bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer and Flow Characteristics of the Jet Array Impingement
Authors: Ren Min , Li Xueying , Ren Jing
Published: September 2021

An experimental and numerical study is performed to investigate heat transfer and pressure loss characteristics for impingement. Experimental heat transfer is measured by the thermochromic liquid crystal. The CFD model uses a steady state RANS approach and the shear stress transport (SST). The effect of Reynolds number (5000–25000), the distance between the holes and the distance from the hole to target on the impingement is investigated in the present study. Local Nusselt number as well as area and line average values are gotten experimentally and numerically. Besides, numerical simulations provide the detailed flow characteristics of the problem and complement experimental measurements. The result shows that the heat transfer increases with Reynolds number increasing. But the qualitative distribution of local heat transfer does not change with the increase of Reynolds number, when it is sensitive to P/D and Z/D. The performance of heat transfer is best when Z/D = 2. And the high heat transfer region of Z/D = 1 is closer to the exit than that of Z/D = 2 and Z/D = 3. The main reason is the effect of cross flow and the momentum of the jet reaching the wall. The performance of heat transfer is best when P/D = 5. And the high heat transfer region of P/D = 4 is closer to the exit than that of P/D = 5 and P/D = 6. The main reason is the effect of cross flow and interactions between jets.
Impact of Swirling Entropy Waves on a High Pressure Turbine
Authors: Notaristefano Andrea , Gaetani Paolo
Published: September 2021

The harsh environment exiting modern gas turbine combustion chamber is characterized by vorticity and temperature perturbations, the latter commonly referred as entropy waves. The interaction of these unsteadiness with the first turbine stage causes non-negligible effects on the aerodynamic performance, blade cooling and noise production. The first of these drawbacks is addressed in this paper by means of an experimental campaign: entropy waves and swirl profile are injected upstream of an axial turbine stage through a novel combustor simulator. Two injection positions and different inlet conditions are considered. Steady and unsteady experimental measurements are carried out through the stage to address the combustor-turbine interaction characterizing the injected disturbance, the nozzle and rotor outlet aerothermal field. The experimental outcomes show a severe reduction of the temperature perturbation already at stator outlet. The generated swirl profile influences significantly the aerodynamic, as it interacts with the stator and rotor secondary flows and wakes. Furthermore, the clocking position changes the region most affected by the disturbance, showing a potential modifying the injection position to minimize the entropy wave and swirl profile impact on the stage. Finally, this work shows that in order to proficiently study entropy waves, the unsteady aerodynamic flow field stator downstream has to be addressed.
Calibration of a CFD Methodology for the Simulation of Roughness Effects on Friction and Heat Transfer in Additive Manufactured Components
Authors: Mazzei Lorenzo , Da Soghe Riccardo , Bianchini Cosimo
Published: September 2021

It is well-known from the literature that surface roughness significantly affects friction and heat transfer. This is even more evident for additive manufactured (AM) components, which are taking an increasingly important role in the gas turbine field. However, the exploitation of numerical approaches to improve their design is hindered by the lack of dedicated correlations and CFD models developed for such high roughness conditions.

Usually the additive manufactured components are simulated considering the surfaces as smooth or applying an equivalent sand-grain roughness (ks) that results in a velocity shift in the boundary layer. However, determining a priori the most appropriate value of ks is challenging, as dozens of correlations are available, returning scattered and uncertain results. A previous work proved how the CFD prediction of friction and heat transfer returns significant deviations, even exploiting the ks values obtained from experimental tests on the very same test case.

That work also allowed identification of a promising CFD methodology based on friction and thermal corrections proposed by Aupoix from ONERA. The aim of this work is to further the assessment and calibration activity of the model, by analyzing additional experimental data of friction factor and Nusselt number from new test cases considering different geometries and flow conditions. The new coupons consisted of straight circular channels and wavy channels. This work represents a further step in the generation of a more validated and general methodology for the high-fidelity CFD analysis of additive-manufactured components.
Comparative Low-Cycle Fatigue Behavior of HAYNES 244 Alloy and Waspaloy
Authors: Fahrmann Michael G.
Published: September 2021

HAYNES® 244® alloy was chiefly developed to address the need for high-strength, low coefficient of thermal expansion (CTE) alloys for seal rings and cases in advanced gas turbine engines. In addition to these attributes, adequate resistance to low-cycle fatigue (LCF) due to cyclic thermal and mechanical loading during service is critical for such applications. The isothermal LCF performance of commercially produced 0.5” (12.5 mm) thick, fully heat treated plate products of 244 alloy was evaluated by means of axial strain-controlled (R = −1) LCF tests covering total strain ranges up to 1.25 % (without dwells), at temperatures ranging from 800–1400°F (427–760°C). In addition, the comparative LCF performance of Waspaloy, a well-established alloy for turbine cases, was evaluated under selected, nominally identical test conditions. S-N curves were constructed and fitted by the Coffin-Manson equation, allowing the delineation of regimes controlled by the elastic and plastic response of the material. Fracture surfaces were examined in the scanning electron microscope to identify fatigue crack initiation sites and crack propagation modes. Differences between the alloys are discussed in terms of tensile strength and cyclic hardening/softening behavior. Implications for fatigue performance of these alloys under cyclic thermal loading conditions are discussed as well.
Manufacturing Technologies for Fir Tree Slots: A Technological and Economic Evaluation
Authors: Heidemanns Lukas , Seelbach Tobias , Küpper Ugur , Seimann Martin , Bergs Thomas
Published: September 2021

Fir tree slots in engine disks pose a great challenge to the production process, especially due to the use of increasingly filigree geometries. Broaching with high-speed steel (HSS) as cutting tool material has been established as the state of the art process. However, this manufacturing process obtains the disadvantages of high tool costs and long waiting times in case of geometry adaptations. Alternative manufacturing technologies, namely electrochemical machining (ECM) and wire electrical discharge machining (WEDM) offer the potential to replace broaching. Because of their removal mechanism being independent of the mechanical properties of the material, these processes are not hindered by increasingly higher thermomechanical material properties. Furthermore, the tool in WEDM is not specific to geometry, allowing fast adaptations. Nevertheless, the technology specific white layer may reduce the mechanical integrity of the engine disk. ECM in contrast has no negative impact on the rim zone of the workpiece but the tool is still specific to the slot geometry. Consequently, this paper experimentally investigates the three different manufacturing technologies in order to evaluate their capability to manufacture fir tree slots with respect to geometric accuracy and surface integrity. Subsequently, the technology specific manufacturing costs are considered to outline the economic potential of each process while taking into account the influence of the batch size.
Effect of Self-Sustained Pulsation of Coolant Flow on Adiabatic Effectiveness and Net Heat Flux Reduction on a Flat Plate
Authors: Rosafio Nicola , Salvadori Simone , Misul Daniela Anna , Baratta Mirko , Carnevale Mauro , Saumweber Christian
Published: September 2021

Advanced film-cooling systems are necessary to guarantee safe working conditions of high-pressure turbine stages. A fair prediction of the inherent unsteady interaction between the main-flow and the jet of cooling air allows for correctly describing the complex flow structures arising close to the cooled region. This proves to be crucial for the design of high-performance cooling systems. Results obtained by means of an experimental campaign performed at the University of Karlsruhe are shown along with unsteady numerical data obtained for the corresponding working conditions. The experimental rig consists of an instrumented plate where the hot flow reaches Mach = 0.6 close to the coolant jet exit section. The numerical campaign models the unsteady film cooling characteristics using a third-order accurate method. The ANSYS® FLUENT® software is used along with a mesh refinement procedure that allows for accurately modelling the flow field. Turbulence is modelled using the k-ω SST model. Time-averaged and time-resolved distributions of adiabatic effectiveness and Net Heat Flux Reduction are analysed to determine to what extent deterministic unsteadiness plays a role in cooling systems. It is found that coolant pulsates due to fluctuations generated by flow separation at the inlet section of the cooling channel. Visualizations of the fluctuating flow field demonstrate that coolant penetration depends on the phase of the pulsation, thus leading to periodically reduced shielding. Eventually, unsteadiness occurring at integral length scales does not provide enough mixing to match the experiments, thus hinting that the dominant phenomena occur at inertial length scales.
High Efficiency Wind Turbine Using Co-Flow Jet Active Flow Control
Authors: Xu Kewei , Zha Gecheng
Published: September 2021

This paper applies Co-flow Jet (CFJ) active flow control airfoil to a NREL horizontal axis wind turbine for power output improvement. CFJ is a zero-net-mass-flux active flow control method that dramatically increases airfoil lift coefficient and suppresses flow separation at a low energy expenditure. The 3D Reynolds Averaged Navier-Stokes (RANS) equations with one-equation Spalart-Allmaras (SA) turbulence model are solved to simulate the 3D flows of the wind turbines. The baseline wind turbine is the NREL 10.06m diameter phase VI wind turbine and is modified to a CFJ blade by implementing CFJ along the span. The baseline wind turbine performance is validated with the experiment at three wind speeds, 7m/s, 15m/s, and 25m/s. The predicted blade surface pressure distributions and power output agree well with the experimental measurements. The study indicates that the CFJ can enhance the power output at the condition where angle of attack is increased to the level that conventional wind turbine is stalled. At the speed of 7m/s that the NREL turbine is designed to achieve the optimum efficiency at the pitch angle of 3°, the CFJ turbine does not increase the power output. When the pitch angle is reduced by 13° to −10°, the baseline wind turbine is stalled and generates negative power output at 7m/s. But the CFJ wind turbine increases the power output by 12.3% assuming CFJ fan efficiency of 80% at the same wind speed. This is an effective method to extract more power from the wind at all speeds. It is particularly useful at low speeds to decrease cut-in speed and increase power output without exceeding the structure limit. At the freestream velocity of 15m/s and the CFJ momentum coefficient Cμ of 0.23, the net power output is increased by 207.7% assuming the CFJ fan efficiency of 80%, compared to the baseline wind turbine due to the removal of flow separation. The CFJ wind turbine appears to open a door to a new area of wind turbine efficiency improvement and adaptive control for optimal loading.
Centrifugal Compressor Polytropic Performance Evaluation Using Cubic Polynomial Approximation for the Temperature-Entropy Polytropic Path
Authors: Taher Matt , Evans B. F.
Published: September 2021

A highly accurate centrifugal compressor polytropic performance approximation method has been developed that is easy to employ. The method is based upon a constant efficiency, temperature-entropy path for real gases. The elegance of this method is its exceedingly simple way of calculating polytropic efficiency with sufficiently high precision as required for compressor performance testing. A constant efficiency polytropic path can be modeled as either a single or several sequential cubic polynomial segments affording solutions that allow for determining thermodynamic state variables along a continuous path. New analytic terms have been developed for slope and curvature of temperature versus entropy along the constant efficiency polytropic path. A broad range of example case results verify the accuracy and ease of use of the method.
Uncertainty in High-Pressure Stator Performance Measurement in an Annular Cascade at Engine-Representative Reynolds and Mach
Authors: Bhatnagar Lakshya , Paniagua Guillermo , Cuadrado David G. , Aye-Addo Papa Aye N. , Castillo Sauca Antonio , Lozano Francisco , Bloxham Matthew
Published: September 2021

The betterment of the turbine performance plays a prime role in all future transportation and energy production systems. Precise uncertainty quantification of experimental measurement of any performance differential is therefore essential for turbine development programs. In this paper, the uncertainty analysis of loss measurements in a high-pressure turbine vane are presented. Tests were performed on a stator geometry at engine representative conditions in a new annular turbine module called BRASTA (Big Rig for Annular Stationary Turbine Analysis) located within the Purdue Experimental Turbine Aerothermal Lab. The aerodynamic probes are described with emphasis on their calibration and uncertainty analysis, first considering single point measurement, followed by the spatial averaging implications. The change of operating conditions and flow blockage due to measurement probes are analyzed using CFD, and corrections are recommended on the measurement data. The test section and its characterization are presented, including calibration of the sonic valve. The sonic valve calibration is necessary to ensure a wide range of operation in Mach and Reynolds. Finally, the vane data are discussed, emphasizing their systematic and stochastic uncertainty.
Virtual Gas Turbines Part I: A Top-Down Geometry Modelling Environment for Turbomachinery Application
Authors: Kulkarni Davendu Y. , Lu Gan , Wang Feng , di Mare Luca
Published: September 2021

The gas turbine engine design involves multi-disciplinary, multi-fidelity iterative design-analysis processes. These highly intertwined processes are nowadays incorporated in automated design frameworks to facilitate high-fidelity, fully coupled, large-scale simulations. The most tedious and time-consuming step in such simulations is the construction of a common geometry database that ensures geometry consistency at every step of the design iteration, is accessible to multi-disciplinary solvers and allows system-level analysis.

This paper presents a novel design-intent-driven geometry modelling environment that is based on a top-down feature-based geometry model generation method. In the proposed object-oriented environment, each feature entity possesses a separate identity, denotes an abstract geometry, and carries a set of characteristics. These geometry features are organised in a turbomachinery feature taxonomy. The engine geometry is represented by a tree-like logical structure of geometry features, wherein abstract features outline the engine architecture, while the detailed geometry is defined by lower-level features. This top-down flexible arrangement of feature-tree enables the design intent to be preserved throughout the design process, allows the design to be modified freely and supports the design intent variations to be propagated throughout the geometry automatically.

The application of the proposed feature-based geometry modelling environment is demonstrated by generating a whole-engine computational geometry. This geometry modelling environment provides an efficient means of rapidly populating complex turbomachinery assemblies. The generated engine geometry is fully scalable, easily modifiable and is re-usable for generating the geometry models of new engines or their derivatives. This capability also enables fast multi-fidelity simulation and optimisation of various gas turbine systems.
Numerical Predictions of Cavitating Flow Within a Liquid Hydrogen Inducer
Authors: Blumenthal Robert F. , Kelecy Franklyn J.
Published: September 2021

With the recent interest in using liquid hydrogen as a fuel source for energy production and transportation, predicting the performance of pumping systems which handle hydrogen has become an important issue. Liquid hydrogen is a cryogenic fluid which exists at extremely low temperatures and presents a myriad of design challenges to ensure a safe, efficient, and robust fuel delivery system. In addition, the typical operating conditions for pumps handling liquid hydrogen are such that vapor formation due to cavitation is present in the flow even when the head rise is relatively unaffected. Cavitation can cause severe damage to pump components and lead to shortened life and eventual failure, especially at the temperatures associated with liquid hydrogen.

The present work was focused on validating CFD methods for accurately predicting cavitating flow in a pump inducer handling cryogenic hydrogen. The CFD code used in this study was Ansys CFX, which is a general-purpose commercial solver with models available for simulating cryogenic cavitation in turbomachinery. The specific model employed for cavitation utilized a Rayleigh-Plesset based multiphase formulation in conjunction with thermodynamic property tables appropriate for cryogenic liquid hydrogen. Adjustments to cavitation model parameters were introduced as a function of fluid temperature to account for the thermal suppression head effects that are present at cryogenic thermal conditions.
Dependence of LPBF Surface Roughness on Laser Incidence Angle and Component Build Orientation
Authors: Subramanian Ramesh , Rule David , Nazik Onur
Published: September 2021

Laser Powder Bed Fusion (LPBF) of metallic components is unlocking new design options for high efficiency gas turbine component designs not possible by conventional manufacturing technologies. Surface roughness is a key characteristic of LPBF components that impacts heat transfer correlations and crack initiation from co-located surface defects — both are critical for gas turbine component durability and performance. However, even for a single material, there is an increasing diversity in laser machines (single vs multi-laser), layer thicknesses (∼20–80 microns) and orientations to the build plate (upskin, vertical and downskin) that result in significant variability in surface roughness. This study systematically compares the surface roughness across the above-mentioned variables to further develop a repeatable correlation of surface roughness to the angle between the substrate normal and laser incidence direction. This presented data will be discussed in detail, to show potential applicability of this process signature curve across materials, machines, and substrate orientations. Future steps to a rapid process qualification standard for surface roughness, across Siemens Energy’s global manufacturing footprint will also be discussed.
Research on Matching Characteristics of Ship-Engine-Propeller of COGAG
Authors: Wang Zhitao , Ma Jiayi , Yu Haichao , Li Tielei
Published: September 2021

The combined gas turbine and gas turbine power propulsion device (COGAG power propulsion device) is an advanced combined power system, which uses multiple gas turbines as the main engine to drive propellers to propel the ship. COGAG power propulsion device has high power density, excellent stability and maneuverability, it receives more and more attention in the field of ship power at home and abroad. This article takes the COGAG power propulsion device as the research object, uses simulation methods to study its steady-state operating characteristics, and conducts a ship-engine-propeller optimization matching analysis based on economy and maneuverability. The research work carried out in this article is as follows.

Firstly, according to the structural relationship between the various components and the system thermal cycle mode of the COGAG power propulsion device, establish the controller, main engine, gear box, clutch, shafting, propeller, ship and other components and simulation models of the system with the modular modeling idea.

Secondly, divide the gears according to ship speed. For the four working modes of single-gas turbine with load, dual-gas turbine with load, three-gas turbine with load, and four-gas turbine with load, analysis the ship-engine-propeller optimization matching of the COGAG power propulsion device based on economy and maneuverability, and calculate the best shaft speed and propeller pitch ratio in each gear, so as to obtain the steady-state operation characteristics of the COGAG power propulsion device based on the ship-engine-propeller matching, which provides a basis for determining the target parameters of the dynamic process.
Identification of Slip Load, Friction Force and External Force Using Unscented Kalman Filter for Frictionally Damped Turbine Blades
Authors: Patel Himanshu , Sinha Alok
Published: September 2021

An Unscented Kalman Filter (UKF) based technique has been developed for parameter estimation of turbine blades with friction dampers. The technique is based on integration of Newmark method, an iterative numerical integration method for structural dynamics, with UKF. The technique has been implemented on a single mode model of a turbine blade with a friction damper. Two approaches are developed. First, both steady state vibration and known forcing data are used to estimate parameters such as friction force and slip load. These parameters are treated as additional states of the system and the augmented state space model is used with UKF to estimate parameters. In the second approach, transient vibration response of the system is used to estimate slip load, friction force and unknown sinusoidal forcing function as well. The frequency of sinusoidal external excitation is assumed to be known. The unknown magnitude and phase of the external excitation are represented as a solution of a second order differential equation, which leads to two additional states in the model. Numerical results are presented for both the cases of known and unknown forcing functions in the presence of modeling and measurement errors. A discussion of these results is presented and the validity of the new approach is corroborated.
Determination of the Area of Rational Use of Hybrid Bearings With Steel Rings and Ceramic Rolling Elements in High-Speed Aircraft Engines
Authors: Lavrentyev Yury , Petrov Nikolay , Nozhnitsky Yury
Published: September 2021

The process of improving gas turbine engines is associated with increased thermodynamic parameters and rotor speed. In advanced aircraft engines the main rotor bearings will operate at speed index dmn > 3 · 106 mm · rpm, where dm is the bearing pitch diameter (mm), and n is the rotational speed (rpm). Under these conditions, significant heat is generated in the bearings, and the use of hybrid rolling bearings with steel rings and ceramic rolling elements looks more attractive due to the ceramic’s low density and low coefficient of thermal expansion.

A computational method for predicting the thermal state of rolling bearings operating at high speed parameters has been developed based on comparative tests of steel and hybrid rolling bearings. Knowing the thermal state of the bearing allows the value of the operating clearance to be set in the bearing, which is important for determining the contact angle and load distribution over the rolling elements.

A comparison with the results from tests of hybrid and steel bearings presented in the previous literature has shown that the calculated values correspond to the experimental data.

Criteria for selecting steel or hybrid bearings are proposed, and areas of rational use for hybrid rolling bearings in aircraft engines are determined.
Experimental Study on Different Tip Clearance of Low-Speed Axial Fan
Authors: Zhang Ming , Li Jia , Dong Xu , Sun Dakun , Sun Xiaofeng
Published: September 2021

Tip clearance flow is not only the source of undesirable noise but also a potential indicator for critical operating conditions with rotating stall or surge. It can induce blade vibration, which would cause premature blade failure when the vibration is strong enough. The paper presents experimental studies on the effects of tip clearance on the stall inception process in a low-speed high-load single stage fan with different tip clearance. From the point of view of flow range, it has been proved by computations that there is an optimal gap value, and an explanation is given according to different stall mechanisms of large and small tip clearance. However, the experiment of no tip clearance is not easy to achieve. In this experiment, a wearable soft wall casing was used to achieve “zero clearance”, and an explicit conclusion was obtained. The pressure rise and efficiency are improved at small tip clearance. Instantaneous Casing Pressure Field Measurement was carried out: instantaneous casing pressure fields were measured by 9 high response pressure transducers mounted on the casing wall. At the near stall point with large tip clearance, a narrow band increase of the amplitudes in the frequency spectrum at roughly half of the blade passing frequency can be observed according to the spectrum of static pressure at points on the endwall near the leading-edge and above the rotor. This phenomenon was explained from two aspects: tip clearance flow structure and pressure signal spectrum.
Theoretical Study on Static Performance of Double-Bump Foil Bearings
Authors: Xu Fangcheng , Chu Jianhua , Luan Wenlin , Zhao Guang
Published: September 2021

In this paper, single-bump foil models with different thickness and double-bump foil models with different initial clearances are established. The structural stiffness and equivalent viscous damping of double-bump foil and single-bump foil are analyzed by finite element simulation. The results show that the double-layer bump foil has variable stiffness and the displacement of the upper bump is greater than the initial gap when the two-layer bumps contact. A model for obtaining static characteristics of aerodynamic compliant foil thrust bearing is established on the basis of the stiffness characteristics of the double-bump foil. This paper solves gas Reynolds equation, the gas film thickness equation and the foil stiffness characteristic equation via the finite element method and the finite difference method. The static characteristics of the thrust bearings including the bearing pressure distribution, the gas film thickness and the friction power consumption have been obtained. The static characteristics of two kinds of foils have been compared and analyzed, and the effect of initial clearance on the static performance of double-bump foil bearings is studied. The results show that the double-bump foil structure can effectively improve the load capacity of thrust bearing. In addition, the static performance of double-bump foil thrust bearings is between the performance of the single-bump foil bearing and the double-bump foil bearing whose foil’s clearance is zero. The smaller the initial clearance is, the easier it will be to form a stable double-bump foil supporting structure.
Open Source Axial Compressor Mean-Line Design Tool for Supercritical Carbon Dioxide
Authors: Wells Kaden , Turner Mark G.
Published: September 2021

This paper presents an open-source axial compressor design code developed for applications using Supercritical CO2 (S-CO2). Real property tables are generated using REFPROP (Reference Fluid Thermodynamic and Transport Properties Database) linked to MATLAB. These tables are created and are provided for S-CO2 and could be created for any fluid in the database. At this time, only a single-phase fluid has been implemented. The tables are imported into the mean-line code and are interpolated with cubic splines to calculate real properties based on two given properties. The mean-line code is written in Python to allow portability and convenient plotting capability. The inputs are simple ascii files with the overall compressor details, stage data, and an optional IGV file. The code uses the axial flow equations of continuity, energy, and angular momentum in addition to velocity triangles to calculate state properties at every station. A free vortex assumption at each between-blade row station is used to calculate information at hub, pitch, and tip. The input for each stage includes the Mach number and absolute flow angle at the rotor leading edge in addition to the total enthalpy rise across each rotor. Loss coefficients, solidity, aspect ratio and axial spacing are also specified for each blade row along with blockage to account for wakes, boundary layers, and bleed. A hub radius is also specified. These parameters allow for a complete set of realistic inputs for the design of axial compressors using S-CO2 as the working fluid. The output can be used to assess the design and is used as the start of higher fidelity design.
Comparison of Model Order Reduction Methods in Thermoacoustic Stability Analysis
Authors: Purwar Naman , Meindl Maximilian , Polifke Wolfgang
Published: September 2021

Model order reduction can play a pivotal role in reducing the cost of repeated computations of large thermoacoustic models required for comprehensive stability analysis and optimization. In this proof-of-concept study, acoustic wave propagation is modeled with a 1D network approach, while acoustic-flame interactions are modeled by a flame transfer function. Three reduction techniques are applied to the acoustic subsystem: firstly modal truncation based on preserving the acoustic eigenmodes, and then two approaches that strive to preserve the input-output transfer behavior of the acoustic subsystem, i.e., truncated balanced realization and iterative rational Krylov algorithm. After reduction, the reduced-order models (ROMs) are coupled with the flame transfer function. Results show that the coupled reduced system from modal truncation accurately captures thermoacoustic cavity modes with weak influence of the flame, but fails for cavity modes strongly influenced by the flame as well as for intrinsic thermoacoustic modes. On the contrary, the coupled ROMs generated with the other two methods accurately predict all types of modes. It is concluded that reduction techniques based on preserving transfer behavior are more suitable for thermoacoustic stability analysis.
Air-Steam Dual Loop Gas Turbine Engine With Pulse Detonation Combustion
Authors: Nageswara Reddy Pereddy
Published: September 2021

Air-steam Dual Loop Gas Turbine Engine (DLGTE) consists of a gas turbine engine with Pulse Detonation Combustor (PDC) (operating by the Humphrey cycle) with the air as the working fluid and a steam turbine engine (operating by the Rankine cycle) with the steam as the working fluid. The temperature of the hot detonation products is reduced to Turbine Inlet Temperature (TIT) by exchanging heat energy between detonation products and water in a Detonation Products to Water Heat Exchanger (DPWHE). The thermodynamic cycle of operation of DLGTE with PDC is analyzed based on quasi-steady state one dimensional formulation, and a computer code is developed in MATLAB to simulate the engine performance at different compressor pressure ratios and TITs. C2H4/air is taken as the fuel-oxidizer. It is found that DLGTE with PDC achieves 40 to 47% thermal efficiency as against 20 to 35% of Base Line Gas Turbine Engine (BLGTE) and 27 to 40% of Combined Cycle Gas Turbine Engine (CCGTE) with a Steady Flow Combustor (SFC) depending on the cycle pressure ratios and TITs. The specific work output of DLGTE is found to increase from 875 to 1200 kJ/kg air as against 180 to 380 kJ/kg air of BLGTE and 200 to 430 kJ/kg air of CCGTE.
Experimental and Computational Investigation of Film Cooling Performance and External Flowfield Effects due to Impingement Coolant Feed in the Leading Edge of a Turbine Blade
Authors: Moore Jacob D. , Easterby Christopher C. , Bogard David G.
Published: September 2021

The effects that leading-edge impingement coolant feeds have on the external flowfield and on film cooling performance in the showerhead have not been studied thoroughly in the literature. To isolate the influence of the impingement feed, experimental adiabatic effectiveness and off-the-wall thermal field measurements were made using a shaped hole geometry fed by an ideal plenum coolant feed and by an engine-realistic impingement coolant feed. The impingement configuration exhibited around 10% higher adiabatic effectiveness levels than the plenum configuration did — a finding in agreement with the few studies isolating this effect. CFD RANS simulations of the impingement and the pseudo-plenum configurations from a companion study were consulted to investigate the root cause of this difference in performance because the experimental data alone did not sufficiently explain it. In the impingement feed simulation, flow remained better attached throughout the hole (both at the inlet and at the diffuser) due to a rotation caused by the impingement flow, leading to better attachment on the exterior surface. This was most significant for the suction side holes at higher blowing ratios wherein the pseudo-plenum caused much more severe separation in the holes than the impingement configuration did.
An Unconventional Method for the Diagnosis and Study of Generator Rotor Thermal Bows
Authors: Chatterton Steven , Pennacchi Paolo , Vania Andrea
Published: September 2021

The rotor thermal sensitivity often affects the dynamic behavior of power unit generators. Owing to this phenomenon, increments of field current and other process parameters that are related to it may cause a shaft thermal bow and significant changes in the synchronous vibration. This symptom can also be caused by many other common malfunctions that affect rotating machines. Therefore, diagnostic techniques aimed at identifying the actual fault are very useful for optimizing maintenance activities. The thermal sensitivity of generator rotors can be deemed as a fault because it is commonly caused by a local deterioration of the winding insulation as well as by jamming phenomena between conductors and rotor slots, caused by friction forces due to the different thermal expansions of these components. This paper shows the results obtained applying a diagnostic method, based on multiple linear regression models, which has been developed for the analysis of generator vibrations caused by thermal sensitivity. Nevertheless, nonlinear relationships between vibration and process parameters have also been taken into account. The capabilities of this diagnostic technique have been validated using the analysis of experimental data collected in a power plant. The results of this investigation are shown and discussed in the paper.
Isentropic Formulation of the Linearized Euler Equations For Perfectly Premixed Combustion Systems
Authors: Romero Vega Pedro , Hofmeister Thomas , Heilmann Gerrit , Hirsch Christoph , Sattelmayer Thomas
Published: September 2021

The linearized Euler equations (LEE) provide an accurate — yet computationally efficient — description of propagation and damping of acoustic waves in geometrically complex, non-uniform reactive mean flows like those found in gas turbine combustion chambers. However, direct application of the LEE to perfectly premixed combustors with highly turbulent flows overestimates entropy waves as the LEE solution inherently contains coupled acoustic, vortical and entropy modes. In the present work, the LEE are decomposed into isentropic and non-isentropic parts ultimately obtaining a simplified set of isentropic LEE, in which only acoustic and vortical modes propagate. In the isentropic LEE, only continuity and momentum equations need to be solved. The energy equation is replaced by the isentropic relation between acoustic pressure and density. From the decomposition, the unsteady heat release term, which acts as a source in the energy equation, naturally arises as a source in the continuity equation. This way, the thermoacoustic coupling is still preserved in the isentropic formulation. The derived isentropic set of equations is first tested with a one-dimensional benchmark configuration consisting of a mean flow temperature jump, non-uniform mean flow velocity and unsteady heat release sources. Solutions of the non-isentropic and isentropic set of LEE are compared and the avoidance of entropy waves proved. Finally, isentropic LEE are used for reproducing the frequency of the self-excited first transversal mode of a lab-scale swirl-stabilized premixed combustor. Furthermore, isentropic and non-isentropic LEE solutions are compared. The non-isentropic LEE yield too high levels of entropy at the combustor exit that may explain the increased damping rate of the non-isentropic LEE solution compared to the isentropic LEE solution. This shows the relevance of isentropic LEE for correctly predicting thermoacoustic stability limits at high frequencies in relevant industrial applications.
Experimental Study on High Pressure Combustion of Decomposed Ammonia: How Can Ammonia Be Best Used in a Gas Turbine?
Authors: Ditaranto Mario , Saanum Inge , Larfeldt Jenny
Published: September 2021

Hydrogen, a carbon-free fuel, is a challenging gas to transport and store, but that can be solved by producing ammonia, a worldwide commonly distributed chemical. Ideally, ammonia should be used directly on site as a fuel, but it has many combustion shortcomings, with a very low reactivity and a high propensity to generate NOx. Alternatively, ammonia could be decomposed back to a mixture of hydrogen and nitrogen which has better combustion properties, but at the expense of an endothermal reaction. Between these two options, a trade off could be a partial decomposition where the end use fuel is a mixture of ammonia, hydrogen, and nitrogen. We present an experimental study aiming at finding optimal NH3-H2-N2 fuel blends to be used in gas turbines and provide manufacturers with guidelines for their use in retrofit and new combustion applications. The industrial burner considered in this study is a small-scale Siemens burner used in the SGT-750 gas turbine, tested in the SINTEF high pressure combustion facility. The overall behaviour of the burner in terms of stability and emissions is characterized as a function of fuel mixtures corresponding to partial and full decomposition of ammonia. It is found that when ammonia is present in the fuel, the NOx emissions although high can be limited if the primary flame zone is operated fuel rich. Increasing pressure has shown to have a strong and favourable effect on NOx formation. When ammonia is fully decomposed to 75% H2 and 25% N2, the opposite behaviour is observed. In conclusion, either low rate or full decomposition are found to be the better options.
One Dimensional Modelling for Pulsed Flow Twin-Entry Turbine
Authors: Yang Bijie , Martinez-Botas Ricardo , Xue Yingxian , Yang Mingyang
Published: September 2021

One-dimensional (1D) modelling is critical for turbomachinery unsteady performance prediction and system response assessment of internal combustion engines. This paper uses a novel 1D modelling (TURBODYNA) and proposes two additional features for the application to a twin-entry turbocharger turbine. Compared to single-entry turbines, twin-entry turbines enhance turbocharger transient response and reduce engine exhaust valve overlap periods. However, out-of-phase high frequency pulsating pressure waves lead to an unsteady mixing process from the two flows and pose great challenges to traditional 1D modelling. The present work resolves the mixing problem by directly solving mass, momentum and energy conservation equations during the mixing process instead of applying constant pressure assumption at the limb-rotor joint.

Comparisons of TURBODYNA and an experimentally validated CFD suggest that TURBODYNA can not only provide a very good agreement on turbine performance, but also accurately capture unsteady features due to flow field inertial and pressure wave propagation. Levels of accuracy achieved by TURBODYNA have proved superior to traditional 1D modelling on turbine performance and the generality of the current 1D modelling has been explored by extending the application to another turbine featuring distinct characteristics.
Predicting the Amplitude of Thermoacoustic Instability Using Universal Scaling Behaviour
Authors: Pavithran Induja , Unni Vishnu R. , Saha Abhishek , Varghese Alan J. , Sujith R. I. , Marwan Norbert , Kurths Jürgen
Published: September 2021

The complex interaction between the turbulent flow, combustion and the acoustic field in gas turbine engines often results in thermoacoustic instability that produces ruinously high-amplitude pressure oscillations. These self-sustained periodic oscillations may result in a sudden failure of engine components and associated electronics, and increased thermal and vibra-tional loads. Estimating the amplitude of the limit cycle oscillations (LCO) that are expected during thermoacoustic instability helps in devising strategies to mitigate and to limit the possible damages due to thermoacoustic instability. We propose two methodologies to estimate the amplitude using only the pressure measurements acquired during stable operation. First, we use the universal scaling relation of the amplitude of the dominant mode of oscillations with the Hurst exponent to predict the amplitude of the LCO. We also present a methodology to estimate the amplitudes of different modes of oscillations separately using ‘spectral measures’ which quantify the sharpening of peaks in the amplitude spectrum. The scaling relation enables us to predict the peak amplitude at thermoacoustic instability, given the data during the safe operating condition. The accuracy of prediction is tested for both methods, using the data acquired from a laboratory-scale turbulent combustor. The estimates are in good agreement with the actual amplitudes.
Cooling Performance of Additively Manufactured Pin Fins in Stacked Microchannels for the Inside-Out Ceramic Turbine Shroud-Cooling Ring
Authors: Dubois P. K. , Landry-Blais A. , Gazzah R. , Sivić S. , Brailovski V. , Picard M.
Published: September 2021

The Inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, has an air-cooled ring which keeps its composite rotating structural shroud within operating temperature. The cooling ring must achieve a significant radial temperature gradient with a minimal amount of cooling. The cooling ring is made through additive manufacturing, which opens the design space to tailored cooling geometries. Additively manufactured pin fin heat transfer enhancers are explored in this work to assess whether they hold any significant performance benefit over current rectangular cross-section open channels. Experimental friction factors and Nusselt numbers were determined for small, densely-packed pin fins over an asymmetrical thermal load.

Results indicate that pressure loss is similar to what can be expected for additively manufactured pin fins, whereas heat transfer is lower due to the extremely tight streamwise pin spacing, in both in-line and staggered pin configurations. A design study presented in this paper suggests that pin fins are beneficial to an ICT for reducing cooling mass flow rate up to 40%, against an increase in cooling ring mass of roughly 50%.
On-Design Component-Level Multiple-Objective Optimization of a Small-Scale Cavity-Stabilized Combustor
Authors: Briones Alejandro M. , Erdmann Timothy J. , Rankin Brent A.
Published: September 2021

This work presents an on-design component-level multiple-objective optimization of a small-scaled uncooled cavity-stabilized combustor. Optimization is performed at the maximum power condition of the engine thermodynamic cycle. The CFD simulations are managed by a supervised machine learning algorithm to divide a continuous and deterministic design space into non-dominated Pareto frontier and dominated design points. Steady, compressible three-dimensional simulations are performed using a multi-phase Realizable k-ε RANS and non-adiabatic FPV combustion model. Conjugate heat transfer through the combustor liner is also considered. There are fifteen geometrical input parameters and four objective functions viz., maximization of combustion efficiency, and minimization of total pressure losses, pattern factor, and critical liner area factor. The baseline combustor design is based on engineering guidelines developed over the past two decades. The small-scale baseline design performs remarkably well. Direct optimization calculations are performed on this baseline design. In terms of Pareto optimality, the baseline design remains in the Pareto frontier throughout the optimization. However, the optimization calculations show improvement from an initial design point population to later iteration design points. The optimization calculations report other non-dominated designs in the Pareto frontier. The Euclidean distance from design points to the utopic point is used to select a “best” and “worst” design point for future fabrication and experimentation. The methodology to perform CFD optimization calculations of a small-scale uncooled combustor is expected to be useful for guiding the design and development of future gas turbine combustors.
Details of Shrouded Stator Hub Cavity Flow in a Multi-Stage Axial Compressor Part 1: Interactions With the Primary Flow
Authors: Kamdar Nitya , Lou Fangyuan , Key Nicole L.
Published: September 2021

The flow in shrouded stator cavities can be quite complex with axial, radial, and circumferential variations. As the leakage flow recirculates and is re-injected into the main flow path upstream of the stator, it deteriorates the near-hub flow field and, thus, degrades the overall aerodynamic performance of the compressor. In addition, the windage heating in the cavity can raise thermal-mechanical concerns. Fully understanding the details of the shrouded-hub cavity flow in a multi-stage environment can enable better hub cavity designs. Since the majority of the open literature presents limited details about the structure of compressor cavity flows in the stator wells and how the cavity wells affect the leakage flow, there is a lack of wholistic knowledge of how these flow parameters are interdependent. To shed light on this topic, a coupled CFD model with inclusion of the stator cavity wells for the Purdue 3-Stage (P3S) Axial Compressor Research Facility using the PAX100 configuration was developed and validated against experimental data. Such a model not only quantifies the impact of cavity leakage flow on compressor performance, but it also provides the capability to investigate the flow structure details including the path of the fluid into and out of the cavity. With the model in place, in this part 1 paper, the influence of the hub leakage flow on compressor performance and its interactions with the primary flow were investigated by varying the clearance ratio of a single stator. The understanding of the primary-hub-leakage flow interactions can offer insights leading to better designs of hub cavities.