Kidney Vortex Research Articles

Film hole layout optimization for multi-row film cooling plate in continuous parameter space under non-uniform inlet temperature distribution

Film cooling is an advanced external cooling technology for protecting gas turbine blades from excessive temperatures. To counteract non-uniform heat loads caused by hot streak and swirl effects at the combustion chamber outlet, fine design of film hole positions is necessary. However, the complexity due to the numerous film holes and their positional parameters presents challenges in the independent optimization of film hole positions in a continuous parameter space. This study proposed an optimization method grounded in the divide and conquer approach to address optimization for film hole layout. The film hole layout was decomposed into multiple single rows and optimized systematically by iteratively refining the single-row film hole layout along the streamwise direction using the expectation maximization algorithm. Optimized layouts for five different inlet temperature distributions were obtained using the proposed method and adiabatic wall temperature distributions were compared and analyzed for optimized and staggered layouts. Additionally, the cooling performance of the optimized layout was evaluated against the staggered layout under conjugate heat transfer conditions and the robustness of the optimized layout under various blowing ratios and peak temperature positions was tested. The results demonstrated that the proposed method can optimize the positions of 52 film holes within 0.3h, and it was generalized to various inlet temperature distributions. By enhancing lateral interactions among downstream film jets, the lifting effect of kidney vortex in the optimized layout was weakened, bringing the film jets closer to the wall and significantly increasing coolant coverage during streamwise development. Comparative analysis reveals the superior cooling performance of the optimized layout at the blowing ratio of 1.0, evidenced by a 15.1% reduction in total input heat transfer rate and a 12.3% enhancement in overall cooling efficiency relative to the staggered layout. Under conditions with blowing ratios ranging from 0.5 to 1.5 and peak temperature position deviations, the average wall temperature of the optimized layout consistently remained lower than the staggered layout, indicating the robustness of the optimized layout to variations in blowing ratio and hot streak position.

Effect of forward and reverse injection on film cooling and thermal stress distribution on a corrugated surface

In the present study, a combined experimental and numerical study is conducted to investigate the three-dimensional film cooling using forward and reverse injection over a corrugated surface. The experiments are performed to analyze the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical model under laboratory conditions (i.e. low temperature). Infrared thermography is used to estimate the temperature distribution and heat transfer coefficient. The numerical study is extended for a wide range of operating parameters at actual operating conditions of the afterburner liner. The outcome of numerical results shows promising results with reverse injection. The issue of kidney vortices with forward injection is mitigated with reverse injection. The reverse injection shows vortices in the plane of corrugation which improves the lateral spreading of coolant. A significant improvement in coolant coverage is reported over conventional forward injection, and the maximum improvement is 146%. Finally, a thermal stress analysis is conducted for film-cooled corrugated liners. The reverse injection shows promising results in terms of coolant coverage which reduces the overall temperature of the corrugated liner, hence thermal stress is significantly reduced.

Research on flow and heat transfer characteristics of supersonic film cooling with different hole-configurations

In order to investigates the flow and heat transfer characteristics under supersonic mainstream conditions among three typical film hole-configurations—cylinder hole (CH), fan-shaped hole (FSH), and laidback fan-shaped hole (LFSH), this study conducted numerical simulation using the ANSYS CFX and based on the assumption of compressible flow. The results indicate that the cooling effectiveness of the CH dramatically decreases as the blowing ratio increases, while FSH and LFSH improves. When the supersonic mainstream encounters the coolant, flow structures such as oblique shock waves, expansion waves, and mixing layers et al., will be generated around the film holes, which have an impact on the flow and heat transfer characteristics. Under the conditions of same blowing ratio, the shock wave intensity of LFSH is significantly lower than the other two holes and the kidney vortices formed by the CH develop further along the mainstream direction. While the strength of the kidney vortices formed by the FSH and the LFSH is weaker. Additionally, the LFSH incurred the least total pressure loss from before the shock wave to after the oblique shock wave. Specifically, at a blowing ratio of 0.8, it achieved a reduction of approximately 20% in total pressure loss compared to the CH.

Achieving Best Turbine Blade Cooling Efficiency from a Cylindrical Cooling Hole with Reverse-Vortex Generator Using Numerical Simulation

This investigation bargains mathematical investigation of the impact of kidney vortex generation (KVG) on the film cooling execution of a round cooling opening which has measurement (d = 20 mm) on a level plate. The collection between the stream cooling air and standard hot gases will result kidney vortex which will wipe out the film cooling adequacy. Two kind of reverse vortex generator (RVG) with various statures (H = 0.5 d and 0.25 d) are intended to eliminate the kidney vortex and examine best film cooling adequacy, where every one of them is mounted to the level plate upstream of the cooling opening by changing its parallel positions (A = 0.0 d, 0.25 d, 0.5 d and 0.75 d) concerning the opening community line and for each kind has diverse distance regard to opening focus line. The changing of blowing proportion (BP = 0.5-1.0) was considered in this investigation. The simulation model was used to simulate the formation of film cooling using a shear stress transfer (SST) model by Workbench 15 software. The outcomes have been introduced in terms of laterally averaged and maximum value of film cooling comparison diagrams, vorticy on x/d = 3.0 and film cooling distribution which clarified how the outcomes acquired. The Cases 04 and 07 gave the best situations for RVG where case 04 gave wide covered for laterally average film cooling efficiency (η = 0.35), while case 07 gave the highest expansion distribution and the maximum value for film cooling efficiency (η = 0.66). The best results are obtained when the blowing ratio (BP = 0.5) due to a lower velocity of cooling air which will made best interaction with the hot air (main stream)which will represent the hot gases in real case.

Experimental and Numerical Investigation of Cylindrical and Shaped Cooling Holes With Forward and Reverse Injection

The present work proposes a suitable injection hole configuration of cylinder and laidback fan-shaped with forward and reverse direction for film cooling of a gas turbine blades application, based on experimental and numerical analysis. The experimental study is conducted for cylindrical hole at blowing ratio (1), injection angle (35°), and density ratio (1.2). The numerical study is performed for a wide range of operating parameters such as blowing ratios on (1-3), density ratios (2.42), mainstream flow Reynolds number as 4000 based on the hydraulic diameter of wind tunnel channel and, injection angle (35°) with the effect of forward and reverse injection of laidback fan shaped. The present study reveals that the formation of kidney vortices mitigated for reverse-shaped holes (secondary air is injected such that its axial velocity component is in the reverse direction to that of the mainstream) results in higher cooling performance with respect to forward-shaped holes. The coolant coverage is likewise more consistent and higher in the lateral direction compared to the forward injection.

Comparisons of Overall Performance Among Double-Jet Film Cooling Holes, Cylinder Holes, and Fan-Shaped Holes

Abstract In this paper, the film-cooling effectiveness (η) and heat transfer coefficient (h) of different film hole geometries are investigated, including double-jet film cooling (DJFC) holes, streamwise cylindrical holes, and fan-shaped holes, both experimentally and numerically. Results reveal that when the blowing ratio is less than 1.0, the DJFC holes have the highest η and the highest h, as well as the highest net heat flux reduction (NHFR). However, a higher blowing ratio (>1.0) leads to a quickly decreasing NHFR of DJFC holes. The asymmetric antikidney vortex and the high turbulent kinetic energy (TKE) are dominant in the performance of the DJFC holes. Owing to medium effectiveness and the lowest heat transfer coefficient, the fan-shaped holes possess the highest net heat flux reduction at M = 2.0 although the value is negative. The relatively weak kidney vortex and the low TKE can explain the phenomena. The cylindrical holes have the lowest η and the lowest NHFR due to the kidney vortex and relatively higher TKE.

Effects of structural parameters of laidback fan-shaped hole on film cooling effectiveness on convex surface

To burden higher turbine inlet temperature, shaped holes are introduced to the film cooling of turbine blade. The structural parameters of shaped holes are the key variables for the cooling design. Relevant literatures conduct studies mainly on the flat surface, which excludes the influence of blade curvature. And their conclusions are inconsistent, appealing for further mechanism study. In this paper, the effects of structural parameters of laidback fan-shaped hole are experimentally investigated on a convex surface. Pressure sensitive paint technique is used to measure the adiabatic effectiveness. Three parameters, including forward expansion angle (0–12 deg), lateral expansion angle (2–20 deg) and length of the diffuser (2–14 mm), at five blowing ratios (0.5, 0.8, 1.0, 1.3 and 1.5) are tested. Numerical simulation is also employed to present the mechanism of jet-mainstream interaction. It is shown that, at the blowing ratio over 0.8, the optimal forward and lateral expansion angle lies in the medium range. Cooling effectiveness increases before the optimal value due to better film attachment but deteriorates after then due to coolant separation within the hole. In contrast, at the blowing ratio of 0.5, the results become different because the coolant attaches well enough that the change of the coolant dissipation rate appears more dominant. The competition of two factors, weaker kidney vortex entrainment and larger shear surface, leads to an unpredictable trend. Finally, suggestions are provided for the parameter selection on the blade suction surface. As a comparison, the same studies are numerically conducted on a flat surface. Distinctly, at high blowing ratio, the effectiveness increases monotonously without a drop at too large expansion because the absence of radial pressure gradient worsens jet attachment and magnifies the effect of promoting jet attachment.

Experimental and numerical study on unsteady entrainment behaviour of ventilated air mass in underwater vehicles

The hydrodynamic characteristics of underwater vehicles are significantly affected by the ventilated cavity covered by the vehicle surface. In this paper, the unsteady flow characteristics of this ventilated cavity are studied using experimental and numerical methods, and the unsteady entrainment behaviour of the ventilated air mass is emphasised. The flow pattern of the ventilated air mass is recorded using a high-speed camera. The large eddy simulation turbulence model is employed for the numerical simulations, and a good agreement is observed between the experimental and numerical results. In the early stage of the formation of the ventilated air mass, the internal structure exhibits a symmetric kidney vortex system, while the ventilated cavity below the vent hole has a continuous hairpin vortex structure. The ventilated air mass experiences a growth stage, an entrainment stage, and a shedding stage. The entrainment behaviour enables the ventilated air mass to quickly fill the ventilated cavity and modifies the surface pressure distribution of the vehicle. As the cavitation number decreases, the radial size of the ventilated cavity increases, and the contact area between the cavity and the water body increases, thus enhancing the vertical drag coefficient of the vehicle.

Improving turbine blade endwall cooling using air/mist mixtures and composite ramp-groove structures

Serrated grooves enhance the film cooling performance of turbine blades through extended lateral diffusion when the air is mixed with mist. This work proposes a novel composite structure combining an upstream ramp and a serrated trench to fully exploit the cooling capability of the air/mist mixtures. The simulations show that the film coverage of the mixtures can be significantly improved because the composite structure has an advantage over the zigzag grooves without slopes, as the kidney vortices induced by the former is smaller than the latter. As a result, the amount of coolant entrained by the vortex pair is greater than that entrained by the mainstream. Also, the influence of the eddy current formed by the proposed cooling structure on the vaporization position of the droplet is analyzed for the first time, concluding that the composite structure can better utilize the latent heat of vaporization of the droplet. The benefits are clearly seen in the blow ratios studied and the improvement is more pronounced at high blow ratios. It is also found that the cooling effectiveness is not linearly related to the ramp angle, because it is obviously affected by the droplet size and concentration, and its high value can only be reached within a certain range of ramp angles. Even under high-temperature and high-pressure conditions, the composite structure can achieve ideal cooling effectiveness at the turbine blade endwall. This work explores the turbine blade endwall cooling structures, offering novel insights into designing endwall cooling structures in new directions.

Aerothermal characteristics of thin double-wall effusion cooling systems with novel slot holes and cellular architectures for gas turbines

Double-wall effusion cooling system is a promising cooling solution for next-generation gas turbines. Thinning the blade wall can bring the coolant closer to the hot stream, thereby enhancing overall cooling effectiveness. However, a thin blade wall creates film cooling holes with a short length-to-diameter ratio, which increases jet-crossflow mixing and reduces coolant attachment, inevitably degrading film cooling performance. Herein, we constructed a new thin double-wall effusion cooling system by integrating novel short slot holes for better coolant attachment and triply periodic minimal surface (TPMS) based cellular architectures for improved internal heat transfer. The effects of wall thickness, film hole shape, and internal turbulators configurations were numerically studied. Adiabatic and overall film cooling effectiveness, vortex structures, and aerodynamics loss were comprehensively assessed. The results demonstrate that the novel slot hole significantly improves the overall film cooling effectiveness under thin wall conditions by enhancing the attachment of kidney vortices to walls. Notably, compared to the short fan-shaped hole (scheme B), the novel slot hole (scheme C) shows an improvement in the averaged overall cooling effectiveness of over 20% and a reduction in the total pressure loss coefficient by 60%. Furthermore, three TPMS-based cellular architectures produce similar overall film cooling effectiveness and reduction of total pressure loss coefficient in the range of 0.57-0.81 and 23%-53%, respectively. This work provides guidance for designing thin double-wall effusion cooling systems for next-generation gas turbines.

Numerical study on film cooling effectiveness from spiral-channel hole

Due to producing better film cooling performance, shaped film holes have attracted a lot of attentions and have been extensively studied. A spiral-channel hole, a new shaped film hole, is proposed to improve the film cooling effectiveness. The flow field, including flow structure inside film hole, velocity distribution and development of vortex pairs, of the spiral-channel hole and cylindrical hole are analyzed based on numerical simulation. And film cooling effectiveness of two types of holes is compared. Compared with the cylindrical hole, the averaged film cooling effectiveness of the spiral-channel hole improves by 97% and 667% in the case of M = 0.5 and M = 1.0, respectively. Inside the spiral-channel hole, the flow field appears a smaller separation zone and the streamline swirls and deviates significantly. The momentum of coolant at outlet of the spiral-channel hole is lower and more uniform in vertical direction and the lateral-velocity at outlet of the spiral-channel hole is larger. As a result, the coolant covers larger area in the spanwise distribution and its coverage area is three times larger than that of the cylindrical hole. The distribution and scale of the vortex, which is composed of large-scale vortex and small-scale vortex and distributes in the vertical direction, is completely different from the kidney vortex pair (cylindrical hole). Eventually, the vortex pairs in the vertical direction merge into a large-scale vortex. Since the destruction of the kidney vortex, this swirling structure is of great significance for improving the film cooling effectiveness.

Numerical study of optimum parameter design for film cooling effectiveness by Taguchi method

The present numerical study investigated a novel film cooling scheme that combines a cylindrical hole with an upstream Barchan-dune ramp and a triangular tab over the hole. Simulations revealed that this arrangement can induce an additional anti-kidney vortex pair on the outside of the original primary kidney vortices to suppress the penetration of the high-temperature mainstream by the cooling flow, increasing cooling effectiveness. Compared with schemes employing only a triangular tab or a Barchan-dune ramp, the novel film cooling scheme achieved superior cooling performance. An optimum parameter design is determined through the Taguchi method. Three parameters were investigated, namely, the Barchan-dune-shaped ramp height, triangular tab length, and blowing ratio, under various incoming temperatures. Analysis of variance revealed that the blowing ratio has the greatest influence on cooling effectiveness. An average cooling effectiveness of 34.1% was achieved by the optimum parameter design.

Investigation on Film Cooling Performance of a Novel Hole Arrangement Based on Combined-Hole Design

Abstract Based on a combined-hole design, a novel hole arrangement was proposed and tested on a flat plate model by numerical simulation. Replacing one row in two rows of staggered holes with a row of smaller holes, the bigger holes in one row and smaller holes in the other row will form combined-hole units. The kidney–vortex pairs in the combined-hole unit will interact with each other and get weakened, finally enhancing film cooling performance. Compared to the original two rows of staggered holes, the coolant mass flowrate will be reduced by 25% for the new hole arrangements. Results show that the area-averaged film cooling effectiveness of the new arrangements is similar or even higher than that of the original one at different blowing ratios. Replacing the second row of holes with smaller holes provide better cooling performance than replacing the first row of holes. The overall film cooling performance is not sensitive to the row space. The highest improvement of film cooling effectiveness is 24% when the blowing ratio is 1. However, as the coolant accumulation and reattachment phenomenon is weakened by the new arrangements, the film cooling performance is not as good as the original one when the blowing ratio is 1.5.

Numerical Investigation on Supersonic Film Cooling Performance with Discrete Film Holes

The effect of the discrete film cooling hole type on flow characteristics and the cooling performance of supersonic film cooling are numerically studied on a flat plate. Three film hole types (cylindrical hole, merged hole, and sister hole) are evaluated. Numerical simulation is conducted under a constant mainstream Mach number and six coolant Mach numbers ranging from . The three-dimensional effects of shock impingement on the flow characteristics and cooling performance are analyzed. The flow features (especially the interaction between the jet flow and the mainstream) are illustrated. The results show that the supersonic film cooling performance is heavily affected by many factors: the shear layer developed from the detached boundary layer, the boundary-layer separation downstream of the film hole, the jet liftoff phenomenon, the kidney vortex, and the oblique shock wave impingement. Those factors, except for the shock wave impingement, are heavily affected by the discrete film hole types and coolant Mach numbers. The shock impingement is not conducive to the lateral expansion of the cooling film. There is an optimal coolant Mach number for the best film cooling effectiveness under three film hole types, and the sister hole yields the best cooling performance.

Film cooling effectiveness enhancement on wall surface with crater hole and SDBD plasma actuation

At three blowing ratios ( M = 0.5, 1, and 1.5), film cooling effectiveness on plain wall surface with designed contoured crater cooling hole was numerically investigated. With variable crater depth (0.4 D≤ d≤2.7 D) and crater expansion angle (18°–30°), the optimal crater hole was determined and then combined with SDBD plasma actuation further. Effects of SDBD plasma actuation frequency (0≤ Dθ≤11.25) and actuation strength (0≤ Ds≤100) were analyzed, and the cases of the conventional cylindrical holes (i.e. baseline cases) were also conducted for comparison. The results showed that the wall film cooling effectiveness gradually rises with increased crater depth and remains stable with crater depth up to 2.3 D. Compared to the baseline case, the laterally averaged wall film cooling effectiveness of the contoured crater hole of d = 2.3 D is increased by over 55%, 500%, and 700% near the hole ( X/ D<3), and nearly 45%, 300%, and over 850% downstream region (3< X/ D<10) at M = 0.5, 1 and 1.5 respectively. Increasing the crater expansion angle also improves the wall film cooling effectiveness by expanding the coolant coverage area and strengthening the coolant attachment onto the wall. Compared with the baseline case, the overall laterally averaged wall film cooling effectiveness is improved by nearly 450% for the crater hole with a 30° outward expansion angle at M = 1. As SDBD plasma actuation frequency and intensity increase, the wall film cooling effectiveness increases and remains stable at Dθ = 6.25 and Ds = 60. The benefits of the contoured crater hole configuration and plasma actuation mainly result from the generation of anti-kidney vortex pair, which can effectively suppress the development of the existing kidney vortex pair and restrain the coolant rising. Compared with the baseline case, the optimized contoured crater hole combined with the plasma actuation at Dθ = 6.25 and Ds = 60 increases the laterally averaged wall film cooling effectiveness by nearly 1200% near the hole ( X/ D<3), and over 600% in the downstream region ( X/ D>3) at M =1.

Topological growth of multi-deck vortex structures above an elevated cross jet

The present numerical study provides a detailed topology-based understanding of the three-dimensional vortical flow interaction process for an elevated square cross jet of low-to-moderate velocity ratio (0.25 ≤R≤ 4.0). For R≤ 0.5, a steady inner-vortex (Iv) formed in the jet pipe owing to the leading-edge jet shear layer roll up as a spiral node. The kinematics of the limiting streamlines and separation-attachment patterns along the jet shear layer confirm the presence of the Iv. For 0.5 < R≤ 1.2, the Iv partly escapes, as its front side remains attached to the pipe hole and the azimuthally extended lee side moved out in a tilted fashion. Moreover, the continuous vortex shedding from the stack created a dominant von Karman-like street that grew along the lower side of the jet wake. Distinctly for R = 4, the intruded convective crossflow pulled up the spiral front node/Iv out of the pipe, which also shifted the onset of the Kelvin–Helmholtz instability upward. Significantly, the pulled-up node/Iv facilitated the above-orifice anti-kidney vortical evolution of the issuing jet shear layer. For the first time, the study displays the triple-deck growth of the kidney and anti-kidney vortices above an elevated square cross jet for 2.5 ≤ R ≤ 4.0 and 1000 ≤ Re ≤ 2000. For 0.5 ≤ R ≤ 1.2, the double-decked kidney vortices involving the primary and the secondary pairs grew above the central jet column. However, the stronger primary pair fast entrained the secondary one close to the orifice edge. With R ≥ 2.5, the lateral jet shear layer experienced an unexpected windward concave warping and restructured to evolve as the anti-kidney third-deck situated above the mid-deck primary kidney vortices. The topological shear layer folding and created kidney/anti-kidney vortices above the elevated square cross jet, for 0.25 ≤R≤ 4.0, appear consistent with the past measurements for a high aspect ratio elliptic flush jet. The anti-kidney vortical growth though was not detected above a square flush jet. The dominating above-orifice topological node in the high-pressure area ensured the anti-kidney vortical growth via the generated local pressure-gradient induced flow acceleration.

Experimental and Numerical Studies of the Film Cooling Effectiveness Downstream of a Curved Diffusion Film Cooling Hole

Film cooling technology is a commonly used method for thermal protection of gas turbines’ hot sections. A new, shaped, film cooling hole is proposed in this study. The geometry is made of a straight-through cylindrical feed hole at an inclination angle of 30° followed by an expansion section. The expansion section is created by the rotation of the same circular hole on the inclination plane about an axis normal to that plane which passes through the center of the feed hole exit area. This shape was designed to decrease the deteriorating effects of kidney vortices by proper distribution of the coolant flow emerging from the hole exit area. Cases with four rotation angles (7°, 14°, 17.5°, and 21°) were studied both experimentally and numerically and for the blowing ratios of 0.5, 1, and 2.0. For comparisons, the commonly used 7°-7°-7° diffusion hole geometry was also tested under otherwise identical conditions. For data collection, the pressure-sensitive paint (PSP) technique was used to measure the film cooling effectiveness. Streamwise- and spanwise-averaged film effectiveness results were obtained to compare the performance of different geometries. The main conclusions were that the case of 21° rotation angle produced the highest film effectiveness and outperformed the 7°-7°-7° diffusion hole geometry.

Combined film and impingement cooling of flat plate with reverse cooling hole

• Performance of combined impingement-film cooling is analyzed for a flat plate. • Effectiveness and pressure drop are compared for forward and reverse injections. • Effectiveness is found to be lower for the reverse injection at lower blowing ratio. • Contrary effect of cooling hole orientation is noticed at higher blowing ratio. • Pressure drop is also lower in case of the reverse orientation of the cooling hole. A numerical model is developed in the present work for analysing cooling performance of combined impingement-film cooling under realistic engine operating conditions. Effect of jet impingement along with the film cooling is analysed on fluid flow, heat transfer, cooling performance and pressure drop for forward and reverse orientations of the cooling hole. Further, effect of hole orientation on the cooling performance is studied under wide range of blowing ratios and jet-to-plate spacings. It is observed that the effect of jet impingement is significant on the cooling performance. Surface temperature of the metallic plate is found to be 50–90 °C lower for the combined jet impingement and film cooling case as compared to the only film cooling case. The improvement in the heat transfer for combined impingement-film cooling is at the cost of increased pressure drop. Film cooling effectiveness for the case of combined impingement-film cooling is found to be dependent on the hole orientation and blowing ratio. The secondary jet penetration into the mainstream increases with increase in the blowing ratio/velocity ratio. Kidney-vortices are formed at a velocity ratio of 1.07 from forward injection which resulted in decreased film cooling effectiveness. These kidney-vortices were not formed for the case of reverse injection and coolant spreads uniformly in the transverse direction. At lower velocity ratios when formation of kidney vortices is not prominent, forward injection results in better film cooling effectiveness compared to the reverse injection. Gas radiation is also considered in the modelling and its effect is found significant on the temperature prediction of the components.

Theoretical model for two-dimensional film cooling effectiveness distribution prediction

Film cooling is commonly categorized as a jet in crossflow phenomenon. Due to its fully three-dimensional flow field, characteristically two-dimensional (2-D) cooling effectiveness distributions are observed on the target wall. A theoretical method for 2-D film cooling effectiveness distribution predictions is developed by modeling the diffusion and convective transportation in the lateral direction. The effective diffusion coefficient is introduced to quantify the combined effects of the turbulent and laminar expansion. The convection effect, mainly the vortex entrainment, is quantified based on the analytical Oseen vortex. The intensity, scale, and location of the kidney vortex are modeled, respectively. The 2-D model in the current study can well satisfy the demand both academically and industrially. The time consumption of a 2-D effectiveness distribution calculation is on the magnitude of 1 ×10−2 s. The prediction error is within 8% if given especially correlated model coefficients, or within 14% otherwise.

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.