bluuebunny/crossref_metadata_2025 huggingface dataset:
Conceptual Design of the Electric Pumps for the High-Performance Engine of a European Lunar Lander
Authors: Danieli Piero , Masi Massimo , Tridello Riccardo , Pessana Mario , Barato Francesco , Chiesa Alessandro
Published: September 2023

This work deals with the design of a high-speed pump to pressurize the fuel and oxidizer of a rocket engine to be installed in a European lunar lander, being developing by NAMMO UK under ESA funding. The use of pumps (Pump-Fed engines) instead of high-pressure branches (Pressure-Fed engines) is dictated by the need of minimizing the weight of the propellant and the pressuring tanks. Electric pumps are very precise in terms of operation control; however, it is necessary they reach a high efficiency in order to minimise the overall dimensions and weight of the batteries that power them. The goal of the present work is to demonstrate that in this specific application, partial-emission pumps can be a valid alternative to the classic centrifugal pumps allowing similar hydraulic performance, easier manufacturability and, mostly, noticeably higher resistance against cavitation. These advantages can certainly make the partial-emission type of pumps competitive especially in case of demanding operating conditions such as those of small rocket engines, characterized by high heads, small flow rates and high rotation speeds. To this purpose, one centrifugal and one PE pump were optimally designed imposing the same design-point operating conditions as required by the project’s application. The two designs were implemented in the computational fluid dynamic software Star CCM+ via 360-degree 3D models and their performance at design point operation were then compared. Results demonstrated that the partial-emission pump allows achieving a cavitation resistance 37% higher than well-designed FE pumps without suffering any efficiency penalisation.
Tuning of Generalized K-Omega Turbulence Model by Using Adjoint Optimization and Machine Learning for Gas Turbine Combustor Applications
Authors: Klavaris George , Xu Min , Patwardhan Saurabh , Verma Ishan , Orsino Stefano , Nakod Pravin
Published: September 2023

For swirl-stabilized gas turbine combustors, turbulence modelling is generally undertaken using Scale-Resolved Simulations (SRS) methods such as Large Eddy Simulations (LES). However, LES is expensive due to large mesh sizes and small time-step size required to estimate the correct large-scale turbulence motion generated within the combustor domain. While Reynolds Averaged Navier Stokes (RANS) models are computationally very efficient in predicting qualitative behaviour, such models lack fidelity to predict complex flow characteristics such as swirl accurately. In previous studies with commercial Computational Fluid Dynamics (CFD) code, the Generalized k-omega (GEKO) based RANS model has been used for simulation of turbulent flows. The free-coefficients of the GEKO model are tuned to predict the characteristics of potential flow undergoing separation. In this paper, LES predictions are used as baseline results which are used to generate a sensitivity field by using an Adjoint solver. Machine learning (ML) via Neural Network (NN) Training is utilized to create a correlation between suitable turbulent flow features and optimal GEKO parameters, aiding the trained model’s generalization. This allows computationally faster simulations of swirling flow with optimized GEKO model compared to LES. In this paper, an industrial configuration named as the DLR PRECCINSTA burner has been used considering a cold non-reacting flow. The computations are performed with LES, and the results match the experiments for directional velocities at different sections within the combustor. The LES solution is used to train the GEKO sensitivity by using an Adjoint solver. The objective function defined in this work is based on the linear combination of difference in velocity components, and a Neural Network is trained to obtain an optimized GEKO model. The results with optimized GEKO agree qualitatively and quantitatively with LES and experiments. The generalization of the NN model is tested on different flow conditions, including a range of Reynolds numbers as well as a reacting flow scenario. The results are showing significant improvements over the baseline solution as compared to the experiment. An optimized workflow is established, which can be used in future studies concerning different geometries with similar flow fields.
The Influence of Different Total Pressure Profile Inlet Distributions on the Performance of a Turbine Vane Frame With Splitter Vanes
Authors: Pramstrahler Simon , Klemm Christian , Peters Andreas , Patinios Marios , García De Albéniz Mikel Lucas , Heitmeir Franz , Marn Andreas
Published: September 2023

A turbine vane frame (TVF) is a component located in between the high-pressure and the low-pressure turbine of future aeroengines. It combines the aerodynamic purposes of a turbine center frame (TCF) and the stator vane row of the first low-pressure turbine stage in one component. Further, it is also used to house structural components and instrumentation, and to guide oil pipes and wires to the inner part of the engine. With the usage of a TVF, the size and weight of the engine can be reduced, and therefore, its efficiency increased. Combined with other technologies, this can help to reach the goals and roadmap demanded by the Strategic Research and Innovation Agenda (SRIA) to reduce the CO2 emissions per passenger kilometer compared to the year 2000 by 75% in the year 2050.

From an aerodynamic point of view, a TVF is a complex component with multiple problematic areas where flow detachments can occur. The TVF investigated in the present paper shows a small separation at the shroud endwall in experimental research. By choosing the right turbulence model, this separation can be reproduced with CFD simulations. However, the separation was very susceptible to different inlet boundary conditions like the total pressure profile distribution and the turbulence intensity. The present paper investigates the influences of multiple inlet total pressure distributions on the secondary flows, boundary layers and the flow field in general in the turbine vane frame. Further, it deals with the impact of the changes in the flow field on the performance of the turbine vane frame. Depending on the design and the operating point of aerodynamic components upstream of the TVF, the total pressure profiles can vary in a significant way. Different concentrations of the total pressure provoke different distributions of the losses in the TVF and therefore impact the performance of the component. Also, different shapes of the total pressure profile at the endwalls affect the boundary layers and therefore impact the secondary flows in the TVF.

In the present paper, two key characteristics describing a simple total pressure profile are investigated: The boundary layer thickness and the skewness of the profile. The description of the effects of those profiles on the TVF can help the design engineers to improve the design of a TVF and upstream components to increase efficiency. A key aspect of the paper is to describe the physical mechanisms of secondary flow and losses in the TVF and if and how separations affect the performance of the TVF.
The Manufacturing and Experimental Validation of a Nickel Superalloy Double-Wall, Effusion Test Specimen
Authors: Murray Alexander V. , Ireland Peter T. , Green Nick R. , Wickins Michael , Hood Richard , Telisinghe Janendra
Published: September 2023

With the hot stage of a modern aeroengine operating with combustor firing temperatures well beyond the melting point of the nickel superalloys from which the turbine blades are manufactured, developments to the methods of cooling of these components are required to advance performance. Double-wall, effusion systems exhibit a quasi-transpiration like cooling effect with recent work demonstrating their exceptional cooling performance. Such systems are characterised by two walls, one with impingement holes and the other with film cooling holes, that are mechanically and thermally connected via pedestals. However, manufacturing such geometries from single crystal nickel superalloys remains a significant barrier to entry into service.

This paper presents a method of manufacturing double-wall effusion specimens from a nickel superalloy commonly used in modern commercial high pressure turbine components. The method maintains the mechanical integrity associated with nickel superalloys. Details of the method are presented alongside x-ray and GOM laser scan data of a flat-plate test article that demonstrates the success of the manufacturing process. Aerothermal testing of the specimen in a bespoke recirculating wind-tunnel facility was undertaken in which the overall cooling effectiveness of the system is obtained. The results reaffirm the excellent cooling performance of double-wall, effusion systems and further validate the manufacturing methodology as a method by which to realise enhanced cooling effectiveness in service.
Improved Prediction of Secondary-Flow Behaviour Through a Novel Turbulence Model Extension for Rotational Effects
Authors: Mimic Dajan , Herbst Florian
Published: September 2023

In this paper, we present a model extension, which enhances the sensitivity two-equation linear eddy-viscosity turbulence models to an altered turbulence production and decay in rotational flow regions. In order to achieve this, the respective production terms of the turbulent kinetic energy and turbulent dissipation rate of the k-ω shear-stress transport (SST) turbulence model are modified using a rotation-sensitive detection term based on the von Kármán length scale.
Design of a Linear Compressor Cascade for Influence Coefficient Method Flutter Testing
Authors: Gambel Julian , Peitsch Dieter , Schneider Sabine
Published: September 2023

A linear cascade module was designed for flutter testing of combined plunge-pitch mode shapes over a range of different stagger and inflow angles in an established low-speed wind tunnel. The iterative approach to the aerodynamic cascade design described in this paper, involved the investigation of multiple layout options and design parameters. It led to a cascade configuration with 13 blades and adjustable diffusershaped bypass ducts on both ends of the cascade. RANS simulations show that this design is capable of replicating on its central 9 blades the steady-state and unsteady aerodynamics of an infinite cascade over a wide range of inflow angles, indicating that the finite cascade is suitable for experimental investigations of aeroelastic parameters.

Aeroelastic simulations of the finite cascade design and a cyclic reference cascade yielded surprising results regarding a beneficial effect of angle of attack on flutter stability that was observed over most of the considered parameter range. This appears to conflict with common aeroelastic understanding and prompts further investigation and experimental validation.
Secondary Flow Control of Turbomachinery Blades Using Vortex Generators
Authors: Putzu Roberto , Ghisu Tiziano , Shahpar Shahrokh
Published: September 2023

Secondary flow control is becoming increasingly important to improve the performance of highly-loaded axial fans and compressors, especially when considering multi-row interactions, where the main passage vortex can significantly reduce the life of downstream components. In this regard, vortex generators (VGs) are investigated to assess their potential to influence the secondary flow in an axial compressor, by increasing the mixing of the main flow with the low-momentum fluid of the boundary-layer. They can also be used to produce a strong vortex that is convected downstream in the desired direction to reduce the main passage vortex strength. They can be capable of reducing viscous effects at the hub and consequently contract the blade passage vortex, thereby mitigating the vorticity production and its effects on downstream components. Despite VGs having been studied extensively especially in external aerodynamics, there is still a lack of studies on their full potential to reduce secondary flows in axial fans and compressors. This work presents a novel way of using vortex generators to reduce secondary flows in the hub region of an axial compressor. The Rolls-Royce in-house CFD suite, with its overset (chimera) mesh capability, is used to generate high-quality multiblock structured meshes rapidly for complex configurations. A parametric analysis using several geometric factors is presented, together with a comparison of using different objective functions to select the optimal VG configuration from a DOE population. A detailed analysis of the effects on pressure loss and secondary flows is reported, paving the way for an automatic optimization of these devices.
Multi-Fidelity Heat Transfer Analysis of Shrouded High-Pressure Turbine Rotor Blades
Authors: Carta Mario , Ghisu Tiziano , Shahpar Shahrokh
Published: September 2023

CFD simulation is frequently used in the field of analysis, design, and optimization of complex geometries such as the film-cooled turbine blades of a modern jet engine. As increasingly higher turbine entry temperatures are being sought for, computational analyses need to be able to provide high-fidelity predictions of the metal temperatures and the heat transfer coefficient on these critical components. To increase the fidelity of the flow simulation, key physical aspects that characterize the operation of these components can be included in the model, particularly the fluid-solid thermal exchange, and the rotor-stator unsteady interaction. These effects that can impact the model’s prediction capabilities are investigated in the present paper. The geometry under study is constituted by a fully-featured high-pressure turbine one-and-a-half stage of a modern commercial jet engine. Rolls-Royce’s in-house software is used to carry out the 3D Reynolds-Averaged Navier-Stokes flow simulations. To enhance the fidelity in terms of fluid-solid thermal interaction, steady-state Conjugate Heat Transfer (CHT) simulations are conducted. The CHT results are then compared to experimental data from a thermal paint test. Phase-lag simulations are run in adiabatic-wall conditions to assess the impact of the stator-rotor interaction on the near-wall gas temperatures.
Computational Assessment of Labyrinth Seal Parametric Variation on Leakage Prediction Using Modified Direct Analytical Model in Transient and Steady Operation
Authors: Ertuğral Gürkan , Uçar Dündar
Published: September 2023

Labyrinth seals are vital for leakage control of gas turbine engines. Over the years, several analytical models have been developed to estimate leakage flow amounts through the labyrinth seals for different seal geometries and operating conditions. This paper presents and covers a modified direct analytical model based on the Vermes equation with updated flow coefficients to accurately calculate the leakage flow rate of straight-through labyrinth seals in a steady and transient operation. A design of experiment study has been performed to derive flow coefficients by changing operating conditions and geometric parameters of labyrinth seals in a commercial one-dimensional compressible flow solver Altair Flow Simulator and a computational fluid dynamics tool ANSYS Fluent. The kinetic energy carry-over coefficient and clearance factor are identified as the most critical factors for flow coefficients. The modified analytical model was validated with several labyrinth seal test cases of Stocker and Wittig et al. Numerical experiments have been performed to enhance the capability of both coefficients and models. The modified analytical model shows good agreement with test cases and predicts the seal leakage flow amount with 95% accuracy for the straight-through labyrinth seals.
Integrated Aero-Mechanical Design and Experimental Validation for Next Generation Compressors for Energy Transition
Authors: Toni Lorenzo , Guglielmo Alberto , Grimaldi Angelo , Cangioli Francesco , Biliotti Davide , Belardini Elisabetta , Meazzini Giulia , Miris Lorenzo
Published: September 2023

Meeting Paris Agreement climate goals and the global warming target of 1.5°C by 2050, requires energy sector to accelerate the path to energy transition to finally achieve net zero emissions. Turbomachinery, and centrifugal compressors in particular, will play a crucial role in this scenario and will be fundamental to turn a necessary, ethical and ambitious goal into an actionable one.

New generations of very efficient centrifugal compressor stages are needed to meet the requirements of low emission compression systems; in order to extend applicability of these high efficiency centrifugal compressor to as many applications as possible, peripheral speed needs to be increased beyond the current limits.

New design philosophies must be followed both for aerodynamics and mechanical designs and the typical limitations in terms of peripheral speed are to be overcome, even when standard alloys are used. Moreover, the more compact the configuration is, the stronger the blade row interactions are, with consequently higher fluid-structure coupling, which is mainly due to the unsteady interactions between structural mode shapes and stationary row wakes and potential fields; in addition to this, the high operating speed leads also to increased static stresses.

This paper then focuses on the aerodynamic and mechanical design challenges of a high-speed centrifugal compressor stage, designed for energy transition applications: numerical outcomes will be compared against experimental results, showing an excellent predictive capability. A full aeromechanical analysis and a dedicated experimental campaign have been carried out as well and the good data match in terms of vibratory response level and aerodynamic damping will be presented and discussed.

These achievements are key technology enablers for different energy transition applications and can be directly used for hydrogen compression systems designs.
Preliminary Wear Investigations With Pressure Actuated Leaf Seals for Superheated Steam Turbine Application
Authors: Wittenberg Andreas , Rühle Tobias , Greving Johannes , Wichern Florian , Friedrichs Jens
Published: September 2023

Pressure Actuated Leaf Seals (PALS) are a promising technology for modern load-follow operation of power plants and turbines. Their strength lies in their radial adaptivity, which enables a significantly smaller radial gap height than conventional labyrinth seals.

In this paper, which is a continuation of ISUAAAT16-022 from 2022, the operating behavior with compressed air and shaft rotation up to 3,000 rpm is investigated, including an analysis of the wear caused by frictional contact between the shaft and the seal leaves. This includes both concentric and eccentric contact behavior. The test seal with a nominal diameter of 300 mm is designed in such a way that it can be used in a similar design in subsequent industry-related superheated steam tests. In addition to the seal performance before, during and after the wear-in process, the frictional torques, temperatures in the flow and on the shaft-contacting leaves as well as the material removal on leaves and shaft running surface are analyzed.

The results show a basically robust operating behavior of the seal with moderate performance deterioration, which can be directly attributed to the increase in the clear gap. However, the shaft wear is higher than for other contact seals, so that further investigations are necessary before use in practice is feasible.
Review of Technologies Used in Gas Journal Bearing Test Rigs
Authors: Rimpel Aaron , Shakil Ali , Kerr Thomas , Lipham Robert
Published: September 2023

Foil bearings are the most prevalent gas bearing technology in use today. Foil gas bearing technology development requires a two-fold approach of analytical and experimental research. Analytical simulation can be used to better understand the underlying physical principles in detail, though this is not trivial due to complex interactions of structural, thermal, and fluid dynamics effects. Targeted experimental testing may then be used to validate the models. However, in practice, foil gas bearings have relied on simplified analytical tools, experience, and empirical approaches to validate and heuristically tune new bearing designs. Static load test rigs have been used to quantify steady-state performance like drag torque and load capacity as well as transient performance like lift-off speed and start/stop wear. Dynamic load test rigs have primarily been used to characterize the stiffness and damping coefficients of the bearings. This paper reviews test rigs employed over the last several decades, focusing on static and dynamic rigs for foil gas journal bearings. Technologies and considerations for the necessary test rig functions are covered: drive system, rig topology, static load mechanism, torque measurement, dynamic excitation and response measurement, and means to test in various gas conditions. A primary goal of this paper is to serve as a reference to future researchers embarking on a new gas journal bearing test rig design who wish to understand the state-of-the-art in this area.
Flight-Path Optimization for a Hybrid-Electric Aircraft
Authors: Papadopoulos Konstantinos I. , Nasoulis Christos P. , Gkoutzamanis Vasilis G. , Kalfas Anestis I.
Published: September 2023

This study aims to illustrate a sequence that optimizes the flight-path trajectory for a hybrid-electric propulsion system at mission level, in addition to identifying the respective optimum power management strategy. An in-house framework for hybrid-electric propulsion system modeling is utilized. A hybrid-electric commuter aircraft serves as a virtual test-bench. Vectorized calculations, decision variable count and optimization algorithms are considered for reducing the computational time of the framework. Performance improvements are evaluated for the aircraft’s design mission profile. Total energy consumption is set as the objective function. Emphasis lies on minimizing the average value and standard deviation of the energy consumption and timeframe metrics. The best performing application decreases computational time by two orders of magnitude, while retaining equal accuracy and consistency as the original model. It is employed for creating a dataset for training an artificial neural network against random mission patterns. The trained network is integrated into a surrogate model. The latter part of the analysis evaluates optimized mission profile characteristics with respect to energy consumption, against a benchmark flight-path. The combined optimization process decreases the multi-hour-scale timeframe by two orders of magnitude to a 3-minute sequence. Using the novel framework, a 12% average energy consumption benefit is calculated for short, medium and long regional missions, against equivalent benchmark profiles.
The Effect of Higher Water Vapor Content in H2-Fired Turbines on High Temperature Durability
Authors: Pint Bruce A. , Pillai Rishi , Romedenne Marie , Dryepondt Sebastien
Published: September 2023

Water vapor is a constituent in many environments of technical significance, especially those associated with combustion, and the switch to hydrogen-firing will increase the concentration of water vapor in the exhaust. A negative influence of water vapor on high temperature oxidation has long been recognized for both metallic and ceramic components by comparing laboratory exposures with and without water vapor. However, the effect of water vapor concentration has not been studied as frequently. Several data sets will be reviewed including alloys for thin-walled gas turbine recuperators and the performance of uncoated superalloys and alumina-forming alloys and coatings including the performance of thermal barrier coatings in furnace cycle testing. Chromia-forming alloys are more severely degraded by water vapor in exhaust due to the volatilization of CrO2(OH)2 and this reaction may be faster with higher water vapor contents. Alumina-forming alloys and coatings exhibit some degradation with the addition of water vapor but no impact of increasing the water vapor content has been observed. For silica-forming ceramics, water vapor has an extreme impact on the growth rate and the performance of environmental barrier coatings can be evaluated based on the underlying silica growth rate.
Development of a 250,000 Lb Thrust Bearing Test Rig With Experimental Results
Authors: Wilkes Jason , Omer Farhan Ahmed , Kerr Thomas
Published: September 2023

As the power density of rotating machinery increases, individual component requirements stay the same, while also needing to decrease in size. The design of high-load roller-element thrust bearings involves minimizing the bearing envelope while also maintaining load capacity and life. This paper introduces a new thrust-bearing test rig that uses spherical point loading to deliver up to 250,000 lbf of axial load at speeds up to 60 rpm. This test rig is unique to the literature both in its bearing load and its ability of the rig to test a bearing to the point of failure. The test shaft is spun by a 25 hp motor with a 50:1 speed reducer. The load is applied from a hydraulic pump and a stinger onto a stationary housing. The test rig uses two thrust bearings in a back-to-back arrangement for transferring the applied thrust. The first bearing is the test-bearing, and shaft / housing sleeves allow for a range of sizes and types. The second bearing is a standard tapered roller thrust bearing and is rated for 20 rpm and 1,100 kN (250,000 lbf). A third bearing provides additional radial support to the system. The rig is capable of testing a range of bearing sizes. The bearing housing and shaft use spacers to accommodate bearings from five to eleven inches in diameter, and zero to two inches in length. The rig measures bearing performance through axial displacement and test-bearing drag torque. Water cooling maintains bearing temperature throughout the test. The paper also presents experimental results for a 10-hour test of a new roller element bearing.
Analysis and Prediction of the Machine Capacity Required to Meet Net Zero by 2050
Authors: Wilkes Jason , Reitz Dan , Ransom David , Hofer Doug , Kurz Rainer , Kerr Thomas , Holland Matthew
Published: September 2023

The following paper presents a unique look at the goal of Net Zero 2050, a goal that many of our governments, companies, and citizens support. This paper will focus on the problem from a capacity standpoint. Essentially, there are a number of heat pumps, gas turbines, steam turbines, and the like that will be needed to achieve Net Zero 2050. Many of these machines, systems, and concepts are only in their initial stages of testing and development. This paper will consider a few predicted 2050 power distributions to assess the machinery needed to meet a net zero goal, and then will focus on looking at the capacity of the current machinery market in each sector. These sets of data will then be used in collaboration with historical trends on the adoption of technologies and power block systems, and will determine whether the target for each industry is appropriate, and even possible from a capacity standpoint.
Experimental Investigation of Direct Flame-Cooling Air Interaction With an Effusion Cooled Combustor Wall
Authors: Xavier Pradip , Blaise Antoine , Quevreux Benjamin , Mille Bruno , Pascaud Stéphane , Viguier Christophe , Grisch Frédéric
Published: September 2023

The development of ultra-compact combustors raises challenges regarding wall thermal management. This study aims to understand the behavior of a reacting flow interacting with a cooling air film generated by an effusion wall. Experiments are carried out in an optically-accessible test rig operating at atmospheric pressure, and generating a premixed methane/air turbulent flame. Particle image velocimetry (PIV) and OH planar-laser induced fluorescence (OH-PLIF) are implemented to assess the cold-flow topology and the flame dynamics. Results indicate that an important turbulent flow activity is present in the developing shear layer, being independent of the hole diameter. The air film creates an aspiration of the mainstream. The blowing ratio modifies the flame wrinkling, amplified by the aspiration of the air film. Changing the main equivalence ratio induces a stronger flame-cooling air film interaction. Eventually, a larger hole diameter with a constant wall porosity increases the hole-to-hole distance, enabling the reactive flow to be engulfed at the wall.
Assessment of Fan Stall Point Identification Ability of Steady RANS Computations With the Helicity-Corrected Spalart-Allmaras Turbulence Model
Authors: Yu Zhifan , Raza Hussain , Defoe Jeff
Published: September 2023

Accurate axial fan/compressor stall point prediction using computational fluid dynamics (CFD) has generally been carried out using unsteady computations, often with slowly ramped back pressure. While this approach tends to be accurate with unsteady Reynolds-Averaged Navier Stokes (URANS) computations, it is computationally expensive, often requiring 4–6 rotor blade passages to be included in the computation and necessitating the solution of many rotor revolutions’ worth of flow time. Recently, some work has shown that the helicity-corrected Spalart-Allmaras (HCSA) turbulence model is able, in steady RANS computations, to predict fan stall points within a few percent of experimentally measured operability limits. In this paper, we directly predict stall points by using a steady, multiple reference frame (MRF) or “frozen rotor” approach which employs the HCSA turbulence model. The machine studied is a low-speed axial fan. Computations are carried out using the open-source CFD software package OpenFOAM. The approach is able to predict the stalling flow coefficient to within 0.006 of the experimentally-measured value. Detailed assessments of the flow field at the last stable operating point and at a point just into stall yield show that the HCSA model is able to predict the same stall inception mechanism captured in URANS.
Considerations for Compressible Film Cooling: A Computational Study of the Effects of Transonic Flows and Varying Mainstream Mach Number
Authors: Fox Dale W. , Furgeson Michael , Bogard David G.
Published: September 2023

Recent evidence suggests that film cooling flows with engine realistic mainstream Mach number have declined performance in comparison to those with conventional low-speed laboratory conditions. Consideration and understanding of these effects are fundamental to improving film cooling research. The proposed computational study investigates the film cooling performance of a 7-7-7 shaped film cooling hole with respect to varying mainstream Mach number, with constant Reynolds number. The cases studied include mainstream Mach numbers from 0.15–0.75, with a fixed, engine realistic, hole Reynolds number of Red = 10, 100. Significant results are then evaluated against varying stagnation temperature ratio and blowing ratio. The results showed that at a blowing ratio of 1.75, the adiabatic effectiveness declines significantly with high mainstream Mach number. The decreased performance is due to supersonic flows and shocks in the film cooling hole that disrupt flow in the diffuser section of the hole. These characteristics are observed across all stagnation temperature ratios considered. In addition to these insights, the study discusses the importance of proper thermal scaling and definition of adiabatic effectiveness when operating at high mainstream Mach number. It is demonstrated that the effects of high-speed flow challenge the efficacy of the conventional parameters used to characterize film cooling performance.
Evaluation of Additively Manufactured Heat Exchanger Tubes Using Experimental and Conjugate Heat Transfer Analysis
Authors: Wright Lesley M. , Liu Jong , Kamrath Benjamin , Morris Mark C.
Published: September 2023

Additive manufacturing offers many benefits for the design and production of gas turbine engine components. Direct metal laser sintering (DMLS) expands the available design space while reducing manufacturing cost and cycle time. Engineers continue to explore opportunities for additive components throughout the engine. Generally in regions of reduced stress, heat exchangers provide an opening for immediate implementation of DMLS components. The surfaces of components manufactured using the DMLS process are rough compared to those produced from traditional casting or subtractive manufacturing methods. Therefore, during the design phase, heat transfer designers must understand the heat transfer augmentation and pressure loss increase associated with the roughness from the DMLS process. In this study, DMLS tubes (as printed) were evaluated experimentally. The experimental results were used for validation of a conjugate heat transfer (CHT) model. With the CHT model accurately capturing the roughness effects of the tubes, the model can be confidently extended to other flow conditions and tube configurations. Within the study, a total of six printed tubes were experimentally tested and presented. Four tubes had a diameter of 4.0 mm, and the remaining tubes were 2.0 mm in diameter. The overall lengths of the tubes varied from 180 mm to 230 mm. The coolant flow rate through all tubes varied, yielding Reynolds numbers from 7,500 to 30,000. The overall pressure loss and heat transfer enhancement was measured in the printed tubes. These results were used to validate a CHT model using STAR-CCM+ for the same geometries and flow conditions. The measured Nusselt numbers were 1.25–2.4 times greater than those predicted by Dittus Boelter correlation for heat transfer in a smooth tube. The heat transfer enhancement came at the expense of increased pressure loss compared to smooth tubes. The frictional losses were 1.75–6.5 times greater than those predicted for smooth tubes. The thermofluidic performance of the additively manufactured tubes was generally well predicted by the Norris correlation for rough tubes. The CHT predictions also compare favorably with the Norris correlation. This experimental and numerical study shows the value of printed tubes for heat exchangers. It also highlights the challenges of measuring and predicting the thermal performance for various size tubes.
Experimental Force Coefficients of a Hydrostatic Thrust Bearing and Comparisons to Predictions
Authors: Lim Homin , Ryu Keun
Published: September 2023

Reliable fluid film bearings for high-performance turbomachinery provide significantly extended operating life with controllable stiffness and damping force coefficients at low cost. Hydrostatic thrust bearings support thrust loads and control axial motions. This paper reports measurements and predictions of static and dynamic load characteristics of a hydrostatic thrust bearing fed with pressurized air. The current bearing model uses dynamic axial periodic motion amplitudes, that is models as a function of the initial film thickness, to predict the dynamic force coefficients. Note that, presently, the recorded frequencies and their amplitudes of pneumatic hammer instability along the axial direction are implemented as an external excitation source. The measured and predicted static stiffnesses increase as the film thickness decrease and supply pressure into the bearing increase. The predicted dynamic force coefficients show a favorable agreement with the test data. Analysis reveals the negative damping coefficients and damping ratios as a distinctive onset condition of the present pneumatic hammer instability of the test bearing. A careful recess design and adequate operation conditions along with an accurate prediction can avoid or prevent undesirable pneumatic hammer instability in hydrostatic thrust bearings. The present work extends the knowledge database of hydrostatic thrust bearings with pneumatic hammer instability and provides their design guideline for various operating conditions.
Experimental Investigation of Acoustic Characteristics of Boundary Condition for a Combustor
Authors: Ikwubuo Melvin , Lee Jong Guen
Published: September 2023

In the reported paper, the reflection coefficient at the exit of the bluff-body combustor is experimentally measured over a range of operating conditions for different exit orifice plates without combustion: Ma = 0.05–0.75, the temperature of air = 300K–600K, exit area blockage ratio = 0–69%. A bluff-body combustor similar to an afterburner is used for the measurement. The exit boundary condition is measured without combustion. Measurement results show that the reflection coefficient is significantly complex (i.e., phase is significant) when the flow rate is near or well below Eldridge and Dowling’s criterion. Eldredge and Dowling developed a criterion for the optimum ratio of flow Mach number and perforated liner porosity (ME = σ), such that maximum absorption (i.e., minimum reflection coefficients) of acoustics can be achieved. A model is proposed as a result of the present experimental study that can predict the real part of the reflection coefficient for exit boundary conditions. The acoustic impedance increases linearly as the Mach number increases and decreases with respect to the blockage ratio. The imaginary part of the reflection coefficient at the exit of the orifice plate decreases and approaches zero as the Mach number increases, indicating that the imaginary part of the reflection coefficient may not be ignored for thermoacoustic modeling when the combustor exit is not choked and the Mach number of the flow is lower than 0.35.
Evaluation of the Feasibility of Prediction of Thermoacoustic Instability Using a Wave-Based Reduced Order Network Model for a Micromixer Combustor
Authors: Hunter Riley , Song Jinkwan , Lee Jong Guen
Published: September 2023

The feasibility of prediction of thermoacoustic instability using a wave-based reduced order network model is evaluated for a micromixer combustor where the flame length is about 43% of the combustor length. A wave-based reduced order network model using a linear acoustic theory is formulated in such a way that the impact of various modeling input parameters such as non-compactness of flame, temperature distribution in the combustor and acoustic boundary conditions on the prediction of onset of combustion dynamics and instability frequency be evaluated. Both global and local flame transfer functions are experimentally determined and incorporated in the network model as the source terms to determine if the compact flame assumption is valid for the prediction. The acoustic boundary conditions as well as the actual temperature distribution are experimentally measured. Modeling results with the global or the local flame transfer function as the source term and with the measured flame temperature show that the prediction of the combustion dynamics does not agree with the experimental results when the analytically modeled boundary conditions are used, warranting the correct determination of acoustic boundary conditions in order to predict the onset of instability correctly. Also, the implementation of distributed flame in the model enhances the accuracy of prediction of thermoacoustic instability for the flame presented in this study.
ICME Simulation of APS Process and Damage in Ceramic Coatings
Authors: Marrey Mallikharjun , Huang Dade , Morscher Gregory N. , Miraj Rashid , Abdi Frank , Ballant Daniel , Jefferson George , Panakarjupally Ragavendra P.
Published: September 2023

This work shows an enhanced Integrated Computational Material Engineering (ICME) method for modeling of multi-material coating of Air Plasma Spray (APS) Ceramic Coating Process. ICME simulation of the APS process includes defects and the effect of defects (bending, curvature, delamination, and cracks), in-service analysis under Burner-Rig and furnace thermal loading conditions, and the effect of high temperature on Thermal Barrier Coatings (TBC) over the metallic substrate of dog bone specimens to demonstrate durability and damage tolerance (D&DT).

To achieve this end, a multi-physics-based ICME methodology and virtual design of experiment (DOE) tools are developed to virtually generate multi-layered materials including high-temperature coatings for use in engine/aircraft high-temperature exhaust regions. The ICME innovation centers around: 1) Thermo-Physics Modeling (plasma, vapor, liquid, solid) to predict the material’s thermal profile, voids, densities, and thermal conductivities; 2) Multiscale Material Modeling of the top coat, bond coat, and substrate to predict material performance: a) temperature-dependent strength, stiffness, residual stresses and strains considering the effect of defects, and b) rumpling, surface waviness, and Thermal Growth Oxidation (TGO); 3) Structural Analysis and D&DT to predict coating and substrate failure evolution (i.e., delamination, oxidation, etc.) during thermo-mechanical in-service loading; and 4) Simulation of residual stress/strains due APS process. The simulation also shows rumpling and TGO growth have little effect on the as-built APS TBC specimen.

Verification was performed using test data on TBC/Haynes230 systems under thermal loading. Tests and predictions were in close agreement. Both test and prediction showed an as-built specimen exhibiting bending during APS process and delamination during Burner-Rig testing.
Identification of Dynamic Force Coefficients for an Additively Manufactured Hermetic Squeeze Film Bearing Support Damper Utilizing a Pass-Through Channel
Authors: Ertas Bugra , Gary Keith , Adcock Tom
Published: September 2023

The following paper presents breakthrough experimental results for a new hermetic squeeze film damper (HSFD) concept that is integrally designed within an externally pressurized tilting-pad radial gas bearing support. The flexibly damped gas bearing module was designed for a 7.2” (183 mm) diameter shaft and fabricated using direct metal laser melting (DMLM); also known as additive manufacturing. The bearing and HSFD were sized based on ongoing studies for oil-free super-critical carbon dioxide (sCO2) power turbines in the 8.5MW-10MW power range. The development of the new damper concept was motivated by past dynamic testing on HSFD, which generated frequency dependent stiffness and damping force coefficients. In efforts to eliminate the frequency dependency, a new HSFD architecture was conceived that adds accumulator volumes and a pass-through channel to previously conceived HSFD flow network designs. The other motivation of the work is the need for developing a cost-effective and reliable oil-free bearing technology that is scalable to large power turbomachinery applications. There were several objectives to the following work. The first objective was to successfully design and fabricate a single piece bearing-damper using additive manufacturing, while dimensionally controlling critical design features. The paper discusses the manufacturing steps and shows cut-ups that reveal adequate clearance control capability with internal damper clearances. The second objective was to perform experimental testing with the new HSFD design in efforts to extract stiffness and damping coefficients for excitation frequencies within 20–160 Hz and peak vibration amplitudes between 0.25 mils (6.35 microns) to 1mil (25.4 microns). The test results for a single HSFD bearing module indicated that the design modifications to the HSFD architecture were successful in eliminating nearly all the frequency dependency for the stiffness force coefficient. The dynamic tests yielded a stiffness coefficient that varied between 112 klb/in (19.6 MN/m) and 96 klb/in (16.8 MN/m). The damping force coefficient however, exhibited relatively more variation with frequency with values residing between 175 lb-s/in (31 kN-s/m) to 214 lb-s/in (37 kNs/m). Finally, the paper advances a three-dimensional fluid-structure interaction (FSI) model using transient finite element analysis (FEA) coupled to a computational fluid dynamics (CFD) model. The FSI analysis performed between 20Hz-80Hz was used to predict the stiffness and damping of the HSFD using a quarter section model of the damper. The FSI analysis was able to support test results by showing only a 6–7.4% change in the magnitude of force coefficients. Stiffness predictions agree reasonably well with experiments whereas damping is underpredicted.
Overall Cooling Effectiveness With Internal Serpentine Channels and Optimized Film Cooling Holes
Authors: Yoon Christopher , Flachs Elise M. , Ellinger Molly R. , Bogard David G.
Published: September 2023

The overall cooling effectiveness for gas turbine airfoils is a function of the combined cooling due to internal cooling configurations and film cooling configurations. Typically, film cooling configurations are evaluated independent of the cooling effects of the internal feed channels, generally based on adiabatic effectiveness measurements. In this study, we consider the coupled effects of internal cooling and film cooling configurations through measurements of overall cooling effectiveness for film cooling holes fed by a coflow/counterflow channel and a serpentine channel. A film cooling hole designed by adjoint optimization techniques (X-AOpt) is compared to a standard shaped hole with 7° forward and lateral expansions (7-7-7 SI). Experiments without film cooling showed that the serpentine channel had 35% to 50% greater overall cooling effectiveness than the straight, coflow channel. Experiments with the X-AOpt hole combined with a serpentine channel showed an area-averaged overall cooling effectiveness of ϕ̿, which was a 70% increase compared to the overall cooling effectiveness of the serpentine channel without film cooling. When the X-AOpt hole was fed with a coflow channel with similar coolant mass flow rate, the overall cooling effectiveness was ϕ̿=0.44, i.e. 30% lower than when using the serpentine channel. Interestingly, adiabatic effectiveness measurements with the X-AOpt holes showed a more uniform hole-to-hole performance when using the serpentine channel compared to the coflow channel.
A Calibration Approach for Accelerated Creep Testing for Electron Beam Melted (EBM) Ti-6Al-4V Using the WCS Model
Authors: Hossain Md Abir , Pellicotte Jacob T. , Stewart Calvin M.
Published: September 2023

This study outlines a model calibration approach for an accelerated creep test called the dynamic negative stepped test (DNST) to enable the rapid screening of creep resistant materials. In DNST, stress is stepped decreased based on the attainment of a sufficient minimum-creep-strain-rate (MCSR) at each stress level. Steps are repeated, torturing the material, until rupture occurs. The DNST is advantageous as a screening test for new alloys. Alloys and Heats with superior creep resistance will be able to survive longer and with greater ductility than those with poor creep resistance. The calibration of a constitutive model to DNST data furnishes predictions of the conventional creep response being between 65–6685 hr from the relatively short (< 130 hr) DNST Data.

In this study, DNSTs are performed on electron beam melted (EBM) Ti-6Al-4V at 650°C with stepping through 150, 75, 60, and 50 MPa. Six build orientations are tested including 0°, 30°, 45°, 60°, 90°, and V (vertical) direction. The Wilshire-Cano-Stewart (WCS) model is employed to calibrate the experimental data. A systematic calibration approach is adopted. Each step is calibrated numerically. A unique set of minimum-creep-strain-rate (MCSR) and stress-rupture (SR) related material constants, i.e., the Wilshire and Sinh constants are obtained for each build direction. A non-homogenous objective function is used to numerically optimize the strain trajectory and damage trajectory constants. To find the best-fit curve, the strain trajectory constants and damage trajectory constants are numerically refined for each step. The WCS model shows a near perfect prediction of the DNST data. Based on the calibrated constants, conventional creep curves are generated in order to determine which build orientations are likely to exhibit poor, moderate, and superior creep resistance. Predictions of MCSR and SR curves over a wide stress range are estimated at outside the experimental range to investigate the extrapolation pedigree of the approach. This will allow the material designers to have more confidence in DNST generated test data for predicting long-term creep response and structural lifetime.