bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Inlet Flow Angle on Turbine Vane Frame Aerodynamic Performance
Authors: Pramstrahler Simon , Peters Andreas , García De Albéniz Mikel Lucas , Leitl Peter Adrian , Heitmeir Franz , Marn Andreas
Published: October 2022

Modern aero-engines are designed for high efficiency and low weight to reduce fuel consumption and achieve reductions in CO2 emissions. According to the goals and roadmap of the “Flightpath 2050” report, the Strategic Research and Innovation Agenda (SRIA) demands a drastic reduction of emissions to balance further air traffic growth. Therefore, technologies and processes allowing for a 75 % reduction in CO2 emissions per passenger kilometer compared to the year 2000 technology standard must be available by 2050. Turbine Vane Frames (TVF) are one technology to increase the efficiency of aero-engines and can therefore help to reach this goal. Turbine Vane Frames are located in-between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) of an aero-engine and have three major purposes: guiding the flow to higher radii, incorporating the function of stator guide vanes of the first stage of the LPT, and passing structural components and oil pipes through the flow channel. A TVF with aft-loaded wide-chord main vanes and splitter vanes was designed, which meets engine-representative mechanical and aerodynamic constraints. A test vehicle consisting of the TVF and a first-stage LPT rotor has been designed and is currently being tested in the subsonic test turbine facility for aerodynamic, aeroacoustic and aeroelastic investigations (STTF-AAAI) at the Graz University of Technology. In the engine, the TVF needs to function at high performance not only at the aerodynamic design point (cruise) but also at off-design conditions. A splittered TVF design features complex flow fields with strong secondary flow interactions, and because of the fundamental design differences, the flow field characteristics within a TVF are different from those in a conventional LPT vane row. This paper discusses the flow field in a splittered TVF with emphasis on secondary flow structures and their interaction with each other and the main flow. To examine the influence of different swirl angle levels on the flow field and loss generation mechanisms inside the TVF, the swirl angle upstream of the TVF is numerically changed in a wide range from positive to negative angles. The objective of this study is to examine the sensitivity of the splitter vanes to large flow angle deviations, as present in part-load operation. Additionally, the flow field downstream of the TVF and its influence on the LPT rotor performance is described in detail. The size and locations of separated flow regions resulting from the off-design incidence of the flow and their impact on the rotor are investigated and quantified. A loss breakdown is presented to discuss the impact of incidence variations on the performance of both the TVF and the LPT.
Influence of RANS Turbulent Inlet Set-Up on the Swirled Hot Streak Redistribution in a Simplified Nozzle Guide Vane Passage: Comparisons With Large-Eddy Simulations
Authors: Wingel Christopher , Binder Nicolas , Bousquet Yannick , Boussuge Jean-François , Buffaz Nicolas , Le Guyader Sébastien
Published: October 2022

A high-pressure turbine is a complex component of a gas turbine from a thermo-mechanical point of view. In modern lean-burn combustion chambers, this complexity is enhanced with the presence of hot streaks together with swirl components and high levels of turbulence coming from the combustion chamber. These radial and azimuthal velocities and temperature distortions have a substantial impact either on the aerodynamics inside the high-pressure turbine or on the aero-thermal behavior of the vanes and blades. It is thus clear that the early development of a high-pressure turbine using numerical simulations must take into account swirled hot streaks.

From a practical point of view, imposing the proper turbulence at the inlet boundary condition is not easy in classical Reynolds-Averaged Navier-Stokes (RANS) methods, where all the turbulence is modeled. This paper studies the redistribution of a swirled hot streak in the simplified case of a bent duct. This work focuses on turbulence modeling. High-fidelity Large-Eddy Simulation (LES) results are used as reference data to validate different RANS set-ups to predict the hot streak redistribution in terms of migration and diffusion.

Results show that imposing the turbulent quantities from a LES causes an immediate destruction of the swirl components and a too-high total temperature diffusion in a RANS approach. It is found that the turbulent length scale, expressed in terms of μT/μ, plays a significant role in the aerodynamic and aero-thermal behavior of the flow. The optimal range for the value of μT/μ differs from what is encountered in the literature on a high-pressure turbine configuration. Also, imposing quantities at the inlet consistent with the LES or measurements does not improve the prediction of the trajectory of the swirl jet or the total temperature distribution. The anisotropy of turbulence is suspected to explain the failure of the usual RANS models.
Pressure Losses Analysis in Two High-Pressure Steam Turbine Control Valves Situated in One Valve Chamber
Authors: Slama Vaclav , Rudas Bartolomej , Simurda David , Hala Jindrich , Luxa Martin
Published: October 2022

Steam turbines belong to the most important systems in power conversion. In order to control their power output at steady state base load or part load conditions, the use of control valves is a widely used method. The flow in a pair of high-pressure steam turbine control valves which are situated in one valve chamber is analyzed in this paper from the pressure losses point of view. The experiments were carried out on a valve model installed in a wind tunnel for high speeds in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences. The flow at different valve cone lifts in both control valves was investigated and results were generalized in the form of so-called valve characteristics. Investigations were carried out on the model with control valve strainers and without them. In order to further understand the reasons of detected pressure loss differences, the numerical simulations were carried out in the Doosan Skoda Power Company using ANSYS software tools. The comparison of results shows which cases of the valve setup are preferable with regard to pressure losses and thus efficiency. Furthermore, an existing pressure loss prediction model for valve pressure loss estimation for each investigated case was updated. This model helps to better design the valve geometry in order to increase overall turbine efficiency.
Assessment of the Impeller/Volute Relationship of Centrifugal Fans From an Aerodynamic and Aeroacoustic Perspective
Authors: Biedermann Till M. , Moutamassik Youssef , Kameier Frank
Published: October 2022

Heavy-duty centrifugal fans require high reliability and first-class performance. Besides, extreme conditions and harsh environments are often encountered, such as in the papermaking process, in steel or cement plants or the chemical and petrochemical industry. Therefore, the design of high performance heavy-duty industrial fans requires robust yet efficient solutions. Previous work indicates a high aerodynamic and aeroacoustic sensitivity concerning the specific position of the volute cut-off (tongue). This effect will be further investigated, not by directly changing the orientation of the cutoff, but by varying the position of the impeller relative to a fixed volute casing. The initial evaluation is done through a numerical study of three influencing parameters, which allows the aerodynamic dependencies to be modelled using low-layer artificial networks. Subsequently, extensive experimental studies were carried out to validate the aerodynamic dependencies and also to incorporate information on the aeroacoustic performance. The obtained results show that the operating point represents the key factor in determining the optimal positioning, with qualitatively comparable dependencies found for both tested fans. From an aeroacoustic point of view, the determined optimal configuration does not necessarily coincide with the observed aerodynamic desires, so careful analysis and a reasonable compromise are required, motivating for a multi-objective optimisation process.
A Comprehensive Analytical Model for Vortex Shedding From Low-Speed Axial Fan Blades
Authors: Daku Gábor , Vad János
Published: October 2022

The paper presents a comprehensive analytical model for the characterization of von Karman vortex shedding in the wake of models of low-speed axial fan blades. The elaborated minimal model is based on the Reynolds-averaged Navier-Stokes and continuity equations. For validation purposes, hot-wire measurements have been carried out in a wind tunnel on representative blade profiles. The measurement data obtained for various streamwise positions downstream of the blade trailing edge, i.e. transversal profiles of mean velocity as well as root-mean-square of fluctuating velocity, are evaluated. As the experimental validation demonstrates, the minimal model fairly localizes the transversal position of the vortex centres, and represents the motion of the vortices along the wake. The validated minimal model serves with the following benefits. a) An extensive understanding of the underlying physics related to the flow field featuring vortex shedding in the near-wake region. Easy-to-use quantitative correlation among the characteristics of wake flow affected by the shed vortices. b) Extension of the literature-based methodology for determination of the transversal distance between the shed vortex rows, being used as scaling parameter for the Strouhal number utilized in calculation of vortex shedding frequency. c) Modelling the behavior of rows of shed vortices farther away from the trailing edge. Such behavior may influence the acoustic signature of VS, and, as such, it is to be considered in fan noise modelling.
Effect of Twist Angle on the Performance of Darrieus Vertical Axis Wind Turbines
Authors: Saad Ahmed S. , Ahmed Mahmoud
Published: October 2022

Conventional straight-bladed Darrieus wind turbines have some drawbacks including large oscillations of coefficient of torque with negative values within a wide range of angle of rotation which decrease the self-starting abilities of the turbine and increase the mechanical vibrations. To solve these weaknesses, the current study proposes twisted-bladed Darrieus turbine instead of the conventional straight-bladed design to flatten the oscillations of torque coefficient in addition to enhancing the self-starting abilities of the Darrieus turbine. The studied angles of twisting are 45, 90, and 135 degrees in addition to the traditional untwisted Darrieus rotor. The trends of coefficient of power against ratio of rotor tip speed in addition to coefficients of dynamic and static torque over a complete cycle (360 degrees) are estimated for all studied twisted-bladed Darrieus turbines. Thus, three dimensional incompressible unsteady Reynolds-Average Navier-Stokes equations in conjunction with the k-ω shear-stress transport turbulence model is developed and numerically simulated utilizing ANSYS Fluent. The developed numerical model is validated using the available measurements from literature. The predicted characteristics of flow field around the proposed twisted-bladed Darrieus turbines are presented and compared with the traditional untwisted design.

Accordingly, results revealed a significant improvement of the coefficient of power is attained by increasing the angle of twisting from 0° to 90°. However, with an additional increase in the angle of twisting beyond 90°, the coefficient of power declined. The turbine with an angle of twisting of 90° attains the largest coefficient of power of 0.318 with a percentage increase of 13.2 % in comparison with the traditional straight-bladed Darrieus turbine which has a peak coefficient of power of 0.281. The traditional untwisted turbine has negative values of coefficient of static torque within a large range of angle of rotation. However, the proposed turbines with twisted blades exhibit lower torque fluctuations and positive static torque values at all angles of rotation resulting in enhancing the self-starting abilities of the Darrieus turbine.
Parameter Optimization of Combustor Dump Diffuser Based on RSM
Authors: Yan Yue , Suo Jianqin , Wu Yanhui
Published: October 2022

At present, dump diffuser is basically adopted in the combustion chamber of aeroengine. The total pressure loss in it may account for 30% or even higher in the combustion chamber. So it is necessary to optimize various geometric parameters in dump diffuser. In order to solve the problem of increasing experimental cost due to multi-parameter optimization, response surface method (RSM) was used to study the performance of dump diffuser’s three geometric parameters at three inlet Mach numbers (Ma = 0.27, 0.20 and 0.10), namely pre-diffuser expansion angle, dump gap ratio and side wall expansion angle. The ratio of static pressure recovery coefficient to total pressure loss coefficient was used to compare the performance of the diffuser. Also the distribution of entropy production rate was used to obtain the pressure loss in the diffuser and analyze the causes. Then the response model was established and the response equation was solved to obtain the combined parameters corresponding to the optimal solution. Finally, the optimization results were predicted and verified. We can see that the influence of three geometric parameters on the diffuser performance is the prediffuser expansion angle, dump gap ratio and the side wall expansion angle in descending order. Compared with the initial average performance, the optimized results under three working conditions are improved by 47.93%, 48.70% and 69.49%, and the relative errors are all less than 6.5%, showing high accuracy.
Investigation of Physics-Informed Neural Networks Based Solution Techniques for Internal Flows
Authors: Post Pascal , Winhart Benjamin , di Mare Francesca
Published: October 2022

In this work, we explore for the first time the possibility and potentials of employing the emerging PINNs approach in internal flow configurations, solving the steady state Euler equations in two dimensions for forward and inverse problems. In addition to a simple bump test case, the PINNs results of a highly loaded transonic linear turbine guide vane cascade are presented. For forward problems, we investigate different formulations of the transport equations and boundary conditions. Overall, PINNs approximate the solution with acceptable accuracy; however, conventional CFD methods are far superior in forward settings. Finally, we demonstrate the capabilities and the tremendous potentials of PINNs regarding hidden fluid mechanics in two distinct inverse settings, intractable for conventional CFD methods. Firstly, we infer complete flow fields based on partial, possible noisy, solution data, e.g., partial surface pressure and velocity field data; even approximating the exit condition of the cascade using only the measured blade pressure distribution is possible. Secondly, we also infer an unknown parameter of the governing equations.
A Computational Investigation of Wall-Film Formation by an Impinging Liquid Jet in Crossflow
Authors: Magnotti Gina M. , Sforzo Brandon A. , Powell Christopher F.
Published: October 2022

Accurate fuel injection modeling remains of critical importance to the simulation of gas turbine engines as the predicted spray structure dictates fuel-air mixing, combustion, and emissions in the combustor. The prefilming airblast atomizer relies on the formation of a thin conical sheet of fuel, which breaks up due to its interaction with the counter-swirling airstreams. Recent x-ray imaging performed at Argonne National Laboratory’s Advanced Photon Source of a prefilming airblast atomizer revealed the formation of a frothy film, which is comprised of both liquid and bubbles. This finding challenges the inherent assumption for existing spray models, which assume that the film is only comprised of liquid fuel, and motivates the detailed investigation of the film formation process. To investigate the physics governing the impingement of a liquid jet in crossflow on a plate, a computational study was carried out. Large Eddy Simulations (LES) coupled with an algebraic volume-of-fluid (VOF) approach were performed to model a liquid water jet interacting with a subsonic crossflow and subsequently impinging on an aluminum plate. For the condition studied, a grid convergence study revealed that a minimum cell size of 25 μm was sufficient to adequately resolve the jet-wall interaction and film formation process, with good agreement with the x-ray measurements. These simulations also predicted the formation of bubbles within the film due to the entrainment of air. The influence of adhesion on the film characteristics and bubble distribution was explored using two different contact angles representing water on polished and unpolished aluminum plates. Although an increase in contact angle was not observed to affect the average film thickness, the lower interfacial tension reduced the number of bubbles that were formed, but increased the average size.
Numerical Investigation of Particle Deposition in Double Wall Effusion Cooled Systems
Authors: Villain Florian Y. A. , Vadgama Nikul , Gaskell Jack G. , Ireland Peter T. , McGilvray Matthew , Gillespie David R. H.
Published: October 2022

In the pursuit of ever-higher thermal efficiency, aero-engines have seen their turbine entry temperatures rise steadily, driving the need for highly effective cooling systems. Double-walled, effusion-cooled turbine blades, which combine arrays of impingement holes and pedestals, with full-coverage external film cooling offer the potential for significantly better cooling than conventional multi-pass blade cooling systems. However, this technology includes intricate geometric features with high curvature which are susceptible to blockage from dust and sand. Such deposition has the potential to compromise the flow and cooling performance.

In this paper, the vulnerability of two generic double-walled cooling schemes, incorporating diamond pedestals, is predicted using Arizona Road Dust as test contaminant and nickel superalloy as substrate. Conducting simulations in commercial CFD software, a bespoke Continuous Random Walk (CRW) turbulent tracking model predicts the arrival of particles at the blade surface. It is combined with a Discrete Element Methods (DEM) based bounce stick model, to predict particle sticking and rebound.

Bulk and spatially resolved deposition statistics are reported for each of the cooling system components. The results are used to investigate the susceptibility of the system to particle blockage and to develop a reduced-order model able to predict deposition fractions based on a newly formulated generalised Stokes number.
Analyses of Damping Sustainability of Additively Manufactured Nickel Alloy Components Subjected to High Strain Loading Cycles
Authors: Hollkamp John P. , Scott-Emuakpor Onome , Celli Dino
Published: October 2022

While integrally bladed rotors in turbine engines have multiple benefits, they are more susceptible to vibration and as a result, high cycle fatigue failure. In response, damping treatments such as viscoelastic layers, hard coatings, and particle dampers have been utilized to reduce vibration of integrally bladed rotors and promote longer service life. In recent experiments, nickel-based alloy 718 structural beams representative of turbine blades were manufactured via laser powder bed fusion (LPBF) with internal geometries containing unfused powder. Compared to fully fused beams, these beams with internal particle dampers have demonstrated a significant improvement in damping performance, suppressing vibrations by as much as 95%. However, the inherent damping of the particle dampers decreases as the strain amplitude increases when some of the unfused powder fuses to the walls of the pockets. This study investigates the effect of the location of the particle dampers within the beam on the sustainability of its damping performance. To compare the effect of the particle damper’s location, the LPBF nickel-based alloy 718 beams are subjected to successive resonance dwells with increasing strain amplitude. After each dwell, the damping performance is assessed via the half-power bandwidth method of the frequency response function. Results from this study indicate that while the location of the particle dampers within the specimen does influence when the damping begins to degrade, it is not the optimal parameter for damping sustainability. The aim of this and future work is to improve the long-term damping performance and viability of the internal particle damper so that it can be more effectively utilized to extend the lifetime of turbomachinery components.
Application of a Distributed Element Roughness Model to Additively Manufactured Internal Cooling Channels
Authors: Altland Samuel , Yang Xiang , Thole Karen , Kunz Robert , McClain Stephen
Published: October 2022

Design for cooling effectiveness in internal flow systems relies on accurate models for dynamic losses and heat transfer. In these systems (e.g., gas turbine blades, intercoolers, heat exchangers), thousands of individual passages of varying configuration and roughness morphology can be present. In recent years, additive manufacturing (AM) has further expanded the design space, but can give rise to large-scale roughness features, whose sizes are comparable to the channel height. The range of roughness length scales in these systems makes CFD of the resolved rough surfaces impractical at a design level. Alternately, volumetric roughness modeling approaches, such as distributed element roughness models (DERM) can be leveraged, as they have computational costs orders of magnitude lower.

In this work, a DERM model based on the Double Averaged Navier-Stokes (DANS) equations is presented and applied to additively manufactured rough channels, representative of gas turbine blade cooling passages. Unique to this formulation of DERM is the specific treatment of the DERM drag coefficient and the spatially averaged Reynolds stresses. This generalized formulation of the drag coefficient allows for improved model accuracy across a wider array of potential roughness fields, without having to rely on calibration for each morphology. A novel two-layer approach to modeling the spatially averaged Reynolds stress is also proposed.

Three different AM rough surfaces documented by McClain et al. [1] were configured opposite smooth walls as well as each other to create a total of six channel configurations. Across the six cases, th roughness trough to peak size ranges from 0.15δ to 0.66δ, where δ is the channel half-width, and the roughness Reynolds number ranges from Rek = 60 to Rek = 300.

DERM predictions for spatially and temporally averaged mean flow quantities are compared to previously reported DNS results. Specifically, we observe good agreement in the mean velocity profiles, stress balances and drag partitions across the case matrix.

While DERM models are typically calibrated to specific deterministic roughness shape families at comparatively small roughness Reynolds numbers, these results demonstrate a wider range of applicability for the present, more generalized formulation. It is demonstrated that the proposed model can accommodate random roughness of large scale, typical of AM.
Bearing Fault Detection on Wind Turbine Gearbox Vibrations Using Generalized Likelihood Ratio-Based Indicators
Authors: Kestel Kayacan , Peeters Cédric , Antoni Jérôme , Sheng Shawn , Helsen Jan
Published: October 2022

Studies in condition monitoring literature often aim to detect rolling element bearing faults because they have one of the biggest shares among defects in turbo machinery. Accordingly, several prognosis and diagnosis methods have been devised to identify fault signatures from vibration signals. A recently proposed method to capture the rolling element bearing degradation provides the groundwork for new indicator families utilizing the generalized likelihood ratio test. This novel approach exploits the cyclostationarity and the impulsiveness of vibration signals independently in order to estimate the most suitable indicators for a given fault. However, the method has yet to be tested on complex experimental vibration signals such as those of a wind turbine gearbox. In this study, the approach is applied to the National Renewable Energy Laboratory Wind Turbine Gearbox Condition Monitoring Round Robin Study data set for bearing fault detection purposes. The data set is measured on an experimental test rig of a wind turbine gearbox; hence the complexity of the vibration signals is similar to a real case. The outcome demonstrates that the proposed method is capable of distinguishing between healthy and damaged vibration signals measured on a complex wind turbine gearbox.
Real Time Precursor Calculation for the Early Detection of Combustion Instabilities
Authors: Meloni R. , Giannini N.
Published: October 2022

The proper control of the pressure fluctuations inside the gas turbine combustors is becoming a key factor to contain the pollutant emissions and extend their operability limits, as a consequence of the leaner and leaner mixture the engines have to operate with. In this context, the mitigation of the combustion instabilities through active control strategies is nowadays taking more and more benefits from the most advanced data science techniques. The employment of such algorithms has not only the aim to detect an instability and bring the engine to operate in a stable window but, more and more often, to anticipate the rising of a dominant frequency in an early stage of growth, with advantages in terms of extension of the life of the mechanical components and, more importantly, the reduction of the number of startups.

In this context, the present papers presents a Reduced Order Model (ROM) derived from the Dynamic Mode Decomposition (DMD) algorithm that can be applied to analyze the time signals acquired by the pressure probes installed in a generic gas turbine combustor. The most useful information that are retrieved from the signal are the frequency content and the corresponding Growth Rate (GR). The latter parameter can be assumed to act like a precursor of the system instability, enabling the possibility to identify a potential issue well in advance with respect to the traditional approaches. This new method can pave the way to new control strategies, depending on the different kind of instabilities detected. Also these aspects will be addressed along this work, focusing the discussion on both thermo-acoustic instabilities and low-frequency tones associated to the flame extintion. Moreover, additional criteria that could be implemented along a control system based on this new methodology will be provided.
Evaluation of Different Regression Models Tuned With Experimental Turbine Cascade Data
Authors: Dellacasagrande Matteo , Lengani Davide , Paliotta Pietro , Petronio Daniele , Simoni Daniele , Bertini Francesco
Published: October 2022

In the present work linear and non-linear regression functions have been tuned with an extensive database describing the unsteady aerodynamic efficiency of low-pressure-turbine cascades. The learning strategy has been first defined using a dataset published in a previous work concerning the loss coefficient measured in a large-scale cascade for a large variation of the Reynolds number, the reduced frequency, and the flow coefficient. Linear models have been educated accounting for the Occam’s razor parsimony criterion, condensing the effects due to the parameter variation in few predictors. Then, these predictors have been used to generate an extended polynomial-base function, and an ℓ1-norm constrain has been included into the optimization process to promote sparsity. Different non-linear models have been also evaluated, introducing the formulation of Gaussian Processes for regression for different kernel functions. The capabilities of the models here tuned are compared by means of cross-validation global and local criteria. Cross-validated error and leverage distribution have been analyzed. The proper compromise between model accuracy and generalizability is identified as a Pareto front in the space of the cross-validation indicators. In addition, a new variance-based indicator for the identification of the best model among the candidate ones has been introduced and its capability in complementing the cross-validation analysis is here discussed.

The learning strategy has been finally replicated adopting an extremely large database, experimentally acquired in the framework of the extensive collaboration between the University of Genova and AvioAero. For confidentiality, results concerning this database are not shown in terms of response surface, but model performances are discussed in order to strengthen the strategy here adopted, that could be useful also to other research groups adopting their own data.
Theoretical Considerations for Scaling Convection in Overall Effectiveness Experiments
Authors: Bryant Carol E. , Rutledge James L.
Published: October 2022

An increasingly common experimental technique allows measurement of overall effectiveness by matching the Biot number between experimental and engine conditions. The measured overall effectiveness distribution correlates to the expected turbine component temperature distribution. While a good deal of work has been devoted to determining the appropriate flow conditions necessary to scale adiabatic effectiveness, very little attention has been paid to the subtleties beyond matching the Biot number that arise when performing experiments on a conducting model to determine overall effectiveness. Notably, the ratio of the internal and external heat transfer coefficient must be matched. The density ratio and more recently, the specific heat ratio, have been shown to play important roles in scaling adiabatic effectiveness; however, in the present work, we demonstrate the requirements for the coolant and freestream flow conditions required to conduct an appropriately scaled overall effectiveness experiment. Since the viscosity and thermal conductivity of the fluids (in addition to density and specific heat) play significant roles that influence heat transfer coefficient behavior, this gives rise to an additional nondimensional parameter that should, in theory, be matched to properly execute an overall effectiveness experiment.

In this paper, we demonstrate that this new nondimensional parameter will be matched provided that Pr∞, Prc, and Rec are matched in addition to the freestream Reynolds number and the advective capacity ratio. We demonstrate the validity of this requirement through computational fluid dynamics simulations, which are well-suited for this since the over-constrained requirements can be overcome by altering gas properties from the real values. Simulations of an internally cooled wall exposed to a hot freestream were performed with various gases to show the sensitivity of the overall effectiveness to these previously ignored requirements. An additional set of simulations on a film cooled plate reveals additional complexities when coolant mixes with the freestream gas.
Hot-Wire Anemometry in High Subsonic Organic Vapor Flows
Authors: Hake Leander , Sundermeier Stephan , Cakievski Leon , Bäumer Joshua , aus der Wiesche Stefan , Matar Camille , Cinnella Paola , Gloerfelt Xavier
Published: October 2022

The present contribution reports the outcome of an experimental and numerical investigation of the behavior of a constant-temperature hot-wire anemometer in the high subsonic flow up to a Mach number of 0.7 of the organic vapor Novec 649 at pressure and temperature levels of typical organic Rankine cycle (ORC) turbine applications. The experiments were carried out in the calibration section of a closed-loop organic vapor wind tunnel test facility enabling the independent variation of Reynolds numbers, Mach numbers, and total temperature within a certain range. It was found that the calibration and the determination of the sensitivity coefficients can be done in a way as proposed by de Souza and Tavoularis for air. The sensitivity coefficients for velocity and density were essentially equal for higher overheat ratios which support the interpretation of the signals and data reduction for turbulent quantities. Computational fluid dynamics (CFD) provided additional insight into potential real gas effects for hot-wire performance.
Abradable Seal Test Rig for Quantifying Abradable Material Performance During Labyrinth Seal Rubs in Centrifugal Compressors: Design and Test Results
Authors: Katcher Kelsi M. , Revak Thomas , Rimpel Aaron , Ratay Jeffrey , Brun Klaus
Published: October 2022

In centrifugal compressors, the shaft seal clearance is critical to equipment efficiency and performance. Applications employing very small seal clearances must rely on abradable materials in the stator (housing) to prevent damage to rotating components in the case of rubs. An interaction (or rub) between the rotating seal geometry and stationary seal material can occur while traversing critical speeds or during upset conditions or transients outside the normal, designed operating range of the compressor such as thermal transients or excessive vibrations. The standard abradable seal material for compressor applications is mica-filled PTFE, but alternative materials are required in applications with elevated temperatures, elevated pressures, or harsh environments where chemical resistance is necessary. The behavior of these various abradable materials during a rub event is not well understood and needs to be further quantified to allow for proper material selection for each compressor design.

In order to determine suitable alternative materials, a rub simulation test rig was developed to quantify the material wear characteristics and thermal stability of various seal samples. The test rig was designed with a 7.24-inch (184-mm) diameter rotating section with representative labyrinth seal teeth. The rotating shaft was coupled with a variable speed motor capable of operating up to 24,000 rpm, allowing for surface speeds up to 754 ft/s. A 180-degree abradable seal section was mounted concentric to the rotating shaft, which may be forced into the rotating seal teeth by a linear actuator to simulate the rub. The test rig was designed to accommodate various interaction rates, initially considering 0.1 and 1 mil/s (2.54 and 25.4 μm/s) to simulate a rub caused by thermal growth and a rub caused by vibration or bow, respectively. Furthermore, the test rig was equipped with an ambient heater and pressure enclosure to evaluate seal materials at elevated temperatures and with various gas compositions. This paper presents the design and capabilities of the abradable seal test rig as well as the initial rub test results for Fluorosint 500.
Scaling Flat Plate Overall Effectiveness Measurements
Authors: McNamara Luke J. , Fischer Jacob P. , Kernan Marta , Rutledge James L.
Published: October 2022

Low temperature experiments are often performed on models of cooled turbine components in order to predict the temperature of the actual turbine component at engine conditions. Designing the scaled experiment properly takes care beyond simply matching the freestream Reynolds number. For instance, it is well known that for the nondimensional surface temperature distribution, or overall effectiveness, to match that at engine conditions, the Biot number of the experimental model must match that of the engine component. Somewhat less clear is the method by which one must scale the coolant flow rate. Widely used for coolant flow rate parameters to be matched are the mass flux ratio (M), the momentum flux ratio (I), or more recently, the advective capacity ratio (ACR). The selection of coolant flowrate parameter has generally been driven based on the results of adiabatic effectiveness experiments and it remains unclear how well these parameters also allow for matched overall effectiveness, which is highly dependent on internal cooling. In the present work, overall effectiveness distributions were measured on a flat plate with three rows of zero-degree compound angle 7-7-7 shaped holes. The influence of various thermodynamic gas properties were examined using several foreign gases as the coolant while matching coolant flow rate parameters M, I, and ACR. It is shown that the thermal conductivity of the coolant plays an outsized role in the overall effectiveness, but this is not accounted with any of the traditional coolant flowrate parameters. With significant thermal conductivity variations possible between the coolant and freestream gas at both engine and experimental conditions, consideration of this effect is of vital importance to the experimentalist.
A Computational Approach to Aerothermal Analysis of Complex Internal Turbine Cooling Geometries
Authors: Coulton Ben , Murray Alexander V. , Ireland Peter T.
Published: October 2022

Gas turbine inlet temperatures continue to rise with increasing cycle thermal efficiency and specific power output. This has led to turbine inlet temperature far exceeding metal capabilities. The result of this is the need for more advanced cooling systems with increasingly complex manufactured internal features that provide higher convective efficiency more akin to transpiration cooling systems.

This paper begins by assessing a previously developed decoupled method for analysing double-wall cooling systems and identifies potential improvements. A modified method is proposed, termed a “semi-decoupled method”, whereby mainstream flow is not simulated. Instead, the mainstream flow properties are projected onto the external surface of the blade enabling the simulation to focus on the complex internal cooling features, thereby drastically reducing computational resource requirements. The cooling films formed by the effusion holes are calculated based on the outlet conditions from each hole and mapped by a correlation adapted from the literature and superimposed onto the external surface, mid-simulation. The film correlation is adapted to accurately capture experimentally observed trends by accounting for lateral spread as the films move downstream. The new method is used to assess how the geometric parameters of the double-wall system impact the cooling effectiveness of a turbine blade geometry.
Impact of HEFA Fuel Properties on Gaseous Emissions and Smoke Number in a Gas Turbine Engine
Authors: Undavalli Vamsikrishna , Hamilton Jerry , Ubogu Emamode , Ahmed Ihab , Khandelwal Bhupendra
Published: October 2022

The study aims to establish the behavior of hydro processed esters and fatty acids (HEFA), as a type of alternative fuel with a conventional Jet A-1 as a reference fuel using a GTCP85 aircraft auxiliary power unit (APU). The research evaluates the impact of fuel properties on emissions using HEFA (blends in 18 proportions) and Jet A-1. With increasing HEFA proportions in the fuel, it is observed that reduction of gaseous emissions is not absolute. No specific trend of gaseous emissions reduction, in terms of aromatic and hydrogen content, were observed for the 18 blend ratios tested. For 50:50 blend of HEFA and Jet A-1, which meets current American Society for Testing and Materials (ASTM) specifications D7566 as drop-in fuel to D1655, the average reduction of NOX, CO, UHC emissions in PPM are ∼ 40%, 18%, and 28%, respectively. In contrast, no significant difference observed in CO2 emissions as compared with Jet A-1. Furthermore, the smoke number is proportional to the aromatic fuel content, fuel density (at 15°C), and carbon content irrespective of load condition. Conversely, the smoke number tends to be inversely proportional to the hydrogen, Sulphur, iso-paraffinic, and heat content of the fuel. Finally, these findings will contribute to the knowledge of fuel properties on impact engine performance and emissions as the aviation industry moves towards 100% SAFs.
Turbine Vane Passage Cooling Experiments With a Close-Coupled Combustor-Turbine Interface Geometry Part 2: Describing the Coolant Coverage
Authors: Nawathe Kedar P. , Nath Aaditya R. , Kim Yong W. , Simon Terrence W.
Published: October 2022

The first stage gas turbine vane surfaces and endwalls require aggressive cooling. This two-part paper introduces a modified design of the combustor-turbine (C-T) interface, the ‘close-coupled interface,’ that is expected to increase cooling performance of vane passage surfaces. While the first part of the paper describes secondary flows and coolant transport in the passage, this part discusses the effects of the new C-T interface geometry on adiabatic cooling effectiveness of the endwall and vane surfaces. Compared to the traditional C-T interface, the coolant requirement is reduced for the same level of cooling effectiveness on all three surfaces for the new C-T interface design, confirming that it is an improvement over the previous design. The endwall crossflow is reduced by combustor coolant injection with the new interface leading to more pitchwise-uniform cooling of the endwall. For the pressure surface, increasing combustor coolant flowrate directly increases phantom cooling effectiveness and spreading of coolant away from the endwall. With the traditional passage vortex seen in the literature replaced by the impingement vortex of the present design, the suction surface receives less phantom cooling than does the pressure surface. However, cooling performance is still improved over that of the previous C-T interface design.
Impact of Operating Conditions and Axial Casing Grooves on the Evolution of Flow Structure Across Blade Rows in an Axial Compressor
Authors: Saraswat Ayush , Koley Subhra Shankha , Katz Joseph
Published: October 2022

Stereo-PIV measurements in a series of axial planes investigate the impact of operating conditions and semicircular axial casing grooves (ACGs) on the evolution of flow structure across multiple blade rows in an axial compressor. The field of view extends radially from the hub to the tip, and circumferentially over entire blade passages. The flow is examined at two operating conditions, namely pre-stall flow rate and near the best efficiency point (BEP) of the untreated casing. Previous studies in this machine have shown that the ACGs improve the stall margin significantly but reduce the peak efficiency. At pre-stall and with untreated casing, intermittent reverse axial flow near the casing induced by backflow vortices (BFVs), tip leakage vortex (TLV), and the leakage flow extend upstream of the rotor leading edge. Although more probable in front of the blade, this backflow occurs along the entire circumference. Inside the rotor, the tip region blockage is characterized by low axial and high circumferential momentum. This region expands radially inward as the flow evolves axially, extending to half of the span by the time it reaches the rotor trailing edge. In contrast, inward of the region affected by blockage, the axial velocity exceeds the spatially averaged value by well above 60%. This extreme nonuniformity diminishes rapidly as the flow enters the stator, resulting, except for the blade wakes, in a nearly uniform axial velocity distribution at the exit from the stator. Previous measurements focusing on the effect of ACGs on tip flows have established that they entrain portions of the TLV and the backward leakage flow, and the outflow from them causes periodic variations in flow angle near the blade tip leading edge. The current data reveals that the outflow with negative axial and circumferential velocity jetting out from the grooves upstream of the rotor generates axially aligned vortices on both sides of each jet. These vortices act as homogenizers by entraining the faster mid-span flow into the tip region, substantially reducing the axial velocity deficit in the spaces between grooves. Consequently, the blockage in the tip region and flow non-uniformity in the passage are reduced substantially. Indeed, passage-averaged velocity profiles obtained by averaging the data circumferentially highlight that the ACGs modify the flow structure over the entire span, increasing the axial velocity at the tip, and decreasing it near the hub. Near BEP, the blockage is confined to the tip region and differences in flow structure with or without ACGs become more subtle. The flow jetting out of the grooves, and axial vortices are weaker but do not vanish. Furthermore, interactions of the TLV with secondary flows entrained from the grooves into the passage cause circumferential expansion of its signature, which presumably affects the compressor performance adversely.
Investigation of Droplet Shedding in an Aeroengine Bearing Chamber Using Convolutional Neural Networks
Authors: Farbrother Katrina , Cagaeo Paloma Paleo , Johnson Kathy , Ambrose Stephen
Published: October 2022

More efficient aeroengines are needed to reduce the environmental impact of civil aviation. Design changes for increased efficiency mean that higher loads are transmitted through the bearings supporting the rotating shafts. Better bearing chamber design is needed to facilitate these improvements, meaning that higher design capability and therefore, and improved understanding of the two phase flow is required to support modelling of the bearing chamber for future design.

Nottingham University’s Bearing Chamber Rig (BCR) is designed to provide quantitative and qualitative two phase flow data in a simplified, representative bearing chamber geometry. Oil is introduced to the chamber via a rotating cup and static configuration and this paper presents data characterising droplet shedding into the chamber. High-speed imaging data is obtained at the 3 o’clock and 9 o’clock positions. Automated image processing is necessary due to the large quantities of data. A Convolutional Neural Network (CNN) has been developed and is used to detect droplets in the images and convert the data to a numerical format including droplet diameter and speed. The CNN used was trained using images from a different but similar experimental test rig and this paper shows that it can also detect droplets with good accuracy in the BCR.

The experimentally obtained droplet data provides better understanding of the two-phase flow behaviour in the test rig and by extension in an aeroengine bearing chamber. Droplet diameters, normalised against nominal film thickness immediately prior to shedding, are found to be around 1.0 and normalised Sauter Mean Diameters are between 1.1 and 1.6 with diameter not significantly affected by shaft speed or oil flowrate within the ranges investigated. Droplet velocities were found to be between 4% and 13% of the cup rim speed with the numerical value showing little variation over the investigated range. This diameter and velocity distribution information supports future design capability.