bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Varying Freestream Turbulence on Flow Transition Over Distributed Surface Roughness
Authors: Jain Ishita , Katiyar S. , Sarkar Subrata
Published: August 2024

High-fidelity Large Eddy Simulations (LES) are used to investigate the influence of distributed surface roughness on the spatially developing laminar boundary layer under varying freestream turbulence (FST) levels of 0.07 to 6%. The inlet Reynolds number based on the momentum thickness and freestream velocity is 360. The square-shaped (SQ) riblets that are employed in the present study are homogeneous in the spanwise direction and distributed in a series along the streamwise length. The aspect ratio (s/k) considered here is 3, where k is the riblet height, and s is the longitudinal spacing between the consecutive rows of riblets. The instantaneous flow structures reveal a Λ vortex-induced breakdown for FST levels below 3.2%, attributed to the near wall streamwise vortices arising from embedded recirculation regions between riblets. On the contrary, at a high FST level of 6%, the flow is characterized by low- and high-speed streaks generated via shear sheltering, resulting in the turbulent flow downstream. Moreover, an exponential growth of velocity fluctuations is apparent for a lower FST, which becomes algebraic for a higher FST. The onset and end of transition shift progressively upstream with an increase in FST. Interestingly, the flow features exhibit self-similarity in the turbulent region irrespective of FST levels.
Optimization of Tip Seal Grooves for Aerodynamic and Durability Improvements of Small-Core Turbines
Authors: Wiese Connor J. , Berdanier Reid A. , Thole Karen A.
Published: August 2024

While the clearance gap between the turbine rotor tip and the outer case in a gas turbine engine is necessary for the operation of the machine, the gap is kept as small as possible due to the detrimental effect of the flow over the turbine tip. With the increased investments in ultra-high bypass ratio gas turbines, blade tip clearances are increasing in relative size to the turbine rotor, as engines move towards smaller core sizes. In this work, a constrained topology optimization of a rotor tip seal with discrete axisymmetric grooves was explored computationally using Reynolds-averaged Navier-Stokes simulations. The differential-evolution-based optimization was applied at two tip clearances representing a nominal and small-core-scaled geometry. Furthermore, optimizations were performed at each tip clearance for blade designs with flat and squealer tips.

The multi-objective optimization was designed to simultaneously maximize rotor efficiency and minimize rotor tip heat load. Several tip seal designs were identified for each tip geometry and tip gap that both increased aerodynamic efficiency and reduced the total heat load into the rotor tip. However, some optimal tip seal designs were composed of grooves that were demonstrated to be detrimental in prior work. Furthermore, grooves were more effective at increasing aerodynamic efficiency when applied to flat tipped geometries — increasing the estimated rotor efficiency by up to 0.9 points over the ungrooved seal baseline with flat tipped blades, as opposed to 0.25 points of improvement over the ungrooved case with squealer tipped blades. Finally, for both tip configurations, optimal seal geometries that were obtained from the small-core scaled clearance gap optimizations generally maintained near optimal performance when evaluated at the design tip clearance, while those geometries developed at the design clearance experienced greater sensitivity to clearance gap changes.
Improving the Fatigue Life of an Additively Manufactured Stainless-Steel Specimen Using a Secondary Grinding Process
Authors: Ramachandran Murali Krishnan , Sumaiya Safia Alam , Golvaskar Mandar , Wood Julia , Sluder Isaac , Rakurty Chandra Sekhar , Rangasamy Nithin , Emuakpor Onome Scott , Kannan Manigandan
Published: August 2024

Grinding, an inexpensive and uncomplicated procedure, is commonly employed in most metallic manufacturing facilities to aid in the manufacturing process. With its abundance within industry, this provides an opportunity to use it as a method to also improve material properties such as strength, and fatigue. In addition to improving surface roughness, prolonging fatigue life, and strengthening material, a grinding process combined with a modified cooling method can raise compressive residual stress on metallic material surfaces. This study uses a typical grinding process and the improved grinding process to show imparted residual stress and surface roughness. Residual stress measurement tools were used to measure residual stresses imparted on the material through the thickness. Microstructural analysis via optical, and SEM microscopy was completed for typical and improved grinding methodologies. Mechanical testing through High Cycle Fatigue (HCF) was completed to verify improvement. To establish standards for the optimal mechanical qualities for a given material, this study will compare two distinct cooling techniques.
Spectral Heat Transfer Coefficient for Thermal Design Analysis - Part 2: Leveraging Diabatic Flow Conditioning for Nonlinear Regime
Authors: He Li
Published: August 2024

There are two main issues of interest in the context of Newton’s law of cooling as applied to turbine aerothermal designs. First, in a linear aerothermal regime in which both the conventional wisdom in general and the law of cooling in particular are notionally established, how do we deal with a non-isothermal wall where the surface temperature is nonuniform? Secondly, what can we do if an aerothermal system becomes nonlinear, manifested by qualitatively large changes of the flow field affected by heat transfer?

In Part 1, a new spectral heat transfer coefficient (SHTC) method has been introduced for blade thermal analysis subject to non-isothermal walls in a linear aerothermal regime. It has been demonstrated definitively that the SHTC approach enables more accurate thermal design analyses of a solid temperature field than the conventional method.

Part 2 is devoted to address the issue of nonlinearity when the temperature field actively interacts with the velocity field as in many practical aerothermal problems. It is noted that the conventional method working rests heavily on an adiabatic state. To move away from the adiabatic state, we take advantage of smooth (’differentiable’) heat flux-wall temperature relation afforded by strong solid diffusion. A local linearization can be utilized by decomposing a full thermal variable into a nonlinear base as the reference and a locally linear perturbation. This split enables us to directly compute a nonlinear base as well as to carry out linearized scaling with the SHTC (or HTC for isothermal walls) on top of the selected nonlinear aerothermal base state. The framework method has been implemented with relatively minor changes of the linear SHTC scaling method as presented in Part 1. The results of several computational case studies clearly and consistently support the validity and effectiveness of the present approach and method implementation.
Flow and Heat Transfer in a Ribbed Converging-Diverging U-Duct Under Rotating and Non-Rotating Conditions
Authors: Kim Wanjae , Shih Tom I-. P. , Bryden Kenneth Mark , Dalton Richard P. , Chang Sung Yong , Park Gyu Sang
Published: August 2024

A numerical study based on steady RANS with the SST turbulence model was performed to investigate the flow and heat transfer in a ribbed U-duct with a rectangular cross section that converges linearly in the radially outward direction and diverges linearly in the radially inward direction under rotating and nonrotating conditions. Parameters examined include rotation number (Roi = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Rei = 46,000, 100,000, and 154,000), and the duct’s taper angle (α = 0° and 1.41°) under conditions relevant to gas turbines used for electric power generation. Results obtained show that increasing the taper angle from 0° to 1.41°, which appears negligibly small, significantly increases both the friction coefficient and the Nusselt number whether there is rotation or not. With rotation at Roi = 0.0336 and Rei = 100,000, the maximum increase in the average friction coefficient and Nusselt number was found to be 41.7% and 36.6% respectively. Without rotation at Rei = 46,000, those are 11.5% and 14.7% respectively.
Effects of Combustor Residual Swirl and Hot Spot on Aerothermal Characteristics and Cooling Performance of Gas Turbine Blade
Authors: Sun Tianyi , Li Zhiyu , Li Zhigang , Li Jun , Xu Qingzong , Du Qiang
Published: August 2024

The swirling flow and the hot spot generated in the aeroengine combustor have significant impacts on the downstream turbine components. This paper numerically investigates the influence of the residual swirl clocking position, direction and the hot spot on the aero-thermal characteristics of the turbine stage cascades and the cooling performance of the rotor blades. Computational results show that the hot spot slightly decreases the total pressure loss of the stage cascades. And the negative residual swirl increases the total pressure loss by about 3–5%. The aero-thermal characteristics and the cooling performance of the rotor blade are scarcely influenced by the residual swirl clocking positions. The hot spot decreases the mass flow of the blade tip holes by 2%, compared to the cases with uniform temperature inlet. The negative residual swirl makes the coolants at the pressure surface develop further downstream, reduces the differences in the leading edge holes mass flow at different spanwise positions and brings more intense heat transfer at the tip and better cooling performance at the blade surface. The flow capacity and the working performance of the turbine stage are also almost unaffected by the residual swirl and hot spot. This article presents a numerical method for turbine stage cascades with the residual swirl and the hot spot, analyzes the impact of combustor outflow conditions on turbine stage performance, and provides reference for CFD aided design of turbine aerodynamic and cooling configurations.
Dirt Ingestion Impacts on Cooling Within a Double-Walled Combustor Liner
Authors: McFerran Kyle , Thole Karen A. , Lynch Stephen P.
Published: August 2024

Double-walled liners consisting of impingement and effusion cooling are commonly used to cool gas turbine combustor chambers. Engine ingestion of particulate such as dirt, sand, or ash leads to particulate deposition and blockage of cooling holes in these liners. Prior work on double-walled liners has shown that deposition leads to flow blockage, however, no experimental work has studied the reductions in cooling that result from the deposition. The goal for the present work was to quantify this reduction in cooling by evaluating the heat transfer coefficient on the cold-side of an effusion plate with and without dirt buildup. Heat transfer coefficients were quantified over a range of Reynolds numbers, pressure ratios, plate-to-plate spacings, and dirt injection amounts. The injection of dirt onto the cold-side effusion plate surface resulted in flow blockages and cooling reductions as high as 55%, with these effects differing for pressure ratio and plate-to-plate spacing. Scan data of the dirty effusion plate was used to characterized the deposition thicknesses for the different parameters tested. Overall, the heat transfer when having deposition on the effusion plate affected the cooling much beyond the insulation effect of the dirt layer. These results suggest that the effects of particulate buildup on the cooling flow field are an important driver in double-wall liners.
A CFD Study on the Performance of Modified H-Shaped VAWTs for Tilted Operation Condition
Authors: Kouaissah Otman , Franchina Nicoletta , Persico Giacomo
Published: August 2024

Wind energy harvesting may see a radical transformation with the introduction of new wind turbine concepts. In fact, the vertical axis configuration offers significant advantages that may accelerate extending the installation capabilities to deep waters, where only floating platforms are feasible and economically convenient. While experimental tests for multi-objective assessment are expensive in terms of costs and time, and analytical methods relying on Blade Element Momentum (BEM) are of limited fidelity, especially when considering novel rotor configurations, advanced simulations carried out using high-fidelity Computational Fluid Dynamics (CFD) techniques are a promising tool for evaluating the aerodynamic performance of wind turbines. CFD simulations enable critical evaluation of real-time, long-term aerodynamic loading and prediction across various operational scenarios. This technique can thus be crucial for optimizing the efficiency of wind turbines and reducing the LCOE.

This paper presents a fully 3D CFD investigation on the aerodynamics and near-wake development of a small-scale H-shaped VAWT and two modified versions, adapted for operating in tilted conditions, which is typical for spar-buoy applications. An in-depth spanwise study of the three versions at the peak power condition is performed. The difference in the swept area and the coning angle effect in combination with the tilt condition are considered. The obtained results have shown the potential to contribute to the ongoing development and advancement of the Floating-VAWT technology. The vortical structures development is also commented to provide better understanding of the physical phenomena taking place. Since the relevant energy harvesting capability being predicted for the newly designed turbines, further simulations aimed at demonstrating the engineering relevance of the machines, utility-scale models of the turbine. The numerical predictions confirm the high performance achievable by the HV-shaped wind turbines, and provide valuable insights for its future installations.
Retrofitting an Existing Combined Cycle Gas Turbine With Post-Combustion Carbon Capture: Assessment of Solvent Selection Impact on Performance
Authors: Verhaeghe Antoine , Bricteux Laurent , Demeyer Frederiek , Blondeau Julien , De Paepe Ward
Published: August 2024

Amine(s)-based post-combustion Carbon Capture (CC) is the most mature and applicable technology to retrofit existing Combined Cycle Gas Turbine (CCGT) assets into low-carbon power plants. However, its deployment is hindered by high CAPEX as well as high OPEX, linked with the energy requirement for the solvent regeneration process, reducing the global plant efficiency. Hence, CC energy penalty reduction is necessary. Next to performing Exhaust Gas Recirculation (EGR), efficient heat integration is a key strategy, involving the extraction of steam from the most suitable location in the steam cycle to supply the CC solvent regeneration heat. The choice of extraction location depends on the required steam quality for solvent regeneration, which, in turn, is influenced by the specific solvent used in the carbon capture process. Therefore, it is imperative to evaluate the different integration strategies for individual solvents and analyse their influence on the overall performance of the plant. In this study, we investigate the use of two distinct solvents: monoethanolamine (MEA), the conventional choice, and a blend of methyldiethanolamine (MDEA) and piperazine (PZ) for CC application to a CCGT. The objective is to conduct a comprehensive comparison between both solvents, examining their heat integration and impact on plant performance for the retrofitting of an existing CCGT with post-combustion carbon capture. To this end, a thermodynamic analysis of a typical CCGT plant equipped with EGR and coupled with an amine(s)-based CC plant has been performed using specific simulation models in Thermoflex and Aspen Plus. Different heat integration strategies are presented and compared for both solvents. Results show that, by extracting steam from the Intermediate Pressure/Low Pressure (IP/LP) crossover, using MDEA/PZ instead of MEA allows to increase the electrical efficiency by 0.5 absolute percentage points, representing an efficiency reduction associated to the CC of 6.2 abs.%. However, extracting steam of higher quality, before the Intermediate Pressure (IP) steam turbine, leads to a more significant performance degradation, with an efficiency penalty of 8.3 abs.%. Consequently, the optimal option for retrofitting existing CCGT with MDEA/PZ-based CC is to extract steam from the IP/LP crossover under full-load operation. Future works will focus on part-load operation of the integrated CCGT-CC.
Compressor Surge Identification in Innovative Heat-Pump Systems Equipped by Vaned Diffuser Centrifugal Compressor
Authors: Niccolini Marmont Du Haut Champ Carlo Alberto , Silvestri Paolo , Reggio Federico , Traverso Alberto , Sishtla Vishnu
Published: August 2024

In the present energy scenario, heat-pumps are assuming an important role to improve energy efficiency in reversible cooling systems. In particular, in case of industrial size plants, centrifugal compressors are preferred with respect to other solutions; nonetheless, they are often subjected to variable operation and therefore they must withstand off-design conditions. For studying unstable operation of refrigerant closed loop systems, Carrier provided the University of Genoa with a small size chiller rig equipped with an innovative high speed centrifugal compressor driven by a variable speed motor. This paper presents the vibro-acoustic signature analysis of such a closed loop rig from a system perspective, mainly focusing on mechanical response of compressor casing. First, its vibro-acoustic characterization is conducted at on-design and stable operation. Afterwards, some surge transients are obtained by progressively closing some valves in plant feeding lines, and meanwhile vibro-acoustic signals are acquired at relevant plant locations to characterize system response just before instability onset. In this way, suitable surge precursors can be defined in incipient surge conditions for early surge detection in this kind of complex plants. Indeed, system dynamics is significantly affected by interposed volumes, and therefore the effect of heat exchangers in system response may be relevant. To this aim, system dynamics is analyzed in detail both in sub-synchronous frequency range and in high frequency region to assess how its vibro-acoustic response varies when moving from stable conditions towards surge. Surge precursors are obtained by relying only on vibro-acoustic signals both in low and high frequency ranges in order to perform early surge detection in such chiller pilot system. The main advantage of the proposed approach is to exploit non-intrusive probes, which allow to define diagnostic indicators without interacting directly with the working fluid, therefore preserving system integrity and reliability.
Investigation of Endwall Secondary Flows in a Low Aspect Ratio Transonic Turbine, Part II: Passage Oblique Shock
Authors: Jennerjohn Christianer Mary K. , McQuilling Mark , McKeever Craig W.
Published: August 2024

With increasing exit Mach number through the transonic regime, increased losses in a turbine can be incurred due to the increase in shock losses. The transonic regime is specifically of interest as it exhibits both a loss bucket behavior as well as the potential for unique trailing edge shedding modes at midspan. As for the endwall secondary flows, there can be increased losses due to the increase in shock interactions with endwall secondary vortices. In this second part of the two part series, the variation in exit isentropic Mach number varied up to 1.15 where the endwall secondary flow development is compared between numerical predictions and experimental results for a low aspect ratio turbine (AR = 0.66 and Zw = 1.0). Experimental results are produced via testing in the SLU linear turbine cascade and include results of airfoil static pressures. Numerical analysis is completed using Cadence Fine/Turbo (RANS modeling with the SST k-omega turbulence closure model) and validated via the experimental data. Numerical predictions include airfoil static pressure loading, passage secondary flow development, shock interactions within the passage, as well as downstream mixing loss characterization. Results show the impact of the exit isentropic Mach number on the shock-vortex and shock-boundary layer interactions affecting the endwall secondary flow development. With increased exit isentropic Mach number, the flow exhibits a transition in the passage shock behavior having a direct impact on the endwall secondary flow development and shock-induced vortices within the passage. However, this work also shows the presence of a shock-vortex interaction with the passage vortex. As a result, the downstream mixing losses are then compared at six downstream planes (0.2 to 3.0Cx) where numerically predicted energy loss is assessed showing the increased rate of production at higher exit isentropic Mach number. The results of this part show evidence and support for a secondary flow model which details the endwall secondary flow development for an oblique shock structure within the transonic regime.
On the Design of a Scaled-Up Pulsed Methane Pyrolysis Reactor for Clean Hydrogen Production
Authors: Bianchini Cosimo , Da Soghe Riccardo , Bertini Davide , Kendrick Donald , Gray Scott , Hinkey John , Aarnio Michael J. , Meloni Roberto
Published: August 2024

In a global hydrogen market rapidly growing to satisfy the requests driven by a Net Zero economy, new solutions for clean and cheap hydrogen production are needed. Ekona has developed a pulsed methane pyrolysis (PMP) hydrogen production system based on a constant volume, combustion-driven process. The PMP reactor is non-catalytic and low-cost and mitigates carbon fouling typical of other methane pyrolysis reactor platforms as proved by the 200 kg of hydrogen/day pilot. A scale-up procedure is on-going to meet the needs of actual applications typically orders of magnitude larger than this initial plant size.

The enclosed paper describes the computational fluid dynamics (CFD) numerical modeling work performed to enlarge the current reactor and combustors, leveraging the lessons learned, up to commercial sizes. Since the process cycle is quite long and complex, the CFD study was broken into three different sections dedicated respectively to: 1) Combustor Mixing, Filling and Purging, 2) Simulated Hot Products Injection into the Reactor, 3) Reactor Filling and Venting and Interaction with concurrent Combustor Activities. Despite sharing a similar numerical method based on transient multi-species CFD simulations with moving meshes exploiting the overset mesh approach to model the valve movement, each section focused on different parts of the cycle (in time) and reactor (in space).

Several geometry variants are tested and ranked in their performance for providing uniform methane/oxygen mixing, obtaining nearly one-dimensional plug flow filling in the combustor, generating adequate mixing between injected combustion products and feedstock in the reactor to uniformly raise pressure and temperature up to pre-pyrolysis conditions, and generating minimal flow anomalies in the reactor to permit smooth feedstock filling and venting due to the interaction with the combustor flow and nozzle tip.
Techno-Economic Analysis of Offshore Wind Power Resources in the Gulf of Aqaba
Authors: Rehman Shafiqur , Ibrahim Nasiru , Irshad Kashif , A. Mohandes Mohamed , Mohammed Abdul Baseer
Published: August 2024

The present work conducted offshore wind power resources assessment (OWPRA) at six offshore locations in the Gulf of Aqaba. The hourly mean wind speed (WS) and direction (WD) data at 100 m above the water surface, in addition to temperature and pressure near water surface level, between 1979 and 2021 (43 years) has been used. Log-term mean WS values at L1 to L6 locations are 5.89, 6.58, 8.34, 7.69, 6.26, and 5.01 m/s and the corresponding wind power density (WPD) (are 221, 263, 547, 394, 205, and 104 W/m2 at 100 m above the water surface; respectively. The windy site identifier index (WSI) with magnitudes of 31.91, 26.17, and 10.12 at L3, L4, and L2 sites further confirms the suitability of these sites as indicated by higher WS and WPD values above. However, the cost of energy, calculated based on an average total installation cost of 4,720.25 USD/kW during 2010 to 2021 are found to be 1.160 USD/kWh and 1.80 USD/kWh, for the best and the worst scenarios corresponding to L3 and L2 sites. The monthly and annual wind variability indices remained < 1 at most of the location, which is an indication of less turbulent windy sites.
A Multi Objective Optimization Framework for Offshore Wind Farm Design in Deep Water Seas
Authors: Barnabei Valerio Francesco , Ancora Tullio Carlo Maria , Conti Michela , Castorrini Alessio , Delibra Giovanni , Rispoli Franco , Corsini Alessandro
Published: August 2024

Floating offshore wind energy will play a key role in the clean energy transition scenario. The number of projects deploying large-scale wind farms is growing in multiple regions, from Northern Europe to the East Coast of the United States, and extending to the Mediterranean Sea. Offshore wind farms face fewer constraints in layout design, as they do not need to consider orography and can generally be situated in vast, open sea areas. Consequently, offshore wind turbines could be arranged in simple layouts, such as grid patterns or staggered rows, spaced uniformly. However, this regular turbine arrangement would result in significant annual energy production (AEP) losses due to wake-rotor interaction. Although increasing spacing between turbines can mitigate this issue, it is not always feasible due to marine space availability. Moreover, when feasible, it can lead to higher costs for additional cabling and maintenance. This paper aims to introduce a multi-objective wind farm optimization framework that employs a genetic algorithm (NSGA II). This framework seeks to maximize the energy production while minimizing OPEX and CAPEX costs, taking into account the wind resource and bathymetry of a specific region. In the paper, two case studies are presented for the optimization of wind farms in the Mediterranean Sea assuming 15MW wind turbines. AEP evaluation of each individual wind farm is obtained with the open-source library FLORIS, while the optimization algorithm relies on the library PyMoo for multi-objective optimization.
Design and Manufacture of EBC Coated SiC/SiC Nozzle Guide Vanes for High-Pressure Turbines
Authors: Süß Fabia , Schöffler Robin , Friedrich Lion , Petersen Anna , Vogel Felix , Frieß Martin , Ebach-Stahl Andrea
Published: August 2024

Increasing the efficiency of jet engines is essential to meet the demanded climate targets. Ceramic matrix composites (CMC) are strong candidates for aircraft applications because they withstand high temperatures, while their density is two-thirds lower than that of conventional nickel-based alloys. This leads to cooling air savings and a lower overall engine weight, resulting in a potential reduction of emissions. To investigate the potential benefits and manufacturing techniques required for the introduction of CMC to the high-pressure turbine of a modern jet engine, the geometry of a nozzle guide vane of an existing turbine was redesigned considering ceramic specific constraints. Then, the liquid silicon infiltration (LSI) process was used to manufacture SiC/SiC nozzle guide vanes. Hi-Nicalon S woven fabric was used together with a CVI-based fiber coating. The outer surface of the vane was ground to meet the requirements for surface roughness, and geometric and positional tolerances. Cylindrical, laser-drilled cooling holes were introduced for trailing edge cooling. In the final step, an environmental barrier coating system (EBC) consisting of yttrium disilicate and yttrium monosilicate layers was applied using PVD processing. Wind tunnel testing under TRL 4 will be performed and vane performance will be evaluated.
Numerical Simulation of a Reacting Hydrogen Jet in a Vitiated Co-Flow Using a Detailed Chemistry Model
Authors: Kulkarni Rohit , Attal Nitesh , Liu Shuaishuai , Shekhawat Yajuvendra , Pomraning Eric , Lee Daniel , Burton Tristan , Senecal Kelly
Published: August 2024

The sequential combustion system in a gas turbine is composed of two complementary combustion stages in series: one premix stage followed by an auto-ignited second stage. This helps in reducing NOx significantly and gives more operation flexibility (lower loads) by redistributing the fuel between the two stages. Staged/sequential combustion is a state-of-the-art method to provide operation flexibility and reduced emissions in gas turbines. A key requisite for such a model is the accurate determination of the flame location to predict emissions, flame dynamics, and temperature distribution. The numerical simulations of such combustion systems must accurately capture auto-ignition and flame propagation to predict the flame position and shape. In this work, the hydrogen lifted flames are simulated using a 2-equation LES model with detailed chemistry and Adaptive Mesh Refinement (AMR). The sensitivity of the flame lift-off height to the co-flow temperature and velocity fluctuations at the inlet is studied. The numerical results of the so-called Cabra H2 flame are validated against experimental [1] and numerical results in the literature [2–8].
Optimization Design of Variable Fillet for Different Boundary Thicknesses in a Highly Loaded Compressor Cascade
Authors: Zhang Gangduo , Zhu Mingmin , Shao Runzhu , Qiang Xiaoqing , Teng Jinfang
Published: August 2024

This paper addresses the aerodynamic challenges associated with the introduction of a hybrid engine, aiming to enhance efficiency and reduce fuel consumption. Focusing on a smaller, higher-loading compressor rear stage, the study explores three critical questions related to pressure gradients, inlet boundary layers, and the scaling of characteristic geometries. Emphasizing the impact of corner separation on compressor efficiency, the research delves into the aerodynamic impact of the fillet in a smaller compressor rear stage cascade.

A numerical study based on a typical compressor stator cascade, NACA65-K48, is presented to elucidate fillet design criteria under varying inlet boundary layer thicknesses. Employing optimization and numerical simulations, the study explores variable fillet geometries and their performance characteristics at different inlet conditions. Flow field analyses at design and near stall conditions reveal the influence of variable fillets on blockage regions and total pressure loss.

The analysis underscores the importance of axial velocity gradient changes influenced by variable fillets, affecting blockage regions and entropy generation. The design criteria of variable fillet for blades operating with end wall blockage are proposed, in consideration of acceleration near suction peak, retraining of separation inside passage and avoiding strong wake after trailing edge. The proposed empirical criteria for variable fillets are validated through simulations on a Controlled Diffusion Airfoil cascade, demonstrating improved performance and flow fields.
Wire EDM for the Manufacture of Fir Tree Slots Using Different Wire Electrodes
Authors: Küpper Ugur , Schulze Brock Daniel , Klink Andreas , Herrig Tim , Bergs Thomas
Published: August 2024

The use of materials with increasing high-temperature strengths for turbine disks brings conventional manufacturing processes to their technical and economical limits. As an alternative manufacturing approach, the wire EDM process was therefore tested in several investigations. Despite the many advantages of this manufacturing process, EDM has significantly lower productivity compared to conventional processes. This can be increased by using enlarged wire diameter of the electrodes (bigger wires). The increased wire diameter improves wear resistance so that higher energies can be used. However, the higher energy input has a negative effect on surface integrity. Especially for safety-critical components, these changes in surface properties must be considered critically. This paper therefore examines the use of bigger wire electrodes for the electrical discharge machining of fir-tree slots on turbine disks. For this purpose, the process performance and surface integrity of Inconel 718 machined by using brass and coated wire electrodes with standard diameters and a new generation of 0.4 mm diameter wire electrodes are compared. Depending on the wire electrode, individual processing technologies are developed and tested with a focus on high productivity and low wire consumption. Finally, a technological and economical assessment is carried out, and the best-performing wire electrode with appropriate technology variant for rough machining a fir tree slot is selected.
Neural Network Based Digital Twin for Performance Prediction of Water Brake Dynamometer
Authors: Song Shuo , Xiao Hong , Jiang Leibo , Liang Yufeng
Published: August 2024

Water brake dynamometer, the core component of aerospace engine testing facilities, is widely used in turbine component testing and turboshaft engine testing. Since the status of the water brake dynamometer system cannot be monitored in detail, equipment maintenance is performed solely based on the operator’s experience, resulting in high risks in the dynamometer equipment operation. Post-test inspections may even reveal damage to the dynamometer bearings and key components. Cavitation and other phenomena require urgent technical solutions to improve health monitoring of key equipment and experimental safety.

This paper proposes a performance prediction method for water brake dynamometers based on machine learning. By conducting physical correlation analysis of key parameters, the characteristics of water brake dynamometer operation are captured. Subsequently, a performance prediction model for water brake dynamometer is built based on digital twin technology and experimental data, enabling an accurate mapping of the dynamometer’s operational state. After turbine test, the digital model is verified by dynamometer operation data set. Predicted operating parameters of the digital model show that the dynamic mean error between predicted values and actual values of multiple core component temperatures is less than 1%. Considering the sensitivity of data changes, these prediction error values are acceptable, which provide valuable reference information.
Modelling the Film Cooling of a Modern High-Pressure Turbine Nozzle Guide Vane in 3D CFD
Authors: Müller Michael , Schöffler Robin , Grunwitz Clemens , Morsbach Christian
Published: August 2024

In this paper, a reduced order film cooling model previously investigated on single cylindrical and laid back fan-shaped cooling holes is extended with a model variant for trailing edge cooling slots. The extended model is evaluated on a modern HPT NGV combining these cooling features and paired with either an eddy viscosity model or a differential RSM. To simulate a worst-case scenario during the maximum take-off operating point, a hot streak from the combustion chamber with a maximum temperature of about 2230 K is directly impinging on this NGV. Compared to resolved RANS simulations, the model performs better on the NGV than on single holes. In particular, the grid dependency is significantly reduced. The model error and grid dependence peak at the leading edge and decrease downstream of the showerhead. When an average film cooling efficiency is considered, three cells per cooling hole diameter were sufficient to approach grid convergence. A more accurate turbulence model also reduced the model error of the film cooling model, with an absolute error in the averaged film cooling effectiveness of 0.2 at the leading edge and 0.1 at the suction and pressure sides of the NGV.
A Gas Flow Network Model for Predicting Ring Dynamics and Leakage in Dry-Running Pistons Seals for High-Pressure Hydrogen Storage
Authors: Sassoli Andrea , Raspanti Sandro , Romani Luca , Capanni Alessio , Bassani Simone , Ferrara Giovanni , Balduzzi Francesco
Published: August 2024

High-pressure hydrogen storage is essential for maximizing hydrogen potential as a clean energy carrier. Achieving pressures up to 700 bar is necessary to increase its volumetric energy density and reciprocating compressors are favored for their ability to handle high flow rates. Furthermore, maintaining high purity of compressed gas necessitates the use of oil-free machines. Given the unique challenges posed by low molecular weight gas, high pressures, and the use of dry seals, accurately estimating leakage flows and piston ring wear in compressor cylinders is vital.

This paper presents a gas flow network model aimed at predicting wear and leakage of dry-running piston seals for high-pressure hydrogen storage. The model accounts for the dynamics of the seals and the fluid dynamics of gas leaking through the narrow clearances between the moving piston and the cylinder liner, therefore considering the interaction between gas flow and seal displacement within piston grooves. Each volume of the network constitutes a 0-D system where mass and energy conservation equations are solved. Given the complexity of both physical phenomena and cavity geometry, the choice of 0-D systems represents a suitable trade-off between calculation speed and result accuracy.

This paper proposes a numerical model designed to evaluate the thermodynamic properties of the volumes and to predict the pressure drop distribution across piston seals. It also assesses friction power generated by dry seals and identifies rings vulnerable to premature wear. Moreover, the model shows that optimizing the geometrical design of the seals minimizes the gas blow-by, enhancing compression efficiency and extending the machine lifespan.
Numerical Analysis of a Flow Control System for High-Pressure Turbine Vanes Subject to Highly Oscillating Inflow Conditions
Authors: Gallis Panagiotis , Salvadori Simone , Misul Daniela Anna
Published: August 2024

Under the prism of introducing pioneering technologies in the propulsive field, the Rotating Detonation Engine (RDE) continuously attracts the Gas Turbine (GT) research community. However, how to effectively couple an RDE with High-Pressure Turbine (HPT) stages is still debated. In fact, time-dependent flow conditions from the RDE greatly affect turbine performance, thus reducing the positive impact of Pressure Gain Combustion (PGC) on the overall cycle efficiency. The present numerical work aims at analysing both the impact of a pulsating inflow on the performance of a newly designed high-pressure turbine vane and the effectiveness of a flow control system in governing the oscillations within the vane passage. First, a baseline vane capable to ingest high enthalpy flow at an inlet Mach number of 0.6 is introduced. A total number of 297 samples are generated by varying the 18 geometrical parameters that characterize the vane’s endwalls and airfoil profile with the help of Latin Hypercube sampling method. Then, an optimization strategy is performed using steady inflow conditions allows for minimizing vane’s loss coefficient, thus providing the final geometry of the new vane. In the second part of the work, a flow control system is proposed by placing a series of holes in the endwalls of the vane. Air at constant stagnation conditions is injected upstream of vane’s leading edge. Unsteady calculations with and without flow control, including similar pulsating conditions from the RDE provide an insight to the generation and evolution of the secondary flow structures inside of the passage. The main outcome of this analysis is that the flow control system intensifies the passage vortices providing less oscillating flow at the vane exit section, which is beneficial for the aerodynamic performance of a subsequent blade row.
Comparison of Ingestion of Different Size Hard and Soft Bodies Into a Representative Fan Assembly Model
Authors: Mattar Rashid E. , Sirivolu Dushyanth , D’Souza Kiran
Published: August 2024

Foreign matter ingestion into a jet engine is a significant hazard to the safety of aircraft. While soft body ingestions (i.e., bird or ice ingestions) have been extensively researched, the threat posed by uncrewed aircraft systems (UASs) is a more recent concern due to their recent rise in popularity and has not been thoroughly studied. To better understand the damage caused by UAS ingestions, it is crucial to examine the resulting ingestion damage in comparison to birds of similar mass. This analysis is an essential initial step in determining how previous knowledge regarding soft body ingestions can relate to this new threat. To properly analyze these ingestions, development of a model that accurately represents a fan assembly is essential. This model should include a fan, as well as representative boundary conditions for the ingestion, such as blade retention systems, nose cone, casing, and shaft. Items that are analyzed during the ingestion include the overall damage to the fan blades, average and peak forces imparted on the retention systems, impact loads with the casing, and transient loads due to impact on the shaft. The foreign object models used were experimentally validated at their nominal sizes to increase confidence in the results. Comparison of the effects of ingestion of UAS and birds of difference mass into the representative fan model are presented and discussed to gain a better understanding of the differences between soft and hard body ingestion.
The Development of Machine Learning Models for Radial Compressor Monitoring With Instability Detection
Authors: Carrattieri Lorenzo , Cravero Carlo , Marsano Davide , Valenti Emiliano , Sishtla Vishnu , Halbe Chaitanya
Published: August 2024

Modern radial compressors are designed to operate with high performance and a wide range of applications while minimizing their environmental impact. It is necessary to study the machine near the stability limit and gain a comprehensive understanding of the fluid dynamic mechanisms that trigger the instability in the system to extend the operating range at high efficiency. Machine learning aids in developing pattern identification models for detecting compressor instability. In a prior study, a two-stage radial compressor for refrigerant gas underwent extensive simulation, capturing unsteady RANS conditions and generating a substantial dataset of pressure signals from multiple probes. Selected signals, coupled with detailed CFD post-processing, revealed fluid-dynamic structures near surge conditions. This study utilizes all pressure signals to assess the stage’s operational state (stable, transient, or unstable/surge). An additional goal is to develop an algorithm predicting flow patterns in different stage sections with minimal pressure signals at the rotor inlet. This is a preliminary step towards the development of a smart monitoring and diagnostic model for the compressor installed in a plant. The developed model consists of three sub-models, trained with CFD results obtained from URANS simulations. The three sub-models are a regression submodule, a classification submodule, and a forecasting algorithm. The regression submodule predicts diffuser static pressure fields, the classification submodule categorizes whether the compressor is in a critical condition or not, and the forecasting algorithm predicts the inducer pressure signals in the future impeller rotations according to the actual operation history. These sub-modules work together to forecast whether the compressor, according to the operation strategy, is going into instability conditions.
Wave Reformer Channel Shape Design for Enhanced Hydrogen Pyrolysis
Authors: Madiot Ghislain , Tüchler Stefan , Akbari Pejman , Copeland Colin D.
Published: August 2024

A wave reformer utilizes shock wave heating resulting from pressure exchange between a driver and a driven (reactant gas) to initiate a thermal decomposition reaction. Although widely applicable to many reactions, this paper will focus on the thermal pyrolysis of methane to produce hydrogen and solid (black) carbon. It uses wave rotor technology that has been applied to other applications but developed specifically here for high-temperature pyrolysis by New Wave Hydrogen Inc. (NWH). This research uses a quasi-two-dimensional (Q2D) model implemented in Ansys Fluent to study the influence of new channel design features on the unsteady flow field and performance characteristics of the wave reformer.

The primary objective of the work is to investigate the impact of variable area channel design on peak temperature (a proxy for thermal pyrolysis), which has received limited attention in existing literature. The model numerically solves the three-dimensional, compressible, and unsteady Navier-Stokes equations, employing the k-ω-SST turbulence model for closure. Additionally, it utilizes a cell-centered approach coupled to multispecies transport equations and a one-step finite-rate chemistry model. The channel’s curvature is controlled with Sigmoid functions to ensure a smooth area transition along the channel.

The Q2D results reveal that as the fluid traverses the converging channel, its temperature increases due to the rising internal energy, necessary for enhancing hydrogen yields. However, an over-reduction in channel cross-section results in a decrease in the driven mass flow rate, subsequently lowering the mass flow ratio. This work shows that, above a given threshold, there is a significant benefit to implementing converging channel designs in wave reformers for enhanced shock heating.
Investigation of Particle Deposition and Erosion Characteristics of Axial Compressor Blades
Authors: Guo Chuanliang , Chen Shaowen , Chen Shuaitong , Zeng Cong
Published: August 2024

This paper presents a numerical simulation study of the erosive and depositional effects of sand and dust particle ingestion within the compressors of aircraft engines, utilizing a gas-solid two-phase flow approach. An Euler-Lagrangian framework is adopted to track individual particles within the flow field, with a focus on the impact of particle parameters on component erosion. The investigation delves into the internal characteristics of erosion and deposition in the compressor, informed by the behavior of the particle trajectories. Findings reveal that an increase in particle size correlates with more erratic particle paths and an intensified erosion of the compressor blades. The impact angle remains relatively unchanged across various particle sizes, indicating that the velocity of impact is the predominant erosive force. Deposition primarily occurs on the leading edge and pressure side of the blades, with total deposition volume escalating with particle diameter. Interestingly, the deposition rate decreases as particle size increases. This study provides insights that are critical for the enhancement of aero-engine design and maintenance protocols.