Coolant Jet Research Articles

Effects of Near-Wall Streamwise Vortex on the Film Cooling Performance of a Fan-Shaped Hole

Abstract Fan-shaped hole is a typical shaped hole frequently used in gas turbine film cooling, which may operate in a complex vortical flow environment of turbine blade rows. It is critical to understand the destructive mechanism of the film cooling by near-wall vortex on the endwall surface. A vortex generator (VG) was installed in front of a discrete fan-shaped hole to produce a vortical environment on a flat plate. Heat transfer effects were experimentally studied for mainstream velocities of 20 m/s by measuring the adiabatic film cooling effectiveness at blowing ratios M = 0.5 to 2.5. Fluid dynamics effects of vortical upwash and downwash movements were numerically analyzed. Results show that near-wall streamwise vortex destroys the film flow and intensifies the mixing of hot gas and coolant flow, which leads to the deterioration of film cooling performance. Film coverage area varies remarkably with respect to the positions of streamwise vortex. An efficient blowing ratio has a strong ability to mitigate the influence of near-wall vortex. At M = 2.5, streamwise vortex can restrain liftoff tendency of coolant jet and retard the decrease of film cooling effects.

Cooling Performance of the Endwall Vertical Hole Considering the Interaction between Cooling Jet and Leading-Edge Horseshoe Vortex

Cooling Performance of the Endwall Vertical Hole Considering the Interaction between Cooling Jet and Leading-Edge Horseshoe Vortex

Effects of Bulk Flow Pulsation on Film Cooling Involving Compound Angle

The main flow could be unsteady in flow fields of film cooling for several reasons such as flow interactions between the rotor and the stator in the turbine. Understanding the characteristics of the film-cooling flow with an unsteady flow is important in the design of gas turbines. The effects of 36-Hz pulsations in the main flow on the streamwise velocity distributions, turbulence statistics, and temperature fluctuations in the film-cooling flow from a cylindrical hole with an orientation angle are investigated by numerical methods. Large-eddy simulation (LES) results match the experimental data with an acceptable accuracy, whereas the Reynolds-averaged Navier–Stokes simulation (RANS) results show large deviations with the experimental data and the LES results. Under 36-Hz pulsations, the URANS results predict a weaker streamwise velocity of the coolant jet that blocks the main flow compared with the LES. With 36-Hz pulsations at the time-averaged blowing ratio of 0.5, urms, the root mean squared fluctuating velocity in the streamwise direction around the coolant core increased due to intensive mixing, and vrms, the root mean squared fluctuating velocity in the wall-normal direction, increased along the trajectory of the injected coolant. Moreover, wrms, the root mean squared fluctuating velocity in the spanwise direction, increased around the wall compared to those at a steady state. The dimensionless temperature fluctuations increased in the region of the core of the coolant compared with those at a steady state. When the orientation angle was 30°, the distribution of the results moved in the z-direction; however, the overall trend was similar to that of a simple angle.

Analysis of Swirl Number Effects on Effusion Flow Behavior Using Time-Resolved Particle Image Velocimetry

Abstract The analysis of the interaction between the swirling and cooling flows, promoted by the liner film cooling system, is a fundamental task for the design of turbine combustion chambers since it influences different aspects such as emissions and cooling capability. In particular, high turbulence values, flow instabilities, and tangential velocity components induced by the swirling flow deeply affect the behavior of effusion cooling jets, demanding for dedicated time-resolved near-wall experimental analysis. The experimental setup of this work consists of a non-reactive single sector linear combustor test rig scaled up with respect to engine dimensions; the test section was equipped with an effusion plate with standard inclined cylindrical holes to simulate the liner cooling system. The rig was instrumented with a 2D time-resolved particle image velocimetry system, focused on different field of views. The degree of swirl for a swirling flow is usually characterized by the swirl number, Sn, defined as the ratio of the tangential momentum flux to axial momentum flux. To assess the impact of such parameter on the near-wall effusion behavior, a set of three different axial swirlers with swirl number equal to Sn = 0.6–0.8–1.0 were designed and tested in the experimental apparatus. An analysis of the main flow field by varying the Sn was first performed in terms of average velocity, root mean square, and Tu values, providing kinetic energy spectra and turbulence length scale information. In a second step, the analysis was focused on the near-wall regions: the strong effects of Sn on the coolant jets were quantified in terms of vorticity analysis and jet oscillation.

Experimental Investigation of the Effect of the Bubble Cone on the Cooling Jets used in the Blown Film Manufacturing Process

Abstract An experimental investigation was performed to characterize the flow field produced by a dual-lip air ring used in the blown-film manufacturing process for a solid model with a blow-up ratio of 3.5 similar to the shape of a typical LLDPE bubble. Distributions of the static and fluctuating pressure on the model and the flow field above the forming cone were measured for a range of settings on the dual-lip air ring. It was found that the distribution of the pressure on the bubble below the forming cone had many features similar to the measurements for a bubble with a blow-up ratio of 2.5 [1]. In the region above the forming cone, the upper jet appeared to merge with the lower jet rather than entraining the lower jet as was observed for a bubble with a blow-up ratio of 2.5 [1]. This resulted in a smaller local maximum in the normalized fluctuating pressure in the region above the forming cone and would likely result in less heat transfer in this region. It was also found that the initial angle of the upper jet exiting the air ring changed when the height of the bubble cone was adjusted for the bubble with the blow-up ratio of 3.5. This affected the static pressure in the region below the location where the upper jet attaches to the bubble and the pressure fluctuations in the region where the upper jet attaches to the surface. Finally, unlike the bubble with the blow-up-ratio of 2.5 [1], the presence of the bubble cone caused a region of negative gauge pressure in the region above the forming cone that should act to stabilize the bubble against the bubble cone. The pressure in this region and the region below the forming cone both decreased when the porosity of the bubble cone was reduced.

Numerical investigation on flow and film cooling characteristics of coolant injection in rotating detonation combustor

The film cooling is a possible active thermal protection solution for the rotating detonation engines. As the rotating detonation wave is of high periodic and unsteady features, the film cooling characteristics inside the rotating detonation combustor are very complicated. To illustrate the influence of rotating detonation wave on the flow dynamics of coolant jets and the thermal protection performance of film cooling in the rotating detonation combustor, a numerical investigation is performed in the current study, on the base of a simplified physical model wherein only single row of film cooling holes in the axial direction is concerned. The results show that both the blocking effect and oscillating effect occur in the transverse jet injection, upon the impact of sweeping of detonation wave and oblique shock wave. Due to the occupancy of momentary combusting flow invasion into the film cooling hole during one cycle of wave sweeping, the inward flow from the film cooling hole to the combustor chamber is not the pure ‘coolant jet’ but instead of a ‘mixed’ jet. The blocking effect of sweeping oblique shock wave front on the coolant jet injection is significantly weaker when compared to the detonation wave front. With the use of film cooling, the time-averaged temperature on the outer wall of the combustor chamber is reduced effectively, especially in the middle and rear sections of the rotating detonation combustor. The coolant jet injection does not change propagation speed of the rotating detonation wave but reduces a little the peak pressure and peak temperature of each cycle.

Turning characteristics of titanium alloy Ti-6Al-4V with high-pressure cutting fluid

This study investigates the effect of high-pressure cutting fluid on the turning characteristics of Ti-6Al-4V alloy. A noncoated carbide tool was used to measure the cutting temperature using a tool-work thermocouple technique, and the cutting characteristics were evaluated with respect to the cutting temperature, chip breakability, and tool wear. Furthermore, the viability of TiAlN/AlCr2O3-coated tool was examined. The coolant jet when placed towards the cutting zone on the rake face is effective in reducing the cutting temperature because of the reduction in the chip-tool contact length. Based on this result, tools with a textured rake face were examined.

High resolution simulation of film cooling with blowing ratio and inclination angle effects based on hybrid thermal lattice Boltzmann method

A series of high resolution simulations on film cooling with varying blowing ratios and inclination angles are carried out by using in-house code based on hybrid thermal lattice Boltzmann method. Three blowing ratios ranging from 0.2-0.8 and four inclination angles from 15? to 60? are chosen for the simulations. The evolutionary mechanism of coherent structure in three domains of film-covering region is studied from the view of space and time. Besides, the influencing mechanism of blowing ratio and inclination angle on flow and heat transfer features of film cooling is uncovered. Results show that hairpin vortex, hairpin packet, and quasi-streamwise vortex appearing in rotating domain play a key role in heat transfer process of film cooling. The strong ejection, sweep and vortex rotation resulted from these vortices enhance the convective heat transfer. It is also found that the size of coherent structure varies significantly with blowing ratio and its integral form shows a strong dependence on inclination angle. Moreover, inclination angle of coolant jet has a significant impact on turbulence fluctuation intensity. The influence of blowing ratio on the attachment of coolant film and film-cooling performance is more obvious than that of inclination angle. It is believed that all of these are related closely to the variation of streamwise and wall-normal jet velocity in the case of various blowing ratios and inclination angles.

Numerical Investigation of Single-Row Double-Jet Film Cooling of a Turbine Guide Vane under High-Temperature and High-Pressure Conditions

Single-row double-jet film cooling (DJFC) of a turbine guide vane is numerically investigated in the present study, under a realistic aero-thermal condition. The double-jet units are positioned at specific locations, with 57% axial chord length (Cx) on the suction side or 28% Cx on the pressure side with respect to the leading edge of the guide vane. Three spanwise spacings (Z) in double-jet unit (Z = 0, 0.5d, and 1.0d, here d is the film hole diameter) and four spanwise injection angles (β = 11°, 17°, 23°, and 29°) are considered in the layout design of double jets. The results show that the layout of double jets affects the coupling of adjacent jets and thus subsequently changes the jet-in-crossflow dynamics. Relative to the spanwise injection angle, the spanwise spacing in a double-jet unit is a more important geometric parameter that affects the jet-in-crossflow dynamics in the downstream flowfield. With the increase in the spanwise injection angle and spanwise spacing in the double-jet unit, the film cooling effectiveness is generally improved. On the suction surface, DJFC does not show any benefit on film cooling improvement under smaller blowing ratios. Only under larger blowing ratios does its positive potential for film cooling enhancement start to show. Compared to the suction surface, the positive potential of the DJFC on enhancing film cooling effectiveness behaves more obviously on the pressure surface. In particular, under large blowing ratios, the DJFC plays dual roles in suppressing jet detachment and broadening the coolant jet spread in a spanwise direction. With regard to the DJFC on the suction surface, its main role in film cooling enhancement relies on the improvement of the spanwise film layer coverage on the film-cooled surface.

Overview on Recent PVT Systems with Jet Impingement

Jet impingement cooling has been utilized to improve the performance of solar energy technologies such as solar collectors, PV systems, PVT systems, and CPV systems. This article provides an overview of current PVT systems using jet impingement. The distinctions between each study, such as research results and PVT system design, are examined and contrasted. The summary demonstrates that solar collectors are the most widely utilized solar energy technology owing to their direct manufacture. There are 20 solar collector studies, 5 for photovoltaic, 9 for photovoltaic thermal, and 8 for concentrator photovoltaic. Geometric characteristics such as jet diameter, spacing, and nozzle height are critical for maximum performance. Furthermore, numerous kinds of coolant jets, such as air, water, and nanofluid, may be seen from the overview. Hybrid systems, such as PVT or CPVT systems, perform better since they create thermal and electrical energy. As a result, more research into developing the hybrid system is advised.

Interaction Mechanism and Loss Analysis of Mixing between Film Cooling Jet and Passage Vortex.

The interaction between the film-cooling jet and vortex structures in the turbine passage plays an important role in the endwall cooling design. In this study, a simplified topology of a blunt body with a half-cylinder is introduced to simulate the formation of the leading-edge horseshoe vortex, where similarity compared with that in the turbine cascade is satisfied. The shaped cooling hole is located in the passage. With this specially designed model, the interaction mechanism between the cooling jet and the passage vortex can therefore be separated from the crossflow and the pressure gradient, which also affect the cooling jet. The loss-analysis method based on the entropy generation rate is introduced, which locates where losses of the cooling capacity occur and reveals the underlying mechanism during the mixing process. Results show that the cooling performance is sensitive to the hole location. The injection/passage vortex interaction can help enhance the coolant lateral coverage, thus improving the cooling performance when the hole is located at the downwash region. The coolant is able to conserve its structure in that, during the interaction process, the kidney vortex with the positive rotating direction can survive with the negative-rotating passage vortex, and the mixture is suppressed. However, the larger-scale passage vortex eats the negative leg of the kidney vortices when the cooling hole is at the upwash region. As a result, the coolant is fully entrained into the main flow. Changes in the blowing ratio alter the overall cooling effectiveness but have a negligible effect on the interaction mechanism. The optimum blowing ratio increases when the hole is located at the downwash region.

Coolant condition and spindle power in high-efficiency-deep-grinding of nickel-based superalloy profile part

ABSTRACT Coolants play an important role in controlling thermal damage in high-efficiency deep grinding (HEDG). The cooling condition in the grinding contact zone (GCZ) determines the cooling effect during the grinding process. Furthermore, when profile grinding is performed, owing to the complexity of the shape, the cooling effect varies at different positions. Therefore, in this study, a device that includes a pressure sensor and semi-natural thermocouples was introduced to evaluate the cooling conditions in the GCZ during HEDG. Thereafter, the influences of the grinding parameters and outlet velocity of the coolant on the pressure distribution were investigated. The grinding speed and outlet velocity of the coolant have significant impacts on the cooling condition, whereas the influences of the infeed speed and depth of cut are limited. The coolant pressure distributions during the profile grinding were measured, analyzed, and optimized. The needle-shaped nozzle, which adapts to the profile, has a better cooling effect than the shoe-shaped nozzle. Moreover, the influence of the coolant delivery on the spindle power was discussed. The outlet velocity of the coolant jet and grinding speed have significant effects on the idle and grinding powers. Therefore, it is recommended to consider the influence of grinding speed during HEDG.

Two-dimensional film-cooling effectiveness prediction based on deconvolution neural network

For film cooling in high-pressure turbines, it is vital to predict the temperature distribution and film cooling effectiveness on the blade surface downstream of the cooling hole. This temperature distribution and film cooling effectiveness depend on the interaction between the hot mainstream and the coolant jet. However, it is difficult to correlate accurately due to the complex mechanism. Based on deep learning techniques, a theoretic model using Deconvolutional Neural Network (Deconv NN) was developed to model the non-linear and high-dimensional mapping between coolant jet parameters and the surface temperature distribution on a flat plate. Computational Fluid Dynamics (CFD) was utilized to provide data for the training models. The input of the model includes blowing ratio, density ratio, hole inclination angle and hole diameters etc. With rigorous testing and validation, it is found that the predicted results are in good agreement with results from CFD. It is compared against the existing semi-empirical correlations and other machine learning techniques, such as support vector machine method. Dataset with different size is tested. The results suggest that the performance and robustness of Deconv NN is much better than other methods.

Film cooling performance and flow structure of single-hole and double-holes with swirling jet

This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance. Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed. Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared. Detailed flow structures and underlying mechanisms are discussed. The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios, and that swirl strength has significant influence on film cooling performance. Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices. The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157% and 173%, respectively.

Experimental study on heat transfer and throughflow losses characteristics of single/triple-row holes with an engine-representative density ratio

In present study, the heat transfer and the throughflow losses characteristics of single/triple-row of fan-shaped and cylindrical film cooling holes with a fixed outlet width are studied experimentally with an engine-representative density ratio. The pressure-sensitive paint (PSP) measurement technology is utilized to test the film cooling performance. The film cooling holes with the inclination angle α which ranged from 20° to 30° and the diffusion angle β which ranged from 0° to 15° are considered. The heat transfer and flow resistance characteristics of film cooling holes under the engine-representative density ratio, DR, of 1.52 as well as the blowing ratio, BR, which ranged from 0.3 to 2.0 are studied. The critical blowing ratios of the secondary flow detaches from wall surface of each hole shape and the hole shape parameters which acquire the highest span-wise averaged adiabatic film cooling efficiency are obtained. Moreover, the experimental results indicate that, within the scope of the investigative parameters pondered in present study, the discharge coefficient and the film cooling performance of the cylindrical hole are significantly lower than that of the fan-shaped film cooling holes. The coolant jet which ejects from the fan-shaped holes does not blow off from the wall surface when BR ≤ 1.5. However, when BR = 2.0, a part of coolant jet begins to detach from the wall surface. In addition, when BR ≤ 1.5, the fan-shaped film cooling hole with the hole shape parameters of α = 20°, β = 15° generates the highest film cooling effectiveness. However, when BR > 1.5, the highest film cooling effectiveness is obtained by the fan-shaped hole with hole shape parameters of α = 25°, β = 10°. Importantly, the discharge coefficient does not change monotonously with the variation of the hole shape parameters. In addition, the fan-shaped film cooling holes with the hole shape parameters of α = 25°, β = 13° as well as those with α = 30°, β = 10° offer the highest discharge coefficient. Finally, the correlations for the discharge coefficients of different hole shape parameters are developed.

Investigation of the Influence of the Airflow Around a Grinding Wheel on the Coolant Supply

The fast rotation of the grinding wheel creates an airflow near its surface, which causes a deflection of the coolant jet. To obtain an efficient and reliable grinding process, it is necessary to consider the airflow when dimensioning the coolant supply. For this purpose, the airflow around rotating grinding wheels was analyzed and characterized. In this research the airflow velocities around the grinding wheel were measured using a Prandtl tube, high-speed records were used to analyze the interactions between coolant supply and the airflow and positions for an effective air deflection were examined. It is found that the influence of the airflow especially depends on the cutting speed and the porosity of the grinding wheel, the airflow is not constant along the width of the grinding wheel and without air deflection the coolant jet requires an exit velocity of at least 50% of the grinding wheel peripheral speed.

Conjugate Heat Transfer Analysis of Flat Plate Subjected to Impingement and Film Cooling

Abstract: The present computational study involves a flat plate subjected to combined effect of jet impingement and film cooling. A conjugate heat transfer model in conjunction with k-ω SST turbulence model is employed to study the turbulence effects. The effect of Reynolds number varying from 389 to 2140 on static temperature, Nusselt number and film cooling effectiveness has be discussed for the blowing ratios of 0.6, 0.8, 1.0. The variation in the size of vortices formed on the impinging surface with Reynolds number is studied. It has been observed that the local Nusselt number shows a rising trend with the increase in Reynolds number, while the static temperatures follow the downfall in its values. As a result, an enhancement in the effectiveness is observed, which is credited to the capabilities of combined impingement and film cooling. At Reynolds number of 972, the coolant jet is found to be attached to the surface, for this condition the heat transfer phenomena for blowing ratios of 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 2.4, 2.6 are studied to understand the flow distribution on the plate surface. Keywords: Jet impingement, film cooling, effectiveness, conjugate heat transfer

Time-Accurate Evaluation of Film Cooling Jet Characteristics for Plenum and Crossflow Coolant Supplies

Abstract Gas turbine film cooling creates complicated and highly unsteady flow structures. This study seeks to examine the unsteady characteristics created by different cooling hole inlet geometries using a fast-response pressure-sensitive paint (PSP) technique able to capture time-accurate measurements at 2000 frames per second, resolving frequencies up to 1000 Hz. Time-accurate and time-averaged measurements are used to evaluate the performance of a plenum-style inlet and a crossflow-style inlet in varying turbulence environments over a flat plate. The results of this study are intended to begin the process of breaking down widely accepted time-averaged film effectiveness trends into the cumulative effects of freestream turbulence and momentum flux ratio, with emphasis on the cooling jet motions they cause. Jet behaviors observed in this study include a sweeping oscillation, unsteady attachment and separation from the plate, and time-accurate and time-averaged flow bias. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. Crossflow-fed cooling holes show bias to the upstream side of the cooling hole with respect to the internal crossflow direction. Plenum-fed cooling holes outperform crossflow-fed cooling holes, and the difference grows with increasing momentum flux ratio. The frequency of both plenum- and crossflow-fed cooling jet motions is influenced by the freestream turbulent velocity fluctuations. The resulting mode shapes show dominant side-to-side sweeping for higher turbulence environments and a separation and reattachment motion for lower turbulence environments. At higher momentum flux ratio, the jets were seen to increasingly favor separation and reattachment motions. The results of this study are intended to better inform existing predictive tools. With a better understanding of the time-accurate behaviors responsible for creating the commonly accepted time-averaged coolant distributions, simple predictive tools may be better equipped to accurately model film cooling flows.

Thermal Transport Analysis of Injected Flow through Combined Rib and Metal Foam in Converging Channels with Application in Electronics Hotspot Removal

The development of miniaturized and more powerful electronic devices and microprocessors has resulted in high heat generation and temperature values in these components. That affects the performance, reliability and lifespan of the devices. In addition, more local hot spots are generated in the components that require even more attention to prevent stress failure and fatigue. As such, the employment of advanced electronics cooling systems is very essential to keep the temperature below the safe temperature. In this work, innovative cooling systems are developed and analyzed employing jet impingement technology, high conductive metal foam, rib structured target surfaces, confined non-uniform small-scale channel, and conductive heat spreader plate. The base of the foam-filled cooling channel is subject to a uniform high heat flux value resembling the electronics device to be cooled. For numerical modeling of thermal transport through foam filled region, the local thermal non-equilibrium model in porous media is utilized resulting in two energy equations for solid and fluid phases. For better understanding of flow and thermal characteristics of jet impingement through the combination of metal foam and rib structured surfaces in confined channels, several effective parameters are studied such as slot and circular jet impingements, the shape and orientation of the ribs, impinging jet velocity, applied heat flux and the thickness of conductive heat spreader plate for hotspot removal. The results show that the fully foam filled channel provides a more efficient cooling in comparison with partially foam filled channel. Furthermore, the results indicate the advantage of utilization of ribs at the stagnation region of the impinging jet, for local thermal treatment of hotspots. The perpendicular cuboid ribs placed at the stagnation zone of the coolant jet impingement provide 13% increase in maximum local Nusselt number while the increase in the pressure drop and required pumping power are as small as 4.2%. Doubling the velocity would result in 35.3% increase in the maximum local Nusselt number, 180% increase in the pressure drop and 460.7% increase in the required pumping power. An increase in the thickness of the conductive heat spreader plate increases the base local temperature but improves local temperature uniformity.

Numerical investigation of blowing ratio, density ratio and axial position of film holes on the vane endwall film cooling effectiveness with upstream step

The aerothermal performance of interrupted slot and film holes was numerically investigated. Previous study indicates that the interrupted slot performs better compared to the conventional slot. In the meanwhile, the step formed along with the interrupted slot affects the film cooling characteristics. In this article, a row of film holes is arranged downstream of the step, and the mass flow rate for the interrupted slot is constant at 1%. Blowing ratio (BR) from 0.5 to 1.5 and density ratio from 1 to 2 were studied for the film holes. Endwall film cooling effectiveness distribution indicates that film cooling is easily affected by the secondary flow inside passage and the upstream step. Coolant traces are split into two parts due to the effects of step vortex and transverse flow. For different density ratios, increasing BR shows a different trend of film cooling effectiveness due to the variation of coolant momentum. The coolant jet is easily affected by the secondary flow when its momentum is low, but tends to liftoff when its momentum is too high. As a result, it is better to position the film holes far away from the upstream step. The total pressure loss coefficient distribution at the passage exit indicates that the coolant injection increases the total pressure loss. But density ratio has smaller effect on the loss variation. Besides, two axial positions of cooling holes were studied to improve the endwall cooling performance. Without the effect of step vortex, the film effectiveness of cooling holes is improved.