity and secondary flow strength were obtained. Reynolds-averaged Navier–Stokes simulations were also conducted, and the Reynolds stress transport model showed relatively good performance when predicting the separation bubble in the U-bend. The secondary flow intensity exponentially decreases after the U-bend, but the rib turbulators maintain the secondary flow at a certain level. Additionally, the high-velocity regions in the inlet zone and beyond the separation bubble create significant flow non-uniformity and inherent shear. At the same time, the turbulence intensity becomes strong at the low-velocity region, which is key for heat transfer enhancement. Therefore, high flow non-uniformity has the potential to enhance heat transfer.

АНАЛІЗ СИСТЕМИ ОБДУВУ ДИСКІВ ОСЬОВОЇ ЧОТИРИСТУПЕНЕВОЇ ВІЛЬНОЇ ТУРБІНИ НА ОСНОВІ МОДЕЛЮВАННЯ ТЕПЛОГІДРАВЛІЧНОГО СТАНУ

A hydraulic analysis of four stage axial power turbine cooling system was performed. A practical application of the existing algorithms of thermal-hydraulic analysis is considered. Reasonable flow-rate distribution among the cooling channels and cooling system air leakage waste reduction are discussed. An implementation of the rotor screen dividing rotor internal cavity into disk and shaft cavities is revealed as the best way to keep the flow-rate balance of cooling air in account of achievement simplicity.This paper also covers a key design concept that the structure of turbine shall be such as to promote good dissipation of heat from blades to disks by means of air flow passing through special channels between rotor parts.A turbine disks’ air-cooling system assessment importance is shown according to the aim of hot gas ingress prevention. It is given a brief description of known theoretical fundamentals on which the used thermal-hydraulic analysis computational method of modeling was based.Flow-rate distribution among the four stage axial power turbine disks’ air-cooling system is noted to be carried out by certain basic design choices such as labyrinth seals, fins and ledges. The most important factors on which the flow-rate distribution depends on are mentioned including a ratio of narrow section hydraulic area to channel section hydraulic area, hydraulic resistance and availability of centrifugal pressure between disks.Narrowing of cooling flow passage section causes air velocity increase and pressure reduction. Even though some recovery of velocity appears downstream the narrowing element, the pressure value changes its magnitude due to vortex losses. Therefore it makes possible to provide the required air distribution.The considered rotor screen structure confirmed its functionality in operating gas turbine plant and it is stated as achieved results. Numeral details of dealt analysis are omitted.Generally, the behavior of flow and heat exchange in area between rotating disks is classified as rather complicated and methods of its modeling are summarized to remain relevant question of further studies.

Characteristics of Volcanic Ash in a Gas Turbine Combustor and Nozzle Guide Vanes

To understand the physics of volcanic ash impact on gas turbine hot-components and develop much-needed tools for engine design and fleet management, the behaviors of volcanic ash in a gas turbine combustor and nozzle guide vanes (NGV) have been numerically investigated. High-fidelity numerical models are generated, and volcanic ash sample, physical, and thermal properties are identified. A simple critical particle viscosity—critical wall temperature model is proposed and implemented in all simulations to account for ash particles bouncing off or sticking on metal walls. The results indicate that due to the particle inertia and combustor geometry, the volcanic ash concentration in the NGV cooling passage generally increases with ash size and density, and is less sensitive to inlet velocity. It can reach three times as high as that at the air inlet for the engine conditions and ash properties investigated. More importantly, a large number of the ash particles entering the NGV cooling chamber are trapped in the cooling flow passage for all four turbine inlet temperature conditions. This may reveal another volcanic ash damage mechanism originated from engine cooling flow passage. Finally, some suggestions are recommended for further research and development in this challenging field. To the best of our knowledge, it is the first study on detailed ash behaviors inside practical gas turbine hot-components in the open literature.

Thermal Behavior of Radial Foil Bearings Supporting an Oil-Free Gas Turbine: Design of the Cooling Flow Passage and Modeling of the Thermal System

Gas foil bearings (GFBs) have many noticeable advantages over the conventional rigid gas bearings, such as frictional damping of the compliance structure and tolerance to the rotor misalignment, so they have been successfully adopted as the key element that makes possible oil-free turbomachinery. As the adoption of the GFB increases, one of the critical elements for its successful implementation is thermal management. Even though heat generation inside the GFB is small due to the low viscosity of the lubricant, many researchers have reported that the system might fail without an appropriate cooling mechanism. The objective of the current research is to demonstrate the reliability of GFBs installed in the hot section of a micro-gas turbine (MGT). For the cooling of the GFBs, we designed a secondary flow passage and thermohydrodynamic (THD) analysis has been done for temperature prediction. In the analysis, the 3D THD model for the radial GFB extended to include the surrounding structure, such as the plenum, chamber, and the rotor in the solution domain by solving global mass and energy balance equations. In the MGT, the pressurized air discharged from the compressor wheel was used as the cooling air source, and it was injected into the plenum between two radial GFBs. We monitored the pressure and temperature of the cooling air along the secondary flow passage during the MGT operation. No thermal instability occurred up to the maximum operation speed of 43,000 rpm. The test results also showed that the pressure drop between the main reservoir and the plenum increases with an increasing operation speed, which indicated an increased cooling air flow into the plenum. The plenum and bearing sleeve temperature was maintained close to the cooling air source temperature for the entire speed due to a sufficient cooling air flow into the bearing. In addition, the direct injection of the cooling air from the main stream lowered the bearing sleeve temperature by 5–20 °C over the injection through the reservoirs. The predicted plenum and bearing sleeve temperatures with the developed THD model show good agreement with the test data.

스크류 압축기 냉각유로 형상 변화가 열유동 특성에 미치는 영향

The thermal-flow characteristics of screw compressor were numerically investigated with various geometrical configurations of its coolant flow passage applied to the separate block for enhancing the heat transfer performance of it. The length ratio(Ls/D=4.8, 5.6, 6.4) and thickness ratio(t/D=0.2, 0.4, 0.6) of the separate block in the flow passage of the water jacket were adopted to design parameters. Results showed that the pressure drop and heat transfer were increased as the length of separate block increases due to the flow separation and centrifugal force. The results were graphically depicted with various flow and geometrical conditions.

Conjugate Heat Transfer of an Internally Air-Cooled Nozzle Guide Vane and Shrouds

In order to assess the life of gas turbine critical components, it is essential to adequately specify their aerothermodynamic working environments. Steady-state analyses of the flow field and conjugate heat transfer of an internally air-cooled nozzle guide vane (NGV) and shrouds of a gas turbine engine at baseline operating conditions are numerically investigated. A high-fidelity CFD model is generated and the simulations are carried out with properly defined boundary conditions. The features of the complicated flow and temperature fields are revealed. In general, the Mach number is lower and the temperature is higher on the NGV pressure side than those on the suction side. There are two high temperature regions on the pressure side, and the temperature across the middle section is relatively low. These findings are closely related to the locations of the holes and outlets of the cooling flow passage, and consistent with the field observations of damaged NGVs. As a technology demonstration, the results provide required information for the life analysis of the NGV/shrouds assembly and improvement of the cooling flow arrangement.

0420 実機ガスタービン第一段動翼を対象とした共役熱伝達解析(OS4-4 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

Conjugate heat transfer simulations were conducted for the first stage rotor blade in an actual gas turbine and compared with experimental results. The objectives of this research are to validate prediction accuracy of temperature distribution on the rotor blade surface and find key factors to improve the prediction accuracy. These simulations were carried out at the similar condition as gas turbine operation. Temperature distributions predicted by the simulations reasonably agreed with those of the experiment near the rotor leading edge part. However, temperature distribution on the pressure side was different between the simulation and experiment. In the internal cooling flow passage, main stream leans toward one side of walls due to Coriolis force and the temperature on this side became lower than the experimental results. It is important for obtaining better prediction accuracy of heat transfer to solve the complex flow phenomena caused by several vortices generated by rotation, flow turning, or the rib-turbulator in the internal cooling flow region.

Head and block split cooling in ICE

The driver of the future engine technology will be the reduction of the CO2 emissions which looks straightforward to fuel consumption saving. The fulfillment of primary pollutants emission levels requested by EURO 6, LEV III or Japanese standards would still add a new innovation stimulus, but the main concept is a more efficient vehicle.Among the more interesting technologies, those related to a revision of the engine cooling, as well as, more generally, those oriented to fulfill the overall vehicle thermal needs appear very promising in terms of expected fuel saving performances. They have an additional advantage related to the low vehicle's cost increase per unit of CO2 saved (or fuel saved). Thermal management is the common way to present such a technological interest and it resumes many innovations based on the idea that a vehicle is a system and all the thermal needs (of the engine and of the vehicle) should be optimized looking at the overall system and not at specific aspects.One of the main goal of thermal management is to decrease engine warm up time considering the weight of the cold phase inside the most common approval cycles. Benefits on primary pollutants emission reduction are matched with those on fuel saving, with a double positive contribution. Many technologies are already available to reach this aim, but thermal management invites to consider a number of other innovations which have to be exploited.The paper makes use of an engine mathematical model previously developed by the Authors to discuss the performances of a traditional cooling flow passage inside an existing engine and two novel circuits which try to implement a split cooling between engine head and block. If head mean temperature is kept colder and engine block warmer, engine performances can be increased reducing friction losses, warm up time and having the possibility to increase volumetric compression ratio.

Study on Performance Evaluation of Automotive Radiator

A complete set of numerical parametric studies on automotive radiator has been presented in detail in this study. The modeling of radiator has been described by two methods, one is finite difference method and the other is thermal resistance concept. In the performance evaluation, a radiator is installed into a test-setup and the various parameters including mass flow rate of coolant, inlet coolant temperature; etc. are varied. A comparative analysis between different coolants is also shown. One coolant as water and other as mixture of water in propylene glycol in a ratio of 40:60 is used. It is observed that that the water is still the best coolant but its limitation is that it is corrosive and contains dissolved salts that degrade the coolant flow passage.

Experimental research on heat transfer of natural convection in vertical rectangular channels with large aspect ratio

This work presents the experimental research on the steady laminar natural convection heat transfer of air in three vertical thin rectangular channels with different gap clearance. The much higher ratio of width to gap clearance (60–24) and the ratio of length to gap clearance (800–320) make the rectangular channels similar with the coolant flow passage in plate type fuel reactors. The vertical rectangular channels were composed of two stainless steal plates and were heated by electrical heating rods. The wall temperatures were detected with the K-type thermocouples which were inserted into the blind holes drilled in the steal plates. Also the air temperatures at the inlet and outlet of the channel were detected. The wall heat fluxes added to the air flow were calculated by the Fourier heat conduction law. The heat transfer characteristics were analyzed, and the average Nusselt numbers in all the three channels could be well correlated with the Rayleigh number or the modified Rayleigh number in a uniform correlation. Furthermore, the maximum wall temperatures were investigated, which is a key parameter for the fuel’s integrity during some accidents. It was found that even the wall heat flux was up to 1500 W/m 2, the maximum wall temperature was lower than 350 °C. All this work is valuable for the plate type reactor’s design and safety analysis.

An investigation of local heat transfer characteristics in a ventilated disc brake with helically fluted surfaces

Local Nusselt numbers in the cooling flow passage of the automobile disc brake with helically fluted surfaces are presented. The flat surface in the flow passage is modified to the helically fluted surface for the purpose of enhancing the heat transfer rate, thereby reducing the thermal stress and deformation in the disc brake. Thermochromic liquid crystals and shroud-transient technique are used to measure spatially-resolved surface temperature distributions, which are used to deduce local Nusselt numbers. The Reynolds number Re ranges from 30,000 to 70,000, the helix angle θ is fixed at 45° and the dimensionless streamwise distance z/d ranges from 1.5 to 4.5. The results show that in general, local Nusselt numbers monotonically decrease with a distance away from both windward and leeward crests of the helical flute and reach a minimum value near its valley for all Re’s and z/d’s tested. The local Nusselt numbers on the helically fluted grooves are maximum 51.6 to 93.7% higher than values measured on the flat surface. The heat transfer enhancement magnitudes become more pronounced with smaller Re and z/d. The largest enhancement occurs at the windward side of the helical flute at z/d=1.5 and Re=30,000. It is also found that at Re=30,000 the average Nusselt numbers on the helically fluted surface are maximum 37% higher than those on the flat surface. The numerical results show that with 10 braking cycles, the temperatures with helically fluted surface are maximum 44.3%, 36.8%, and 36.6% lower than those with the flat surface in the inlet, the center, and the outlet, respectively.

Local Heat Transfer Measurements and Numerical Analysis in the Cooling Passage of the Ventilated Disc Brake with Semi-Cylindrically Grooved Surface

The local heat transfer measurements in the cooling flow passage having both flat surface and semi-cylindrically grooved surface geometries inside the automobile disc brake were made. A uniform wall heat flux boundary condition on both surface geometries was created using gold film Intrex. Liquid crystal was used to measure the surface temperature. The experiments were made at Reynolds number (based on the hydraulic diameter of the rectangular duct) of Re=23,000, groove pitch-to-width (P/D) from 3 to 7, and groove depth-to-width (H/D) from 0.15 to 0.2. The results show that the magnitudes in the average Nusselt number on the grooved surface are maximum 92.8% higher than those on the flat surface without groove. A computer program utilizing the coupled FEM numerical technique that can predict the temperature distributions on the disc brake to analyze the thermal deformation has been developed.

Coolant Flow Distribution and Pressure Loss in ONAN Transformer Windings—Part I: Theory and Model Development

A comprehensive resistance network-based hydraulic model for mass flow distribution and pressure loss in disk-type oil-cooled transformer windings with zigzag cooling flow passages is presented. The number, size, and location of the horizontal ducts and fluid properties are considered variable, and the distribution of mass flow rates is determined by associated pressure losses, including the so-called minor losses. Axisymmetry of the winding geometry is taken into consideration, and the pressure loss calculation is based on the discretization of flow domains in order to tackle the nonuniformity of the cross-sectional area in the horizontal ducts and to provide easy coupling with thermal analysis for the cooling of winding disks. Successive under relaxation method is used for numerical convergence.

Solution to shape identification problem of unsteady heat‐conduction fields

AbstractThis paper presents a numerical analysis method for shape determination problems of unsteady heat‐conduction fields in which time histories of temperature distributions on prescribed subboundaries or time histories of gradient distributions of temperature in prescribed subdomains have prescribed distributions. The square error integrals between the actual distributions and the prescribed distributions on the prescribed subboundaries or in the prescribed subdomains during the specified period of time are used as objective functionals. Reshaping is accomplished by the traction method that was proposed as a solution to shape optimization problems of domains in which boundary value problems are defined. The shape gradient functions of these shape determination problems are derived theoretically using the Lagrange multiplier method and the formulation of material derivative. The time histories of temperature distributions are evaluated using the finite‐element method for a space integral and the Crank–Nicolson method for a time integral. Numerical analyses of nozzle and coolant flow passage in a wing are demonstrated to confirm the validity of this method. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 212–226, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10086

Mass/Heat Transfer in Dimpled Two‐Pass Coolant Passages with Rotation

Mass/heat transfer measurements are made in dimpled (hemispherical depressions) inlet and outlet coolant flow passages using the naphthalene sublimation method. The leading and trailing surfaces are dimpled, while the side walls are kept smooth. Measurements are made at a Reynolds number of 21,000 and for Rotation numbers of 0 and 0.2. The measurements indicate that dimples enhance surface mass/heat transfer. This enhancement is stronger in the inlet passage than in the outlet passage. Peak mass/heat transfer occurs immediately downstream of the dimples, while the minimum mass/heat transfer occurs in the dimple region itself. Higher mass/heat transfer is also observed along the lateral edges of the dimple. The location of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.

Boundary shape determination of steady‐state heat‐conduction fields

AbstractIn this paper, a practical method of numerical analysis for the boundary shape design of steady‐state heat‐conduction fields to control the temperature distribution to a prescribed distribution is presented. Reshaping was accomplished by the traction method proposed by one of the authors as a solution to domain optimization problems in which elliptic boundary value problems were defined. In this study, we formulated a temperature square error norm minimization problem between the prescribed distribution and the actual distribution on prescribed boundaries and theoretically derived a shape gradient function for this problem. We developed a convenient numerical method using a general‐purpose FEM program for the temperature prescribed problem. The successful results for the two‐dimensional problems of an erosion surface on a blast furnace hearth and a coolant flow passage in a wing demonstrate the validity of the presented method. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 245–258, 2001

Simultaneous Prediction of External Flow-Field and Temperature in Internally Cooled 3-D Turbine Blade Material

A two-dimensional (2-D) and a three-dimensional (3-D) conjugate heat transfer (convection-conduction) prediction codes were developed where the compressible turbulent flow Navier-Stokes equations are solved simultaneously in the flow-field and in the solid material of the structure thus automatically predicting correct magnitudes and distribution of surface temperatures and heat fluxes. The only thermal boundary conditions are the convection heat transfer coefficients specified on the surfaces of the internal coolant flow passages and the coolant bulk temperature of internally cooled gas turbine blade. This approach eliminates the need to specify hot surface temperature or heat flux distribution. The conjugate codes use hybrid unstructured triangular/quadrilateral grids in 2-D and unstructured prismatic grids in 3-D throughout the flow-field and in the surrounding structure. The codes are capable of conjugate heat transfer prediction in arbitrarily shaped internally cooled configurations. The computer codes have been successfully tested on internally cooled turbine airfoil cascades and 3-D turbine blades by the conjugate solution of the flow-field and the temperature field inside the structure.Copyright © 2000 by ASME

Solution to Shape Identification Problem of Unsteady Heat-Conduction Fields.

This paper presents a numerical analysis method for shape determination problems of unsteady heat-conduction fields in which time-histories of temperature distributions on prescribed subboundaries or time-histories of gradient distributions of temperature in prescribed subdomains have prescribed distributions. The square error integrals between the actual distributions and the prescribed distributions on the prescribed subboundaries or in the prescribed subdomains during the specified period of time are used as objective functionals. Reshaping is accomplished by the traction method that was proposed as a solution to shape optimization problems of domains in which boundary velue problems are defined. The shape gradient functions of these shape determination problems are derived theoretically using the Lagrange multiplier method and the formulation of material derivative. The time-histories of temperature distributions are evaluated using the finite element method for space integral and the Crank-Nicolson method for time integral. Numerical analyses of nozzle and coolant flow passage in wing are demonstrated to confirm the validity of this presented method.

An inverse design problem of estimating optimal shape of cooling passages in turbine blades

An inverse design problem is solved to determine the shape of complex coolant flow passages in internal cooled turbine blades by using the conjugate gradient method (CGM). One of the advantages of using CGM lies in that it can easily handle problems having a huge number of unknown parameters and it converges very fast. The boundary element method (BEM) is used to calculate the direct, sensitivity and adjoint problems due to its characteristics of easily-handling the problem considered here. Results obtained by using the CGM to solve the inverse problems are verified based on the numerical experiments in the analysis model. One concludes that the CGM is applied successfully in estimating the arbitrary shape of cavities and the rate of convergence is also very fast even when the number of unknown parameters is large. Moreover, the design model of the inverse problem is also performed to estimate the optimal shape of cooling passages in accordance with the desired blade surface temperature distributions.