Hongmei Jiang

This study investigates the influence of turbine blade tip clearance on thermal characteristics and flow structures through combined experimental and numerical methods. Three different tip clearance sizes (t = 0.50%, 0.83%, and 1.33% of the blade height) are analyzed in detail to reveal the underlying physical mechanisms of over-tip leakage (OTL) flow. The results demonstrate that enlarging the tip gap considerably increases the leakage mass flux, leading to a corresponding rise in the area-averaged heat transfer coefficient (HTC) on the tip by 8.2%. A distinctive stripe-like HTC pattern is observed in the midchord region of the tip, which is fundamentally attributed to the mixing of high-energy main leakage flow and low-energy near-wall fluid. As the clearance size increases, the scale of the leakage vortex expands, resulting in larger-scale heat transfer stripes. Furthermore, the study reveals that the heat transfer performance of transonic OTL flow is strongly influenced by complex shock wave structures. Flow separation and reattachment, induced by shock reflection and shock–boundary layer interaction, create alternating regions of high and low thermal load. In larger clearance cases, the emergence of normal shocks downstream further intensifies the heat load near the pressure side. The interaction between shock waves and the boundary layer, together with flow reattachment, increases heat load nonuniformity, and the high heat transfer region moves toward the midchord of the tip.

A self-adaptive loss physics-informed neural network (SAL-PINN) method is proposed to address the challenges of limited generalization capability exhibited by purely data-driven neural networks under sparse data conditions and the insufficient accuracy of standard physics-informed neural networks in capturing complex flow details. This method enables high-fidelity reconstruction of the plane turbine cascade flow field with limited measurement points. By incorporating a dynamic weight balancing mechanism, SAL-PINN adaptively adjusts the loss function weights for regions characterized by different numerical scales within the flow field, thereby facilitating targeted reinforcement learning for critical regions. This approach yields excellent performance in predicting both global flow structures and local flow details. The results demonstrate that under sparse data conditions, SAL-PINN achieves a further reduction in prediction errors for key physical quantities across the entire field by approximately 1.5%–2.0% compared to the standard physics-informed neural networks. In boundary regions with complex flows, the error reduction is even more pronounced, reaching 12.0%–25.4%. This study also systematically evaluates the models' sensitivity to data volume, revealing that the incorporation of physical information significantly reduces their dependence on data, while the adaptive weighting mechanism further diminishes this sensitivity. This work provides an effective solution for achieving high-accuracy flow field reconstruction with minimal data, offering significant potential for engineering applications, particularly in scenarios where experimental measurements are high-cost.

Ceramic matrix composites (CMCs) are increasingly utilized in aero-engine blades owing to their exceptional mechanical and thermal properties. However, variability in material components and processing technologies leads to dispersion in equivalent performance, potentially affecting the reliability of CMC turbine blades. Focused on unidirectional fiber-reinforced CMCs, the present study integrates numerical simulations and neural network models to investigate the influence of mesoscale geometric and thermal parameter variabilities on the dispersion of the equivalent thermal conductivity (ETC). Based on the obtained probability density function of ETC, further quantitative analysis is conducted to assess the effect on the maximum surface temperature, high-temperature area proportion, temperature variation range, and temperature standard deviation of turbine blades. The results indicate that the ETC is most predominantly sensitive to the fiber diameter. The coefficient of variation for the axial-direction ETC remains identical to the input parameters while that for the normal-direction ETC is significantly amplified under the nonlinear heat transfer features. The ETC dispersion induces a 14% fluctuation in the high-temperature area proportion at the blade surface and a maximum temperature variation over 10 K at the leading edge region.

The relative casing motion can significantly influence the HP turbine blade tip aerothermal performance. The existing experimental facilities either can not achieve high rotating speeds, or have difficulties to gain full optical access to the tip region. In this study, spatially resolved squealer tip heat transfer data were obtained from Infrared thermal measurement by using a novel high-speed disk rotor rig which can mimic the high-speed casing relative motion close to actual operating turbines. The Mach number and Reynolds number were also engine realistic. Distributions of tip heat transfer coefficient at a relative casing speed of 140 m/s were compared with results at stationary condition. Distinctly different thermal performance with the effect of casing motion were observed both experimentally and numerically. With closely coupled RANS CFD analysis, the flow physics behind are further discussed. The key finding in the present study highlights the importance of relative casing motion for tip aerothermal management.

The formation mechanism of high thermal load at the blade tip plays an important role in effective cooling design and persistent operation of turbine blades. In this study, experimental investigation was conducted in a blow-down transonic wind tunnel to enable full optical access of a high-pressure turbine blade tip surface. Spatially resolved tip heat transfer coefficient was obtained for a flat tip by infrared transient thermal measurement. Combined with closely coupled unsteady self-adaptive turbulence eddy simulation numerical analysis, this paper first reveals alternating bands of high and low heat transfer coefficients (HTC) of the tip surface. Experimental data and computational fluid dynamics results consistently show this striped distribution of HTC, which indicates variations in the local heat transfer intensity. This phenomenon is linked to the formation of different types of vortices within the blade tip clearance. The clockwise (along flow direction) vortices originated from the detachment of the separation bubble, driven by the pressure gradient cross the clearance. As the clockwise vortices move cross the clearance, they induce low-energy fluid near the wall to form counterclockwise vortices, which alternate with the clockwise vortices in space. This alternating vortex pattern directly causes the high HTC stripes observed on the blade tip.

The high-speed relative casing motion between the casing and the turbine blade tip introduces significant complexities to the flow field near the tip, resulting in alterations to the heat transfer distribution on the suction surface of the blade near the tip, and further influences the arrangement of film cooling arrangements. However, due to the challenges associated with measuring heat transfer, the influence of cooling injection on the near-tip region of the suction side under high-speed relative casing motion still remains uncertain. This study aims to address this knowledge gap by conducting experiments on a high-speed disk rotor experimental rig. The heat transfer coefficient and cooling effectiveness are investigated for different cooling hole arrangements. Additionally, based on the computational fluid dynamic (CFD) method, the interaction mechanism of cooling injections under high-speed relative casing movement is comprehensively discussed. It is observed that the cooling effect, which would be effective under stationary conditions, is greatly diminished or even rendered ineffective when subjected to high-speed relative casing conditions. Furthermore, arranging the cooling holes at the location where the interaction between the over-tip-leakage flow and the passage flow occurs would be an effective approach to enhance the cooling performance on the blade near-tip suction side. The effect of different relative casing speeds on suction side near-tip region cooling injection performances is also numerically investigated. These findings contribute to a better understanding of the considerations involved in the film cooling design of turbine blades.

The relative casing motion can significantly alter the over-tip-leakage (OTL) flow aerodynamic performances. Traditional tip experimental facilities for relative motion researches, including stationary linear cascade with low-speed moving belt, annular cascade with rotating outer wall, and full-scale experimental rig with rotating blade, were either extremely costly or not capable to reproduce engine-representative casing Mach number. Very recently, a novel design concept for high-speed disk rotor rig has been proposed for tip research. Subsequent to this research, the present study evaluates the aerodynamic performances and the periodicity of the disk rotor rig design using Reynolds-averaged Navier–Stokes computational fluid dynamics simulation. Furthermore, first-of-its-kind experimental results of total pressure loss distributions measured by five-hole probe under high relative casing Mach number are reported. The results demonstrate the applicability of the disk rotor experimental rig for tip aerodynamic investigations.

The relative casing motion can significantly influence the turbine blade tip aerothermal performance. In this study, experimental investigation was conducted in a newly developed high-speed disk rotor rig which can mimic engine realistic high-speed casing relative motion while enabling full optical access to a transonic turbine blade tip surface. Spatially-resolved tip heat transfer data, including heat transfer coefficient and film cooling effectiveness, were obtained for a cooled transonic squealer tip by infrared transient thermal measurement. Combined with closely coupled Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, this paper reveals an interesting interaction mechanism between the cooling injections from the pressure side and the cavity floor with and without the effect of relative casing motion. Both experimental data and CFD results show a consistent trend in both heat transfer and cooling performance. With cavity cooling only, the cooling performance reduces with the effect of relative casing motion. However, with additional cooling injection from the pressure side, a significant improvement in the combined cooling performance with the relative casing motion can be observed. Such opposite trend highlights the importance of relative casing motion when ranking different tip cooling designs. With the consideration of relative casing motion, extra tip cooling benefit can be obtained by combining cooling injections from two different locations.

The high-speed Over-Tip-Leakage (OTL) flow has a significant impact on the aerodynamic performance of the High-Pressure Turbine (HPT) passage and generates high thermal load for the blade tip. Different tip sealing and cooling design strategies are applied to reduce the OTL loss and help turbine survive in a high temperature environment. High-speed linear cascade experimental rigs play an important role in understanding the flow physics and evaluating their performance. Multiple blades and passages are often required to maintain a reasonable flow periodicity. To match the engine representative Reynolds number and Mach number, a high-speed multi-passage cascade design inevitably demands more compressed air supply. A very large amount of heating power is also required if the engine condition wall-to-gas temperature ratio needs to be matched. In this study, a simplified 2-Passage linear cascade rig for high-speed tip heat transfer research was developed. Both the design method and the rig performance are presented. Different from existing design method to match two-dimensional blade loading, this study shows there are other design flexibilities, such as assist blade tip gap, tailboard adjustment, and profiling adjustment, to match the periodic three-dimensional OTL flow structures. The design method was validated by experimental effort. High resolution tip heat transfer coefficient distribution at stationary and rotating conditions (Rotating Mach number = 0.35) are reported. The enlarged test model can offer much more improved resolution of optical measurement near the tip region.

In high-pressure turbines, there is a large difference in temperature between the mainstream and the turbine blade surface. Most of the turbine blade tip heat transfer studies were conducted under the assumption that the Over-Tip-Leakage (OTL) flow field is independent of the wall thermal condition. Recent numerical and experimental studies have revealed that the two-way coupling effect between aerodynamics and heat transfer should not be neglected. The heat transfer coefficient obtained by the conventional method is not able to match the realistic engine condition accurately. This study investigates the impact of the wall thermal boundary condition on the tip cooling performance of squealer turbine blades. The RANS CFD result was validated against experimental tip heat transfer data obtained from a high-speed test rig with the effect of high-speed relative casing motion. The aerothermal performance for both uncooled and cooled squealer tips was studied at two different gas-to-wall temperature ratios, 1.7 and 1.1; the reference temperature is 204 K. It was found that the location and strength of cavity vortices varied with different wall thermal boundary conditions, leading to different signatures in tip heat transfer and cooling performance. It is recommended that the experimental heat transfer data and film cooling effectiveness obtained at the near-adiabatic wall boundary condition should be corrected before their application to the tip cooling design process. It would be more reliable to match the wall-to-gas temperature ratio during the tip experimental study.