bluuebunny/crossref_metadata_2025 huggingface dataset:
Plastic Limit Analysis Using the Simplified Theory of Plastic Zones
Authors: Hübel Hartwig
Published: January 2021

The simplified theory of plastic zones (STPZ) was mainly developed to determine strain ranges and accumulated strains in the state of shakedown at cyclic loading between prescribed levels of loading. Kinematic hardening is an indispensable feature of the STPZ. The plastic limit load, however, is defined for monotonic loading and elastic–plastic material behavior without hardening. Simply assigning a zero value or a numerically very low value of the tangent modulus when applying the STPZ is generally not possible due to arising numerical instabilities. It is, therefore, not immediately obvious how the STPZ can be used to determine the maximum load level that can be applied to a structure without developing a kinematic mechanism. This paper describes the theory and the analysis steps required and provides some illustrative examples. Typically, between one and three linear elastic analyses and some local calculations are required to provide either the exact value or at least a reasonable estimate of a range of the plastic limit load, as well as of the associated stress and strain fields and displacements that are not provided by classical limit analysis.
Improvement of Turboshaft Restart Time Through an Experimental and Numerical Investigation
Authors: Ferrand Antoine , Bellenoue Marc , Bertin Yves , Marconi Patrick
Published: January 2021

Inflight shutdown of one engine for twin-engine helicopters has proven beneficial for fuel consumption. A new flight mode is then considered, in which one engine is put into sleep mode while the second engine runs at nominal load. The ability to restart the engine in sleep mode is then critical for safety reasons. Indeed, the certification of this flight mode involves ensuring a close-to-zero failure rate for in-flight restarts and a fast restart capability of the shutdown engine (focus of this paper). Fast restart capability is necessary in case of a failure of the operating engine. Indeed, there is no more power available, and the helicopter can lose up to 15–20 meters per second during autorotation. The restart time becomes a critical parameter to limit the loss of altitude. The aim of the paper is to assess the potential restart time saving using an approach combining test rig data analysis and numerical results generated by a thermodynamic model able to simulate at low rotational speed. It is important to understand the detailed phenomenology of the startup process and the various subsystems involved, first to highlight the influencing parameters and then to establish an exhaustive listing of the possible time optimizations. The results of this study show that a fast restart going from sleep mode to max power speed can be up to 60% faster than a conventional restart going from sleep mode to idle speed, which is significantly faster.
Simulation and Experimental Investigation of a New Type of Combined Seal Structure
Authors: Li Jin , Fu Xiaoli , Yan Shenglin
Published: January 2021

Based on the study of leakage characteristics of labyrinth seal structure (LSS), a new type of combined seal structure (CSS) consisting of the labyrinth structure and the nozzle structure has been proposed. The sealing characteristics of CSS and LSS are compared by means of numerical simulation and experiments, and the effects of the internal resistance of the device, structural geometric parameters and other factors on the leakage characteristics of CSS are studied. The results illustrate the following conclusions: (a) When the inlet flow is 12 m3/h and the internal resistance of the device is 2000–4000 Pa, the leakage rate of CSS decreases by 30%–40% in comparison with that of LSS, which indicates that the performance of CSS is much better than that of LSS. (b) The leakage rate increases as the internal resistance of the device increases. When the internal resistance of the device increases from 2000 Pa to 8000 Pa, the leakage rate increases from 26% to 72%. (c) When the internal resistance of the device is constant, the larger the inlet flow, the smaller the leakage rate. (d) The choice of nozzle radius in structural geometric parameters is more important for the leakage rate than the tooth height and teeth numbers. When the nozzle radius decreases, ΔPAB (pressure difference between the labyrinth structure and the nozzle structure) and the leakage rate decrease accordingly.
Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays
Authors: Otto Marcel , Gupta Gaurav , Tran Patrick K. , Ghosh Shinjan , Kapat Jayanta S.
Published: January 2021

Arrays of staggered pin fins are a typical geometry found in the trailing edge region of modern airfoils. If coolant is supplied by bleeding from the mid-section of the airfoil instead of provided through the root, the channel length is insufficiently long to reach a fully developed flow which is commonly found from the fifth row downstream. This present study focuses on the developing section (four rows) of a staggered array with a height-to-diameter ratio of 2 and a spanwise and streamwise spacing of 2.5, respectively. Measurements are conducted at Reynolds numbers of 10,000 and 30,000 based on the maximum velocity and pin diameter. Stereoscopic particle image velocimetry (PIV) is used to describe the flow field and turbulence characteristics in the wake of the first and third row pin. It is found that the dominating vortical structures depend highly on the Reynolds number. A transient thermochromic liquid crystal (TLC) technique is used to obtain local heat transfer coefficients on the endwall which are then discussed in the context with the vortical structures. The structure of the horseshoe vortex and the transient wake shedding behaves differently in the first and third row. The interaction of both vortex systems affects directly the endwall heat transfer. The results are supplemented by a thorough discussion of TLC and PIV uncertainty.
A Review of Journal Bearing Induced Nonlinear Rotordynamic Vibrations
Authors: Kim Sitae , Shin Dongil , Palazzolo Alan B.
Published: January 2021

Nonlinear elements found in fluid film journal bearings and their surrounding structures are known to induce sub- and super-synchronous, chaos and thermally induced instability responses in rotor-bearing systems. The current review summarizes the literature on journal bearing induced nonlinear, rotordynamic forces, and responses. Nonlinear, thermo-elasto-hydrodynamic (TEHD) aspects of journal bearings has become increasingly important in high-performance turbomachines. These have significant influence on bearing dynamic performance and thermally induced, rotordynamic instability problems. Techniques for developing TEHD bearing models are discussed in the second section. Nonlinear solution methodology, including bifurcation determination and time and frequency domain methods such as harmonic balance, shooting and continuation, etc., is presented in the third section. Numerical tools to determine nonlinear vibration responses, including chaos, along with examples of bearing induced nonlinear vibrations are presented in the fourth and fifth sections, respectively.
Performance Analysis of Solar-Powered Organic Rankine Cycle With Energy Storage in Different Climate Zones in the United States
Authors: Hemmati Hadis , Zhang Jian , Spayde Emily , Mago Pedro J. , Cho Heejin
Published: January 2021

Solar-powered organic Rankine cycle (ORC) is considered a promising technology and has the potential to provide clean electric energy. Extensive studies on the design of ORC systems have been conducted and reported in the literature. However, few studies have presented the influence of climate zones on the performance of a solar-powered ORC, especially for an integrated ORC and energy storage system. This paper presents an analysis to determine the performance of solar-powered ORCs with electric energy storage (EES) systems to supply electricity to buildings in different climate zones in the United States. The building type evaluated in this paper is a large office, and the energy consumption of the facility in each climate location was determined using EnergyPlus. The ORC-EES operational strategy used in this investigation is described as follows: when solar irradiation is adequate to produce power, the ORC charges the EES. Then, when there is no solar energy available, the EES provides power to the building. The ORC-EES is evaluated based on the potential to reduce the operational cost, the primary energy consumption, and the carbon dioxide emission. Furthermore, the influence of the number of solar collectors and the EES size on the performance of the ORC-EES system is investigated.
Vibration Analysis and Methods of Dry Friction Damping of Tubed Vortex Reducer
Authors: Chen Siyuan , Wang Yanrong , Wei Dasheng , Luo Yanbin , Gao Shimin
Published: January 2021

The tubed vortex reducer is a new structure of aero-engine, which is widely used in advanced large bypass ratio high performance turbofan engines. It is usually installed between the rear two-stage discs of the high-pressure compressor, and reduces the generation of free vortex by restricting the flow path of the cooling airflow, thereby reducing the pressure loss of the cooling airflow and improving the engine efficiency. In this paper, vibration analysis of tubed vortex reducer is carried out by experiments and numerical simulations. Using the finite element method, the natural vibration characteristics of the vortex reducer are calculated with ANSYS. The sensitivity analysis of the impact of design parameters on the vibration characteristics is carried out. In addition, the vibration test bench of the vortex reducer is set up, and the vibration test of the vortex reducer is conducted by means of frequency sweeping and hammer hitting respectively. The experimental results satisfactorily reproduce the simulation results. Then the theoretical model of dry friction damping of vortex reducer is established. Based on the dynamic model of the complex contact system composed of vortex reducer and damping sleeve, the relationship between energy dissipation in different directions is derived. And a method evaluating the performance of vibration reduction is presented for calculating its equivalent damping ratio. Finally, the influence of the key design parameters and different installation methods on the damping ratio is analyzed. Overall, this work can provide reference for vibration reduction design and optimization of vortex reducer.
Size and Reynolds Number Effects on Compressor Performance and Scaling
Authors: Chen Hua
Published: January 2021

Performance of small turbocharger compressors is greatly affected by their size and size related Reynolds number. Although the effect of Reynolds number on compressors’ efficiency is well known, the effects of Reynolds number have on other performance and design parameters of these compressors are little recognized in open literature. This paper reports the effects of Reynolds number and size on peak efficiency and surge flow of turbocharger compressors, studies the influences of Reynolds number on optimum compressor blade count. Test results show that when a compressor is scaled up (Reynolds number increases), its stability is generally reduced, and vice versa when scaled down. How this feature can be utilised in compressor design is discussed, and an example is given to show how compressor efficiency and flow range may be improved when scaling down by employing a more stable vaneless diffuser and reducing impeller blade number. Finally, the effect of Reynolds number on blade number selection for different sizes of a compressor is studied through CFD and test, and based on these experiences and the theory of flow on flat plate, a design guide line is proposed for the optimum blade numbers in compressor scaling for both impellers with and without splitter.
Large Eddy Simulation of Wake-Shear Layer Interactions Over a Multi-Element Aerofoil
Authors: Naskar Souvik , Sarkar S.
Published: January 2021

Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.
Transfer Function Based Optimization of Film Hole Sizes With Conjugate Heat Transfer Analysis
Authors: Dutta Sandip , Smith Reid
Published: January 2021

With the improvements of 3D metal printing of turbine components, it is now feasible to produce ready to use production quality parts without casting and conventional machining. This new manufacturing technique has opened new frontiers in cooling optimizations that could not be practiced before. For example, it is now or in-the-near-future possible to have unconventional diameters of film holes. This paper seeks to optimize each film hole diameter at the leading edge of a turbine to achieve an optimum thermal objective. The design technique developed uses a transfer function-based learning model and can be used for both stationary and rotating airfoils. Proposed optimization procedure will also work on other parts of an airfoil; but our current analysis is limited to the leading-edge region. To apply this work on other critical regions, the corresponding heat transfer coefficients need to be implemented while building the transfer functions suitable for that specific component; however, the underlying optimization technique stays the same for any other component. Any optimization technique needs cost and benefit criteria. Cost is minimized in optimization to get maximum benefit with given constraints. In gas-turbine heat transfer, there is a ceiling constraint on maximum temperature that must be satisfied. This study minimizes the coolant flow with satisfying the constraints on average metal temperature and metal temperature variations that limit the life of turbine components. Proposed methodology provides a scientific basis for the sizing of film holes and is expected to decrease developmental cost of efficient thermal designs.
Circumferential Combustor Cavity Flow Fields With Decreasing Core Flow
Authors: Bohan Brian T. , Polanka Marc D. , Goss Larry P.
Published: January 2021

Prior research into Ultra Compact Combustors (UCC) showed an axial length savings compared to traditional gas-turbine combustors. This savings is achieved by swirling the reactants circumferentially in a recessed cavity around the outside diameter of the engine. A similar circumferential combustor is envisioned for a new engine configuration that positions the combustor outboard of a radial compressor and an inflow turbine. This configuration will offer an axial length savings for the entire engine, not just the combustor. The new engine configuration will not utilize a core flow path and thus requires all engine air from the compressor to pass through, or around, the combustor cavity. This report characterizes the cavity flow behavior as the core flow quantity was reduced from 80% of the total engine mass flow rate down to zero, representing the new engine configuration, while maintaining constant cavity mass flow rates. Velocity profiles were obtained with particle-shadow image velocimetry (PSV) in cold flow and with particle streak emission velocimetry (PSEV) in reacting flow experiments. The cold flow results showed that the core flow produced a suction and removed fluid from the circumferential cavity resulting in a lower cavity mass flow rate. This behavior resulted in lower circumferential velocities at higher core flow percentages and the fastest cavity velocity with zero core flow. Reacting flows produced a similar result with the fastest cavity velocities achieved at reduced, but non-zero core flows, and the slowest velocities at the highest and zero core flows. Overall, it was found that there was no negative impact on performance from the removal of the core flow that would prohibit development of the new engine.
Experimental Study on the Wear-in Behaviour of Brush Seals
Authors: Hildebrandt Manuel , Munz Oliver , Schwitzke Corina , Bauer Hans-Jörg
Published: January 2021

Although some investigations on the wear behaviour of brush seals can be found in the literature, not all aspects are yet understood during the wear-in process of the seal in operation. However, it is important to understand all aspects in order to ensure a long service life of the seal. The present paper gives an overview of the procedure, the results and the knowledge gained through the long-term rub tests carried out with a tungsten carbide coated rotor with the aim of determining the time required to wear the seal in (“time-on-condition”). The total test duration of the cyclic tests was approx. 100 h. The measurements have shown that on the basis of the applied test procedure the initial wear-in phase is completed after approx. 40 cumulated operating hours and only very little wear occurs afterwards. Furthermore, it could be shown that the major part of the wear occurred within a short period of time within these 40 h and that the properties of the test cycle have a great influence on the wear-in time. The coupling of the rubbing intensity with time is achieved by measuring the transient rotor temperatures during rubbing.

The tests carried out have also shown that the influence of the concentricity properties of the rotor can resulting in rotor temperature deviations over the circumference (“hot spots”).
Measurements of Multiple Pure Tone Propagation From a High Bypass Turbofan Rotor in an Internal Flow Facility
Authors: Bozak Richard F.
Published: January 2021

An important noise source in modern high bypass ratio turbofans is from multiple pure tones produced by the fan during takeoff. An experiment conducted on a 1.5 pressure ratio fan in an internal flow facility provided dynamic pressure measurements to investigate multiple pure tone generation and propagation. Since multiple pure tones are generated by blade shock variation primarily due to the fan’s blade stagger angle differences, the blade stagger angles were measured with an array of over-the-rotor dynamic pressure transducers. Multiple pure tone measurements were made with 30 wall-mounted dynamic pressure transducers from 0.4 to 1.1 diameters upstream of the rotor. Measured blade stagger angle differences correspond to the the shock amplitude variation measured upstream. The acoustic field was extracted from the dynamic pressure signals using principal component analysis as well as duct mode beamforming. Shocks traveling out the inlet were found to couple to duct modes propagating at similar angles. Over-the-rotor acoustic liners appear to reduce rotor shock variation resulting in a reduction of sub-harmonic multiple pure tone sound pressure levels by 3–4 dB.
Methods for Measuring and Computing the Adiabatic-Wall Temperature
Authors: Peck James , Liu Jason , Bryden Kenneth M. , Shih Tom I-P.
Published: January 2021

For convective heat transfer involving multiple sources of different temperatures in the flow field such as in film cooling, the adiabatic-wall temperature, Tad, is used as the reference temperature to define the heat-transfer coefficient (HTC). Studies based on computational Fluid Dynamics (CFD) have always obtained Tad by requiring the cooled or heated surface to be adiabatic. Similarly, most experimental studies that measured Tad have sought to mimic adiabatic wall by using solids with very low thermal conductivity. Other experimental studies have obtained Tad by making two assumptions: (1) Tad at any given point on the cooled or heated surface is independent of the surface temperature, Ts, and the surface heat flux, qs″, at that point and (2) the HTC, had, which equals qs″/(Ts – Tad), depends only on the ratio of qs″ to Ts – Tad. With these two assumptions, measuring qs″ at two different Ts or vice versa at a point yields Tad and had at that point. In this study, CFD simulations, based on steady RANS, were performed to assess the assumptions invoked by CFD and experimental studies that seek to obtain Tad and had. The assessment was made by studying film cooling of a flat plate with an adiabatic wall and with isothermal walls, where the temperature of the isothermal wall, Ts, ranged from the lowest to the highest temperatures in the flow. Results from this study show Tad obtained by enforcing an adiabatic wall does not satisfy the requirement: where and when Ts – Tad = 0, qs″ = 0. Therefore, had approaches infinity where Ts – Tad is either zero or nearly zero, but qs″ ≠ 0. Also, obtaining Tad and had by measuring two sets of (Ts, qs″) was found to yield non-unique values that depended strongly upon the pair of (Ts, qs″) chosen. To overcome the shortcomings of existing methods, a new method was developed in this study to obtain Tad that does satisfy the requirement: Ts – Tad = 0 where and when qs″ = 0. Also, the method developed yields an had that is continuous across Ts – Tad = 0. By using the new method developed, errors in Tad and had obtained by existing methods were assessed.
Complex Energy Networks Optimization: Part I — Development and Validation of a Software for Optimal Load Allocation
Authors: Ancona M. A. , Bianchi M. , Branchini L. , De Pascale A. , Melino F. , Peretto A. , Rosati J.
Published: January 2021

The growing diffusion of the distributed generation systems, due to the European and national legislations which impose the fossil fuel and greenhouse gas emissions reduction and the renewable sources exploitation, have led to an increase in the complexity of the existing energy networks.

The main issue of the complex energy grids is their management, which consists in the resolution and optimization of the load allocation problem by minimizing the primary energy consumption and, thus, improving the overall efficiency.

In this context, the aim of this paper is to develop and validate a non-linear algorithm suitable for the resolution of the load allocation problem. In detail, the software COMBO, which has been developed by the University of Bologna, is based on a non-heuristic algorithm and allows to optimize a complex energy network — characterized by electrical, thermal, cooling and fuel fluxes — by evaluating all the possible combinations of solutions. The objective function of the software consists in the minimization of the total cost of energy production, including not only the variable costs, but also the costs related to the environmental impact of the energy systems. In this paper the mathematical model of the algorithm at the basis of the software COMBO is presented and described in detail.

Furthermore, the software has been validated by its application to a case study and comparing the results with the ones obtained with a previously developed software based on a genetic algorithm (heuristic non-linear method).
Improving the Safety of Power Plants by Developing a Digital Twin and an Expert System for Adaptive-Predictive Analysis of the Operability of Gas Turbine Units
Authors: Polyakov Roman , Paholkin Eugenii , Kudryavcev Igor , Krupenin Nikolay
Published: January 2021

The article describes general approaches to creating an intelligent system for monitoring and diagnosing the operability of energy supply facilities. The general concept of the adaptive-predictive analysis system and the construction of an artificial neural network for its use in the predictive module for predicting the type and time of failure occurrence is given. The basic principles of training a neural network for recognizing various types of failures are also given. Critical remarks of the concept of creating a digital twin of such a complex object for modeling as energy-generating equipment are given.
A Review of the Prospect and Challenges for Developing and Marketing a Brayton-Cycle Based Power Genset Gas-Turbine Using Supercritical CO2: Part I — The General System Challenges
Authors: Chen Jinbo , Engeda Abraham
Published: January 2021

Around the 1960s, the proposal of the supercritical dioxide (s-CCO2) power-cycle was first introduced; however, because of various obstacles, the development was slow at that time. With current worldwide emission and power problems, the s-CO2 power cycle has regained more attention because of its unique properties as a working fluid for power-cycle, and zero-emission potential. Each s-CO2 power cycle requires various components for compression, expansion, and heat exchange operation. Among various working fluid, s-CO2 has four significant advantages favorable for developers: 1. Relatively low and achievable critical conditions (∼7.3Mpa, ∼31°C). 2. The high density (∼400kg/m3) results in a very compact turbomachinery design. 3. The low dynamic-viscosity of s-CO2 can reduce the overall flow friction loss. 4. Low compressibility value which can reduce the overall system compression works. All these advantages make the s-CO2 the perfect working fluid for next-generation high-efficiency power-cycle design. This paper in two parts reviews the s-CO2 cycle technologies for power generation and critically assesses the recent challenges and development status. This paper, Part I, focuses on the general cycle concepts, thermodynamic properties, materials selection, and other components considerations.
Prospect and Challenges for Developing and Marketing a Brayton-Cycle Based Power Genset Gas-Turbine Using Supercritical CO2: Part II — The Turbomachinery Components Design Challenges
Authors: Engeda Abraham , Chen Jinbo
Published: January 2021

Since the 1960s the idea of using supercritical dioxide (S-CO2) as the working fluid in a Brayton power-cycle has been entertained [1]. But due to technical limitations of the time, the idea did not progress forward much. Presently, due to the availability of more knowhow, better technological platform, and advanced analysis tools, many believe it is time to revisit the idea of using supercritical dioxide (s-CO2) as the working fluid for power generation. Among various working fluids, s-CO2 has several significant advantages over other fluids. Primarily the attractive qualities of s-CO2 are high efficiency, much smaller turbomachinery size and plant footprint (and therefore lower capital cost), and the potential for full carbon capture. However, the realization of these benefits will depend on overcoming several technical, engineering and materials science challenges. Even though theoretically, the concept is highly attractive and promising, there is yet a major hurdle to be passed, namely the designing, developing, and testing of a reasonable size (10MWe or higher) prototype of a s-CO2 Brayton-cycle-based power gas turbine. This paper, Part II, in two parts reviews the s-CO2 Brayton cycle technologies for power generation and critically assesses the recent challenges and development status. This present paper (Part-II) in two parts focuses on the turbomachinery components (specifically the compressor) design and challenges.
Preliminary Research on Future Smart Engine Architecture
Authors: Liu Yudong , Chen Min , Tang Hailong
Published: January 2021

Aero engines that fit the future have now increasingly attracted the attention of aerospace industry and academia. With this trend, many research projects have been carried out to explore future aero engine technologies. This paper focuses on engine design field, and aims to satisfy the future flight missions that may be unpredictably varying. However, the intrinsic strong coupling of engine component matching mechanism blocks acceleration of engine design. Under this condition, this paper comes up with the concept of smart engine architecture that via a series of engine decoupling strategies, the components can be decoupled to an extent that by properly selecting and assembling them, an engine that satisfies certain flight mission can be designed, this is named mission-oriented pluggable design mode in this paper. Following this idea, a multi-purpose engine design scheme is presented to demonstrate the potential of this engine design mode, and further value of smart engine architecture is discussed.
BEARCAT: The SAFRAN Brand New Test Engine Heavily Instrumented for Accurate Comparison With CFD Calculations
Authors: Champion-Réaud Jean-Louis , Bidan Guillaume , Breining Jean-Luc , Lambert Pierre-Alain , Mendes Carlos , Zouloumian Nicolas
Published: January 2021

In this paper, we detail the development and goals of a brand new turboshaft engine called BEARCAT. “BEARCAT” is an acronyme for ‘’Banc d’Essai Avancé pour la Recherche en Combustion et Aérothermique des Turbomachines’’. BEARCAT is based on a MAKILA engine, a turboshaft developed by Safran Helicopter Engines (formerly Turboméca) and powering the H215 (2 Makila 1A1, 1820 SHP each) and the H225 (2 Makila 2A1, 2000 SHP each) of Airbus Helicopters. BEARCAT is developed by SAFRAN-Tech, the Research and Technology Center of the SAFRAN Group. This test engine is devoted to the fine characterization of aero-thermal phenomena occurring within the combustion chamber and the High Pressure Turbine as well as their interactions. Therefore, BEARCAT differs from a standard test engine by the implementation of metrologies inside the combustion chamber and the 2-stage High Pressure Turbine, in order to perform both steady and non-steady flow measurements which will be used to validate CFD codes and models. The engine instrumentation induces thorough modifications of several engine parts and also the development of original technical solutions to ensure metrologies integration in minimizing their impact on performances.
Downstream Vortex Generators to Enhance Film-Cooling Effectiveness
Authors: Lee Chien-Shing , Bryden Kenneth M. , Shih Tom I-P.
Published: January 2021

CFD simulation based on steady RANS were performed to assess the usefulness of adding a pair of “downstream” vortex generators (VGs) to improve the effectiveness of film cooling a flat plate through one row of inclined holes. Each VG in the pair is a rectangular plate with span S, chord C, and thickness t that is oriented at +45 or −45 degrees with respect to a plane that passes through the center of the film-cooling hole and placed at a distance D downstream of the hole, where D is the hole diameter. The separation between the VGs in the pair is smallest at their leading edges (0.72D) so that the VGs form a V-shape. Parameters studied include: S/D = 0.0, 0.25, 0.5, 1.0; C/D = 0.0, 0.2, 0.4; and blowing ratios of BR = 0.5, 1.0, and 2.0. Results obtained show “downstream” VGs can significantly increase lateral spreading of the film-cooling jet and thereby greatly improve film-cooling effectiveness. Results obtained also show the effects of S/D, C/D, and BR on adiabatic effectiveness, pressure loss, and vortical structures formed.
Pre-Stall Waves: Precursors to Stall Inception in a Contra-Rotating Axial Fan
Authors: Madasseri Payyappalli Manas , Pradeep A. M.
Published: January 2021

Stall in a compressor or a fan is often associated with pre-stall waves, that could act as precursors. The present study aims to understand in detail the pre-stall waves leading to instabilities in a low aspect ratio, low hub-tip ratio contra-rotating axial fan. Apart from a clean inflow condition, experiments on the contra-rotating fan are also carried out for two radial distortion conditions, namely, hub-radial and tip-radial distortions, and three circumferential distortion conditions, namely, simple-circumferential, hub-complex-circumferential and tip-complex-circumferential distortions. The results primarily concluded that operating rotor-2 at a speed higher than the design speed could possibly suppress the pre-stall disturbances. Towards the fully developed stall, the waves that are associated with low frequencies speed up and thus these waves become intermediate frequency waves. The fluid phenomena that trigger the stall are associated with high frequencies and these subsequently stretch to low frequencies at the onset of fully developed stall. The low-frequency waves and high frequency waves compromise to reach an intermediate frequency range during the fully developed stall. Further, it is observed that disturbances associated with low frequencies as well as high frequencies co-exist during the fully developed stall regime. There is also a region in the frequency spectra where no disturbances are excited and this region appears to be a “no excitation zone”. This paper thus concludes that there possibly exists a mechanism through which the energy is transferred between different frequencies during the pre-stall and fully developed stall regimes.
Towards Quantitative Wall Shear Stress Measurements: Calibration of Liquid Crystals
Authors: Melekidis Stefanos , Elfner Maximilian , Bauer Hans-Jörg
Published: January 2021

The wall shear stress distribution on an aerodynamically loaded component is of both practical and fundamental importance. Significant examples are the improvement of the performance of a vehicle, e.g. drag reduction, and more basic problems, such as the characterization of surface flows, e.g. with respect to flow control. The liquid crystal technique represents a promising diagnostics for measuring wall shear stress magnitude and orientation. In contrast to most other techniques, the direct measurement of two-dimensional wall shear stress distributions is straightforward.

In order to establish quantitative measurements of wall shear stress using the liquid crystal technique, an in-depth understanding of the influencing parameters is required. For their investigation, a novel generic flat plate test section was designed. The experiments are performed in such a way that a turbulent boundary layer is triggered at a corresponding Reynolds number within the test section. Due to the generic test case, precise and well-known flow boundary conditions can be established, which in turn are validated by probe measurements. Velocity and temperature profiles are recorded with high spatial resolution using a miniaturized combined Pitot-thermocouple probe. Furthermore, the operational range of the new test rig is presented. Preliminary wall shear stress measurements confirm the well-defined flow conditions in the test section and the potential of the measurement technique.
Topological Optimization of Under-Platform Dampers With Moving Morphable Components and Global Optimization Algorithm for Nonlinear Frequency Response
Authors: Denimal E. , El Haddad F. , Wong C. , Salles L.
Published: January 2021

To limit the risk of High Cycle Fatigue, underplatform dampers are traditionally used in aircraft engines to control the level of vibration. Many studies demonstrate the impact of the geometry of the damper on its efficiency, thus the consideration of topological optimization to find the best layout of the damper seems natural. Because of the nonlinear behaviour of the structure due to the friction contact interface, classical methods of topological optimization are not usable. The present study proposes to optimize the layout of an underplatform damper to reduce the level of nonlinear vibrations computed with the Multi-Harmonic Balance Method. The approach of topological optimization employed is based on the Moving Morphable Components framework together with the Kriging and the Efficient Global Optimization algorithm to solve the optimization problem. The results show that the level of vibration of the structure can be reduced of 30% and allow for the identification of different efficient geometries.
Investigation of Film Cooling Using Time-Resolved Stereo Particle Image Velocimetry
Authors: Stichling Katharina , Elfner Maximilian , Bauer Hans-Jörg
Published: January 2021

In the present study an existing test rig at the Institute of Thermal Turbomachinery (ITS), Karlsruhe Institute of Technology (KIT) designed for generic film cooling studies is adopted to accommodate time resolved stereoscopic particle image velocimetry measurements. Through a similarity analysis the test rig geometry is scaled by a factor of about 20. Operating conditions of hot gas and cooling air inlet and exit can be imposed that are compliant with realistic engine conditions including density ratio. The cooling air is supplied by a parallel-to-hot gas coolant flow-configuration with a coolant Reynolds number of 30,000. Time-resolved and time-averaged stereo particle image velocimetry data for a film cooling flow at high density ratio and a range of blowing ratios is presented in this study. The investigated film cooling hole constitutes a 10°-10°-10° laidback fan-shaped hole with a wide spacing of P/D = 8 to insure the absence of jet interaction. The inclination angle amounts to 35°. The time-resolved data indicates transient behaviour of the film cooling jet.
A High-Fidelity Modeling Tool to Support the Design of Oxy-Combustors for Direct-Fired sCO2 Cycles
Authors: Zambon Andrea C. , Hosangadi Ashvin , Weathers Tim , Winquist Mark , Mays Jeff , Miyata Shinjiro , Subbaraman Ganesan
Published: January 2021

The challenge in the design of oxy-combustors for direct-fired supercritical CO2 (sCO2) cycles is in addressing disparate performance metrics and objectives. Key design parameters to consider include among others: injector design for mixing and flame stability, split of recycled CO2 diluent between injectors and cooling films, target flame temperatures to control non-condensable products, and strategies to inject the diluent CO2 for film cooling and thermal control. In order to support novel oxy-combustor designs, a high-fidelity yet numerically efficient modeling framework based on the CRUNCH CFD® flow solver is presented, featuring key physics-based sub-models relevant in this regime. For computational efficiency in modeling large kinetic sets, a flamelet/progress variable (FPV) based tabulatedchemistry approach is utilized featuring a three-stream extension to allow for the simulation of the CO2 film cooling stream in addition to the fuel and oxidizer streams. Finite-rate chemistry effects are modeled in terms of multiple progress variables for the primary flame as well as for slower-evolving chemical species such as NOx and SOx contaminants. Real fluid effects are modeled using advanced equations of states. The predictive capabilities of this computationally-tractable design support tool are demonstrated on a conceptual injector design for an oxy-combustor operating near 30 MPa. Simulations results provide quantitative feedback on the effectiveness of the film cooling as well as the level of contaminants (CO, NO, and N) in the exhaust due to impurities entering from the injectors. These results indicate that this framework would be a useful tool for refining and optimizing the oxy-combustor designs as well as risk mitigation analyses.
Controller Design for Acceleration and Deceleration of a Turbofan Aircraft Engine
Authors: Zhou Jian , Xin Changkun
Published: January 2021

Controls for transient operation of aircraft engine are highly important due to the fact that the transient performance depends on how the engine responds to throttle command via the control system. The Ndot control is widely used in modern aircraft engine that can produce a consistent acceleration/deceleration throughout the complicated engine conditions.

Two different forms of Ndot controllers are designed for a commercial turbofan engine, which are proposed in this paper. One controller is based on PI controller in tandem with an integrator. And the other is an integral controller associated with feedforward structure. The control structure also contains two cascaded 1-order filters in the feedback loop and a lead compensator on the forward path to improve transient response. The anti-windup design is highlighted in this paper, and a bumpless transfer can be expected during the entire MAX/MIN fuel selection process. The controller design procedure and parameter tuning are fully demonstrated to make the engineering approach more straightforward.

Those two control schemes are further evaluated and compared under engine nominal condition and deteriorated conditions via digital simulation. The simulation results are satisfactory and implicates that both of the controllers can meet the design requirements. The control accuracy of the one with feedforward structure is a little better than the other of PI with integrator. However, the latter design demonstrates better robustness and provides more consistent performance for all engine conditions.
Gas Turbine Transient Performance Simulation With Simplified Heat Soakage Model
Authors: Li Zhuo-Jun , Li Yi-Guang , Korakianitis Theodosios
Published: January 2021

Reliable transient performance is crucial in handling an aircraft gas turbine engine from one steady state to another. The assessment of transient performance stability is normally done during the detailed design stage when component design details become available. Consequently, design iterations may be necessary and costly if engine transient handling and stability are not satisfactory. To make engine design more cost and time effective, it has become important to assess the transient performance stability at conceptual and preliminary design stage with the inclusion of key impact factors such as fuel control schedule, rotor dynamics and heat soakage. However, due to lack of detailed engine structural and geometrical information at the initial design stage, such transient performance simulation and assessment may have to ignore heat soakage effect.

In this paper, a novel generically simplified heat soakage model for three major gas path components of gas turbine engines including compressors, turbines and combustors has been introduced to support more realistic transient performance simulation of gas turbine engines at conceptual and preliminary design stage. Such heat soakage model only requires thermodynamic design parameters as input, which is normally available during such design stages. The model has been implemented into in-house transient performance simulation software and applied to a model twin-spool turbojet engine to test its effectiveness. A comparison between transient performance simulated with and without the heat soakage effects demonstrate that the results are promising.

Although the introduced heat soakage model is less accurate than that using detailed component geometrical information, it is able to include the major heat soakage effect in transient performance simulation and provide engine transient stability analysis to support conceptual and preliminary engine designs.
Modeling of Axial Compressor With Large Tip Clearances
Authors: Evans Simon , Yi Junsok , Nolan Sean , Joseph Liselle , Ni Michael , Kulkarni Sameer
Published: January 2021

In the drive for lower fuel consumption through increased bypass ratio and increased overall pressure ratio (OPR), engine designs for the next generation of single-aisle aircraft will require core sizes below 3 lb/s and OPRs above 50. Traditionally, these core sizes are the domain of centrifugal compressors, but materials limit pressure ratio in these machines to well below 50. An all-axial high pressure compressor (HPC) at this core size, however, comes with limitations associated with the small blade spans at the back of the HPC, as clearances, fillets and leading edges do not scale with the core size. The result is a substantial efficiency penalty, driven primarily by the tip leakage flow produced by the larger clearance-to-span ratio, which negates the cycle efficiency benefits of the high OPR. In order to enable small-core, high-OPR, all-axial compressors mitigating technologies need to be developed and implemented to reduce the large clearance-to-span efficiency penalty. However, for this technology development to be successful, it is imperative that predictive design tools accurately model the overall flow physics and trends of the technologies developed. In this paper we describe an effort to determine whether different modeling standards are required for a large clearance-to-span ratio, and if so, identify criteria for an appropriate solver and/or mesh. Multiple models are run and results compared with data collected in the NASA Glenn Research Center’s Low-Speed Axial Compressor. These comparisons show that steady Reynolds-Averaged Navier-Stokes (RANS) solvers can predict the pressure-rise characteristic to an acceptable level of accuracy, if careful attention is paid to mesh topology in the tip region. However, unsteady tools are necessary to accurately capture radial profiles of blockage and total pressure. The Delayed-Detached Eddy Simulation model was also used to run this geometry, but did not resolve any additional features not captured by the unsteady RANS simulation near stall.
Towards Multidisciplinary Turbine Blade Tolerance Design Assessment Using Adjoint Methods
Authors: Liefke Alexander , Jaksch Peter , Schmitz Sebastian , Marciniak Vincent , Janoske Uwe , Gottschalk Hanno
Published: January 2021

This paper shows how to use discrete CFD and FEM adjoint surface sensitivities to derive objective-based tolerances for turbine blades, instead of relying on geometric tolerances. For this purpose a multidisciplinary adjoint evaluation tool chain is introduced to quantify the effect of real manufacturing imperfections on aerodynamic efficiency and probabilistic low cycle fatigue life time.

Before the adjoint method is applied, a numerical validation of the CFD and FEM adjoint gradients is performed using 102 heavy duty turbine vane scans. The results show that the relative error for adjoint CFD gradients is below 0.5%, while the FEM life time gradient relative errors are below 5%. The adjoint assessment tool chain further reduces the computational cost by around 85% for the investigated test case compared to non-linear methods.

Through the application of the presented tool chain, the definition of specified objective-based tolerances becomes available as a design assessment tool and allows to improve overall turbine efficiency and the accuracy of life time prediction.