bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polytropic Change of State Calculations With Condensation or Evaporation and its Use for Thermal Power Cycles
Authors: Wettstein Hans E. 
Published: August 2015

In the paper [1] three polytropic change of state calculation methods for air gases and CO2 are compared. The conclusions are that the most used formulas can produce with the same input data deviations in terms of polytropic efficiency up to 1.5% points even for nearly ideal gases like nitrogen. The paper suggests therefore a recursive algorithm, which is based directly on the classic definition of a polytropic change of state. This definition assumes a constant dissipation rate during an adiabatic change of state. The proposed algorithm can be applied for any gas with an equation of state, which is an unambiguous function of the two variables pressure p and temperature T.
The latter condition is not fulfilled by steam in the wetness range because the specific volume v depends not only from p and T but also from the vapor fraction x. The aim of this paper is the development of an analogous recursive “constant dissipation rate algorithm” for a two phase mixture assuming equilibrium conditions between the vapor and the liquid fractions. The method shall be demonstrated with expanding wet steam. The result of the algorithm will be the discharge enthalpy, temperature and the discharge vapor fraction for given initial pressure and temperature, discharge pressure and polytropic efficiency.
Based on the developed formulas some well-known but nevertheless paradoxically perceived results and comparisons with expanding dry air can be shown.
Investigation in the Technical and Economic Feasibility of a Low-Pressure Steam Cycle for the Waste Heat Utilization of a Cogeneration Plant
Authors: Laux Christoph , Goebel Johannes , Neef Matthias , Gotter Andreas 
Published: August 2015

This paper deals with the investigation in the technical and economic feasibility of a low-pressure steam cycle for the waste heat utilization of a combined heat and power (CHP) plant. The proposed steam cycle uses a pressure level below atmospheric pressure which allows to use the heat from the motor’s coolant for evaporation. The cycle is designed to increase the maximum electrical efficiency of a gas fired reciprocating engine and to increase operational flexibility for varying heat demand. Since organic Rankine cycle (ORC) plants are already being successfully used for waste heat recovery, advantages of the low-pressure steam Rankine cycle (SRC) over an ORC are highlighted.
Many ORC fluids are toxic or flammable and thus have an increased risk potential compared to water. An additional advantage of water compared to ORC fluids is the possibility of superheating above 500 °C.
The technical feasibility of the proposed cycle is studied by the detailed design of the individual system components such as turbine, heat exchangers and auxiliary parts. This includes the detailed thermodynamic design of the full cycle for the calculation of plant efficiencies.
As a basis for future experimental investigations, a cogeneration plant with an electrical output of 50 kWel was selected as a heat source for the steam cycle. The design geometries of the turbine and the heat exchanger are presented along with efficiency and cost predictions. A subsonic radial turbine with a rotational speed of 155,000 rpm was selected. The maximum turbine output is about 7.5 kW. The use of a flash evaporator is investigated to reduce the size and the costs for the evaporator.
The suggested steam cycle helps to increase the electrical efficiency of the CHP plant by 4.5% points from an original 36.5% to 41.0%. The steam cycle itself has an electrical efficiency of approximately 9%. Additionally, the condensation temperature in this steam cycle is high enough to be extracted as useful heat output to generate domestic water with a temperature of 50°C.
Unsteady Pressure Interaction of an Axial Flow Fan With a Stabilization Ring in Tunnel and Metro Applications
Authors: Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David 
Published: August 2015

Ventilation fans operating in underground metropolitan tunnels are subjected to abrupt changes in operations due to the pressure wavefronts generated by the passage of the trains, and the magnitude of these pressure waves is increasing due to increasing speed of passing trains in modern mass transport systems. To avoid fans being driven into stall designers can fit fans with a stabilisation ring, i.e. a casing treatment that was found to mitigate the mechanical consequences of being inadvertedly driven into stall due to pressure pulses.
A stabilisation ring is a circumferential cavity in the casing of the fan, placed upstream of the rotor in order to allow the fluid to recirculate in stalled operations. A series of fins inside this cavity is used in order to drive the recirculating fluid back into the blade vane with a proper alignment with the leading edge of the rotor.
Following a previous RANS investigation that lead to the conclusion that the drive mechanism of the stabilisation ring onto the fan is based on azimuthal pressure unbalance we present here a U-RANS investigation aiming at understanding the dynamics of the interaction of the anti-stall ring with the fan and to provide insight on possible development of the geometry of the casing treatment.
The fan selected for this study is a real fan for tunnel and metro applications (9 rotor blades, 1490 rpm) with a real-geometry stabilisation ring (27 fins). Computations account for different operating points (peak efficiency, design point, peak pressure and stalled operations) and rely on the low-Reynolds cubic k-ε model of Lien et al. All the simulations were carried out with the open-source OpenFOAM code. Results were validated against available experimental data and then analysed to understand the unsteady interaction between the rotor of the fan and the cavity of the stabilisation ring.
Optimisation of a High Pressure Ratio Radial-Inflow Turbine: Coupled CFD-FE Analysis
Authors: Shanechi Mohsen Modir , Odabaee Mostafa , Hooman Kamel 
Published: August 2015

The optimisation of a 5.7 air pressure ratio single stage radial-inflow turbine applied in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit (MPSPU) is performed using coupled CFD-FE method. The commercial software ANSYS-Vista RTD along with a built-in module, BladeGen, is used to conduct a meanline design and, consequently, create the 3D geometry of the flow passage. Carefully examining the proposed design against the geometrical and experimental data, ANSYS-TurboGrid is applied to generate computational mesh. CFD simulations are then performed with ANSYS-CFX in which three-dimensional Reynolds-Averaged Navier-Stokes equations are solved subject to appropriate boundary conditions. Conducting the CFD simulations, the pressure and temperature distributions are imported to the ANSYS-FE module. The von Mises stress σv distribution is then calculated taking into account the centrifugal force acting on the turbine wheel.
To obtain the optimised geometry, 25 major design points are regenerated where the meridional parameters, tip clearance, and blade thickness distribution are systematically changed. Furthermore, constraints are defined as high aerothermodynamic performance and acceptable vibration with a stress distribution less than yield limit of the turbine material. Results of coupled CFD-FE method show the power, efficiency, stress and deformation. Finally, performance of the optimised radial-inflow turbine indicates enhanced aero-thermodynamics (ηTS and) and structural performance (σv) compared to the MPSPU turbine design.
A Strategy for Parameterization and Optimization of Turbine Cooling Channels
Authors: Dieu Donavan , Deletrain Yves , Van Liefferinge Raphaël , Hirsch Charles 
Published: August 2015

Cooled turbine blades represent a major component of gas turbine technology due their potential for enhancing overall cycle performance. Due to the difficulty of performing detailed experiments on these complex internal configurations, the only option is to rely intensively on high fidelity CFD modeling and subsequent optimization to enhance the heat transfer coefficient (HTC) by exploration of a broad design space.
The optimization strategy relies on the following steps: parametric modeling of cooling passages; automatic grid generation; validation of the most reliable turbulence models and boundary conditions; optimization process based on genetic algorithms.
The parametric blade modeler AutoBlade™ has been upgraded to generate CAD geometries of cooling channels, including ribs, different section shapes, U-turns.
From those geometries, the full hexahedral mesher HEXPRESS™ is able to automatically generate high quality unstructured meshes with the possibility to insert viscous sublayers to provide adequate resolution in boundary layer regions. The mesh generator can also deal with multi-domain problems allowing conjugate heat transfer (CHT) method.
CFD options were analyzed in order to obtain numerical results as accurate as possible for the optimization process. It appears that low Reynolds grids were necessary to reproduce the thermal effects due to the strong temperature gradient near solid walls. The preconditioning technique seems to be essential for density based flow to obtain realistic results for flows at low Mach number. The anisotropic EARSM turbulence model appears to provide good heat transfer predictions. In addition, the question to include or not CHT is raised: the study also compares the heat transfer obtained in case of imposed static temperature conditions on the coolant to the ones obtained by means of CHT. The results highlight that CHT is more realistic.
Optimization of HTC is performed on three baseline configurations by variation of geometric parameters including the aspect ratio of the channel cross section, the shape, position and size of the ribs. The main objective consists in maximization the heat fluxes while limiting the head loss.
The optimization process starts from an initial database of high-fidelity CHT simulations obtained by design of experiment methods. To predict a potential optimum, an evolutionary algorithm is run on an artificial neural network for a very quick evaluation of the objectives from the database. The process is iterative: starting from potential candidates, the CFD process is launched to validate the guess and populate the database.
Results and optimized geometries will be presented in the full paper.
Nonlinear Modal Analysis of Mistuned Periodic Structures Subjected to Dry Friction
Authors: Joannin C. , Chouvion B. , Thouverez F. , Mbaye M. , Ousty J.-P. 
Published: August 2015

This paper deals with the dynamics of a cyclic system, representative of a bladed-disk subjected to dry friction forces, and exhibiting structural mistuning. The nonlinear complex modes are computed by solving the eigenproblem associated to the free response of the whole structure, and are then used to better understand the forced response to a traveling wave excitation.
Similarly to the underlying linear system, the tuned model possesses pairs of modes that can be linearly combined to form traveling waves, unlike those of the mistuned structure. However, due to the nonlinearity, the modal properties are not constant but vary with the vibration amplitude in both cases.
A qualitative analysis is also performed to assess the impact of the mistuning magnitude on the response, and suggests that further statistical investigations could be of great interest for the design of bladed disks, in terms of vibration mitigation and robustness.
High Order Large Eddy Simulations for a Transonic Turbine Blade Using Hybrid Unstructured Meshes
Authors: Lu Yi , Dawes W. N. 
Published: August 2015

Large eddy simulations were performed for a transonic turbine blade on hybrid unstructured meshes. High order accuracy in both space and time discretization is achieved by using a space time extension of flux reconstruction method(STEFR), and in particular, local time-stepping is enabled for time-accurate unsteady simulations. A piecewise integration in-cell method is introduced for shock-capturing within the STEFR method. This method is completely local in both space and time directions, without any explicit addition to the discretisation, which is suitable for the predictor-corrector type space time extension allowing local timestepping. A volume averaged compensation method is used to construct a conservative form of the Chain-Rule scheme for the flux divergence part of the flux reconstruction discretisation, which is proved stable and efficient to solve flow problems with physical discontinuities. This work successfully extends the application of the STEFR method to solve transonic/supersonic unsteady flows. The numerical validation for the 1D burgers equation and its comparison with traditional multi-stage Runge-Kutta method with uniform time-stepping, indicate that this piecewise integration in-cell method is accurate and more robust with STEFR method using local time-stepping.
A significant advantage of this method is the successfully implementation on hybrid unstructured meshes, which makes it very efficient and scalable to solve multi-scale, complex geometries flow problems. The moving shock, shock-boundary layer interaction, shock-wake interaction were crisply resolved and analyzed for the transonic turbine blade, VKI-LS59, and detail post-processing is presented with the comparison with experimental data in this paper.
Ambient Temperature Impact on Pressurized SOFC Hybrid Systems
Authors: Larosa Luca , Traverso Alberto , Zaccaria Valentina 
Published: August 2015

In this paper advanced control strategies based on Model Predictive Control (MPC) method are compared against a traditional PID controller in a Gas Turbine Pressurized SOFC hybrid system.
A model of the integrated mGT-SOFC hybrid system has been developed to analyze the impact of ambient temperature changes on system performance and dynamic behaviour. Four different MIMO controllers (multi input multi output) based on a linearized system model have been implemented in order to control fuel cell temperature and power with different ambient temperatures. Fuel cell temperature is regulated by manipulating the cell by-pass mass flow, while power is regulated by changing the fuel cell electrical current and fuel mass flow (the fuel utilization factor is kept constant). Load following simulations have been carried out as follows: the same load ramp from 100% to 80% of fuel cell power and back has been set and studied under three different ambient conditions, 263K, 288K and 313K (−10°C, 15°C and 40°C).
MPC demonstrated superior performance over the two distributed PID controls, thanks to the better setpoint tracking on the cell temperature, which is particularly evident when the ambient temperature deviates from the nominal condition. This is mainly explained by the capability of MPC in including the effects of non-linearities of the real system.
Dynamic Behavior of a Solar Hybrid Gas Turbine System
Authors: Felsmann Christian , Gampe Uwe , Freimark Manfred 
Published: August 2015

Solar hybrid gas turbine technology has the potential to increase the efficiency of future solar thermal power plants by utilizing solar heat at a much higher temperature level than state of the art plants based on steam turbine cycles. In a previous paper the authors pointed out, that further development steps are required for example in the field of component development and in the investigation of the system dynamics to realize a mature technology for commercial application [1].
In this paper new findings on system dynamics are presented based on the simulation model of a solar hybrid gas turbine with parallel arrangement of the combustion chamber and solar receivers. The operational behavior of the system is described by means of two different scenarios. The System operation in a stand-alone electrical supply network is investigated in the first scenario. Here it is shown that fast load changes in the network lead to a higher shaft speed deviation of the electric generator compared to pure fossil fired systems. In the second scenario a generator load rejection, as a worst case, is analyzed. The results make clear that additional relief concepts like blow-off valves are necessary as the standard gas turbine protection does not meet the specific requirements of the solar hybrid operation. In general the results show, that the solar hybrid operational modes are much more challenging for the gas turbines control and safety system compared to pure fossil fired plants due to the increased volumetric storage capacity of the system.
CCPP Operational Flexibility Extension Below 30% Load Using Reheat Burner Switch-Off Concept
Authors: Therkorn Dirk , Gassner Martin , Lonneux Vincent , Zhang Mengbin , Bernero Stefano 
Published: August 2015

Highly competitive and volatile energy markets are currently observed, as resulting from the increased use of intermittent renewable sources. Gas turbine combined cycle power plants (CCPP) owners therefore require reliable, flexible capacity with fast response time to the grid, while being compliant with environmental limitations. In response to these requirements, a new operation concept was developed to extend the operational flexibility by reducing the achievable Minimum Environmental Load (MEL), usually limited by increasing pollutant emissions.
The developed concept exploits the unique feature of the GT24/26 sequential combustion architecture, where low part load operation is only limited by CO emissions produced by the reheat (SEV) burners. A significant reduction of CO below the legal limits in the Low Part Load (LPL) range is thereby achieved by individually switching the SEV burners with a new operation concept that allows to reduce load without needing to significantly reduce both local hot gas temperatures and CCPP efficiency.
Comprehensive assessments of the impact on operation, emissions and lifetime were performed and accompanied by extensive testing with additional validation instrumentation. This has confirmed moderate temperature spreads in the downstream components, which is a benefit of sequential combustion technology due to the high inlet temperature into the SEV combustor. The following commercial implementation in the field has proven a reduction of MEL down to 26% plant load, corresponding to 18% gas turbine load. The extended operation range is emission compliant and provides frequency response capability at high plant efficiency. The experience accumulated over more than one year of successful commercial operation confirms the potential and reliability of the concept, which the customers are exploiting by regularly operating in the LPL range.
Clocking Effects of Inlet Non-Uniformities in a Fully Cooled High-Pressure Vane: A Conjugate Heat Transfer Analysis
Authors: Griffini Duccio , Insinna Massimiliano , Salvadori Simone , Martelli Francesco 
Published: August 2015

A high-pressure vane equipped with a realistic film-cooling configuration has been studied. The vane is characterized by the presence of multiple rows of fan-shaped holes along pressure and suction side while the leading edge is protected by a showerhead system of cylindrical holes. Steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations have been performed. A preliminary grid sensitivity analysis with uniform inlet flow has been used to quantify the effect of spatial discretization. Turbulence model has been assessed in comparison with available experimental data.
The effects of the relative alignment between combustion chamber and high-pressure vanes are then investigated considering realistic inflow conditions in terms of hot spot and swirl. The inlet profiles used are derived from the EU-funded project TATEF2. Two different clocking positions are considered: the first one where hot spot and swirl core are aligned with passage and the second one where they are aligned with the leading edge.
Comparisons between metal temperature distributions obtained from conjugate heat transfer simulations are performed evidencing the role of swirl in determining both the hot streak trajectory within the passage and the coolant redistribution. The leading edge aligned configuration is resulted to be the most problematic in terms of thermal load, leading to increased average and local vane temperature peaks on both suction side and pressure side with respect to the passage aligned case.
A strong sensitivity of both injected coolant mass flow and heat removed by heat sink effect has also been highlighted for the showerhead cooling system.
Adiabatic Effectiveness and Flow Field Measurements in a Realistic Effusion Cooled Lean Burn Combustor
Authors: Andreini Antonio , Becchi Riccardo , Facchini Bruno , Mazzei Lorenzo , Picchi Alessio , Turrini Fabio 
Published: August 2015

Over the last ten years there have been significant technological advances toward the reduction of NOx emissions from civil aircraft engines, strongly aimed at meeting stricter and stricter legislation requirements. Nowadays, the most prominent way to meet the target of reducing NOx emissions in modern combustors is represented by lean burn swirl stabilized technology. The high amount of air admitted through a lean-burn injection system is characterized by very complex flow structures such as recirculations, vortex breakdown and precessing vortex core, that may deeply interact in the near wall region of the combustor liner. This interaction makes challenging the estimation of film cooling distribution, commonly generated by slot and effusion systems.
The main purpose of the present work is the characterization of the flow field and the adiabatic effectiveness due to the interaction of swirling flow, generated by real geometry injectors, and a liner cooling scheme made up of a slot injection and an effusion array. The experimental apparatus has been developed within EU project LEMCOTEC and consists of a non-reactive three sectors planar rig; the test model is characterized by a complete cooling system and three swirlers, replicating the geometry of a GE Avio PERM (Partially Evaporated and Rapid Mixing) injector technology.
Flow field measurements have been performed by means of a standard 2D PIV (Particle Image Velocimetry) technique, while adiabatic effectiveness maps have been obtained using PSP (Pressure Sensitive Paint) technique. PIV results show the effect of coolant injection in the corner vortex region, while the PSP measurements highlight the impact of swirled flow on the liner film protection separating the contribution of slot and effusion flows. Furthermore an additional analysis, exploiting experimental results in terms of heat transfer coefficient, has been performed to estimate the net heat flux reduction (NHFR) on the cooled test plate.