Cooling Flow Research Articles

Numerical Analysis of Film Cooling Flow Dynamics and Thermodynamics for Perfect and Imperfect Cooling Holes

Numerical Analysis of Film Cooling Flow Dynamics and Thermodynamics for Perfect and Imperfect Cooling Holes

Structural Analysis & Effect of Impingement Cooling Flow in the Internal Surface on Temperature Distribution of a Vane in Gas Turbine Using Taguchi Technique

Abstract: Gas turbine always consider one of the most important systems in the modern engineering applications, because it has continuous ability to generate electric power. In gas turbines the major portion of performance dependency lies upon turbine blade design ,the blades are considered one of the important and expensive parts in the gas turbines , where the blades of first stage from failure .The blades of the gas turbine suffer from tensile stresses due to centrifugal forces resulting from the high rotational speed and because of the loading of densegasses at a high temperature and speed ,as the centrifugal force is one of the problems that thedesigner of the turbine blades faces , as the designer aims to reduce stresses within the permissible limit. CFD study was carried out for evaluating the performance of a utility Steam Turbine. The flow in a turbine blade passage is complex and involves understanding of energy conversion in three dimensional geometries. The performance of turbine depends on efficient energy conversion and analyzing the flow path behavior in the various componentsof Steam Turbine. This study seeks the optimization of an axial turbine from a small gas turbine engine developed by ITA using Computational Fluid Dynamics (CFD) and Multi- Objective Optimization techniques focused on geometry changes to maximize the turbine performance. The simulation process will be done through the use of the commercial software SolidWorks.

Protective Film on the Plate Surface in Cooling Flow Through an Inclined Slotted Channel Under the Influence of a Harmonically Changing Pressure

Protective Film on the Plate Surface in Cooling Flow Through an Inclined Slotted Channel Under the Influence of a Harmonically Changing Pressure

Computationally Efficient Workflow for Conjugate Heat Transfer With Large Eddy Simulation for Gas Turbine Combustors

Abstract Typical gas turbine combustor (GTC) and high-pressure turbine stage generally employs 10,000 to 100,000 small passages of cooling holes. Such an arrangement protects the solid walls through impingement and effusion cooling. The former provides solid wall internal cooling, and the latter helps to reduce the metal temperature by developing a thin film around it. High-fidelity simulations are primarily utilized in the industry such that accurate prediction from numerical tools can aid advancement in the performance of such machines. In this paper, a numerical study using ansys fluent has been conducted with large eddy simulation (LES), conjugate heat transfer (CHT), and radiation to explore the relative benefits of implicit and explicit fluid–solid thermal couplings. The simulations of LES with CHT are performed for well-documented experiments of heated nozzle exhaust passing over a film-cooled plate (Wernet et al., 2020, “PIV and Rotational Raman-Based Temperature Measurements for CFD Validation of a Perforated Plate Cooling Flow: Part I,” AIAA 2020-1230, Session, AIAA Scitech 2020 Forum, Orlando, FL, Jan. 6–10, 2020). The accuracy of the modeling approach is assessed by comparing CHT predictions of fluid velocity and solid-plate temperatures with experiments. Acceleration techniques for LES–CHT simulations are explored in this paper with an emphasis on thermal coupling, radiation, etc. The effects of mesh sensitivity and flow solution approach are presented in detail. LES–CHT results generally match the experiments at various blowing ratios both qualitatively and quantitatively. The comparisons in the paper allow the selection of best practices for CHT modeling in GTC. A generic combustor model with effusion cooling hole arrays is used in the paper to establish the workflow for modeling LES with CHT in the industrial-type combustor. Various acceleration techniques are utilized to show an overall improvement in solution performance with the same level of accuracy.

Film Cooling Effectiveness and Flow Structures of Butterfly-Shaped Film Cooling Hole Configuration

Abstract Film cooling is applied to various high-temperature components of a gas turbine and greatly affected by the shape of the injection hole. Numerous studies have been conducted to investigate various film cooling structures to increase the film cooling effectiveness by inducing coolants toward the surface. In this study, a butterfly-shaped film cooling hole configuration is proposed, which consists of a pair of asymmetric fan-shaped holes installed adjacently. This novel structure enhances film cooling effectiveness by utilizing the interaction between coolant jets from the asymmetrical film cooling holes. In this study, the film cooling effectiveness of the butterfly-shaped hole configuration was experimentally characterized under low-speed conditions on a flat plate, and was compared with that of widely used fan-shaped holes. Also, a numerical study was conducted to understand and visualize the flow structures generated by the butterfly-shaped film cooling configuration. As a result, an anti-vortex structure was observed near the hole exit. The film cooling effectiveness of the butterfly-shaped hole configuration was also compared with that of the fan-shaped hole. The film cooling effectiveness of the butterfly-shaped hole configuration was 1.9% higher than that of the optimized fan-shaped film cooling hole at its optimized condition. It was also found that the film cooling effectiveness increased with the blowing ratio for the butterfly-shaped hole configuration. It is expected that the film cooling effectiveness can be further improved by adjusting the shape parameters of the butterfly-shaped hole.

Numerical Investigation of Film Cooling Effectiveness and Flow Field Characteristics over a Flat Plate with in-Hole Swirl Generator

Numerical Investigation of Film Cooling Effectiveness and Flow Field Characteristics over a Flat Plate with in-Hole Swirl Generator

Performance Analysis of Nanofluid-based Photovoltaic Thermal Collector with Different Convection Cooling Flow

Using solar energy through photovoltaic (PV) panels has excellent potential as an alternative energy source. However, the problem of high operating temperatures causing a reduction in work efficiency needs to be addressed. This study aimed to analyze the development of a cooling system to increase PV panels' electrical and thermal efficiency. The research involved analyzing the use of TiO2, Al2O3, and ZnO working fluids by adding 0.5 vol% to water in an active cooling method. The cooling system involved a rectangular spiral and a rectangular tube behind the PV panel. A solar simulator simulated solar radiation with intensity variations to analyze the cooling system's performance in different working conditions. The results showed that the heat exchanger with a nanofluid configuration reduced the panel temperature by 14 oC, which increased the electrical efficiency by up to 4.7% in the ZnO nanofluid. In the rectangular spiral configuration, the ZnO nanofluid reduced the panel temperature from 60 to 45 oC, increasing the Isc value from 2.16A to 2.9A and the Voc value from 21.5V to 23V. This resulted in a maximum power increase of the panel to 53W. Doi: 10.28991/CEJ-2023-09-08-08 Full Text: PDF

Magnetic Resonance Velocimetry Measurements of Internal Blade Cooling Flow and Computational Fluid Dynamic Validation by Data Matching With the Experimental Data

Abstract The optimal Reynolds-averaged Navier–Stokes (RANS) turbulence model to be used in a Computational Fluid Dynamics (CFD) simulation varies depending on the application. Conventionally, the model is selected from benchmark tests and experience, but its performance is difficult to predict. For this reason, this study presents a cost-effective CFD validation routine, which uses three-dimensional experimental velocity data obtained in replicas of the specific flow system. Magnetic Resonance Velocimetry is used as the measurement technique. Since the objective is only the validation of the turbulence model, the experiment and the simulation are performed with simplified flow conditions, hence stationary isothermal isovolumetric flow without inertial forces. The routine applies a data-matching routine to align the two three-dimensional data sets before they are interpolated on a common grid. Various error metrics are presented, which provide the degree of the CFD modeling error and indicate its source. For demonstration, the validation routine is used to evaluate RANS-CFD results of a three-pass internal cooling system of a high-pressure turbine airfoil used in a small industrial gas turbine. The simulations are performed with the eddy-viscosity-based turbulence model k–ω shear stress transport (SST), the Reynolds-stress Speziale, Sarkar and Gatski (SSG), and baseline-Explicit algebraic Reynolds stress model turbulence (BSL-EARSM) models. The results indicate strong local errors in the examined turbulence models. None of the models performed well enough, underlining that every RANS-CFD application needs to be validated.

Optimized Film Cooling Flow on a Contoured Endwall Within a Transonic Annular Cascade

AbstractFilm cooling was measured on the endwall of a five-vane annular cascade in a blowdown wind tunnel at an exit Mach number of 0.9. The adiabatic film cooling effectiveness was calculated from the partial pressure of oxygen measured with binary pressure-sensitive paint (BPSP). Cylindrical film cooling holes were located in the upstream and passage regions with the coolant-to-mainstream mass flow ratio (MFR) independently varied for each region. One row was located upstream of the vanes and supplied by an upstream plenum. Two rows were located in the passage between two vanes and supplied by a downstream plenum. Three total MFRs were investigated: 1%, 1.5%, and 2%. For a given total MFR, four combinations of upstream and downstream MFRs were compared to an even split of coolant. Coolant-to-mainstream density ratios (DRs) of 1.0 and 2.0 were investigated. The most efficient use of coolant hinged on balancing the downstream MFR for the second row due to the endwall pressure gradient preventing coolant from exiting the holes or a high jet velocity causing liftoff. For this row, selecting the optimum MFR increased the area-averaged film cooling effectiveness by up to 200% with a reduction in row 1 of less than 25%. At high downstream MFRs, increasing the density ratio delayed liftoff and increased film cooling effectiveness in row 2 by 65%. However, at low MFRs, increasing the density ratio reduced film cooling effectiveness in row 2 by 60%.

Liquid Cooling Flow Field Design and Thermal Analysis of Proton Exchange Membrane Fuel Cells for Space Applications

Proton exchange membrane (PEM) fuel cells are a promising technology with many features, including having a high energy density, efficiency, lightness, and producing energy directly instead of storing it. PEM fuel cells are currently used in mobile vehicles, military applications, portable systems, stationary systems, and air-independent propulsion systems for sea and space. Elimination of the cooling problems associated with PEM fuel cells in space applications is of great importance to produce more efficient systems. With this motivation in mind, this study examined PEM fuel cell elements and cooling flow channel design for space applications. The effect of the designed flow channel on the PEM fuel cell temperature distribution was investigated. Five different PEM fuel cell cooling channels were designed and modeled computationally, and the most suitable cooling channel design was selected based on the thermal analysis. While modeling the PEM fuel cell, space environment operating conditions, pure reactant supply (oxygen and hydrogen), electrochemical reaction in the membrane, physical properties of liquid coolant, physical properties of fuel cell elements, and heat transfer in the fuel cell were considered. The temperature distribution obtained as a result of the thermal analysis was examined, and it was seen that the PEM fuel cell cooling channel design was successful in maintaining the operating temperature of the PEM fuel cell. According to the data obtained, the cooler inlet temperature is approximately 40°C and the cooler outlet temperature is approximately 75°C in flat serpentine design. These values were obtained as a result of the analysis made with a mixture of 50% ethylene glycol and 50% water selected as the liquid coolant. As a result, a fuel cell can be formed by producing a fit bipolar plate with the analyzed PEM fuel cell cooling flow channel design, and current density and homogeneity can be determined by applying single-cell performance tests to the fuel cell.

Hidden Cooling Flows in clusters of Galaxies II: a wider sample

ABSTRACT We have recently uncovered Hidden Cooling Flows (HCFs) in the XMM Reflection Grating Spectrometer spectra of three clusters of galaxies; Centaurus, Perseus, and A1835. Here, we search for them in a wider sample of objects: the X-ray brightest group NGC 5044; four moderate X-ray luminosity clusters Sersic 159, A262, A2052, and RX J0821; and three high X-ray luminosity clusters RX J1532, MACS 1931, and the Phoenix cluster. Finally, we examine two Virgo elliptical galaxies, M49 and M84. All statistically allow the addition of an HCF. We find a significant detection of an HCF in six clusters and two elliptical galaxies. The hidden mass cooling rates are $5{\!-\!}40\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ for the normal clusters, $1000\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ or more for the extreme clusters, and $1{\!-\!}2\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ for the elliptical galaxies. We discuss the implications of the results for the composition of the innermost parts of the massive host galaxies and look forward to future observations.

High-Degree Collisional Moments of Inelastic Maxwell Mixtures—Application to the Homogeneous Cooling and Uniform Shear Flow States

The Boltzmann equation for d-dimensional inelastic Maxwell models is considered to determine the collisional moments of the second, third and fourth degree in a granular binary mixture. These collisional moments are exactly evaluated in terms of the velocity moments of the distribution function of each species when diffusion is absent (mass flux of each species vanishes). The corresponding associated eigenvalues as well as cross coefficients are obtained as functions of the coefficients of normal restitution and the parameters of the mixture (masses, diameters and composition). The results are applied to the analysis of the time evolution of the moments (scaled with a thermal speed) in two different nonequilibrium situations: the homogeneous cooling state (HCS) and the uniform (or simple) shear flow (USF) state. In the case of the HCS, in contrast to what happens for simple granular gases, it is demonstrated that the third and fourth degree moments could diverge in time for given values of the parameters of the system. An exhaustive study on the influence of the parameter space of the mixture on the time behavior of these moments is carried out. Then, the time evolution of the second- and third-degree velocity moments in the USF is studied in the tracer limit (namely, when the concentration of one of the species is negligible). As expected, while the second-degree moments are always convergent, the third-degree moments of the tracer species can be also divergent in the long time limit.

Calculating Cooled Turbine Efficiency With Weighted Cooling Flow Distributions

Abstract The ability to accurately characterize the thermal efficiency of turbine stages with cooled components is essential to advance turbine technologies. There are many methods for calculating aerodynamic efficiency of turbomachinery components, with most encompassing either single point or simple integrated values at the inlet and exit locations. For cooled turbine stages, there is an added complexity of how to incorporate cooling flow streams. Although these techniques may include multiple cooling flows, a fully mixed assumption is often invoked without directly accounting for distributions of cooling flow in the annulus. However, the distribution of cooling flows in turbine stages may vary significantly depending on the location and nature of injection. This study addresses how calculated efficiency may vary depending upon how cooling flows are injected and the manner in which these cooling flows are accounted. The analyses utilize experimentally measured cooling flow concentration profiles to motivate a new approach for calculating cooled turbine efficiency with weighted cooling flow distributions. Validation data for a one-stage high-pressure turbine geometry from the energy efficient engine (E3) program are assessed to determine the range of influence for cooling flow distributions. Results show that cooling flows injected at similar axial positions can have unequal influences on integrated stage efficiency based on known distributions of cooling flow and other properties at the turbine stage exit plane. In some cases, deviations approaching half a point of efficiency can be observed relative to traditional equations, and the magnitude of influence is shown to increase as stage total pressure ratio decreases.

Investigating the Influence of Mainstream Turbulence and Large Vortices on Gas Turbine Trenched Film Cooling Flows Using Planar Temperature-Velocity Imaging

Abstract Film cooling is a critical gas turbine technology to reduce heat loads on the combustion chamber and the turbine vanes and blades. To improve film cooling performance, trenched cooling configurations where the holes are connected by a cross-stream slot in the surface have been developed. In this study, for the first time, we experimentally examine the influence of mainstream turbulence and large vortices on trenched film cooling flows. We apply an imaging technique based on thermographic phosphor particles seeded into the flow to measure 2D time-resolved gas temperature and velocity distributions in film cooling flows established in a closed-loop heated wind tunnel. Two trenched configurations (straight and an optimized zigzag design) are compared with ordinary effusion holes at momentum ratios (I=3.5,5.7, and 8.3) relevant to gas turbine combustors. Furthermore, two turbulence generation methods were used to create realistic mainstream turbulence levels (Tu=16.4% and 22.7%) and large vortices, so film cooling flows at typical wind tunnel turbulence (Tu=5.3%) can be compared with combustor-relevant conditions. By comparing the film position derived from the time-average temperature fields, the optimized trench performs best at low momentum ratios and turbulence levels but the performance rapidly drops when the momentum ratio rises or the turbulence level is increased. The straight trench performs best across all conditions studied and this configuration is therefore recommended for combustor liner cooling where main flow turbulence levels are high. In general, increased turbulence intensity reduces the effective length of the cooling film for all geometries. The straight trench, however, produces a more stable cooling film than typical effusion holes or the optimized trench configuration. Both phase-locked and time-resolved data indicate that, in the presence of a dominating frequency in the turbulent main flow field produced using a vortex generator, there are instances where the cooling films are strongly disturbed in the streamwise direction and hot gas is locally in contact with the surface.

Computational Fluid Dynamics-Based Numerical Analysis for Studying the Effect of Mini-Channel Cooling Plate, Flow Characteristics, and Battery Arrangement for Cylindrical Lithium-Ion Battery Pack

Abstract Battery Thermal Management System (BTMS) is crucial to maintain peak temperature and temperature difference of lithium-ion battery pack in appropriate range, thus ensuring best performance, extended cycle life and safety. Liquid cooling BTMS is extensively researched for prismatic cells, but only a few studies are present on application of liquid cooling BTMS for cylindrical cells. Further, existing studies on liquid cooling for cylindrical cells majorly focus on effect of flowrate, flow direction, and number of channels. In this study, a novel mini-channel cooling plate-based liquid cooling BTMS is proposed for a battery pack of 20 cells. Computational fluid dynamics (CFD)-based numerical analysis was performed on three-dimensional model of battery pack to investigate effects of parameters associated with cooling plate and mini-channel design, flow characteristics, and battery arrangement on temperature uniformity, heat removal rate, parasitic power consumption and weight of the battery pack. The study concluded that installation of aluminum cylindrical enclosure on cells could drastically enhance heat removal and temperature uniformity. Altering flow directions in mini-channel could enhance thermal performance. The research demonstrated that for case 2d (inlet and outlet are staggered in each cooling plate), the temperature difference can be reduced by 16.5% when compared to unidirectional flow. Mini-channel with square cross section offers better heat removal and fewer flow resistance compared to circular and elliptical. Although converging mini-channels offer better thermal performance, it drastically increases the pumping power. The battery pack was successful in limiting peak temperature and temperature difference to 303.26 K and 1.98 K, respectively, for 4 C discharge rate.

Numerical Investigation and Optimization of Cooling Flow Field Design for Proton Exchange Membrane Fuel Cell

High temperatures and non-uniform temperatures both have a negative bearing on the performance of proton exchange membrane fuel cells. The temperature of proton exchange membrane fuel cells can be lowered by reasonably distributed cooling channels. The flow field distribution of five different cooling plates is designed, and the temperature uniformity, pressure drop and velocity of each cooling flow field are analyzed by computational fluid dynamics technology. The results show that while the pressure drop is high, the flow channel distribution of a multi-spiral flow field and honeycomb structure flow field contribute more to improving the temperature uniformity. As the coolant is blocked by the uniform plate, it is found that although the flow field channel with a uniform plate has poor performance in terms of temperature uniformity, its heat dissipation capacity is still better than that of the traditional serpentine flow field. The multi-spiral flow field has the strongest ability to maintain the temperature stability in the cooling plate when the heat flux increases. The increase in Reynolds number, although increasing the pressure drop, can reduce the maximum temperature and temperature difference of the flow field, ameliorate the temperature uniformity and improve the heat transfer capacity of the cooling plate.

Reducing the Core Losses of Fe-Si-B Amorphous Alloy Ribbons by High Cooling Rate Planar Flow Casting.

In the planar flow casting (PFC) process, the cooling rate significantly affects the structure and properties of a cast ribbon. The influence of the thermal conductivity of the cooling wheel substrate on cooling rate was simulated by a numerical method, and it is shown that a higher thermal conductivity of the cooling wheel substrate leads to a higher cooling rate in the PFC process. Two copper-beryllium (Cu-2Be) rings with thermal conductivities of 175.3 W/m·K and 206.5 W/m·K were manufactured and installed onto a wheel core as the substrate of the cooling wheel. The effects of cooling rate on the soft magnetic properties of Fe-Si-B amorphous ribbons were investigated by pragmatic ribbon casting. The results show that the increment in the thermal conductivity of the cooling wheel substrate from 175.3 W/m·K to 206.5 W/m·K lowered the coercive force of amorphous ribbon from 2.48 A/m to 1.92 A/m and reduced the core losses at 1.4 T and 50 Hz by up to 22.1%.

Numerical Study on Cooling Heat Transfer and Flow Characteristics of Supercritical Co2 in Six-Start Spirally Fluted Tubes

Numerical Study on Cooling Heat Transfer and Flow Characteristics of Supercritical Co2 in Six-Start Spirally Fluted Tubes

Impact of Inflow Turbulence on Large-Eddy Simulation of Film Cooling Flows

Impact of Inflow Turbulence on Large-Eddy Simulation of Film Cooling Flows

Large Eddy Simulations on Film Cooling Flow Behaviors with Upstream Turbulent Boundary Layer Generated by Circular Cylinder

Large eddy simulations on film cooling hole array on a flat plate was carried out to investigate upstream turbulence effect. Circular cylinders were configured to create a turbulent boundary layer and its diameter has been adjusted to generate 13% upstream turbulence intensity in the main flow. Due to the small pitch to diameter configuration of the cylinder, two-dimensional LES analysis was carried out in advance and the results showed that LES was an essential method to resolve flow field around and downstream circular cylinder, which was not available in RANS simulations. The three-dimensional LES results showed reasonable agreement in turbulence intensity and normalized velocity distributions along the vertical with measured data. According to the blowing ratio, the cooling flow coverage on the surface along the stream-wise direction was varied and well agreed with measured data. Additionally, upstream boundary flows were partially ingested inside the cooling hole and discharged again near along the centerline of the cooling hole. This accounted for film cooling effectiveness distribution inside the cooling hole surface and along the centerline. The current study revealed that the LES for predicting turbulent boundary layer behaviors due to upstream turbulence generation source was an effective and feasible method. Moreover, the LES effectively resolved flow fields such as film cooling flow behaviors and corresponding film cooling effectiveness distributions.