bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three-Dimensional Fluid Topology Optimization and Validation of a Heat Exchanger With Turbulent Flow
Authors: Pietropaoli M. , Gaymann A. , Montomoli F. 
Published: January 2021

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.