Impingement Holes Research Articles

Fatigue notch strengthening effect of nickel-based single crystal superalloys under different stress ratios

Nickel-based single crystal superalloys (Ni-SXs) are widely used in turbine blades of aircraft engines. With the increasing demand for higher temperature-bearing capacity, the introduction of film cooling holes, impingement holes, and trailing edge slots for cooling induces stress concentration, which compromises the structural integrity of the blades, generates complex multiaxial stress states, and adversely affects their operational performance. In this study, Ni-SXs, DD6, was utilized to investigate the influence of stress ratios on fatigue performance under complex stress states. Low cycle fatigue (LCF) tests were carried out at different stress ratios with stress concentration coefficient Kt = 1.0, 2.0 and 3.0. The results indicate that the notched specimens exhibit a significant fatigue notch strengthening effect under high stress ratios. The fracture surface and microstructure also indicate that under high stress ratios loading, the notches exhibit significant creep failure characteristics. This means that the main cause of fatigue notch strengthening is similar to creep notch strengthening effect. A macroscopic anisotropic constitutive model coupled with damage was developed and applied to finite element analysis of notched specimens. The results demonstrate that as the stress ratio rises, the stress relaxation effect at the notch becomes more pronounced, yet the level of damage diminishes. Additionally, a stress-equivalent model based on Bridgman stress was proposed, which effectively unifies the lifetime trends of notched and smooth specimens, predicting lifetimes within a threefold error band.

Multi-step optimization of hybrid cooling array via integrating Taguchi method and long short-term memory neural network

In advanced aero-engines, the pursuit of higher propulsive efficiency and power output creates an imbalance in the supply and demand of cooling air. In response, this study establishes a multi-step optimization platform for the hybrid cooling array, with the dual objectives of improving the cooling efficiency and coolant utilization. The design space involves the impingement hole diameter, film hole pitch in the spanwise and streamwise directions, thickness of the cellular partition and film cooling plate, height of impingement channel, and configuration inclination. Furthermore, two types of coolant supply condition are incorporated into the study. To attain the dual objectives, we specify a fixed constraint on the coolant supply per unit area. Taguchi method is chosen for the initial design of partial factors that have a weak nonlinear relationship with the cooling effectiveness. Optimization is conducted by long short-term memory model combined with manta ray foraging optimization algorithm for the residual factors which maintain a strong nonlinear relationship with the cooling effectiveness. Using the Taguchi method, the optimal combination for maximum cooling performance and relative contribution level of initial design factors have been successfully determined, and a set of mechanism analyses are given accordingly. LSTM model achieved a high reconstruction precision for the laterally averaged cooling effectiveness (ηlat¯) of the hybrid cooling array, with mean absolute error of 0.31 % and 0.83 % for ηlat¯, determination coefficient of 0.9997 and 0.9988 for the area-averaged overall cooling effectiveness (ηov¯), in the training and testing group, respectively. Meanwhile, the optimized cooling array exhibits an encouraging performance, with 8.94 % and 10.37 % improvements on ηov¯ for two coolant supplies, respectively. It is believed that the proposed framework can be generalized to optimize other forms of hybrid cooling array.

Large-Eddy simulation of flow and thermal behavior in jet impingement on a flat plate under rotating conditions

As an effective method for enhancing local heat transfer, impingement cooling is widely used in various applications. The present study focuses on the impingement jets in rotating channels and investigates the influence of additional force on the flow structure and heat transfer with large eddy simulations (LES). The second-order statistics of impinging jets give a deeper understanding of the turbulent dynamics in impinging jets and provide practical guidance for optimizing jet designs. In this paper, a model of three equally spaced impingement holes with a jet spacing between adjacent impingement holes of 5.25D and the jet to the target distance of 3.75D is simulated. The jet Reynolds number is kept fixed at 16000 and different rotation numbers of 0, 0.0042,0.0083, and 0.0125 are investigated. The LES results are compared with experimental results and show the WALE SGS model is the most suitable for impingement jet simulation. The numerical results reveal that rotation has an unignorable influence on the flow structure and heat transfer. Rotation induced the centrifugal buoyancy force and the Coriolis force has a large effect on the flow structure of the jet. Compared with the stationary condition, the jet shifts towards the -X direction and + Y direction causing an uneven velocity distribution in the impingement chamber under rotating conditions. The uneven velocity induces more turbulence in the jet and triggers additional vortices in the impingement chamber, especially on the +y side of the jet. The shifting of the jet also weakens the impingement cooling performance. The Nusselt number decreases with the increase of the Rotation number.

A conjugate study on the application of combined impingement and film cooling for a turbine blade tip

The blade tip region is facing an extremely harsh environment, and it is critical to apply the cooling method here. Conventional film cooling (FC) has been commonly used for tip cooling till now, but it consumes a lot of coolant thereby reducing the gas turbine operating efficiency. It has been verified that the combined impingement and film cooling (CIFC) technique shows better cooling performance than the FC case, but its performance on the tip region is not yet known. Therefore, in this paper, the combined impingement and film cooling technique was implemented for the blade tip region, and was compared with the conventional film cooling using a conjugate method. Then, based on the CIFC technique, overall cooling effectiveness (φ) distributions of the tip were obtained via the Infrared thermography with different impingement hole layouts, blowing ratios (M = 1.0–2.5), and relative impingement distances (Xn = 1.5, 3.0, 6.0). The validated numerical simulations were adopted for additional analysis. The results show that, compared with the conventional FC, the application of the CIFC technique can increase the tip φ (increased by 70 %–80 %) and decrease the tip solid temperature. Moreover, the low φ values were detected near the leading edge (LE), and placing more impingement holes near the LE will help increase the φ values here. What’s more, increasing the relative impingement distance would weaken the cooling performance. At a coolant M = 1.0, the φ was decreased by 4.1 % and 12.9 % from Xn = 1.5 to Xn = 6.0, respectively. The application of the CIFC technique for the tip region can diminish the coolant supply and hence can be a reference in the tip cooling design.

Impact of distance on heat transfer at the leading edge of blades in a rotating state

To enhance the high-temperature capability of turbine blades and meet the requirements of advanced design, this research examines the intricate flow characteristics and the heat transfer occurring on the internal walls effects of leading-edge impingement cooling structures under different impingement distances. In this study, copper block method is employed for heat transfer testing, extending the testing range of rotating impingement cooling channels from Redj = 1 × 104, Ro = 0.2 to Redj = 5 × 104, Ro = 2.0. The findings reveal that the Nusselt number along the channel is significantly influenced by flow distribution and turbulence intensity. At lower Re (Re ≤ 2 × 104), the flow velocity increases along the channel due to the decrease in pressure drop, resulting in enhanced heat transfer. However, at higher Re (Re ＞ 2 × 104), increased flow rate leads to intensified turbulence and thickening of the boundary layer, consuming fluid energy and reducing the temperature difference, thereby adversely affecting heat exchange around the impingement holes. Moreover, Nu decreases with increasing rotation speed, with the highest average decrease of 15.3 % when Ro reaches 0.25. For cases where Redj ＜ 4.3 × 104, an impingement distance-to-diameter ratio (Z/D) = 2 exhibits optimal heat transfer performance. Conversely, when Redj＞4.3 × 104, the influence of impingement distance will diminish. Larger impingement distances increase the HTC but are accompanied by increased non-uniformity. Therefore, selecting an appropriate impingement distance can reduce boundary layer formation and flow separation, thereby forming an optimal flow structure, which contributes to promoting heat exchange and improving heat transfer uniformity. A correlation based on geometrical parameters has been proposed to predict the average Nusselt number for jet impingement arrays with varying geometrical configurations.

The Manufacturing and Experimental Validation of a Nickel Superalloy Double-Wall, Effusion Test Specimen

Abstract With the hot stage of a modern aeroengine operating with combustor firing temperatures well beyond the melting point of the nickel superalloys from which the turbine blades are manufactured, developments to the methods of cooling of these components are required to advance performance. Double-wall, effusion systems exhibit a quasi-transpiration like cooling effect with recent work demonstrating their exceptional cooling performance. Such systems are characterized by two walls, one with impingement holes and the other with film cooling holes, that are mechanically and thermally connected via pedestals. However, manufacturing such geometries from single-crystal nickel superalloys remains a significant barrier to entry into service. This paper presents a method of manufacturing double-wall effusion specimens from a nickel superalloy commonly used in modern commercial high-pressure turbine components. The method maintains the mechanical integrity associated with nickel superalloys. Details of the method are presented alongside X-ray and GOM laser scan data of a flat-plate test article that demonstrates the success of the manufacturing process. Aerothermal testing of the specimen in a bespoke recirculating wind-tunnel facility was undertaken in which the overall cooling effectiveness of the system is obtained. The results reaffirm the excellent cooling performance of double-wall, effusion systems and further validate the manufacturing methodology as a method by which to realize enhanced cooling effectiveness in service.

Transient film outflow performances of laminated cooling configurations in leading edges of turbine vane

In this work, time-resolved quantitative light sheet technique is used to capture the transient outflow performances of the laminated cooling in turbine vane leading edges. A series of numerical simulations are performed to deeply understand the intrinsic flow and heat transfer mechanisms. Two laminated structures are compared, one is a traditional design with uniform hole-diameter (UD), and the other contains non-uniform hole-diameters (NUD) with locally-enlarged film and impingement holes on pressure side. Time-averaged results show that NUD can obtain a higher film effectiveness and a better film coverage due to the decreased momentum of cooling air-jet, and the relative improvement from UD can achieve 58.7%. The unsteadiness analysis of transient film is conducted by quantifying the standard deviation of instantaneous data, and it shows that the fluctuation of cooling air-jet mainly originates from Kelvin-Helmholtz instability at mainstream/coolant interfaces and separation vortex. The new design of NUD can also obtain a low near-wall unsteadiness level, because the separation vortex disappears on target surface, which implies a lower risk of thermal damage. Moreover, the mass flow rate of cooling air is an important factor on transient film performance, which can aggravate the separation of cooling air-jet and cause a higher unsteadiness level.

High temperature creep property of a novel porous double layer cooling structure for gas turbine blades

This article investigates the high-temperature creep macroscopic and microscopic fracture mechanism of the porous double layer (PDL) cooling structure through experiments, and predicts the creep life of the structure using the back propagation (BP) neural network model based on the bone point stress method. The high temperature creep fracture of the PDL cooling structure is determined by the macro structure characteristics and the microstructure properties. Impingement holes and effusion holes, as stress concentration region, provide a place for crack initiation. The crack growth rate of effusion plate is greater than that of impingement plate. When the creep crack extends to a certain length, the effusion plate breaks first, and then the impingement plate breaks instantaneously. At the interface between carbide and matrix, microcracks are prone to occur due to stress concentration and inconsistent deformation, thereby promoting the initiation and propagation of macroscopic cracks. The BP neural network model based on the bone point method has a good prediction result for the creep life of the PDL cooling structure, and the maximum prediction error is 9%.

Experimental study on cooling characteristics of an air-cooled evaporative flame holder under combustion conditions

The flame holder needs an integrated design with the cooling structure in advanced ramjet or afterburner combustors. Experimental studies were carried out on the air-cooled evaporative flame holder with impingement-film-slot composite cooling structure under combustion conditions. The effects of blowing ratio M (0.54–2.74) and fuel-air ratio FAR (0.0016–0.0027) on the cooling characteristics of the flame holder were studied under mainstream inlet temperature T = 600 K, inlet Mach Number Ma = 0.15 and on-duty combustion conditions. The results show that the air-cooled evaporative flame holder can stabilize the flame after adding cold air. When the blowing ratio M increases, the wall temperature decreases and the cooling effectiveness increases. The average cooling effectiveness is only 0.237 at M = 0.54 and can reach 0.595 at M = 2.74. The distribution of cooling effectiveness on the inner surface of the flame holder is similar at different blowing ratios. Along the flow direction of the inner surface, the first row of cooling structure A uses the impingement jet and the guide ring to form the initial cooling film. The cooling effectiveness of the first row A is from 0.352 to 0.433 at M = 1.89. The next row B downstream the impingement holes and guide ring uses discrete film holes and has a high cooling effectiveness ranging from 0.578 to 0.815 at M = 1.89. The row C with discrete film holes downstream of B is close to the combustion recirculation zone and has a higher heat load. The cooling effectiveness of row C is 11.7%–23.5% lower than that of row B. The last row D with slot holes is at the trailing edge heated by the hot gas in the recirculation zone. The protective effect of the cooling film is poor in row D and the cooling effectiveness is only about 0.268–0.276 at M = 1.89. In the spanwise direction, the cooling effectiveness is higher near the cold air inlet and lower away from the cold inlet. The increase of the fuel-air ratio (FAR) mainly affects the combustion temperature and wall temperature, and has little effect on the cooling effectiveness. When the fuel-air ratio increases from 0.0016 to 0.0027, the average cooling effectiveness varies from 0.502 to 0.558. As the fuel-air ratio increases, the distribution pattern of cooling effectiveness at all measuring points has little change.

Flow structure comparison of film cooling versus hybrid cooling: a CFD study

Abstract Film and jet impingement cooling are widely used techniques in gas turbine vane and blade cooling. The present work investigates and compares the flow structure of a film-cooled flat plate with a hybrid cooling scheme. The hybrid cooling scheme combines both impingement hole and film holes and is named combined impingement-film (IFC) cooling. Experimental validation and computational analyses are carried out on a flat plate with film holes. Different flow parameters, such as velocity pattern, Turbulent kinetic energy, and streamline flow structure, are compared for the two cases in different regions of the flat plate. It is observed that the hybrid scheme shows advantages over film cooling. The jet-to-jet interaction, jet crossflow interaction, and vortex formation are the main factors affecting film cooling performance. There is a 52 % drop in turbulent kinetic energy for the hybrid cooling compared to the film cooling at the film hole exit. More mixing in the coolant and mainstream interaction is observed for the FC case than in the IFC.

Numerical research on the particle transport and deposition in the impingement-film cooling passage

With the aim of exploring the particle transport and deposition characteristics in the internal cooling channel of turbine blades, the computational fluid dynamics-discrete element method is used to implement the numerical simulation of particle transport and deposition in the impingement-film cooling passage. First, the unsteady development process of the particle transport and deposition with the increase in injection particle mass is obtained. Then, the effect of jets Reynolds number, particle Stokes number, and initial particle volume fraction on the particle deposition characteristics is presented. Finally, the particle deposition mechanism in the impingement-film cooling passage of turbine blades is revealed. The results show that the conical-shape particle deposition layer is formed at the impingement stagnation point region and the banded-shape particle deposition layer is formed between adjacent impingement holes. The cooling gas carrying particles is injected from the impact hole and subjected to the fluid shear force. Then, the cooling gas carrying particles gradually developed into the conical-shape free jets. In addition, the symmetrical vortex structure is formed due to the collision of the adjacent jets. Therefore, the particle deposition layer is formed on the impingement target surface, which is caused by the energy attenuation due to the continuous collision of the particle with the particle and the particle with the wall. The increase in the jets Reynolds number inhibits the particle deposition behavior, and the increase in the Stokes number accelerates the particle deposition behavior.

Thermal analysis of guide vanes with full double wall cooling structure with focusing on leading edge cooling

In order to explore the thermal characteristics of the leading edge structure of the full double wall cooling structure guide vane, a double wall cooling structure guide vane is established on the basis of the vane model and the proven simulation method including of k-ε model and Fluid-Structure interaction method. Air film holes, impingement holes and spoiler columns with different forms are constructed at the leading edge of the vane, and the thermal characteristics of various structures are discussed through 3D simulation under many kinds of cooling conditions. The 30° left deviation of air film hole with good combination of dynamic and static pressure showed the most excellent air film coverage effect. The scheme of adding a row of impingement holes has better air film effect than the scheme of increasing the diameter of the impingement holes, due to the fact that the high-speed airflow from large diameter impingement hole accounts for about only 50% of the total airflow. The flow turbulence degree in the 30° left-deviation air film hole is much higher than that of the vertical angle. The compound angle and spoiler columns in local design can improve the local cooling effect, on the outer and inner surfaces of the vanes, respectively.

Multi-objective design of laminated cooling configuration applied in gas turbine based on fuzzy grey relational analysis

Laminated cooling is a compound system consisting of different cooling units that can provide effective protection to the hot components in next generation gas turbines. In the present work, using validated numerical simulations, the influential levels of geometrical parameters in laminated cooling configuration (film hole diameter, pin-fin diameter, impingement hole diameter and film hole inclined angle) on multi-objective functions (overall cooling effectiveness, friction loss and temperature uniformity) are calculated and ranked by fuzzy grey relational analysis (FGRA). The FGRA results indicate that the film hole diameter is the primary influence factor on the overall cooling effectiveness and temperature uniformity, but insensitive to the friction loss. Based on this finding, two novel laminated cooling configurations with revised film-hole shapes, i.e., fan-shaped film holes and discrete rectangular film slots, are proposed to meet the multi-objective requirement. Through calculations, it is proved that the overall cooling effectiveness of the discrete film slots with a width of 0.5 mm can be increased by approximately 20%, whereas the additional friction loss is negligible (the increase of flow resistance coefficient is only 0.06 at mass flow ratio equals to 1.19%). Meanwhile, the acceptable temperature uniformity along with high overall cooling effectiveness, low friction loss can be obtained with the design of the fan-shaped film holes. The present work provides a novel analytical method for the multi-influence-factor problem and multi-objective design of complex laminated cooling system in gas turbine application.

Investigation of impingement heat transfer in double-wall cooling structures with corrugated impingement plate at small Reynolds numbers

This study investigated an impingement/effusion cooling scheme with a corrugated jet plate applicable to a high-temperature exhaust cooling nozzle. The primary objective was to evaluate the effect of the corrugated wall jet on the impingement heat transfer and flow loss in a narrow target chamber under a low jet Reynolds number ranging from 450 to 2700. Sinusoidal curves with different wavelengths were employed to model the corrugated jet plate, where impingement holes were located at the trough of the plate. The location of the impingement holes creates a staggering pattern relative to the effusion holes. The corrugated jet plates with relative ripple amplitudes (A/d) considered were 0.2, 0.5 and 0.8, and the results were compared with those of a flat jet plate. Three relative average jet-to-plate spacings, Have/d, were selected for use: 1.6, 2.6, and 3.6. The heat transferred over a smooth target surface by multiple jets was measured using the transient liquid crystal (TLC) method. Results show that the amplitude of the corrugated plate was found to profoundly influence the heat transfer of the target surface. The use of corrugated jet plates yielded a better heat transfer performance at a relatively high Re and low impinging distance. The optimal heat transfer performance was achieved at A/d of 0.5, which was 28 % higher than the flat plate. The discharge coefficient for the corrugated jet plate was 2–9.4 % lower than that of the flat jet plate at all Have/d and Re values, and the minimum discharge coefficient was reached at A/d of 0.2. Furthermore, internal impingement heat transfer and flow resistance characteristics of the corrugated impingement/effusion were correlated according to the experimental data.

EFFECT OF JET TO PLATE SPACING ON FILM COOLING PERFORMANCE IN A COMBINED IMPINGEMENT AND FILM COOLING ARRANGEMENT

The influence of jet to plate spacing on conjugate heat transfer from a flat plate with combined impingement and film cooling has been studied both numerically and experimentally. The flow configuration consists of a matrix of impingement holes and multiple staggered rows of cylindrical film holes. One side of the plate is impinged with air jets, while the other side is exposed to hot mainstream as well as the vented air from the film cooling holes. The effect of increasing jet to plate ratio (H/D = 0.4, 1.2, and 2.0) on film cooling flow structure and heat transfer is analyzed under conjugate boundary conditions. The flow and temperature patterns are predicted in the entire computational domain; namely, the plenum chamber, film holes, and mainstream-coolant interaction zone. The mainstream Reynolds number is varied from 49,050 to 130,800 while keeping the jet Reynolds number constant at 825 and the blowing ratio ranging from 0.6 to 1.6. The velocity, turbulence, and temperature distributions at the exit of the film hole together define the film coverage on the interaction surface. The thermochromic liquid crystal (TLC) technique is used to evaluate the surface temperature of the plate and validate the computed values of the surface effectiveness. Both measured and computed effectiveness distributions are found to be comparable. Increase in the H/D values beyond a certain limit causes decrease in film effectiveness on the interaction surface, especially downstream of the film hole. The influence of H/D is noticed for all the three blowing ratios investigated, albeit to varying degree.

Experimental and numerical studies on the enhanced heat transfer performance and the flow resistance characteristics of the double-wall cooling structure with jet impingement holes and pin fins

The double-wall cooling as one of the most important cooling techniques of the hot-end components of aero-engine, the heat transfer performance of double-wall cooling structure can be significantly enhanced by the combination of jet impingement cooling and pin fins. Therefore, the double-wall cooling structure with jet impingement holes and pin fins has very important engineering application value. For the double-wall cooling structures with jet impingement holes and pin fins, the experimental studies have been carried out based on various of geometrical and flow parameters. Furthermore, the corresponding numerical simulations have also been carried out according to the corresponding experimental study conditions. In order to approximate to the real double-wall enhanced heat transfer structure of the hot-end components of the aero-engine, in present experimental and numerical studies, the double-wall enhanced heat transfer structure with the double-side outflow channel and the advantage of structural symmetry is adopted. Based on the numerical simulation results, the internal flow field structure, the flow resistance characteristics and the interior enhanced heat transfer performance of the double-wall cooling structure with jet impingement holes and pin fins are analyzed in detail. In addition, the main reasons why the pin fins can enhance the heat transfer performance of the double-wall cooling structure that with jet impingement holes and pin fins are further revealed. Actually, the enhanced heat transfer performance of the double-wall cooling structure is the results of the interactions between the internal jet impingement cooling, the internal crossflow and the turbulent flow of pin fins. Moreover, the influences of the jet impingement Reynolds number (Re), the non-dimensional row spacing (X/D) and the non-dimensional hole pitch (Y/D) of jet impingement holes, and the dimensionless diameter (Dp/D) of the pin fins on the enhanced heat transfer performance, the internal flow characteristics, the distributions of local Nusselt number Nu and the flow resistance characteristics of the double-wall cooling structure with jet impingement holes and pin fins are further revealed. Importantly, for all numerical simulation conditions, the distribution differences of the enhanced heat transfer performances on the wall surface of the pin fins and on the wall surface of the jet impingement target plate with the variations of the geometrical parameters and the flow parameters are analyzed in detail. The numerical results indicate that the area-averaged Nusselt number Nu═ on the wall surface of the pin fins is higher than that on the internal wall surface of the jet impingement target plate. With the increase of the pin fins diameter Dp/D, the Nu═ on the whole internal wall surface of the double-wall cooling structure presents a tendency of firstly decrease and then gradually increase. In addition, the Nu═ on the entire interior wall surface of the double-wall cooling structure decreases with the increase of row spacing X/D, but it is not sensitive to the variation of hole pitch Y/D. Moreover, for the discharge coefficient of the double-wall cooling structure, it gradually increases with the increase of the jet impingement Reynolds number Re, the row spacing X/D and hole pitch Y/D of jet impingement holes, but it decreases with the increase of the diameter Dp/D of pin fins. Finally, for 3 ≤ X/D ≤ 5, 3 ≤ Y/D ≤ 5, 1≤Dp/D ≤ 2, and 9000 ≤ Re ≤ 30,000, a correlation of the area-averaged Nusselt number Nu═ is given, which is in good agreement with the experimental results.

Experimental investigations into the effusion plate wall temperature of impingement/effusion cooling systems for gas turbine combustors

Cooling technologies are playing critical roles in the development of advanced gas turbine combustors. The present experimental investigation has studied the effects of geometric factors such as gap distance, impingement hole diameter, and effusion hole arrangement on the wall temperature of a novel impingement-effusion cooling system. The wall temperature of the effusion plate was directly measured by high-precision thermocouples. The wall temperature distribution of the cooling unit was obtained by biharmonic spline interpolation based on the measured temperature data. The cooling performance of cooling systems with different structures under different working conditions was compared. The experimental results indicate that the increase of gap distance weakens the strength of impinging jet, and the overall cooling performance decreases, accordingly. The smaller the diameter of the impingement hole is, the weaker the cooling film is, leading to a poor overall cooling performance at the same cooling airflow. However, better overall cooling performance can be obtained at the same blowing ratio at the cost of much more cooling airflow. Dense and uniform effusion hole arrangement has a very favorable impact on improving the cooling film quality and cooling performance.

Uniform impingement heat transfer distribution in corrugated channel with an anti-crossflow-wing

For a further improvement of impingement jet array heat transfer in a corrugated channel, a wing-shaped structure design is proposed to weaken crossflow degradation. The naphthalene sublimation method was used to measure local heat/mass transfer distributions in the present study. Pressure drop characteristics were examined through pressure measurements. Detailed flow structures were analyzed through numerical simulations. In order to validate the superiority of the current wing structure, it was compared with the impingement heat transfer values from a typical rectangular channel and a conventional corrugated channel. The hole diameter-based Reynolds number was fixed to 10,000. The impingement distance and spacing between holes were h/d = 1 and s/d = 5, respectively. The hole patterns were designed to be in-lined in all cases. As the wing structure was added to the corrugated channel, the impingement supply flows of downstream holes became axisymmetric. The wing structure noticeably suppressed the re-entry flow from the corrugated channel back into the main/impingement channel, particularly under the downstream row of impingement holes. As a result, the overall area-averaged Sherwood number increased by about 6.4%, and the heat transfer non-uniformity in the streamwise direction was significantly reduced.

Experiment investigation of impingement/effusion cooling on overall cooling effectiveness and temperature gradients of afterburner heat shields in a high-performance aircraft engine

Considering that the jet impingement cooling method applied to the combustion chamber and turbine blade has a beneficial effect on the cooling performance, the impingement/effusion cooling was applied in the afterburner heat shield (DCH) to improve the reliability and durability of the afterburner cylinder. Although the impingement/effusion cooling scheme has been numerously investigated on the internal heat transfer, its investigation of conjugated heat transfer characteristics is limited as applying in the afterburner heat shield. This paper aims to investigate the effects of adding array impingement and area ratio on the conjugate heat transfer of afterburner heat shield. The surface temperatures on the mainstream side of DCH in the upstream (UR), midstream (MR), and downstream (DR) regions were measured using IR thermography under a high-temperature ratio between mainstream and coolant (Tg/Tc = 2). The overall cooling effectiveness (ϕ) and temperature uniformity (RSD) were plenty compared with the single-layer effusion cooling heat shield (ECH) at three momentum flux ratios (I = 0.02,0.22,0.50). Moreover, the area ratio of film to impingement holes (Af/Ai) was enlarged from 1 to 4 to obtain high cooling effectiveness and low-temperature gradient. The results indicate that when I is larger than 0.22, the area-averaged ϕ of DCH compared with ECH can be improved by about 16% over the whole measured regions, and 20% in the UR with the lowest ϕ. In addition, the drop coefficient of the RSD of DCH can reach 18%. In comparison with the DCH at Af/Ai = 1, the DCH with an area ratio of 4 can achieve gains of 80% and 45% on ϕ and RSD, respectively. Therefore, adding array impingement on the coolant side of DCH and increasing Af/Ai cannot only effectively reduce the surface temperature of the heat shield and form efficient cooling in the UR, but also increase the temperature uniformity over the entire heat shield, thereby improving the reliability and durability of the afterburner cylinder. Furthermore, the comprehensive and new database can be used to evaluate the computational fluid dynamics simulations in related coupled and decoupled research.

Numerical simulation on heat transfer and entropy generation of impingement cooling on boss shaped surface

Using impingement jet to cool the external cavity of the end wall of the gas turbine guide blade is very effective for prolonging the service life of the gas turbine and ensuring its safety operation. In this paper, the numerical simulation method is used to study the impingement cooling heat transfer performance of the boss shaped surface in the external cavity of the end wall of the gas turbine guide blade, and the entropy generation of the impingement heat transfer process is analyzed. The results show that the average Nusselt number on the impingement target surface and the impingement hole surface increase with the increase of the Reynolds number of the impingement jet. When the Reynolds number is constant, the average Nusselt number of impingement target surface and impingement hole surface decrease with the increase of impingement target distance, but the cooling range on the impingement target surface increases and the heat transfer is more uniform. With the increase of the width of the boss shaped upper surface, the cooling range on the impingement target surface relatively decreases, and the average Nusselt numbers of the impingement target surface decreases and that of the impingement hole surface increases respectively. The heat transfer of the upper surface of the boss is better than that of the lower surface on both sides. The entropy generation in the process of impingement cooling mainly comes from the entropy production caused by viscous dissipation and the entropy flow caused by heat transfer. The entropy production in the flow vortex region is the main reason for the entropy generation. The research conclusions can provide basis and reference for optimizing the structural and operating parameters of boss shaped impingement cavity and improving its impingement heat transfer effect.