Nonaxisymmetric Endwall Contouring Research Articles

Experimental and numerical investigation on turbine flow control through integrating endwall contouring with section profiling at different Mach numbers

The efficiency of turbomachinery is notably impacted by losses occurring within the turbine cascade, which are intricately linked to the configuration and intensity of secondary flows. Non-axisymmetric endwall contouring, as well as three-dimensional blade designs, are effective methodologies for regulating secondary flows within the cascade passage. These passive control strategies are garnering increased attention due to their adaptability under off-design conditions. However, previous investigations have primarily scrutinized the flow intricacies in linear cascades. This study provides an in-depth examination of the adaptation of endwall contouring, both independently and in conjunction with section profiling, within annular cascades and a specific emphasis on Mach numbers and their influence on secondary flow control. Employing a blend of experimental and numerical techniques, the research elucidates how radial pressure gradients impact pressure distributions near the throat, leading to notable discrepancies in secondary structures between the lower and upper passages. Furthermore, the study highlights how endwall contouring significantly inhibits the progression of secondary vortices. The integration of endwall contouring with section profiling demonstrates enhanced performance by modulating flow angles compared to endwall contouring in isolation. Notably, the effects of these methodologies on pressure variations and secondary flow control exhibit an escalating trend with increasing Mach numbers, attributed to flow compressibility effects. Additionally, the study observes a consistent trend in the ability to mitigate losses as Mach numbers vary.

Effect of non-axisymmetric endwall contouring and swirling inlet flow on film cooling performance of turbine endwall

Non-axisymmetric endwall contouring (NEC) is one of the verified approaches to suppress secondary flows and improve aerodynamic performance. However, the design of NEC brings significant challenges to the design of endwall cooling structures. Herein, a pressure-sensitive paint experimental approach was used to obtain the film cooling effectiveness of the NEC endwall with a purge slot in this study. Three NEC types were adopted: NEC (COS), NEC (SIN), and NEC (−SIN). In addition, lean premixed combustion technology was used to achieve lower levels of NOx emissions. The turbine inlet was characterized by high turbulence and strong swirling. The effects of different swirling angles (±10, ±20, and ±30°) and densities were further explored. Due to the NEC profiling changing the secondary flow near the endwall area, coolant from the purge slot was better attached to the slot exit position, leading to a significant increase in the size of the high-cooling-efficiency region. With the mass flow ratio (MFR) varying from 0.5 to 2%, the film cooling effectiveness of the flat and NEC endwalls had similar variation characteristics. When the MFR = 0.5%, the area-averaged cooling efficiencies of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could be improved by 2, 12.5, and 20%, respectively. Positive swirling and smaller negative swirling inflow could improve the film cooling effectiveness inside the channel. The case of SA = +20° had the best improvement, where the film cooling effectiveness of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could reach up to 29, 35, 36, and 34%, respectively. The NEC (−SIN) endwall was less sensitive to the effects of the swirling inflow.

Flow mechanism of a highly loaded low pressure turbine cascade with integrated-optimized end wall contouring and root lean

The end wall loss of modern highly loaded low pressure turbine (LPT) has been greatly increased, due to the enhanced secondary flow loss and boundary layer separation loss. Thus, it is of great significance to develop effective flow control strategies to improve the end wall flow condition and aerodynamic performance of modern LPT. This research carried out a numerical investigation on the coupled flow control strategy, which combined non-axisymmetric end wall contouring (NEC) and root tangential lean (RTL), based on a highly loaded LPT cascade (Zweifel = 1.59). Meanwhile, the optimization process was used to get the optimal design parameters of the coupled method NEC&RTL. The results indicate that the optimal coupled configuration can reduce the total pressure loss coefficient by 12.68% and the non-dimensional secondary kinetic energy by 23.91%. Compared with the reference cascade without modification, the coupled method is found to improve the end wall flow conditions: the passage vortex is weakened both in size and strength, mainly attributed to the smaller cross-passage pressure gradient resulting from NEC; the closed separation bubble near end wall and the three-dimensional separation flow before trailing edge are eliminated, due to the great downward pressure gradient near end wall resulting from RTL; and the counter vortex is eliminated and the slender back flow is weakened under the additional coupling flow control effect of NEC&RTL. Therefore, the coupled flow control method can not only highlight the advantages of the independent methods, but also induce external flow control superiorities, demonstrating the application prospect of the coupled flow control strategy on the highly loaded LPT.

Experimental test of a compressor cascade with non-axisymmetric end-wall contouring at off-design conditions

End-wall losses in axial flow turbomachinery, particularly in compressors, constitute a significant challenge due to their adverse impact on overall efficiency. Pioneering works in this field have demonstrated the potential for end-wall loss reduction by improving end-wall profiles. However, many previous efforts have concentrated solely on design conditions, largely disregarding the behavior of these contoured end-walls under off-design conditions—where compressors often operate. This study investigates the adaptability of a non-axisymmetric end-wall contour, performing well under design conditions, to off-design scenarios, focusing particularly on the influence of Mach numbers on its ability to control corner separation effects. Experimental research was conducted using a combination of surface static pressure taps and aerodynamic probes to quantitatively and qualitatively analyze the effect of the non-axisymmetric end-wall contour on reducing losses. Quantitative outcomes demonstrate a notable decrease in overall losses in the blade cascade due to this end-wall contour. For all tested Mach numbers, the average loss reduces by 4% at 0 degrees of incidence, with a 0.9° decrease in deviation angle, and an 8% average loss reduction at 5 degrees of incidence, accompanied by a 1.5° decrease in deviation angle. Qualitative findings suggest that the mechanism by which the non-axisymmetric end-wall contour reduces blade cascade losses involves the enhancement of pitchwise pressure gradients. This enhancement redirects low-momentum fluid toward the blade's suction surface, diminishing its reach in the pitchwise direction. However, it also intensifies loss in the low-momentum fluid core. Additionally, the presence of a convex feature in the rear section of the blade passage mitigates pitchwise static-pressure gradients, effectively ameliorating secondary flows and preventing their further decline. Moreover, it was observed that the control effectiveness of the end-wall contour on corner separation increases with higher Mach numbers.

Static pressure redistribution mechanism of non-axisymmetric endwall based on radial equilibrium

Non-axisymmetric endwall contouring has been proved to be an effective flow control technique in turbomachinery. Several different flow control mechanisms and qualitative design strategies have been proposed. The endwall contouring mechanism based on the flow governing equations is significant for exploring the quantitative design strategies of the non-axisymmetric endwall contouring. In this paper, the static pressure redistribution mechanism of endwall contouring was explained based on the radial equilibrium equation. A quantified expression of the static pressure redistribution mechanism was proposed. Compressor cascades were simulated using an experimentally validated numerical method to validate the static pressure redistribution mechanism. A geometric parameter named meridional curvature (Cme) is defined to quantify the concave and convex features of the endwall. Results indicate that the contoured endwall changes the streamline curvature, inducing a centrifugal acceleration. Consequently, the radial pressure gradient is reformed to maintain the radial equilibrium. The convex endwall represented by positive Cme increases the radial pressure gradient, decreasing the endwall static pressure, while the concave endwall represented by negative Cme increases the endwall static pressure. The Cme helps to establish the quantified relation between the change in the endwall radial pressure gradient and the endwall geometry. Besides, there is a great correlation between the distributions of the Cme and the change in the endwall static pressure. It can be concluded that the parameter Cme can be considered as a significant parameter to parameterize the endwall surface and to explore the quantitative design strategies of the non-axisymmetric endwall contouring.

Effect of Slot Jet Flow on Non-Axisymmetric Endwall Cooling Performance of High-Load Turbines

As vane inlet temperatures and turbine loadings are increasing, the aerodynamic and thermal management for the endwalls of gas turbines have received increased attention. Non-axisymmetric endwalls are becoming popular due to their proficient capabilities to modify the secondary flow fields and to change the film cooling performance on the endwalls. In this study, by considering the interaction between mainstream and purge flow based on non-axisymmetric endwall contouring, the numerical research model used in the present research was established. Based on the validated numerical method, the influence of the non-axisymmetric endwall contouring on the film-cooling effectiveness and aerodynamic characteristics was studied. Furthermore, the effect of different inclination angles on the film-cooling performance of the contoured endwalls was also investigated. The results indicate that for the high-load turbine vane used in this research, various types of non-axisymmetric endwall contouring can alter the aero-dynamic characteristics and cooling performance simultaneously. By inhibiting the secondary flows, non-axisymmetric endwall contouring can reduce the total cascade pressure loss coefficient by 0.305%. In addition, non-axisymmetric endwall contouring can significantly enhance the effective coverage area of purge flow up to 28.29%, and the endwall near the suction side can achieve better cooling performance. Finally, non-axisymmetric endwall contouring can improve the protective effect of large-angle purge flow.

Influence of Purge Flow Injection on the Performance of an Axial Turbine With Three-Dimensional Airfoils and Non-Axisymmetric Endwall Contouring

Abstract In this paper, we present the evaluation of the aerodynamic robustness to rim seal purge flow of an optimized 1.5-stage axial turbine configuration with a bowed stator profile and endwall contouring. Performance maps obtained by experiments and numerical simulations show that the efficiency benefit gained by this optimized configuration is partially reduced, but not eliminated, by the injection of purge flow through the cavity downstream of the first stator. Measurements with five-hole probes and hot-wire probes, as well as unsteady RANS simulations, give detailed insights into the physical effects of the purge flow inside the rotor passage. There, when no purge flow is injected, the optimized configuration diminishes the formation of loss-inducing secondary flow structures near the hub and the casing. When purge flow is injected, however, new strong secondary flow structures are induced near the hub. These vortices generate additional losses and thereby partially negate the efficiency benefits gained by the optimization. From the data, we found that this influence of the purge flow is limited to the lower half of the channel height. The data also show that the optimized configuration is able to reduce the vorticity near the casing regardless of the purge flow injection, which in turn leads to an efficiency increase in this area. Together, these effects lead to a reduction of the previously gained efficiency benefit by the optimized configuration when it is subjected to purge flow injection. However, compared to a baseline configuration with cylindrical endwalls also subject to purge flow injection, the overall efficiency is still increased by 0.38%.

Numerical Investigation into a New Method of Non-Axisymmetric End Wall Contouring for Axial Compressors

To deal with corner separation in high-load axial compressors, this paper proposes a new end wall contouring method aimed at controlling the end wall secondary flow in more than one local area, generating a geometry with fewer control variables that is applicable for multiple working conditions. The new method defines more than one surface unit function, with different effects on end wall secondary flow. Then, the geometry of these surface unit functions will be superposed to generate the end wall contouring, to combine their flow control effects. After applying the new method to a bi-objective optimization design process, with 15 design variables aimed at minimizing the loss of cascade at 0° and 4° incidence, the optimal design reduces the total pressure loss of the high-load cascade by 5% under the former incidence and by 3% under the latter. The most effective design rule is constructing an end wall surface with the rising suction side and sinking pressure side in the blade channel, while locally raising the SS corner with a gentle upstream slope. According to the analysis, the design variables of the new method show an intuitive influence on the variation of end wall geometry and the movement of secondary flow. The corner separation has been effectively suppressed, with fewer control variables than before. It, thus, indicates the advantage of the newly developed end wall contouring method compared with previous studies.

Endwall contour design targeting on optimum aerodynamic efficiency of turbine stage and sealing effectiveness of rim seal

Endwall contour optimization design utilized to improve the aerodynamic performance has impact on the flow field near rim seal, and it consequently affects the sealing performance. Combined with Kriging agent model, NSGA-II genetic algorithm and CFD which solves the three-dimensional unsteady Reynolds-averaged Navier–Stokes equations coupled with a fully developed shear stress transport turbulent model, this paper constructs an optimization design system for turbine non-axisymmetric endwall contour design in order to improve aerodynamic efficiency and sealing effectiveness simultaneously. The numerical method for predicting the flow in wheel-space and sealing performance of turbine rim seal is validated on the basis of published experimental data. The base flat endwall design, and two optimal endwall contour designs are selected to investigate the aerodynamic and sealing performance. The results show that the aerodynamic and sealing performance can be improved at the same time. Compared with the base flat endwall design, the total-to-total efficiency is increased by 0.23% and the sealing effectiveness is increased by 11.49% for optimal design 1 at optimal design point. Optimal design 1 can significantly reduce the aerodynamic loss and for different sealing flow rates, the total-to-total efficiency is greater than that of base flat endwall design. Compared with the base flat endwall design, the total-to-total efficiency is increased by 0.15% and the sealing effectiveness is increased by 15.43% for optimal design 2 at optimal design point. The influence of endwall contour on sealing effectiveness is obvious when the cooling flow rate is small. The work of this paper provides a reference for the design of non-axisymmetric endwall with comprehensive optimization of turbine aerodynamic and rim sealing performance.

Non-axisymmetric endwall contour optimization and performance assessment as affected by simulated swirl purge flow and backward hole injection

A shape optimization system was constructed using the kriging model, NSGA-II algorithm and CFD simulation, and the endwall contour was optimized targeting on balancing the endwall cooling and blade phantom cooling performances. Off-design conditions of simulated swirl purge flow and backward hole injection were introduced to evaluate the aero-thermal performances of the optimal non-axisymmetric endwall. The results show that two optimal contours are able to increase the endwall adiabatic effectiveness separately by 3.518% and 2.177%, but the flat endwall achieves the best phantom cooling performance. Under both design and off-design condition, the slot coolant coverage on pressure side endwall is enlarge by contours. The swirled slot leakage is able to weaken the tendency for the hole coolant to cover the suction side hot ring on both contoured and flat endwall. With the increase of SR, the averaged phantom cooling effectiveness is decreased when slot MFR = 1.0% but increased when MFR = 1.5%. When MFR = 1.0%, the averaged endwall Nu between 0.4 < z/Cax < 0.8 is decreased by 15% in optimal_2. When MFR = 1.5%, the averaged Nu for the upstream part endwall is increased by approximately 20% when SR = 0.6 compared with SR = 1.0. The net heat flux reduction of the pressure side endwall is increased by contouring, but the swirled purge flow dramatically decreases this protection effect. This research provides insights into the designing of non-axisymmetric endwall in off-design film cooling condition.

Effective strategy of non-axisymmetric endwall contouring in a linear compressor cascade

The corner separation and the related secondary flow have great impact on the compressor performance, and non-axisymmetric endwall contouring is proved effective in improving compressor efficiency. The aim of the study is to improve the compressor performance by two local endwall contouring strategies at the design and off-design conditions. The endwall is parameterized and the Bezier curve is used to loft the endwall surface. The design of the contoured endwall is based on a multi-point optimization method to minimize the aerodynamic pressure loss. In order to identify the influence of the contoured endwall, a detailed flow analysis is conducted on four effective contoured endwall designs. The selected endwall geometries exhibit great control ability on the corner separation and significantly reduce the pressure loss at the two operating conditions. The directional concave near the leading edge can induce strong streamwise pressure gradient and accelerate the endwall flow, greatly reducing the cross-passage pressure gradient. The convex structures near the concave edge and at the outlet can block the cross-flow and prevent the interaction between the cross-flow and the suction corner flow. The benefit of the contoured endwall is mainly due to the re-distributed endwall static pressure and blocking of the cross-flow movement. In terms of the control effect, the shape of the concave also matters and better control effect is observed on the deep and wide concave. The flow will be guided by the concave, and the best suppression on corner separation is observed on the concave which follows the suction side. The results also indicate that the relief of the hub corner separation slightly increases the shroud pressure loss.

A simultaneous use of a leading-edge fillet and a non-axisymmetrically contoured endwall in a turbine stage

Secondary flow minimization is a crucial problem in a turbine passage. In the present paper, three different strategies are investigated to reduce the secondary-flow-related total pressure loss. These are leading-edge fillet, non-axisymmetric endwall contouring, and combining these two approaches. An experimental investigation in a single-stage turbine facility and RANS-based computations are performed to evaluate the designs. The experiments are carried out in the large-scale Axial Flow Turbine Research Facility AFTRF. A reference Flat Insert is installed on the nozzle guide vane passage's hub surface to allow future endwall design implementation during the experimental phase. The stereolithography manufactured reference insert has a constant thickness with a cylindrical shape. This investigation also uses four different leading-edge fillets, and they are attached to cylindrical Flat Insert initially. The same fillets are also attached to a contoured endwall. Simultaneous use of a leading-edge fillet and a non-axisymmetric contoured endwall for secondary flow control is the main objective of this research. Total pressure measurements are taken at the rotor inlet plane with a Kiel probe. The probe traversing is completed along one vane pitch and from 8% to 38% span. The leading-edge fillets effectively managed to weaken the horseshoe vortex occurring in front of the leading-edge. In one of the fillet cases sitting on the Flat Insert, the computational results at the NGV exit showed that the mass-averaged loss value was reduced by 1.31%. Three fillet designs decreased the area-averaged loss with a maximum reduction of 15.06%.

Multi-Objective Optimization of Non-Axisymmetric Contoured Endwall for Axial Turbines

Multi-Objective Optimization of Non-Axisymmetric Contoured Endwall for Axial Turbines

Effects of varying non-axisymmetric contours of the turbine endwall on aerodynamics and heat transfer Aspects:A sensitivity analysis study

Non-axisymmetric endwall contouring of gas turbines has been widely employed as an effective way to improve the aerodynamic performance or heat transfer features. Though efforts have been exerted by previous investigators to generate improved contoured endwall designs, better understandings of the physics behind the phenomenon that non-axisymmetric contoured endwall configurations change the aerodynamic or heat transfer performances are still in demand. In this study, a global sensitivity analysis (GSA) methodology is used to determine shape changes at which locations on the endwall have the most significant impact on the aerodynamic or endwall heat transfer performances. Then, typical non-axisymmetric contoured endwall cases found by a multi-objective optimization approach are studied to understand further why shape changes in such locations impact the passage aero-thermal aspects so much. The results show that the most prominent areas for the passage aerodynamic performance are at the passage mid-pitch from the passage forepart to the aft part by impacting the stream-wise acceleration features. The locations at the passage's aft part influence the heat transfer features most due to high velocity, thus large heat transfer coefficient values there.

Full coverage film cooling on a non-axisymmetric contoured endwall and the baseline endwall

Full coverage film cooling arrangement is widely needed in nozzle guide vanes (NGVs) to keep the turbine surfaces from melting due to the unprecedented high turbine inlet temperature. Meanwhile, to reduce the passage aerodynamic losses, non-axisymmetric endwall contouring are widely applied. The employment of endwall contouring will impact the full coverage film cooling performance, thus changing the turbine durability. Thus, it is important to deeper know the effect of non-axisymmetric endwall contouring on endwall full coverage film cooling performance. In this study, Pressure Sensitivity Paint (PSP) technique is used to measure the full coverage film cooling effectiveness (η) distributions on a non-axisymmetric contoured endwall (CE) and the corresponding baseline endwall (BE) with several coolant mass flow ratios (MFRs). Meanwhile, cases with the corresponding experimental conditions by computational fluid dynamics (CFD) are done to calculate the blowing ratio (BR) and MFR distributions of the film cooling holes. The η distributions on the CE and the BE are compared, and the effect of MFR on the CE full coverage film cooling performance are documented. In addition, different turbulence models are evaluated on the ability to model the endwall film cooling problems by comparing the CFD results with the experimental results. With small MFR values, the film cooling performance are worse on the CE in the near-hole regions at the fore part of the passage but better on the CE in the far-hole regions and at the aft part of the passage than that on the BE. While with large MFRvalues, the CE perform better than the BE throughout the endwall surface.

Development of an automated non-axisymmetric endwall contour design system for the rotor of a 1-stage research turbine – Part 2 computed and experimental results

In this paper, we present the computed flow results for those endwall designs produced using the automated non-axisymmetric endwall design procedure and target objective functions detailed in Part 1 of this paper, and where available, compare these with experimental measurements made using the CSIR low-speed research turbine used as the test case for the designs. Experimental measurements were taken immediately aft (X3) as well as downstream (X4) of the rotor row using a drilled 5-hole elbow probe, and both the computed as well as physical results were processed identically to ensure as high a degree of comparability between the computed and physical datasets. For the two initial cases (the η tt- and C ske-based designs), the results of the experiments confirmed the predictions of the simulations, although unexpected flow separations which were not predicted by the computational fluid dynamics (CFD) resulted in poorer agreement for the two remaining contoured cases. In general, the results of the CFD, as confirmed by the experiment, showed that the best metric for the design of the endwall contours for this rig was that based on the rotor total–total efficiency although importantly, the well-known coefficient of secondary kinetic energy ( C ske), even when formulated using a reasonably simple approach, was able to produce closely competitive results to the efficiency-based metric. These findings are significant firstly because, to date, the use of efficiency is not widespread for the design of non-axisymmetric endwall contours, and secondly, because in cases where the efficiency might be difficult to measure and/or predict, the C ske may form a robust if only slightly less effective alternative.

Effect of axial turbine non-axisymmetric endwall contouring on film cooling at different locations

Non-axisymmetric endwall contouring in axial turbines are becoming popular to improve the passage aerodynamic performance or the endwall heat transfer characteristics. Meanwhile, endwall contouring changes the film cooling performance on the endwall surface by modifying the secondary flow fields and the endwall surface shapes, thus impacting the turbine efficiency and durability. Better understandings of the non-axisymmetric contoured endwall film cooling performances are in great need. In this study, adiabatic film cooling effectiveness (η) of discrete film cooling hole injections at different axial locations on an non-axisymmetric contoured endwall and a baseline endwall with different density ratios and matched averaged blowing ratios to the engine conditions are studied experimentally using Pressure Sensitivity Paint (PSP) technique. Computational fluid dynamics (CFD) simulations are also carried out to look into the local flow fields. The results show that the differences in endwall η distributions between the contoured endwall and the baseline endwall are dominated by the streamwise pressure gradients, i.e. at locations with smaller streamwise pressure gradient values on the contoured endwall than those on the flat endwall, the local η values on the contoured endwall are smaller than those on the flat endwall, and vice versa.

An Advanced Single-Stage Turbine Facility for Investigating Nonaxisymmetric Contoured Endwalls in the Presence of Purge Flow

AbstractIn modern gas turbines, endwall contouring (EWC) is employed to modify the static pressure field downstream of the vanes and minimize the growth of secondary flow structures developed in the blade passage. Purge flow (or egress) from the upstream rim-seal interferes with the mainstream flow, adding to the loss generated in the rotor. Despite this, EWC is typically designed without consideration of mainstream–egress interactions. The performance gains offered by EWC can be reduced, or in the limit eliminated, when purge air is considered. In addition, EWC can result in a reduction in sealing effectiveness across the rim seal. Consequently, industry is pursuing a combined design approach that encompasses the rim-seal, seal-clearance profile, and EWC on the rotor endwall. This paper presents the design of and preliminary results from a new single-stage axial turbine facility developed to investigate the fundamental fluid dynamics of egress–mainstream flow interactions. To the authors' knowledge, this is the only test facility in the world capable of investigating the interaction effects between cavity flows, rim seals, and EWC. The design of optical measurement capabilities for future studies, employing volumetric velocimetry (VV) and planar laser-induced fluorescence (PLIF), is also presented. The fluid-dynamically scaled rig operates at benign pressures and temperatures suited to these techniques and is modular. The facility enables expedient interchange of EWC (integrated into the rotor bling), blade-fillet and rim-seal geometries. The measurements presented in this paper include: gas concentration effectiveness and swirl measurements on the stator wall and in the wheel-space core; pressure distributions around the nozzle guide vanes (NGV) at three different spanwise locations; pitchwise static pressure distributions downstream of the NGV at four axial locations on the stator platform.

Development of an automated non-axisymmetric endwall contour design system for the rotor of a 1-stage research turbine – part 1: System design

Secondary flows are a well-known source of loss in turbomachinery flows, contributing up to 30% of the total aerodynamic blade row loss. With the increase in pressure on aero-engine manufacturers to produce lighter, more powerful and increasingly more efficient engines, the mitigation of the losses associated with secondary flow has become significantly more important than in the past. This is because the production of secondary flow is closely related to the amount of loading and hence the work output of a blade row, which then allows part counts and overall engine weight to be reduced. Similarly, higher efficiency engines demand larger engine pressure ratios which in turn lead to reduced blade passage heights in which secondary flows then dominate. This article discusses the design and application of an automated turbine non-axisymmetric endwall contour optimization procedure for the rotor of a low speed, 1-stage research turbine, which was used as part of a research program to determine the most effective objective functions for reducing turbine secondary flows. In order to produce as effective as possible designs, the optimization procedure was coupled to a computational fluid dynamics routine with as high a degree of fidelity as possible and an efficient global optimization scheme based on the so-called efficient global optimization algorithm. In order to compliment the requirements of the efficient global optimization approach, as well as offset some of the computational requirements of the computational fluid dynamics, the DACE metamodel was used as an underlying surrogate model.

Thermal Management of a Transonic Turbine: Leakage Flow and Endwall Contouring Effects

Comparison of heat transfer performance of a nonaxisymmetric contoured endwall to a planar baseline endwall in the presence of leakage flow through a stator-rotor rim seal interface is reported in this paper. Heat transfer experiments were performed on a high turning turbine airfoil passage at a transonic exit Mach number at different leakages to mainstream mass flow ratios. The contoured endwall geometry was optimized for secondary flow aerodynamic losses. Transient infrared thermography was used to measure the endwall surface temperature. Simultaneous calculation of the heat transfer coefficient (HTC) and adiabatic cooling effectiveness (ETA) was performed assuming one-dimensional semi-infinite transient conduction. Results show nominal reduction in the area-averaged HTC but significantly higher coolant film coverage using the contoured endwall compared to baseline endwall at different levels of coolant MFR. Interestingly, significant reduction in the area-averaged heat transfer coefficient was observed for cases without coolant flow in the presence of a purge slot when compared with a solid cascade without any cooling features. The backward-facing step seemed to have a first-order impact on endwall heat transfer coefficient distribution compared to coolant blowing cases. The contoured endwall also showed major improvement in net heat flux reduction (combining the effects of the HTC and ETA) especially near the suction side of the platform.