bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Study on Rotating Stall in Industrial Centrifugal Compressor
Authors: Miura Toshimasa , Yamashita Hideaki , Takeuchi Ryota , Sakai Naoto
Published: January 2021

Centrifugal compressors employed in the oil and gas industry are operated at high gas pressure conditions and are used in a wide operation range. Accurate prediction of the rotating stall and the destabilizing aerodynamic force is one of the key technologies for these compressors, because rotating stall can sometimes cause severe problems with subsynchronous shaft vibration and limit its operation range. Thus, the aim of this study is to establish a method of accurately predicting the inception of rotating stall and its effect on shaft vibration. To achieve this, numerical investigations are carried out by unsteady Reynolds-averaged Navier-Stokes (RANS) simulation with a full annulus model of the compressor stage. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a high-pressure compressor test rig that contains a shrouded impeller and a vaneless diffuser is built. To investigate the effect of the rotating stall on the shaft vibration, an experiment is carried out at relatively high gas pressure with the inlet pressure level exceeding 30 barA.

In the first part of the study, the accuracy of compressor performance prediction is studied by steady computational fluid dynamics (CFD) simulation. It is found that by taking the wall roughness effect into account, the predicted performance shows good agreement with the experimental result. Thus, a subsequent study of the rotating stall is also carried out by considering its effect.

In the second part of the study, the accuracy of predicting the rotating stall is studied. In the experiment, two types of rotating stall are measured. One is a multiple-cell stall induced in the vaneless diffuser, for which the speed of rotation is relatively low and the other is a one-cell stall induced in the impeller region. The properties of the multiple-cell stall agree with the previous experimental and numerical studies, and the rotating stall has the limited effect on shaft vibration. Conversely, the one-cell stall shows severe subsynchronous vibration. In this study, both types of stall prediction are examined by CFD simulation. It is found that the simulation can predict the inception of the rotating stall with relatively high accuracy as the predicted results show good agreement with the experimental results in terms of cell count, rotation speed, pressure fluctuation level and the effect on shaft vibration. Through this study, the effectiveness of unsteady CFD simulation is confirmed for these types of stall and vibration prediction.
Numerical Investigation of Effect of Blade Surface Slot on the Performance and Flow Field of a Low Speed Centrifugal Fan
Authors: Zhang HaoGuang , Dong FeiYang , Zhang XuDong , Chu WuLi
Published: January 2021

The main objective of this study is to understand the mechanisms of affecting the performance and flow field of a low speed centrifugal fan with blade surface slots. In the investigation, a spanwise slot, which is placed within the range of about 60% to 100% of the blade span, is applied to each blade surface of the impeller, and the partial blade pressure and suction surfaces for each blade are connected via the blade surface slot. The full-passage unsteady numerical results indicate that the performance of fan including the volute is improved among the overall mass flow rate by applying the blade surface slot, and the blade surface slots generate about an enhancement of 3.6% for the total pressure improvement, an improvement of 2.6% for the efficiency respectively at the design mass flow rate.

The flow field analyses show that the injecting flows discharging from the blade surface slots can encourage the low energy flows near the blade suction surface in some blade passages. Hence, the boundary layer separations of the blade suction surface are restrained by the injecting flows, and the flow condition in the passag is considerately improved. Moreover, the adverse effect caused by the low energy flows is very serious in the partial blade passages near the shroud, while the flows in the blade surface slots have few positive effect on the low energy flows. So, the improvement by the slots on the flow fields is very small near the shroud region. Because the boundary layer separations on the blade suction surface are absent in most of the blade passages at about 60% of the blade span, the flows emerging from the slots have passive effects on the passage mainstreams. Further, in the case of blade surface slots, there is an obvious vortex near the blade trailing edge at about 60% of the blade span, and the vortex is close to the blade suction surface at some instants. As a result, the wake flow losses in the passage become large with the application of the slots. Briefly, within the slotted span range, the improvement of the flow field in the blade passages becomes large and then gets small, as the blade span decreases. Furthermore, the flow condition in the volute is improved thanks to the amelioration of the flows in some blade passages, and the degree of the second flows in the volute is weakened with the application of blade surface slots. Consequently, the flow losses in the volute are reduced effectively.
Experimental and Numerical Study on Pressure Losses and Flow Fluctuations in a High-Pressure Valve Assembly of Steam Turbine Governing System
Authors: Slama Vaclav , Mrozek Lukas , Rudas Bartolomej , Simurda David , Hala Jindrich , Luxa Martin
Published: January 2021

Aerodynamic measurements and numerical simulations carried out on a model of a high-pressure valve assembly used for nozzle governing of a turbine with 135MW output are described in this paper. Aim of the study is to investigate effects of control valve’s strainers on pressure losses and unsteadiness in the flow field. It is an important task since undesirable flow fluctuations can lead to operational reliability issues. Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) where an aerodynamic tunnel is installed. Numerical simulations were carried out in the Doosan Skoda Power (DSP) Company using ANSYS software tools. The experimental model consists of one of two identical parts of the real valve assembly. It means it consists of an inlet pipeline, a stop valve, a valve chamber with two independent control valves, its diffusers and outlet pipelines. The numerical model consists of both assembly parts and includes also an A-wheel control stage in order to simulate the real turbine operating points. The different lifts of the main cone in each control valve for its useful combinations were investigated. Results were evaluated on the model with control valve’s strainers, which were historically used in order to stabilize the flow, and without them. The results of the experimental measurement were compared with the numerical results in the form of pressure losses prediction. From measured pressure fluctuations, it was found out where and for which conditions a danger of flow instabilities occurs. It can be concluded that there is a border, in terms of operating conditions, where the flow field starts to be unstable and this border is different dependent of the fact whether the control valve’s strainers are used or not. Therefore, the areas of safe and danger operational reliability can be predicted. The influence of the control valve’s strainers on the maximal amplitude of periodic fluctuations appears only for the cases when valves are highly overloaded. For normal operating conditions, there is no difference. As a result, the control valve’s strainers do not have to be used in standard applications of valve assemblies. Furthermore, a loss model for valve pressure loss estimation could be updated. Therefore, a pressure loss should be predicted with a sufficient accuracy for each new turbine bid with similar valve assemblies.
Three-Dimensional Fluid Topology Optimization and Validation of a Heat Exchanger With Turbulent Flow
Authors: Pietropaoli M. , Gaymann A. , Montomoli F.
Published: January 2021

The present work shows an innovative design framework for fluid Topology Optimization (TO) able to fully exploit the flexibility offered by Additive Manufacturing (AM) in the production of fluid-structure interaction systems. We present a geometry optimization method able to automatically design complex and efficient heat exchangers, adapted to maximizing fluid-structure heat transfer while minimizing turbulent flow pressure drop. The core of the method is the in-house Fluid Topology Optimization solver extended to include conjugate heat transfer problems. The TO method consists in emulating a sedimentation process inside an empty cavity in which a fluid dynamics problem is numerically solved. A design variable, in this case impermeability, is iteratively updated across the fluid dynamics domain. This mechanism leads to the formation of internal solid structures accordingly to a Lagrangian multi-objective optimization approach, adopted to include a multi-objective function. The solution of the optimization routine is the set of solidified structures, shaping the final optimized geometry. In order to match engineering applications, real conditions are implemented: an impermeability dependent thermal conductivity is included and a smoother operator is adopted to bound numerical thermal conductivity gradients across solid and fluid regions. The optimization is performed on a 3-dimensional straight duct: on the walls the temperature is constant and a coolant turbulent flow is simulated (Re 10000) inside the duct. The solver builds structures enhancing the heat transfer level between the walls of the domain and a coolant flow, by generating counter rotating vortices and complex fluid patterns. This is consistent to solution proposed in the open literature, such as v-shaped ribs, even if the geometry generated is more complex and efficient. The solution is validated with a high fidelity numerical simulation on StarCCM+, using a Detached Eddy Simulation (DES). Validation results shows higher heat transfer efficiency compared to the results present in the literature: the average Nusselt number computed on the domain walls is about 20% higher than the value obtained through experimental investigations on v-shape ribbed ducts. It is the first time that this method is applied and validated on real working conditions.
Deposition of Fuel Impurities Within Thermal Barrier Coatings in Gas Turbine Hot Gas Paths
Authors: Holländer Christian , Stamm Werner , Lüsebrink Oliver , Harders Harald , Singheiser Lorenz
Published: January 2021

For the reliable operation of modern gas turbines, Thermal Barrier Coatings (TBCs) need to withstand a wide range of ambient conditions resulting from impurities in inlet air or fuels. A novel deposition model has been developed that enables the prediction of deposition and transport of gaseous species originating from impurities in the gas turbine working media. The successful alignment of conditions in real engines with model results will allow to address the increasing demand for more fuel- and operational flexibility of current and future gas turbines.

When analyzing deposition of detrimental hot gas constituents, previous efforts largely focus on the investigation of solid and molten deposit interaction with TBCs. Recent literature and observations in gas turbines indicate that not only liquids can penetrate porous TBCs, but the deposition from gas phase inside of pores and cracks is also an aspect of TBC degradation.

To investigate this vapor deposition process, a diffusion model has been coupled with a thermodynamic equilibrium solver. The diffusion model calculates vapor transport of trace elements through pores and gaps in the TBC, where the thermodynamic equilibrium solver calculates local thermodynamic equilibria to predict whether deposition takes place.

The model can calculate deposition rates within TBCs by taking into account the chemical composition of impurities in the hot gas as well as pressure, temperature profile in the TBC, and the TBC’s pore structure. Utilizing the model, a wide range of different fuel chemistries can be analyzed to draw conclusions regarding possible effects on TBC lifetime.

In this work the model is applied to discuss deposition properties of calcium. In recent literature calcium has — in some cases — been reported to deposit inside of TBCs as pure anhydrite (CaSO4). An actual anhydrite finding in the TBC of a stationary gas turbine blade was reproduced applying the introduced model. The vapor deposition is shown to occur within and on top of the TBC, depending on a number of factors, such as: pressure, temperatures, calcium to silicon ratio and calcium to sulfur ratio.
Impact of Multi-Row Aerodynamic Interaction on the Forced Response Behaviour of an Embedded Compressor Rotor
Authors: Hegde Shreyas , Kielb Robert , Zori Laith , Campregher Rubens
Published: January 2021

This paper focuses on the impact of multi-row interaction on the forced response behavior of an embedded compressor rotor at higher order modes. The authors in previous papers have discussed about the multi-row influence at the torsional mode resonant crossing and this paper extends the study to higher order modes. The paper talks about both the steady and unsteady influence of having additional rows in the configuration. It makes use of the time transformation (TT) method available in CFX to reduce the number of passages required in each row. Since the number of vanes from both the stators and the inlet guide vanes (IGV) is the same, the excitations from upstream rows and the potential field influence of the downstream row all contribute to the forcing, which is quantified both in terms of modal force and individual blade response. This paper describes the multi-row influence on the chordwise bending modes at both the peak efficiency (PE) and the high loading (HL) operating condition. To ascertain this influence, a 3-row case with just the two neighboring stators (S1, R2, S2 a 4-row case with the downstream rotor as well (S1, R2, S2, R3) and a 5-row with the upstream IGV were considered. While the 3-row case helped to determine the influence of neighboring stators on the forcing, the 4-row case provided the influence of the downstream rotor on the forced response behavior. Since the number of IGV vanes was the same as the neighboring stators the nature of interference between the stator and IGV wakes was determined as well. The 4-row case helped investigate physical wave reflections off a downstream rotating row, which had a significant influence on the modal force.

The final section of the paper focuses on the mistuning response, which essentially couples frequency variations with the structural and aerodynamic aspects to predict individual blade responses, which are compared to experimental data. A mistuning analysis was carried out with the frequency mistuning present in the experimental facility Some of the key conclusions from this investigation are: 1) The interference of the IGV with the downstream stator (S1) is destructive at peak efficiency and constructive at high loading in line with the previous observation at torsional modes; 2) Physical wave reflections are constructive at all operating conditions at higher order modes unlike torsional modes where it was destructive; 3) The 3-row case gives the most accurate prediction in terms of average blade response and the 5-row case in terms of maximum blade response. Hence one of the significant findings is that, the aeromechanical behavior can be ascertained to a great deal of accuracy using just 3-rows at higher order modes crossings.
Preference-Inspired Multi-Objective Throughflow-Design Optimization Approach of Axial Flow Compressor and its Application
Authors: He Youwei , Sun Jinju , Song Peng , Wang Xuesong
Published: January 2021

Throughflow design of multi-stage axial flow compressor still takes the upmost importance throughout the compressor whole design procedure as it generally fixes 80%∼90% of the final design. The incorporation of multi-objective evolutionary algorithms (MOEA) into throughflow design has been proven effective. In the existing works, the MOEA commonly uses thousands of objective evaluations to obtain a representative approximation of the complete Pareto front (PF), which usually consists of tens and hundreds of solutions. Once the representative PF is obtained, several typical solutions on the PF (especially the extreme ones and/or compromised ones) will be chosen and then examined by the decision-makers. But the remained considerable solutions on the PF are left behind, leading to a significant waste of computational resources. The preference-inspired MOEA has been suggested to resolve this problem as its focus on obtaining solutions in the region of interests only.

In this work, a preference-inspired multi-objective axial flow compressor throughflow design optimization approach is developed through integrating the preference-inspired reference vector guided evolutionary algorithm and the open-source axial flow compressor axisymmetric throughflow design code of T-AXI. In terms of the objective definition for the multi-objective throughflow design, efficiency, stall margin, and blade counts are taken as the focuses. Specifically, the equivalent relative velocity ratio is adopted to form an operability parameter to assess designs with better or worse stall margin of the whole compressor. The developed method is used in the design of a 6-stage axial flow compressor at the throughflow level, which is a 3-objective problem with 58 variables. Preference-inspired and non-preference optimization are compared to verify the cost-saving benefit of incorporating the preferences into multi-objective optimization. Designs in the preferred target regions are obtained which demonstrates the practical ability of the proposed preference-inspired throughflow optimization design method for multi-stage axial flow compressors.
Thermodynamic and Mechanical Design Concept for Micro-Turbojet to Micro-Turboshaft Engine Conversion
Authors: Öttl Christoph , Willinger Reinhard
Published: January 2021

In this work, a design concept for micro-turbojet to micro-turboshaft engine conversion is presented. This is motivated by a lack of available micro-turboshaft engines which is shown in the market survey conducted. Thus, the presented concept deals with the conversion of an existing micro-turbojet engine to a micro-turboshaft engine for a specific power output. The conversion is shown using the micro-turbojet engine OLYMPUS HP from AMT Netherlands. Furthermore, the simultaneously developed analytical preliminary design of the additional single-stage power turbine is shown besides a thermodynamic cycle simulation. This has been done to obtain the unknown gas generator outlet condition which is similar to the power turbine’s inlet condition. Within the cycle calculation, occurring losses due to the small dimensions have also been considered. During the design process, different combinations of work coefficient and mean diameter of the power turbine were investigated to minimize the required gear box ratio for a given rotor speed in terms of weight minimization. To keep losses in the power turbine low, the preliminary blade row has finally been improved using CFD calculations.
An Energy Method for Assessing the Damping of Turbine Blade Underplatform Damper and Forced Response Verification
Authors: Gao Shimin , Wang Yanrong , Sun Zhiwei
Published: January 2021

Rotating turbine blades in aircraft gas turbines are subject to high loads which can result in high cycle fatigue (HCF) failure. In order to reduce the vibration of blades, underplatform dampers are widely used to increase the damping by dry friction dissipating the vibration energy. This paper proposes an energy method (EM) for assessing the damping effect of underplatform dampers with the contacts of one cylinder and one flat without calculating the forced response. In this method the characteristic curve of the damping ratio of the damper on the vibration stress of the blade is used to design the damper. The design objective is that the damper can provide an optimal damping ratio on a given range of vibration stress if resonance occurs. This paper proposes a method for calculating the response and the performance plot based on the above characteristic curve to compare with Direct Time Integration (DTI). The effects of parameters such as contact stiffness, modal data and rotation speed, friction coefficient, damper mass on the damping ratio characteristics are analyzed. Based on the allowable vibration stress of the blade, the design process of the underplatform dampers using damping ratio characteristic curve is given. The proposed method is suitable and efficient for situations where the presence of the damper does not greatly affect the mode shape of the blade.
Open Rotor Engine Cycle Modeling and Performance Assessment
Authors: Zhang Ziyu , Zhou Li , Zhang Xiaobo , Wang Zhanxue
Published: January 2021

Aiming to enable dramatic reductions in the environment impact and fuel consumption of future civil aviation, NASA and European related research institutions are committed to developing new concepts and technologies in which counter rotating open rotor (CROR) concept can achieve this objective. In order to evaluate its potential impact, an open rotor engine performance model needs to be established.

This paper presents the modeling method of an open rotor engine with the geared counter rotating open rotor (GOR) as object, and implements it in an in-house modular program of gas turbine performance prediction. In addition, the steady-state performance of the model is analyzed, and the model accuracy is verified based on the existing data. On this basis, the performance of open rotor engine and high bypass ratio turbofan engine is compared and results show that the counter rotating open rotor engine has obvious fuel saving advantages.
The Optimization of Hydrogen Oxygen Cycles
Authors: Schouten Bram , Klein Sikke
Published: January 2021

Todays renewables, wind and solar power, have a fluctuating nature, making the grid less stable. However, with the increasing share of intermittent sources of renewable power, novel options have to be created to stabilize the power grid. One of these options is energy storage via the conversion of excess power to hydrogen during periods of high generation from wind and/or solar. In periods of power shortages hydrogen is converted back to power. In this work, a number of high efficiency thermodynamic cycles, based upon the Graz cycle and the Toshiba Reheat Rankine cycle, both a coupled closed Brayton cycle with a Rankine cycle, are investigated and improvements are proposed leading to LHV efficiencies of 75%. Also the addition of fuel cells to the cycles is studied leading to potential LHV efficiencies of 85%. Application of pressurized H2/O2 usage leads to several improvements over conventional thermodynamic cycles and conventional fuel cells.
An Experimentally Validated Low Order Model of the Thermal Response of Double-Wall Effusion Cooling Systems for HP Turbine Blades
Authors: Murray Alexander V. , Ireland Peter T. , Romero Eduardo
Published: January 2021

Transpiration cooling represents the pinnacle of turbine cooling and is characterised by an intrinsic material porosity which achieves high internal convective cooling, and full coverage cooling films on the external surface subjected to the hot gases. Quasi-transpiration systems, such as the double-wall effusion system discussed here, attempt to replicate the cooling effect of transpiration systems. The double-wall system is characterised by a large internal wetted area providing high internal convective cooling performance, with a highly porous external wall allowing the formation of a protective film over the external surface.

This paper presents a low-order thermal model of a double-wall system designed to rapidly ascertain cooling performance based solely on the geometry, solid thermal conductivity, and approximate surface heat transfer coefficients. The performance of the model is initially validated using experimental data with heat transfer coefficients for the low order model obtained from fully conjugate CFD simulations.

Following this, a more controlled CFD study is undertaken with both fully conjugate and fluid only simulations performed on several double-wall geometries to ascertain both overall effectiveness and film effectiveness data. Data from these simulations are used as inputs to the low order thermal model developed and the results compared. The low order model successfully captures both the trends and absolute cooling effectiveness achieved by the various double-wall geometries. The model therefore provides an extremely powerful tool in which the cooling performance of double-wall geometries can be near instantaneously predicted during the initial design stage, potentially allowing geometry optimisation to rapidly occur prior to more in-depth, costly and time-consuming analyses of the systems being performed. This potential benefit is demonstrated via the implementation of the model with input boundary conditions obtained using empirical correlations.
Energetically Consistent Computation of Combustor Stability With a Model Consisting of a Helmholtz-FEM-Domain and a Low-Order Network
Authors: Heilmann Gerrit , Hirsch Christoph , Sattelmayer Thomas
Published: January 2021

An efficient approach for the detection of the acoustic damping of gas turbine combustors is the combination of spatially resolved FEM approaches based on the Helmholtz equation with low-order networks for all elements leading to acoustic damping. A fundamental problem of such hybrid approaches is that the flow is considered in the networks, but not in the spatially resolved FEM area. Without special treatment of the coupling plane and the boundary conditions this leads to serious errors in the calculation of the damping rate. The purpose of the paper is the derivation of the required correction procedures, which allow the energetically consistent formulation of such hybrid models and lead to correct damping rates. The time averaged equation of acoustic energy flux for non-uniform fluid flows is expressed in terms of reflection coefficients and compared to the equivalent formulation for vanishing mean flows. An existing transformation for boundary conditions to obtain equal energy flux at the interface between network and Helmholtz domain is analyzed in detail. The findings are then used to derive an energetically consistent transformation of transfer matrices to couple two FEM domains via a network model. The relevance of energetically consistent transfer matrices for stability analysis is demonstrated with a generic test case. The central partition is acoustically characterized via a low order model considering mean flow. The resulting acoustic two-port is transformed to obtain an energetically consistent transfer matrix for a subsequent FEM discretized eigenvalue analysis of the remaining geometry. The eigenvalues of energetically consistent calculations are finally compared to eigenvalues of energetically inconsistent setups.
Investigation of Unsteady Pressure Fluctuations in a Simplified Steam Turbine Control Valve
Authors: Windemuth Christian , Lange Martin , Mailach Ronald
Published: January 2021

Steam turbines are among the most important systems in commercial and industrial power conversion. As the amount of renewable energies increases, power plants formerly operated at steady state base load are now experiencing increased times at part load conditions. Besides other methods, the use of control valves is a widely spread method for controlling the power output of a steam turbine. In difference to other throttling approaches, the control valve enables fast load gradients as the boiler can be operated at constant conditions and allows a quicker response on variable power requirements.

At part load, a significant amount of energy is dissipated across the valve, as the total inlet pressure of the turbine is decreased across the valve. At these conditions, the flow through the valve becomes trans- and supersonic and large pressure fluctuations appear within the downstream part of the valve. As a result, unsteady forces are acting on the valve structure and vibrations can be triggered, leading to mechanical stresses and possible failures of the valve.

Besides more complex valve geometries, a spherical valve shape is still often used in smaller and industrial steam turbines. Because of the smooth head contour, the flow is prone to remain attached to the head surface and interact with the flow coming from the opposite side. This behaviour is accompanied by flow instabilities and large pressure fluctuations, leading to unsteady forces and possible couplings with mechanical frequencies. The spherical valve shape was therefore chosen as the experimental test geometry for the investigation of the unsteady flow field and fluid-structure-interactions within a scaled steam turbine control valve.

Using numerical methods, the test valve is investigated and the time dependent pressure distribution in the downstream diffuser is evaluated. The evolution of the flow stability will be discussed for different pressure ratios. Pressure signals retrieved from the control valve test rig will be used to compare the numerical results to experimental data.
A CFD-Based Prediction Method for Tip Clearance Losses and Deviations in Axial Turbines
Authors: Buske Clemens
Published: January 2021

Accurate loss models are crucial for reliable turbine performance predictions using low-fidelity tools. However, the complex flow structure of the blade tip gap flow impedes an experimental deduction of a realistic tip clearance loss model. In this work, validated, high-fidelity CFD simulations are used to substitute the cost- and time-consuming experiments of a parameter study and to develop a modern, flexible and universal tip clearance model. The CFD model is based on a single stage high-pressure turbine. Inflow conditions and geometry of the rotor were specifically varied to separately study the effects of the significant parameters on the tip clearance loss and deviation. Partial correlations were formulated for each effect and combined to a new tip clearance model. Apart from commonly considered parameters such as gap height, blade loading and solidity, other parameters that are well known to have an effect but are still disregarded in most conventional loss correlations are also investigated, such as incidence, Reynolds number, rotor speed and boundary layer thickness. Furthermore, a downstream progression model is presented that reflects the local conditions of the incompletely mixed out wake flow. Interrelations between the effects are modeled by a Kriging surrogate model, which was refined by the space filling technique. The new model was validated by additional CFD simulations at unprobed operation conditions. In addition, the new model was implemented into a through flow method. Performance calculations were performed for a four-stage air turbine and compared with experimental data. In comparison with the conventional tip clearance correlations, the new model improves the performance predictions at all operation points.
Transonic Fan Blade Redesign Approach to Attenuate Nonsynchronous Vibration
Authors: Lu Yaozhi , Lad Bharat , Vahdati Mehdi
Published: January 2021

Due to manufacturing tolerance and deterioration during operation, different blades in a fan assembly exhibit geometric variability. This leads to asymmetry which will be amplified in the running geometry by centrifugal and aerodynamic loads. This study investigates a phenomenon known as Alternate Passage Divergence (APD), where the blade untwist creates an alternating pattern in passage geometry and stagger angle around the circumference. After the formation of alternating tip stagger pattern, APD’s unsteady effect, APD-induced Non-Synchronous Vibration (APD-NSV), can cause the blades from one group to switch to the other creating a travelling wave pattern around the circumference. Thus, it can potentially lead to high cycle fatigue issues. More importantly, this phenomenon occurs close to, or at, peak efficiency conditions and can significantly reduce overall efficiency. Therefore, it is vital to attenuate the NSV behaviour. In this study, an redesign approach is investigated.
Adjoint-Based Calculation of Parametric Thermoacoustic Maps of an Industrial Combustion Chamber
Authors: Silva Camilo F. , Prieto Laura , Ancharek Maximiliano , Marigliani Pablo , Mensah Georg A.
Published: January 2021

The aim of the present study is to efficiently calculate parametric thermoacoustic maps of typical combustion chambers. Two configurations are considered: an academic configuration based on a Rijke tube, and an industrial combustion chamber, which is the core of a recently developed micro-turbine for power generation. Such maps can be understood as the collection of loci of thermoacoustic eigen frequencies obtained under systematic variations of some defined parameters, while considering the Helmholtz equation as the thermoacoustic model of interest. In this study we consider variations on two parameters: the gain n and time-delay τ associated with a generic flame response model. We also show the feasibility of the proposed approach when considering more realistic flame responses. A straight-forward way to calculate such a thermoacoustic map is by solving the Helmholtz equation, and, thus, the corresponding non-linear eigenvalue problem, one time per parameter combination. With that approach, the non-linear eigenvalue problem needs to be solved hundreds or thousands of times if an adequate resolution of the thermoacoustic map is sought. Such a strategy may be computationally unaffordable. In order to overcome this difficulty, the present work utilizes an adjoint-based, high-order perturbation method. The actual eigenvalue problem is only solved once at a baseline point. After applying the perturbation equations at that point, a polynomial rational function — the Padé approximant — is obtained to estimate the eigen-frequency drift that results for a small or large perturbation in the flame response. It is demonstrated, for both academic and industrial test cases, that the obtained maps are accurate. Additionally, it is shown that these maps reveal a large variety of thermoacoustic features, such as stability boundaries, intrinsic thermoacoustic modes, and exceptional points. The numerical costs for such calculations are negligible even for the industrial combustion chamber investigated.
Ice Crystal Icing Investigation on a Honeywell Uncertified Research Engine in an Altitude Simulation Icing Facility
Authors: Flegel Ashlie B.
Published: January 2021

A Honeywell Uncertified Research Engine was exposed to various ice crystal conditions in the NASA Glenn Propulsion Systems Laboratory. Simulations using NASA’s 1D Icing Risk Analysis tool were used to determine potential inlet conditions that could lead to ice crystal accretion along the inlet of the core flowpath and into the high pressure compressor. These conditions were simulated in the facility to develop baseline conditions. Parameters were then varied to move or change accretion characteristics. Data were acquired at altitudes varying from 5 kft to 45 kft, at nominal ice particle Median Volumetric Diameters from 20 μm to 100 μm, and total water contents of 1 g/m3 to 12 g/m3. Engine and flight parameters such as fan speed, Mach number, and inlet temperature were also varied. The engine was instrumented with total temperature and pressure probes. Static pressure taps were installed at the leading edge of the fan stator, front frame hub, the shroud of the inlet guide vane, and first two rotors. Metal temperatures were acquired for the inlet guide vane and vane stators 1–2. In-situ measurements of the particle size distribution were acquired three meters upstream of the engine forward fan flange and one meter downstream of the fan in the bypass in order to study particle break-up behavior. Cameras were installed in the engine to capture ice accretions at the leading edge of the fan stator, splitter lip, and inlet guide vane. Additional measurements acquired but not discussed in this paper include: high speed pressure transducers installed at the trailing edge of the first stage rotor and light extinction probes used to acquire particle concentrations at the fan exit stator plane and at the inlet to the core and bypass. The goal of this study was to understand the key parameters of accretion, acquire particle break-up data aft of the fan, and generate a unique icing dataset for model and tool development. The work described in this paper focuses on the effect of particle break-up. It was found that there was significant particle break-up downstream of the fan in the bypass, especially with larger initial particle sizes. The metal temperatures on the inlet guide vanes and stators show a temperature increase with increasing particle size. Accretion behavior observed was very similar at the fan stator and splitter lip across all test cases. However at the inlet guide vanes, the accretion decreased with increasing particle size.
SBES/FGM Simulation of Film-Cooled Surface Heat Transfer and Near-Wall Reaction
Authors: Xia Yu , Sharkey Patrick , Orsino Stefano , Kuron Mike , Menter Florian , Verma Ishan , Malecki Robert , Sen Baris
Published: January 2021

Accurate numerical prediction of surface heat transfer in the presence of film cooling within aero-engine sub-components, such as blade effusion holes and combustor liners, has long been a goal of the aero-engine industry. It requires accurate simulation of the turbulent mixing and reaction processes between freestream and the cooling flow. In this study, the Stress Blended Eddy Simulation (SBES) turbulence model is used together with the Flamelet Generated Manifold (FGM) combustion model to calculate the surface heat flux upstream and downstream of an effusion cooling hole. The SBES model employs a blending function to automatically switch between RANS and LES based on the local flow features, and thus significantly reduces the computational cost compared to a full LES simulation. All simulations are run using ANSYS Fluent®, a commercial finite-volume CFD solver. The test case corresponds to an experimental rig run at MIT, which is essentially a flat plate brushed by a uniform freestream of argon with ethylene seeded inside, and is cooled by either a reacting air or non-reacting nitrogen jet inclined at 35 degrees to the freestream. Calculations are performed for both reacting and non-reacting jet cooling cases across a range of jet-to-stream blowing ratios, and compared with the experimental data. The effects of mesh resolution are also investigated. Calculations are also performed across a range of Damköhler number (i.e. flow to chemical time ratio) from zero to 30, with unity blowing ratio, and the differences in the maximum surface heat flux magnitude in the reacting and non-reacting cases at a specific location downstream of the hole are investigated.

Results from these analyses show good correlation with the experimental heat flux data upstream and downstream of the cooling hole, including the heat flux augmentation due to local reaction. Results from the Damköhler number sweep also show a good match with the experimental data across the range investigated.
Flow and Heat Transfer in a Ribbed Channel With Complex Structure Characters
Authors: Liu Yu chao , Guo Tao , Han Zong yu , Zhu Hui ren
Published: January 2021

The ribbed channels are widely used in the internal cooling structure of turbine blade. Many investigations on this kind of channel were carried on in the channel with rectangle cross section and straight inlet. Nevertheless, in mid-chord region of a real blade, the channel characters are more complex and may affect the heat transfer performance in the channel.

The heat transfer investigation in a channel with 3 legs was conducted by numerical simulation. Aim to get the influence of channel structure feature to heat transfer and flow characteristics, the channel was simplified from a real turbine internal cooling channel and main structure features were kept. In order to make the velocity in the first leg close to that in the real structure, the entrance is changed to the contraction entrance. The first leg of channel section is simplified as trapezoid. The legs are connected by 2 U-turns with bend angle for imitating the bend because of the airfoil in real blade. A supplement hole in the inlet of 3rd leg was kept as same as the real channel. Some coolant was supplement to the 3rd leg. Furthermore, 3 rib arrangements (45° ribs, 135° ribs and V-shape ribs) were studied for presenting the interaction between rib arrangement and channel structure character.

The results show that: 1) the shape of the inlet cross section has a continuous effect on the irregular velocity in the first leg, the velocity pattern cause by inlet may interact with the secondary flow caused by ribs and lead to different heat transfer distribution compared with the channel with uniform inlet velocity and rectangle cross section. The heat transfer performance in channel with 135° ribs is different from that in the channel with 45° ribs. 2) In the second leg, the secondary flow is generated at the inlet by the bending structure of the leg connection. This secondary flow may suppress or promote the secondary flow produced by ribs. The composed secondary flow leads to the asymmetry flow pattern in the channel and causes the different heat transfer performance in two ribbed walls. 3) In the third leg, the interaction between the flow coming from the supplement hole, the secondary flow caused by ribs and the flow coming from upstream form the complex flow structure. The different rib angle affects the position of high-velocity area. 4) The heat transfer distribution is asymmetry because of the asymmetry channel cross section and bending connecting of legs. The heat transfer performance is different between that in channel with 45° ribs and 135° ribs, whereas is same in the channel with rectangle cross section. Generally speaking, the heat transfer performance is best in the channel with V-shape ribs and is worst in the channel with 45° ribs.
Can Water Dilution Avoid Flashback on a Hydrogen Enriched Micro Gas Turbine Combustion? A Large Eddy Simulations Study
Authors: Pappa Alessio , Bricteux Laurent , Bénard Pierre , De Paepe Ward
Published: January 2021

Considering the growing interest in Power-to-Fuel, i.e. production of H2 using electrolysis to store excess renewable electricity, combustion-based technologies still have a role to play in the future of power generation. Especially in a decentralized production with small-scale cogeneration, micro Gas Turbines (mGTs) offer great advantages related to their high adaptability and flexibility, in terms of operation and fuel. Hydrogen (or hydrogen enriched methane) combustion is well-known to lead to flame and combustion instabilities. The high temperatures and reaction rates reached in the combustor can potentially lead to flashback. In the past, combustion air humidification (i.e. water addition) has proven effective to reduce temperatures and reaction rates, leading to significant NOx emission reductions. Therefore, combustion air humidification can open a path to stabilize hydrogen combustion in a classical mGT combustor. However accurate data assessing the impact of humidification on the combustion is still missing for real mGT combustor geometries and operating conditions.

In this framework, this paper presents a comparison between pure methane and hydrogen enriched methane/air combustions, with and without combustion air humidification, in a typical mGT combustion chamber (Turbec T100) using Large Eddy Simulations (LES) analysis. In a first step, the necessary minimal water dilution, to reach stable and low emissions combustion with hydrogen, was assessed using a 1D approach. The one-dimensional unstretched laminar flame is computed for both pure methane (reference case) and hydrogen enriched methane/air combustion cases. The results of this comparison show that, for the hydrogen enriched combustion, the same level of flame speed as in the reference case can be reached by adding 10% (in mass fraction) of water. In a second step, the feasibility and flexibility of humidified hydrogen enriched methane/air combustion in an industrial mGT combustor have been demonstrated by performing high fidelity LES on a 3D geometry. Results show that steam dilution helped to lower the reactivity of hydrogen, and thus prevents flashback, enabling the use of hydrogen blends in the mGT at similar CO levels, compared to the reference case. These results will help to design future combustor towards more stability.
Prediction of Tip Leakage Vortex Dynamics in an Axial Compressor Cascade Using RANS Analyses
Authors: Ricci Martina , Pacciani Roberto , Marconcini Michele , Arnone Andrea
Published: January 2021

The tip leakage flow in turbine and compressor blade rows is responsible for a relevant fraction of the total loss. It contributes to unsteadiness, and have an important impact on the operability range of compressor stages. Experimental investigations and, more recently, scale-resolving CFD approaches have helped in clarifying the flow mechanism determining the dynamics of the tip leakage vortex. Due to their continuing fundamental role in design verifications, it is important to establish whether RANS/URANS approaches are able to reproduce the effects of such a flow feature, in order to correctly drive the design of the next generation of turbomachinery. Base studies are needed in order to accomplish this goal.

In the present work the tip leakage flow in axial compressor rotor blade cascade have been studied. The cascade was tested experimentally in Virginia Tech Low Speed Cascade Wind Tunnel in both stationary and moving endwall configurations. Numerical analyses were performed using the TRAF code, a state-of-the-art in-house-developed 3D RANS/URANS flow solver. The impact of the numerical framework was investigated selecting different advection schemes including a central scheme with artificial dissipation and a high-resolution upwind strategy. In addition, two turbulence models have been used, the Wilcox linear k–ω model and a non-linear eddy viscosity model (Realizable Quadratic Eddy Viscosity Model), which accounts for turbulence anisotropy. The numerical results are scrutinized using the available measurements. A detailed discussion of the vortex evolution inside the blade passage and downstream of the blade trailing edge is presented in terms of streamwise velocity, streamwise vorticity, and turbulent kinetic energy contours. The purpose is to identify guidelines for obtaining the best representation of the vortex dynamics, with the methodologies usually employed in routine design iterations and, at the same time, evidence their weak aspects that need further modelling efforts.