bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Analysis of Blade Platform Leakage in Axial Compressors
Authors: Petermann Jannik , Pommerening Marvin , Gümmer Volker , Becker Bernd 
Published: October 2022

Abstract
This paper deals with the complex interacting flow between the main flow in the gas path of compressors and the hub gap leakage in the rotor blade row when considering the real geometry of the platform. The results of the present investigation agreed well with previous findings while complementing the overall compressor model. Significant local differences of the flow field between simplified endwalls and a real geometry case were detected when both circumferential and streamwise platform gaps were taken into account. At design conditions, rotor hub leakage caused by inter-platform gaps of 2.6% passage pitch reduced polytropic rotor efficiency and total pressure ratio by as much as 3.2% and 2.3%, respectively, relative to the smooth endwall setup. Front circumferential leakage was found to intensify with the presence of inter-platform leakage. The latter contributed to the formation of a large recirculation region and increased secondary flow close to the blade’s trailing edge on its suction side. A steep deterioration of the row performance from zero to non-zero midpassage massflow was observed, implying that emphasis should be placed on the avoidance of any inter-platform leakage. Flow vectors, surface streamlines, and schematic leakage paths illustrate the aerodynamic conditions under the influence of endwall leakage.
Optimized Film Cooling Flow on a Contoured Endwall Within a Transonic Annular Cascade
Authors: Burdett Timothy A. , Ullah Izhar , Wright Lesley M. , Han Je-Chin , McClintic John W. , Crites Daniel C. , Riahi Ardeshir 
Published: October 2022

Abstract
Film cooling was measured on the endwall of a five-vane annular cascade in a blowdown wind tunnel at an exit Mach number of 0.9. The adiabatic film cooling effectiveness was calculated from the partial pressure of oxygen measured with binary pressure sensitive paint (BPSP). Cylindrical film cooling holes were located in the upstream and passage regions with the coolant-to-mainstream mass flow ratio (MFR) independently varied for each region. One row was located upstream of the vanes and supplied by an upstream plenum. Two rows were located in the passage between two vanes and supplied by a downstream plenum. Three total MFRs were investigated: 1%, 1.5%, and 2%. For a given total MFR, four combinations of upstream and downstream MFRs were compared to an even split of coolant. Coolant-to-mainstream density ratios (DRs) of 1.0 and 2.0 were investigated. The most efficient use of coolant hinged on balancing the downstream MFR for the second row due to the endwall pressure gradient preventing coolant from exiting the holes or a high jet velocity causing liftoff. For this row, selecting the optimum MFR increased the area-averaged film cooling effectiveness by up to 200% with a reduction in row 1 of less than 25%. At high downstream MFRs, increasing the density ratio delayed liftoff and increased film cooling effectiveness in row 2 by 65%. However, at low MFRs, increasing the density ratio reduced film cooling effectiveness in row 2 by 60%.
Microstructural Evolution of Wrought and AM Haynes 188 Under Long Term Thermal Exposure
Authors: Gowreesan Vamadevan , Greaves Wayne , Pardhi Yogi , Barrios Karen 
Published: October 2022

Abstract
Haynes 188 is a cobalt-based superalloy used in hot section gas turbine components due to its excellent oxidation resistance and elevated temperature stability. Parts made from Haynes 188 are traditionally manufactured from wrought or forged material. Additive manufacturing (AM) may be a less time consuming and more cost-effective alternative, particularly for replacement parts. Additionally, necessary design changes can be quickly introduced into service using additive manufacturing. It is important to understand the effect of long-term thermal exposure on additively manufactured parts before they are put into demanding high temperature applications. Data on the effect of long-term thermal exposure on wrought Haynes 188 is readily available in the open literature. However, such data for additively manufactured Haynes 188 is scarce.
This paper discusses an experimental study that investigated the microstructural evolution in wrought and AM Haynes 188 under long-term thermal exposure. Optical metallography and scanning electron microscopy (SEM) were performed on wrought and AM Haynes 188 in the virgin and long-term thermally exposed conditions. Mechanical test samples from the coupons were then extracted and tested in both conditions. Lastly, the fracture surfaces of the mechanical test specimens were evaluated by SEM fractography and metallography of sections through the fracture surfaces. The findings help to understand how long-term thermal exposure affects the microstructure and mechanical properties of wrought and AM Haynes 188. Most importantly, it illustrates a significant difference in microstructural response of the two materials to long term thermal exposure and its effect on mechanical properties.
Some Properties of the Exit Velocity Triangle of a Radial Compressor Impeller
Authors: Casey Michael , Robinson Chris 
Published: October 2022

Abstract
A diagram is described which demonstrates important aspects of the exit velocity triangle of a radial compressor impeller with no inlet swirl. Although this diagram is based on work dating back to 1941, it is not widely known in the radial compressor community. It aids the selection of the exit velocity triangle for impellers and gives significant insight into impeller-diffuser matching. It can be used to analyse performance maps from both experimental and CFD studies.
Important aspects made clear in the diagram are as follows:
• The degree of reaction and the de Haller number of the impeller are both determined primarily by the work coefficient, and both decrease as the work coefficient increases.
• The degree of reaction is also affected by the exit flow coefficient and for typical backswept impeller designs it remains nearly constant at off-design flow conditions.
• The inlet and exit velocity triangles can be shown in the same diagram to visualize the deceleration of the relative velocity along the casing streamline and of the meridional velocity across an impeller, together with the acceleration of the relative flow on the hub streamline.
• The slope of the impeller gas path work coefficient versus exit flow coefficient in this diagram at off-design conditions provides a new approach to estimate the mean slip factor from a measured or calculated compressor performance map.
• Different impeller design styles can be categorized in this diagram to show that different impellers are needed for use with vaned and vaneless diffusers.
• The absolute velocity at the diffuser inlet of a backswept impeller increases with a decrease in flow rate along the operating line, which is an important aid to compressor stability.
Part-Load of Steam Rankine Cycles for Solar Salts-Based Concentrating Solar Power Plants
Authors: Belverato Davide , Martelli Emanuele , Binotti Marco , Pilotti Lorenzo , Giaconia Alberto 
Published: October 2022

Abstract
This work proposes two ad hoc part-load control strategies for steam cycles adopted in concentrated solar power plants. The control strategies are designed to keep the molten salt temperature above the minimum allowed value set by solidification issues in the 30–100 % load range. Particularly critical is the temperature of molten salts in contact with the heat exchanger tubes, the so called skin temperature. The first control strategy adopts a turbine with controlled extraction and readmission valve while the second strategy employs a throttling valve and a feedwater preheating loop. Off-design simulations show that both strategies are capable of avoiding the molten salts solidification issue but at the cost of a non negligible penalty (up to −1.9 percentage points) in power block efficiency at low loads (30–50%). The off-design analysis considers also the effect of ambient temperature variations and the optimization of the cooling fan rotational speed. The results are used to derive best-fit polymonials relating the power block efficiency to the ambient temperature and load.
Conjugate Heat Transfer Characteristics in a Vane Blade With Different Dimple/Protrusion/Pin Fin Configuration for Trailing Region
Authors: Du Wei , Luo Lei , Wang Songtao 
Published: October 2022

Abstract
The high inlet temperature of gas turbine induces high heat load and serious thermal stress problem in the trailing because of the structural and aerodynamic limitations. Thus, it is vital to further improve the cooling performance in the trailing edge area. The configuration with dimple/protrusion/pin fin is proposed to increase the heat transfer and decrease the blade surface temperature in the trailing region. This paper numerically investigated the conjugate heat transfer characteristics in a vane blade with different dimple/protrusion/pin fin configurations for trailing region. There are three different dimple/protrusion locations (in the middle of two rows of pin fin, near the leading edge of each pin fin, a near the trailing edge of each pin fin) and two different dimple/protrusion depth are considered in this paper.
The inlet temperature for the hot gas is 1678K, the mass flow ratio of the cooling air is 6.3% of the hot gas. Seven different configurations for the dimple/protrusion/pin fin are involved. The temperature distribution, aerodynamic efficiency and cooling air loss are analyzed. It is found that the configurations of dimple/protrusion/pin fin have significant effect on the temperature distributions and aerodynamics of gas turbine. The pure pin fin configuration has the highest temperature in the trailing region and the pin fin combined with the protrusion configuration has the lowest temperature in the trailing region. The trailing edge temperature can drop up to 20 K after adoption the dimple/protrusion.
Operation of Large Industrial Gas Turbines During Periods of Low Electricity Demands
Authors: Ingistov Steve , Vassiliev Vladimir , Savic Sasha , Mulder Sebastiaan 
Published: October 2022

Abstract
When grid power demand is low or the power price is negative, running a gas turbine at Full Speed No Load (FSNL) provides a way to avoid producing power, while maintaining the ability to both generate process steam for industrial purposes in a Heat Recovery Steam Generator (HRSG) and to respond quickly to sudden surges in grid power demand. In this paper, turbine thermodynamics of FSNL, closure of inlet guide vanes (IGV), and compressor bleed rates are analysed for General Electric’s 7EA gas turbine using the software Thermoflow.
This study shows that FSNL can be achieved only by bleeding of compressor mass flow through two available bleeds, one in the front section of the compressor, and one in the back section of the turbine. This paper shows that bleeding from bleed 1 will lower compressor work, saving fuel, but it will also drop the exhaust temperature too low, preventing steam production. With extraction from bleed 2, the exhaust temperature remains high. Either way, the exhaust energy is reduced due to reduction of mass flow, but steam generation in reduced amount is possible. The extracted mass flow is choked and limited by the critical section in the flow path of the compressor bleed. In this study, the required minimal size of the slot in bleed 2 is identified for a range of IGV positions.
Assessment of the Flow Field and Heat Transfer in an NGV Using Magnetic Resonance Velocimetry, Thermochromic Liquid Crystals and CFD
Authors: Bruschewski Martin , Wüstenhagen Carolin , Domnick Clemens , Krewinkel Robert , Shiau Chao-Cheng , Grundmann Sven , Han Je-Chin 
Published: October 2022

Abstract
Computational Fluid Dynamics (CFD) is the standard tool in the turbomachinery industry to analyze and optimize internal cooling systems of turbine components, but the code applied has to be validated. This paper presents a combined experimental and numerical study on the flow field and heat transfer in a cooling system consisting of a three-pass serpentine with rib turbulators and trailing edge ejection. The cooling geometry is taken from a stator vane currently used in an industrial gas turbine and operates at a coolant inlet Reynolds number of 45,000. As an experimental technique, magnetic resonance velocimentry (MRV) was used to obtain the three-dimensional time-averaged velocity field of the isothermal flow. The measurements were conducted in a large-scale model and resulted in 3.2 million velocity vectors and a measurement uncertainty of 6.1% of the bulk inlet velocity. The local wall heat transfer was measured in a separate experiment using thermochromic liquid crystals (TLC). These measurements yielded the distribution of the heat transfer coefficient on both the pressure and the suction side internal walls with a measurement uncertainty of 12%. The experimental data are used as reference for the numerical study. In total, eight turbulence models are evaluated here, including one-equation, two-equation, algebraic and differential Reynolds stress models, and a scale-adaptive simulation. The results show the differences between the velocity fields and the heat transfer coefficient distribution, allowing for the identification of the optimum turbulence model for this particular type of flow.
Identification of Fluctuation Modes for a Cylindrical Film Cooling Hole Using the Spectral Proper Orthogonal Decomposition Method
Authors: Rosafio Nicola , De Cosmo Giove , Salvadori Simone , Carnevale Mauro , Misul Daniela Anna 
Published: October 2022

Abstract
Film cooling is the main technology adopted to guarantee safe working conditions of vanes and blades in high-pressure turbine stages. Recent experimental investigations highlighted that unsteady interaction between the coolant jet and the hot gas contributes to the lateral dispersion of cold flow over the cooled surface. Hence, considering the harsh working environment of these devices, a fair prediction of their thermal performance requires accurate modelling of the interaction between cold and hot gases. In this paper, an experimental setup originally studied at the University of Karlsruhe during the EU-funded TATEF project is numerically investigated to determine the influence of high-frequency unsteady fluctuations on the thermal performance of the cooling device. The case study consists of a film cooling hole positioned on a flat plate, working at engine-like conditions. Unsteady Reynolds-Averaged Navier-Stokes equations are solved for a compressible flow in transonic regime on a hybrid mesh. Turbulence is modelled using the Scale-Adaptive Simulation method to correctly predict the interaction between the coolant and the main flow. Three different sets of conditions are analyzed by varying the blowing ratio from 0.5 to 1.5, aiming at highlighting the unsteady mechanisms occurring for different penetrations of the coolant into the hot gas. Time-averaged unsteady results are compared with the available experimental data to determine to what extent hybrid modelling allows for correctly predicting film cooling performance at different blowing ratios. Instantaneous solutions are then analyzed to investigate the time-dependent flow field in the vicinity of the jet exit section and on the cooled surface. Spectral Proper Orthogonal Decomposition is enforced to identify the principal fluctuation modes associated with the time-dependent coolant penetration into the main flow.
Large Eddy Simulation Based Optimization of a Fan-Shaped Cooling Hole Geometry to Enhance Cooling Performance
Authors: Agarwal Shubham , Gicquel Laurent , Duchaine Florent , Odier Nicolas , Dombard Jérôme , Bonneau Damien , Slusarz Michel 
Published: October 2022

Abstract
In this study, a shaped hole optimization approach based on Large Eddy Simulations and Efficient Global Optimization (EGO) is presented. The shape of a fan-shaped hole used for turbine film cooling is then optimized to maximize the film cooling performance and the numerical problem is modeled using flow configurations close to those in real gas turbine conditions. Four of the most important geometrical parameters defining a cooling hole shape, namely the depth of the expanded section, the hole inclination angle and the forward and the lateral expansion angles are selected as the design variables to obtain the optimal hole shape. Forty design cases at start are selected via an Optimal Latin Hypercube Sampling method (OLHS) and further more are added during the successive iteration steps of the optimization algorithm. The handling of these design cases including the CAD creation of the geometries, computational domains, meshes and finally the numerical setup is handled by the LES based autonomous tool which has been previously validated [1]. Finally, the Bayesian based EGO [2] method along with the Expected Improvement (EI) as the acquisition function is used to maximize the surface averaged film cooling effectiveness as the objective function. After several database enrichment steps to reduce the overall modal error of the response surface an optimal shape of the cooling hole with the highest cooling performance is obtained. The optimal geometry thus obtained has a significantly higher cooling performance than the reference hole shape which is also confirmed via the study of the fluid flow distribution in both the cases. Overall, this study shows that, Large Eddy Simulations can be successfully coupled along with an EGO based optimization approach to obtain the optimal shaped cooling hole in a computer-aided optimization setting.
Using Machine Learning for Loss Prediction in a Hybrid Meanline Modeling Method to Deliver Improved Radial Turbine Performance Prediction
Authors: Ren Pangbo , Stuart Charles , Spence Stephen , Inomata Ryosuke , Kobayashi Takayuki , Morita Isao 
Published: October 2022

Abstract
Low fidelity modelling approaches remain attractive due to an unrivalled ability to predict full turbine performance maps quickly compared to high fidelity approaches such as CFD, especially in the preliminary design process. As improvements in performance on a component level approach a point of diminishing returns, the ability to efficiently optimize the complete charging system for a given duty is a topic attracting significant research interest. In the case of turbocharging applications, existing engine and powertrain simulations require turbine maps to calculate the turbine performance, which are usually obtained from experimental testing. Unfortunately, the need for extrapolation is unavoidable because of the limited range of testing data available, leading to inaccuracies especially at off-design conditions. To enable intensive modelling and optimization of complete vehicle powertrains for different drive cycles, the current piece of work seeks to combine the advantages of machine learning techniques and physical meanline modelling to facilitate faster, more accurate predictions of complete turbocharger maps.
This paper presents a novel methodology for turbocharger turbine rotor and nozzle performance prediction based on hybrid modelling. The turbine rotor and nozzle were parameterized to conduct CFD simulations for a wide variety of turbine geometries, which were used to form a database to train an Artificial Neural Network (ANN). The predicted losses provided by the ANN were then utilized in the meanline code, substituting for the conventional empirical loss models. As well as removing the need for empirical loss models, modifications were undertaken to the meanline approach to further enhance modelling accuracy. Firstly, in order to accurately characterize the stage mass flow capacity, the losses occurring in the nozzle and rotor were subdivided into those occurring before and after the throat. A second novel aspect is that the aerodynamic blockage level at the rotor throat was implemented as a variable rather than a constant value. By training the ANN to predict the variation of blockage with geometry and operating condition, a more accurate depiction of the changing secondary flow fields could be achieved.
The capabilities of the hybrid meanline modelling method were evaluated on several unseen test cases. The resulting predictions of efficiency and mass flow rate demonstrated strong correlation with CFD results and experimental test results. The hybrid meanline modelling method therefore displays great potential in wide range radial turbine performance prediction with enhanced accuracy in comparison to traditional approaches.
The New Chapter of Transonic Compressor Cascade Design at the DLR
Authors: Munoz Lopez Edwin J. , Hergt Alexander , Grund Sebastian 
Published: October 2022

Abstract
The approach to design compressor blades has been transformed over the years by the advent of efficient numerical optimization algorithms and increasing computing power. This has allowed designers to focus on finding the best optimization methodology for a desired application. However, transonic flow conditions on compressor blades still present considerable modeling and optimization challenges, making the optimization of even a 2D blade section a non-trivial undertaking. This paper then focuses on the design of a new state-of-the-art transonic compressor cascade for future wind tunnel test campaigns at the DLR. For this purpose, a thorough review was performed of similar cascades previously tested at the DLR’s Transonic Cascade Wind Tunnel. From this review, a main reference was picked corresponding to a modern cascade with notably good efficiency at high aerodynamic loading. The data gathered informed the definition of the optimization’s design strategy applied with the DLR’s in-house optimizer, AutoOpti. The process chain was evaluated with the DLR’s CFD solver for turbomachinery applications, TRACE, by performing RANS simulations with the k-ω SST turbulence model and γ-ReΘ transition model. The optimization was set to minimize two separate objective functions: the first one focused on the efficiency at the aerodynamic design point, while the second one was focused on the efficiency over the cascade’s working range. The result is a Pareto front of cascades with a wide variety of design characteristics and a considerable improvement in efficiency over the working range of about 24%. This improvement was achieved while maintaining a similar aerodynamic blade loading, quantified by a maximum increase of 3% of the de Haller number. Further post-optimization analyses were performed to select the “best” cascade for future wind tunnel test campaigns. The significant improvements obtained with respect to the reference and with a wide variety of cascade designs demonstrates that there is still much to be learned about blade design through optimization; even for 2D cascades and specially in transonic flow conditions.
Experimental Analysis of the Leakage Characteristics of Three Types of Annular Segmented Seals
Authors: Fourt Erwan , Arghir Mihai , Jolly Pascal , Andasmas Mohamed 
Published: October 2022

Abstract
This paper presents an experimental analysis of the leakage characteristics of three kind of segmented seals. The segments of the first seal has smooth pads while the second seal has pads with pockets. The pads of the third seal are smooth but the rotor is textured with inclined grooves. The pockets or the textures lift the segments from the rotor and create a radial clearance. This is reflected by the leakage flow rate, the friction torque and the seal’s temperature. These characteristics are hereby measured on a dedicated test rig. The presented results are dimensionless, the measured values for the three types of seals types being divided by the same maximum value. This makes it possible to compare the performance of different segmented seal technologies. The assumptions made on the position of the segment during the tests (opened or closed against the rotor) are thus verified.