bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of the Influence of Steam Ingestion on Compressor Stability Using a Corrected Correlation Method
Authors: Xu Haoyang , Hu Jun , Tu Baofeng
Published: January 2021

In order to simulate the stall boundary of a compressor more accurately under steam ingestion condition, a two-dimensional stability analysis model is developed. The model simulates compressor flow by solving compressible, two-dimensional, unsteady Euler equations with appropriate source terms. Normally, viscosity is considered for compressor flow when compressor characteristics, expressed by the Navier-Stokes equations or experiments, are used to calculate the source terms, and engineering applications pay more attention to compressor characteristics rather than detailed flow field. Therefore, the control equations are assumed to be non-viscous in this work. A corrected correlation method that does not need numerous computations under different proportions of steam is proposed at present. The method reflects the effects of gas properties on the compressor characteristic lines — a quality absent in traditional correlation method. It is most significant for the paper to adopt the proposed corrected correlation to reduce the number of independent parameters that describe compressor characteristics under different proportions of steam compared with the traditional correlation. Then the source terms associate with compressor inlet parameters by adopting the corrected correlation method to establish a modified model. The model is used to calculate the stall boundary under steam ingestion, and the results are compared with clean condition to investigate the effects of steam properties on stall boundary. As more steam is ingested, the corrected similar flow increases at the stall point while the total pressure ratio decreases when total temperature distortion remains constant. If you want to describe compressor characteristics under ingesting other gases, just modify these parameters related to gas properties in the corrected correlation.
Protection and Identification of Thermoacoustic Azimuthal Modes
Authors: Ghirardo G. , Gant F. , Boudy F. , Bothien M. R.
Published: January 2021

This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular the amplitude, orientation, and nature of the acoustic field of azimuthal order n is characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient α and for the turbulent combustion noise, modelled by means of the background noise coefficient σ. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with α and σ, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier component affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a non-homogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain β and a nonlinear saturation constant κ. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters {α, β, κ, σ} is then carried out on engine timeseries data. The optimal four parameters {α, σ, β, κ} are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.
Aerodynamic Investigation of Guide Vane Configurations Downstream a Rotating Detonation Combustor
Authors: Asli Majid , Stathopoulos Panagiotis , Paschereit Christian Oliver
Published: January 2021

Pressure Gain Combustion (PGC) is considered a possible solution to increase gas turbine cycle efficiency, due to the lower entropy generation in the combustion process. However, the highly unsteady flow produced by PGC makes it more difficult to extract work from its exhaust gas. Any outlet restriction downstream of PGC, such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the operation of conventional turbines. Therefore, evaluating early turbine design parameters for such applications is of great interest. Additionally, experimental measurements and data acquisition present researchers with challenges that have to do mostly with the high temperature exhaust of PGC and the high frequency of its operation. Numerical simulations can provide important insights into PGC exhaust flow and its interaction with turbine blades. In this paper, a Rotating Detonation Combustor (RDC) and a row of nozzle guide vanes have been modeled based on the data from literature and an available experimental setup at TU Berlin. Five guide vane configurations with different geometrical parameters have been modeled. URANS simulations were done for all guide vane arrangements to investigate the effect of solidity and blade type representing different outlet restrictions on the RDC exhaust flow. Total pressure loss and velocity fluctuation were computed upstream and downstream of the vanes. The results analzed the connection between total pressure loss and the vanes solidity and thickness to chord ratio. It is observed that more than 57% of the upstream velocity angle fluctuation amplitude was damped by the vanes. Furthermore, the area reduction was found to be the significant driving factor for damping the velocity angle fluctuations, whether in the form of solidity or thickness on chord ratio increment. A further study of the flow field details revealed that the vane passages act as convergent divergent nozzles in the unsteady flow field and no compression wave exists upstream. This RDC exhaust flow investigation is an important primary step from a turbomachinery standpoint, which provided details of blade behavior in such an unsteady flow field.
Bio-Inspired High Pressure Turbine Optimization Strategy for Hybrid-Electric Engines Operating at Off-Design
Authors: Juangphanich Paht , Paniagua Guillermo , Shyam Vikram
Published: January 2021

Incident tolerant turbine design is a major challenge for any turbomachinery designer. High Pressure Turbines experience large aerodynamic losses when operating at reduced massflow and lower RPM. Turbine performance is adversely impacted at positive incidence angles due to shifting of the stagnation point towards the pressure side. This can cause a separation bubble in the aft suction side region. In marine life, a diverse range of animals have developed wavy surfaces along their fins and bodies to prevent stall or flow separation at engine-relevant Reynolds numbers, but for incompressible fluids.

This paper describes a novel parameterization strategy for optimizing wavy-shaped airfoils to offer superior performance at off-design operation, in the present case, at positive incidence. The methodology can be applied to all types of aircraft engines: one, two, or three spool engine configurations. The parameterized geometries are compatible with existing gas turbine manufacturing processes including casting and additive manufacturing [1,2]. The objective of the optimization was to discover the appropriate waveform combinations at the airfoil leading edge, trailing edge, and suction side characterized by their amplitude, phase, and frequency, such that the airfoils offer the lowest possible pressure losses at 15 degrees positive incidence. The optimization was performed on a high pressure turbine passage, optimized for best efficiency at nominal conditions, while maintaining the same exit flow angle and massflow. The Reynolds number is 850,000. Based on 286 designs produced, the results of the optimization show a clear benefit at positive incidence, at the expense of a slightly lower performance at nominal conditions. A final comparison of the optimized rotor with stage is included in the analysis.
Numerical Modeling and Design Challenges of Boundary Layer Ingesting Fans
Authors: Sieradzki Adam , Kwiatkowski Tomasz , Turner Mark , Łukasik Borys
Published: January 2021

Studies show that Boundary Layer Ingesting (BLI) propulsion systems can provide significant fuel burn reduction relative to pylon-mounted turbofan engines. However, together with great potential, this type of propulsion can lead to serious difficulties and engineering challenges. A low-speed fan has been designed for a uniform flow at the inlet using an open source design code with optimization. Numerical analyses of the fan with a uniform flow at the inlet, and one exposed to the distorted non-axisymmetric flow were performed. These required the use of full-annulus unsteady time-marching CFD model. The model was validated with experimental data obtained in a test rig which was designed and built specially for that research.

The first crucial negative effect of the distorted inlet velocity profile is a variable incidence angle of the rotor. Both the CFD calculations and the experiment show the axial velocity non-uniformity and induced non-uniform swirl in front of the rotor, due to boundary layer ingestion and flow redistribution. As a result, significant changes in the angle of attack of the blades and corresponding unsteady rotor loads are observed. The simulations and measurements were performed for different operating conditions to obtain performance curves and assess the BLI influence at the design point and beyond. This demonstrated the second problem arising from the operation of the fan with the distorted flow at the inlet, which is a reduction of the stall margin (48% reduction from experimental results). The whole stage was previously optimized for axisymmetric flow in order to simultaneously ensure a required value of stall margin and the highest possible efficiency at the design point. The experimental efficiency of the rig at the design point with distorted inlet was 2.05% lower than the undistorted inlet. The CFD model show a 1.25% reduction. Similar reductions are shown for other operating points.
Aero Engine Concepts Beyond 2030: Part 3 — Experimental Demonstration of Technological Feasibility
Authors: Schmitz Oliver , Kaiser Sascha , Klingels Hermann , Kufner Petra , Obermüller Martin , Henke Martin , Zanger Jan , Grimm Felix , Schuldt Simon , Marcellan Anna , Cirigliano Daniele , Kutne Peter , Heron-Himmel Alex , Schneider Stephan , Richter Judith , Weigand Bernhard , Göhler-Stroh Anne , Seitz Arne , Hornung Mirko
Published: January 2021

Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. The first part focuses on the novel steam injecting and recovering aero engine concept. In the second part, the free-piston composite cycle engine concept is presented.

Complementary to the two technical publications, this third part describes the cooperative project, which was initiated by an interdisciplinary consortium, aiming at the demonstration and the proof of concept of both aforementioned aero engine concepts.

At the beginning of the project, simulations on propulsion, aircraft system, and test bench level will be conducted. On this basis, preliminary tests and fundamental experiments are planned in order to establish a solid basis for the demonstration. Finally, a system demonstration will be carried out at the laboratory level. Thus, the project allows for a final judgement on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.
Mistuning Effects on the Nonlinear Friction Saturation of Flutter Vibration Amplitude
Authors: Martel Carlos , Rodríguez Salvador
Published: January 2021

The blade vibration level of an aerodynamically unstable rotor is a quantity of crucial importance to correctly estimate the blade fatigue life. This amplitude is the result of the balance between the energy pumped into the blades by the gas flow, and the nonlinear dissipation at the blade-disk contact interfaces. In a tuned configuration, the blade displacements can be described as a travelling wave consisting of one fundamental nodal diameter and frequency and its higher harmonics, and the problem can be reduced to the computation of a time periodic solution in just one sector. This simplification is no longer valid for a mistuned bladed disk. The resulting nonlinear vibration of the mistuned system is a combination of several travelling waves with different number of nodal diameters, coupled through mistuning. In this case, the complete bladed disk has to be considered, which requires an extremely high computational cost, and, for this reason, reduced order models (ROM) are required to analyze this situation. In this work, we use a 3 DOF/sector mass-spring system to describe the nonlinear friction saturation of the flutter vibration amplitude of a realistic mistuned bladed disk. The convergence of the solution of the mass-spring system is still quite slow because of the presence of many unstable modes with very similar growth rates. In order to speed-up the simulations a simpler asymptotic ROM is derived from the mass-spring model, which allows for much faster integration times. The simulations of the asymptotic ROM are compared with the measurements obtained in the European project FUTURE, where an aerodynamically unstable LPT rotor was tested with different intentional mistuning patterns.
Deposition Pattern Analysis on a Fouled Multistage Test Compressor
Authors: Suman Alessio , Vulpio Alessandro , Casari Nicola , Pinelli Michele , Kurz Rainer , Brun Klaus
Published: January 2021

Compressor fouling is one of the main causes of gas turbine performance degradation. Microsized particles adhere to the blade surfaces increasing the surface roughness and modifying the airfoil shape. In the present work, the contamination of the Allison 250 C18 multistage compressor engine with four sorts of micrometric dust has been provided. The tests were performed changing the relative humidity at the compressor inlet and the unit rotational speed.

After each test, a photographic inspection of the internal fouled parts has been realized and the digital pictures have been analyzed employing an image processing package. The deposits build-up of stator vanes and rotor blades have been post-processed and the most affected regions of each compressor stage have been highlighted. Besides, a numerical simulation of the machine has been performed. The numerical flow field has been used to highlight the blade regions which show the most favorable conditions for particle deposition. A theoretical model has been applied to the flow field to simulate the particle deposition. The combination of the deposition model with the results of the CFD simulations gives the chance to better understand the experimentally-founded deposition patterns. Those results have been finally compared to the pictures of the patterns. The possibility to detect and measure the deposition patterns on a rotating test rig and the comparison with models and experiments gave the possibility to assess in detail the particle deposition phenomenon on a multistage axial compressor flow path.
Acquisition and Processing Considerations for Infrared Images of Rotating Turbine Blades
Authors: Knisely Brian F. , Berdanier Reid A. , Thole Karen A. , Haldeman Charles W. , Markham James R. , Cosgrove Joseph E. , Carlson Andrew E. , Scire James J.
Published: January 2021

As designers aim to increase efficiency in gas turbines for aircraft propulsion and power generation, spatially-resolved experimental measurements are needed to validate computational models and compare improvement gains of new cooling designs. Infrared (IR) thermography is one such method for obtaining spatially-resolved temperature measurements. As technological advances in thermal detectors enable faster integration times, surface temperature measurements of rotating turbine blades become possible to capture including the smallest features. This paper outlines opportunities enabled by the latest IR detector technologies for capturing spatially-resolved rotating blade temperatures, while also addressing some of the challenges of implementing IR for turbine rigs such as the one in the Steady Thermal Aero Research Turbine (START) Laboratory. This paper documents critical steps in achieving accurate measurements including calibration, integration times, spatial noise, and motion blur. From these results, recommendations are provided for achieving accurate IR measurements collected in a rotating turbine facility to study film cooling.
Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames
Authors: Torres Monclard Kevin , Gicquel Olivier , Vicquelin Ronan
Published: January 2021

The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results.

A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates.

The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.
Numerical Stability Analysis of Oil Collector Case Self-Excited Vibrations
Authors: Shuvaev Nikolay V. , Voronova Natalia O. , Vinogradov Kirill A.
Published: January 2021

The investigation subject is an Oil Collector Case which is a thin axisymmetric stator part with console binding to the turbine rear frame. It had been suffering from high level vibrations and needed fixing measures to apply. Self-excited vibrations supposed as the main reason for defects to occur.

The problem was examined in the engine and test rig conditions. The energetic method which is usually applied to blade flutter problems was used for aeroelastic stability analysis.

Radial surface displacements were set according to the harmonic oscillation function that corresponds to the oil collector’s first bending eigenmode with two nodal diameters. 3D aerodynamic model represents a 180° sector, thus ensures that surface displacements and gas parameters on periodic surfaces are equal.

A set of simulations was carried out and calculated; the aerodynamic damping coefficient values showed aeroelastic instability predisposition in both the engine and test rig conditions for most test cases. Influence of such model parameters as seal radial clearance, pressure ratio, inlet air temperature, wave propagation direction and rotor speed was investigated.

A detailed analysis showed that for instability case positive aerodynamic work region lies inside the oil collector cavern downstream labyrinth seal where pressure wave and surface displacement speed wave are close to synchrony. Probable excitation mechanisms were described and discussed. It was demonstrated that aeroelastic instability of the same type as it was in the engine conditions can be reproduced in the test rig conditions.
An Experimental Study on the Leakage Flow on the Film Cooling Effectiveness of a Gas Turbine Shroud
Authors: Kim Gi Mun , Lee Soo In , Jeong Jin Young , Kwak Jae Su , Kim Seokbeom , Choi Jung Uk
Published: January 2021

In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and results in locally non-uniform and high heat transfer on the surfaces. In this study, the effects of leakage flow through the slot between gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment were experimentally investigated. The experiment was carried out in a linear cascade with five blades. Instead of vane, a row of rods at the location of the vane trailing edge was installed to consider the wake effect. The leakage flow was introduced through the slot between vane and blade rows and additional coolant air was injected from the cooling holes installed at the vane outer zone. The effects of the slot geometry, hole size, and blowing ratio on the film cooling effectiveness were experimentally investigated by using a pressure sensitive paint technique. CO2 gas and the mixture of SF6 and N2 (25%+75%) were used as leakage flow in order to simulate leakage flow to mainstream density ratios of 1.5 and 2.0, respectively. Results showed that the area averaged film cooling effectiveness was more affected by the slot width than the cooling hole size at the same blowing ratio, and the lower density ratio cases showed higher film cooling effectiveness than that of higher density ratio case at the same cooling configuration.
Improving Characteristics of a Cooled Transonic Vane of Low Pressure Turbine Under Nonuniform Inlet Conditions
Authors: Granovskiy A. V. , Afanasiev I. V. , Kostege V. K. , Marchukov E. Yu.
Published: January 2021

Vanes of low-pressure turbines (LPT) run under inlet conditions generated by a preceding high-pressure turbine (HPT). HP stages are generally cooled and transonic as well due to the large pressure ratio necessary to reduce the gas temperature upstream of the downstream stages. Therefore radial distributions of inlet flow angle, total pressure and total temperature at the boundary upstream of the LPT are highly non–uniform. Such non-uniform inlet conditions can result in enhanced level of the total losses including the secondary losses. Moreover, vanes of LPT have meridional openings along inner and outer boundaries of the flow path, which causes intensification of the secondary flows leading to an increase in secondary losses. In this case the special meridional contouring of the vanes’ outer and inner surfaces allows a decrease in the flare angle namely meridional opening in the rear part of the vane. In this work, in order to compensate the negative effect of non-uniform inlet conditions, meridional opening and low aspect ratio, 3D profiling of the vane row is used as a way of reducing secondary losses. Some variants of LPT vanes with various complex 3D shapes are investigated. In particular, vane variants with a “reversed bow”, a “bowed” and a “lean” in the circumferential direction have been examined. Significant modification of the vane row is limited by cooling system design, which has to incorporate a deflector in the inner hollow of the vane to improve cooling effectiveness. A compromise between aerodynamic quality and cooling limitations has been achieved.
Benefit and Critical Factors for the Performance of the Boundary Layer Ingesting Propulsion
Authors: Lee B. J. , Liou May-Fun , Celestina Mark , To Waiming
Published: January 2021

The benefit of the boundary layer ingestion (BLI) is described in the perspective of the propulsion and engine development. A power saving map of the BLI engines is derived based on the correlation of the wake velocity ratio of the ingested boundary layer profile and the propulsive efficiency. The ratio of the mass flow rate between BLI and non-BLI propulsors is introduced to quantify the power saving of the BLI engine relative to a clean inlet flow engine which generates same amount of thrust. The wake recovery factor from the jet flow out of the BLI engine is employed to find an adequate sizing of the BLI engine for the given design requirement. The effects of the fan pressure ratio on the power saving are also investigated to explore the feasible range of the BLI engine design. The derived correlation is validated with CFD analyses. A numerical experiment is carried out by varying the wake velocity ratio through different BLI engines sized with respect to an influencing body. Consequently, the propulsor efficiency is quantified and presented by the saving in the actual shaft power. The efficiency penalty, pressure ratio of the BLI fan stage are correlated with the power saving and the correlation is validated through BLI2DTF and R4 fan stage CFD analyses based on rig test data.
Experimental Study of Vaneless Diffuser Rotating Stall Development and Cell Merging Phenomena
Authors: Grapow Filip , Olasek Krzysztof , Liśkiewicz Grzegorz , Magiera Radomir , Kryłłowicz Władysław
Published: January 2021

This paper describes the vaneless diffuser rotating stall (VDRS) development and cell merging phenomena. A centrifugal compressor’s lifespan may be limited by flow instabilities occurring in off-design operation. One such instability is the VDRS, which generates oscillating, asymmetrical flow fields in the diffuser and, thus, undesired forces acting on the rotor. Understanding and prevention of VDRS behavior is crucial for achieving safe and undisturbed compressor operation.

Experimental measurements of centrifugal compressors operating under the influence of VDRS have been presented. Two different approaches were used for the identification of VDRS: pressure measurements and 2D PIV. Frequency analysis based on spectral maps and cell development processes were investigated.

The presented results showed that mass flow rate has an impact on the rotating frequency of both the entire structure and single cells. Additionally, it affects radial cell size, which grows with compressor throttling and ultimately reaches the length of the diffuser. During the experiments, the cell merging phenomenon was observed which has not been widely described in the literature.

The results presented in this paper allow better understanding of vaneless diffuser rotating stall behavior. The phenomenon of the change of cell size and frequency could be very important for machine fatigue. Cell merging could also have an impact on the machine’s vibrations and flow stability. Since it is believed that VDRS is one of the factors inducing surge, its understanding and prevention may have positive influence on surge margins.
Fatigue of an Advanced SiC/SiC Ceramic Matrix Composite With an Environmental Barrier Coating at Elevated Temperature in Air and in Steam
Authors: Williams T. M. , Ruggles-Wrenn M. B.
Published: January 2021

Uniaxial tension-tension fatigue performance of a SiC/SiC composite with an ytterbium-disilicate environmental barrier coating (EBC) was investigated at 1200°C in laboratory air and in steam. The composite is reinforced with Hi-Nicalon™ SiC fibers and has a melt-infiltrated matrix processed by chemical vapor infiltration of SiC followed by infiltration with SiC particulate slurry and molten Si. The EBC consists of a Si bond coat and an ytterbium disilicate (Yb2Si2O7) top coat applied via air plasma spraying (APS). Basic tensile properties of the EBC/SiC/SiC composite were evaluated at 1200°C. Tension-tension fatigue was examined for maximum stresses of 110–140 MPa in air and in steam. To assess the efficacy of the EBC, experimental results obtained for the coated composite are compared to those obtained for a control composite without the EBC. Surface grit-blasting inherent in the EBC application process degrades tensile strength of the composite. However, the EBC effectively protects the composite from oxidation embrittlement during cyclic loading in air or in steam. Fatigue runout defined as survival of 200,000 cycles (55.6 h at a frequency of 1.0 Hz) was achieved at 110 MPa in air and in steam. The retained properties of pre-fatigued specimens were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. Damage and failure of the EBC/SiC/SiC composite are attributed to growth of cracks originating from numerous processing defects (voids) present in the composite interior.
Correlation Between Engine and Aircraft Loadings for Several Mission Types
Authors: Templalexis Ioannis , Lionis Ioannis , Kitinos Sotiris
Published: January 2021

Fighter aircraft constitutes a well-defined class of aircraft. Their extensive use on a daily basis by operators stands as a strong motive behind studies that concern their rate of “exhaustion ”. For an aircraft operator either civil or military, it is very important at any point in time to have a clear view of the engines’ and the aircrafts’ operating condition. This is valuable information in order to foresee undesired incidences and in order to schedule missions in accordance to the actual and anticipated maintenance needs. For the latter, the operator would also need to know the rate of the engine and the aircraft life consumption per mission.

The current study concerns the F-16 Block 52M aircraft, powered by the Pratt and Whitney F100-PW-229 engine. Aircraft is continuously subjected to crack growth mechanisms while flying. On the other hand, engines also go through Low Cycle Fatigue (LCF) cycles and creep prominent conditions while being in operation. The engine and the aircraft structural condition are continuously monitored, based on real time data recordings. To the extent of the authors’ knowledge, that is a common practice for most F-16 users. However, what was found to be missing from the international literature was a study to quantify any potential correlation between the aircraft loading and the engine loading for all typical mission types an aircraft of this type undertakes. For users that have already installed an aircraft loading monitoring system like “Aircraft Structural Integrity Program” (ASIP) it would be very useful to set a “rule of thumb” aside regarding the degree of correlation between aircraft and engine loading.

Engine life consumption rate was estimated based on the creep and LCF failure mechanisms applied on the most critical engine section, the turbine. Engine recordings were picked from an arbitrary sample of 200 flights of a certain aircraft, wherein most typical mission types could be found. Turbine and subsequently blade temperature as well as blade stress were calculated using a very narrow time step. These data along with blade material data were fed in the Larson Miller model, to set an algorithm for estimating life consumption due to creep. Engine Total Accumulated Cycles (TACs) which account for LCF loading, are directly measured by the engine recorder, based on an embedded algorithm.

Aircraft loading is calculated based on the accelerations the aircraft structures encounter during flight. These are also recorded under a very narrow time step.

Last step was the correlation of the engine life consumption against the aircrafts’ loading for typical mission types. Scatter diagrams and statistical measures were used, in order to define the degree of correlation between them.
The Influence of Turbulence and Reynolds Number on Multiple Slot Film Cooling Over the Suction Surface
Authors: Soma L. W. , Ames F. E. , Acharya S.
Published: January 2021

Developing robust film cooling protection on the suction surface of a vane is critical to managing the high heat loads which exist there. Suction surface film cooling often produces high levels of film cooling but can be influenced by secondary flows and some dissipation due to free-stream turbulence. Directly downstream from suction surface film cooling, heat loads are often significantly mitigated and internal cooling levels can be modest. One thermodynamically efficient way to cool the suction surface of a vane is with a counter cooling scheme. This combined internal/external cooling method moves cooling air in a direction opposite to the external flow through an internal convection array. The coolant is then discharged upstream where the high level of film cooling can offset the reduced cooling potential of the spent cooling air.

The present suction surface film cooling arrangement combines a slot film cooling discharge on the near suction surface from an incremental impingement cooling method with a second from a counter cooling section. A second counter cooling section is added further downstream on the suction surface. The internal cooling plenums replicate the geometry of the cooling methods to ensure the fluid dynamics of the flow discharging from the slots are representative of the actual internal cooling geometry. These film cooling flows have been tested at blowing ratios of 0.5 and 1.0 for the initial slot and blowing ratios of 0.15 and 0.3 for the two downstream slots. The measurements have been taken at exit chord Reynolds numbers of 500,000, 1,000,000, and 2,000,000 with inlet turbulence levels ranging from 0.7% to 12.6%. Film cooling effectiveness measurements were acquired using both thermocouples and infrared thermography. The infrared thermography shows the influence of secondary flows on film cooling coverage near the suction surface endwall junction. The film cooling effectiveness results at varied blowing ratios, turbulence levels and Reynolds numbers document the impact of these major variables on suction surface slot film cooling. The results provide a consistent picture of the slot film cooling for the present three slot arrangement on the suction surface and they support the development of an advanced double wall cooling method.
Recuperator Performance Assessment in Humidified Micro Gas Turbine Applications Using Experimental Data Extended With Preliminary Support Vector Regression Model Analysis
Authors: De Paepe Ward , Pappa Alessio , Coppitters Diederik , Montero Carrerro Marina , Tsirikoglou Panagiotis , Contino Francesco
Published: January 2021

Cycle humidification applied to micro Gas Turbines (mGTs) offers a solution to overcome their limited operational flexibility in terms of variable electrical and thermal power production when used in a Combined Heat and Power (CHP) application. Although the positive impact of this cycle humidification on the performance has already been proven numerically and experimentally, very detailed modeling of the system performance remains challenging, especially the determination of the recuperator effectiveness, which has the highest impact on the final cycle performance. Indeed, the recuperator performance depends strongly on the mass flow rate of the air stream and its humidification level, two parameters that are difficult to measure accurately. Accurate modeling of the recuperator performance under both dry and humidified conditions is thus essential for correct assessment of the potential of humidified mGT cycles in Decentralized Energy Systems (DES).

In this paper, we present a detailed analysis of the recuperator performance under humidified conditions using averaged experimental data, extended with the application of a Support Vector Regression (SVR) on a time series to improve noise-modeling of the output signal, and thus enhance the accuracy of the monitoring process. In a first step, the missing experimental parameters, air mass flow rate and humidity level, were obtained indirectly, using rotational speed, fuel flow rate, exhaust gas composition and pressure level measurements in combination with the compressor map. Despite the low accuracy, some general trends regarding the recuperator performance could be observed based on these experimental data, indicating that the recuperator, despite having an increased total exchanged heat flux, is actually too small to exploit the full potential of the humidification. In a second step, by means of the SVR model, a first attempt was made to improve the accuracy and reduce the scatter on the recuperator performance determination. The predicted results with the SVR indicated indeed a reduced scatter on the determinations of the air mass flow rate and the amount of introduced water, opening a pathway towards online recuperator performance prediction.
Matching of Synchronous Motors and Centrifugal Compressors: Oil and Gas Industry Practice
Authors: Taher Matt , Ristanovic Dragan , Meher-Homji Cyrus , Pillai Pradeep
Published: January 2021

Synchronous motor driven centrifugal compressors are widely used in the oil and gas industry. In evaluating the optimum selection of synchronous motor drivers for centrifugal compressors, it is important to understand the factors influencing a proper match for a centrifugal compressor and its synchronous motor driver. The buyer should specify process requirements and define possible operating scenarios for the entire life of the motor driven centrifugal compressor train. The compressor designer will use the buyer-specified process conditions to model the aerothermodynamic behavior of the compressor and characterize its performance. Performance, controllability, starting capabilities as well as the optimum power margin required for a future-oriented design must also be considered. This paper reviews the criteria for evaluating the optimal combination of a centrifugal compressor and its synchronous motor driver as an integral package. It also addresses API standard requirements on synchronous motor driven centrifugal compressors. Design considerations for optimal selection and proper sizing of compressor drivers include large starting torque requirements to enable compressor start from settle-out conditions and to prevent flaring are addressed. Start-up capabilities of the motor driver can significantly impact the reliability and operability of the compressor train. API 617 on centrifugal compressors refers to API 546 for synchronous motor drivers. In this paper, requirements of API 617 and 546 are reviewed and several important design and sizing requirements are presented. In the effort to optimize plant design, and maintain the performance requirements, the paper discusses optimization options, such as direct on-line starting method to explore the motor rating limits, and the use of synchronous motors for power factor correction to eliminate or reduce the need for reactive power compensation by capacitor banks. This paper presents a novel approach to show constant reactive power lines on traditional V curves. It also complements capability curves of synchronous motors with lines of constant efficiency. The paper discusses variable frequency drive options currently used for synchronous motors in compressor applications. The paper addresses the available variable frequency drive types, their impact on the electrical grid, and motor design considerations with a view to summarizing factors important to the selection of variable frequency drives.
Dynamic Model Based Identification of Cavitation Compliance and Mass Flow Gain Factor in Rocket Engine Turbopump Inducers
Authors: Wan Y. , Manfredi M. , Pasini A. , Spakovszky Z.
Published: January 2021

Cavitation dynamics continue to pose a significant risk in the development and operation of launch vehicle (LV) propulsion systems. In addition to generating unsteady loads that can directly damage turbopump hardware, cavitation dynamics often couple with LV fluid feed systems, producing system wide POGO instability that can cause catastrophic failures. Despite its importance, the current understanding of cavitation dynamics, and especially pump transfer matrices, is limited. Given the relatively sparse amount of inducer transfer matrix data available, there is a critical need for more in-depth characterization of the cavitation dynamics in turbopump inducers to avoid POGO instability. This paper defines and validates a new reduced-order approach to infer key parameters such as cavitation compliance, K, and mass flow gain factor, M, from simple, single sensor unsteady pressure measurements during inducer inlet pressure ramps. The utility of this approach is demonstrated for a range of inducer geometries reported in the literature. The results are in agreement with experimental data and the paper provides a new capability supporting the assessment of launch vehicle POGO instability.
A Novel Controlled-Motion Test Rig to Evaluate Effect of Synchronous and Subsynchronous Lateral Vibration on Reliability and Performance of Mechanical Seals in Pumps
Authors: Norrbin Clay S. , Delgado Adolfo
Published: January 2021

Mechanical seals are commonly used in rotating machinery to contain liquid leakage past a rotating shaft. Pumps vibration often exhibit both synchronous and sub-synchronous whirling, which may lead to premature failure of mechanical seals. A test rig was developed to simulate a running pump environment for the mechanical seal. The controlled-motion test rig comprises a flexibly-mounted-rotor connected to a pair of electrohydraulic shakers. This configuration allows imposing whirl orbits to a flexibly-mounted-rotor (FMR) mechanical seal at any prescribed frequency independent of rotor speed. A 6-axis load cell provides direct measurements of the reaction forces at the mechanical seal stationary component. Five Eddy current sensors and capacity probes track the 5 DOFs of the mechanical seal dynamic face. The flow loop is a modified plan 54 with an external pump capable of delivering 32 lpm at 14 bar using VG 2 mineral oil, and an external heat exchanger to regulate oil temperature. Tests were performed on a 3-inch (76.2 mm) FMR seal. Input rotor whirl vibration was increased to 10 mils pk-pk (254 microns), while cooling flow (VG2 mineral oil) was set to 8 lpm and pressure was varied from 1.7–6.9 lpm. The measurements include steady state values of temperature, power loss, clearance and leakage; and dynamic measurements of seal face wobble, wobble-imposed torque, relative lateral movement and fluid film shear.
Partial Premixing Effects on the Reacting Jet of a High Pressure Axially Staged Combustor
Authors: Genova Tommy , Otero Michelle , Reyes Jonathan , Ahmed Kareem , Martin Scott
Published: January 2021

The effects of partial premixing on a reacting jet-in-crossflow is investigated in a five atmosphere axially staged combustor at stationary gas turbine relevant conditions. The facility consists of a dump style headend burner that provides a crossflow with a quasi-uniform velocity and temperature profile to the axial stage to isolate the effects of the jet-in-crossflow. The headend burner is run with methane and air at a lean equivalence ratio to match industry emissions standards. For the current work,, the total air to the headend and axial stage is kept constant, and fuel is split between the headend and axial stage to represent different gas turbine loading conditions. For the cases analyzed, the fuel split to the axial stage went up to 25%. The axial stage consists of an optically accessible test section with a coaxial injector that provides variability to how long the methane and air can mix before entering the facility. Three different premixed levels are studied: fully premixed, non-premixed, and partially premixed. The flow-field characteristics of the reacting jet-in-crossflow are analyzed using particle image velocimetry (PIV), and flame behavior is quantified by employing CH* chemiluminescence. NO measurements are made at the exit of the facility using a Horiba emissions analyzer. Two different flames are observed: flames that burn in the leeward recirculation region and flames that burn at the core of the jet.
The Influence of Wake Chopping on Wet-Steam Turbine Modelling
Authors: Vasilj Andrej , Schuster Sebastian , White Alexander
Published: January 2021

The formation of water droplets within condensing steam turbines is a complex process that occurs at supersaturated, non-equilibrium conditions and is influenced by the unsteady segmentation of blade wakes by successive blade rows. This is often referred to as ‘wake chopping’, and its effect on the condensation process is the subject of this paper. The practical significance is that thermodynamic ‘wetness losses’ (which constitute a major fraction of the overall loss) are strongly affected by droplet size. Likewise, droplet deposition and the various ensuing two-phase phenomena (such as film migration and coarse-water formation) also depend on the spectrum of droplet sizes in the primary fog.

The majority of wake-chopping models presented in the literature adopt a stochastic approach, whereby large numbers of fluid particles are tracked through (some representation of) the turbine flowfield, assigning a random number at each successive blade row to represent the particle’s pitchwise location, and hence its level of dissipation. This study contributes to the existing literature by adding: (a) a comprehensive study of the sensitivity to key model parameters (e.g., blade wake shape and wake decay rate); (b) an assessment of the impact of circumferential pressure variations; (c) a study of the implications for wetness losses and (d) a study of the implications for deposition rates.
Investigation on Influence Mechanism of Wall Coating on Infrared Radiation Signature of Serpentine Nozzle
Authors: Shi Jie , Zhou Li , Wang Zhanxue , Shi Jingwei
Published: January 2021

Stealth performance is one of the most important factors to evaluate the technical level of modern battleplane. Serpentine nozzle can block the direct radiation transmission path between the high-temperature components in exhaust system and the infrared detector, thus suppressing the infrared radiation signature. However, due to the reflection characteristics of nozzle wall, this method can also cause indirect transmission of infrared radiation through the wall reflection to form a local high radiation area. Motivated by previous researches on the application of serpentine nozzle wall coating in electromagnetic radiation suppression. Wall coating is applied to serpentine nozzle to suppress infrared radiation intensity in this paper. Aiming at the situation of turbofan engine using serpentine nozzle, the influence mechanism of coating position, area and emissivity of serpentine nozzle on infrared radiation signature is calculated and analyzed, and the scheme of wall coating which has the least coating area and can effectively suppress infrared radiation transmission is also studied. The results show that reducing wall coating emissivity will strengthen the indirect transmission of infrared radiation, then cause the increase of exhaust system infrared radiation intensity, while increasing wall coating emissivity will reduce wall coating reflectivity, and the local high radiation area caused by indirect radiation transmission can be effectively prevented. The research also found that the infrared radiation signature of exhaust system can be effected only when the emissivity adjustment of serpentine nozzle wall which can be detected directly by infrared detector. After adopting the optimized wall emissivity coating scheme, the infrared radiation intensity of serpentine nozzle for turbofan can be reduced by 51.3% on the original basis while the coating area only accounts for 25.1% of the nozzle area.