bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Physics-Based Dynamic Model for Boilers: Part 1 — Model Development and Validation
Authors: Blom Matthew J. , Brear Michael J. , Manzie Chris G. , Wiese Ashley P. 
Published: August 2017

This paper is the first part of a two part study that develops, validates and integrates a one-dimensional, physics-based, dynamic boiler model suitable for application with model based control. Part 1 of this study extends and validates the existing, higher order modelling framework of Badmus et. al. [1] to boilers. This requires derivation of particular, one-dimensional forms of the equations for heat, mass and momentum transfer in single (liquid and gas) phase and two phase fluids with real fluid properties. The so-called ‘forcing term’ mapping functions in these equations only require knowledge of steady state system behaviour, and so can be obtained from steady state measurements throughout the boiler system. Additional models are also presented for other boiler components, including the steam drum in sub-critical boilers.
The overall framework is then used to develop and validate a model of a GW scale, sub-critical boiler in an operating, electrical power plant. Overall, the model achieves reasonable agreement with the power plant dynamics during normal transient operations, including acceptable tracking of the drum dynamics and the steam at the boiler outlet. As such, this modelling framework appears suitable for developing models of sufficient fidelity yet retain an appropriate form for model reduction using singular perturbation analysis techniques, as demonstrated in Part 2 [2] of this study.
Optimization of the Vibration Behavior at Speed-Synchronous Resonance of a Large Turbine Blade During Speed-Up and Coast-Down Under Consideration of Mistuning
Authors: Lübbe Bertold , Siewert Christian 
Published: August 2017

During start-up and coast-down of the turbine train large last stage moving blades may show elevated amplitude levels. In cases where the excitation mechanism results from a rotor imbalance, it is well known that the occurring amplitude level can be influenced by the turbine set-up as well as the mode of operation during start-up and coast-down. For example, by increasing speed gradients the exposure time in which the blade row is operated at or close to speed-synchronous resonance is reduced and hence the excitation is minimized.
To evaluate the blade response during transient operation an analytical model is developed which allows for an accurate description of the exciting inertia forces resulting from rotor imbalance. In the present paper, the effect of a small-scale variation of the tuned blades’ resonance frequency and intentional mistuning of the blade row, (Siewert & Stüer, 2014), on the obtainable resonance amplitudes and the potentially accumulated fatigue is assessed. The results show a significant increase in robustness against transient excitation by application of a dedicated tuning, allowing for enhanced flexible operation of large last stage moving blades.
Evaluation of a Micro Gas Turbine With Post-Combustion CO2 Capture for Exhaust Gas Recirculation Potential With Two Experimentally Validated Models
Authors: Nikpey Somehsaraei Homam , Ali Usman , Font-Palma Carolina , Mansouri Majoumerd Mohammad , Akram Muhammad , Pourkashanian Mohamed , Assadi Mohsen 
Published: August 2017

The growing global energy demand is facing concerns raised by increasing greenhouse gas emissions, predominantly CO2. Despite substantial progress in the field of renewable energy in recent years, quick balancing responses and back-up services are still necessary to maintain the grid load and stability, due to increased penetration of intermittent renewable energy sources, such as solar and wind.
In a scenario of natural gas availability, gas turbine power may be a substitute for back-up/balancing load. Rapid start-up and shut down, high ramp rate, and low emissions and maintenance have been achieved in commercial gas turbine cycles. This industry still needs innovative cycle configurations, e.g. exhaust gas recirculation (EGR), to achieve higher system performance and lower emissions in the current competitive power generation market. Together with reduced NOx emissions, EGR cycle provides an exhaust gas with higher CO2 concentration compared to the simple gas turbine/combined cycle, favorable for post-combustion carbon capture.
This paper presents an evaluation of EGR potential for improved gas turbine cycle performance and integration with a post-combustion CO2 capture process. It also highlights features of two software tools with different capabilities for performance analysis of gas turbine cycles, integrated with post-combustion capture. The study is based on a combined heat and power micro gas turbine (MGT), Turbec T100, of 100kWe output. Detailed models for the baseline MGT and amine capture plant were developed in two software tools, IPSEpro and Aspen Hysys. These models were validated against experimental work conducted at the UK PACT National Core Facilities. Characteristics maps for the compressor and the turbine were used for the MGT modeling. The performance indicators of systems with and without EGR, and when varying the EGR ratio and ambient temperature, were calculated and are presented in this paper.
Techno-Economic Study of Wind Farm Forecast Error Compensation by Flexible Heat-Driven CHP Units
Authors: Bexten Thomas , Wirsum Manfred , Roscher Björn , Schelenz Ralf , Jacobs Georg , Weintraub Daniel , Jeschke Peter 
Published: August 2017

Many energy supply systems around the world are currently undergoing a phase of transition that is mainly characterized by a continuing increase in installed renewable power generation capacities. Aiming at a better integration of these additional capacities, operators of wind farms in Germany are obliged to bindingly forecast their power production. In order to maintain the continuous stability of the electricity grid, deviations from these forecasts have to be compensated by the grid operator, who charges the wind farm operators accordingly. An alternative way to compensate for forecast errors is the utilization of flexible and dispatchable energy conversion and storage units by the wind farm operator.
Heat-driven combined heat and power (CHP) units with heat storage systems offer the potential of limited short-term load adjustments to compensate forecast errors while simultaneously fulfilling their main task of providing heat.
The main objectives of the present study are the evaluation of the main technical parameters and the economic viability of the described application.
The study utilizes a theoretical scenario incorporating a gas turbine as a CHP unit providing heat for an industrial process, a heat storage and an associated wind farm. A generic wind farm power generation forecast error model is developed, providing realistic forecast errors for the study. Detailed models of all system components are developed and integrated into a common simulation environment, allowing for simulations of the overall system operation with varying heat storage capacities. The simulation results show that the combination of a heat-driven CHP gas turbine and a heat storage system makes a significant contribution to the compensation of the wind farm power generation forecast errors. Distinct correlations between the heat storage capacity and the remaining forecast errors are identified. The net balance energy costs resulting from the remaining demand for balance energy after the partial forecast error compensation are investigated as the main parameter for the economic viability. No distinctive correlation between the heat storage capacity and the net balance energy costs can be identified. This is the result of the stochastic character of the net balance energy price.
Experimental Analysis of Angled Injection Aerostatic Hybrid Bearings
Authors: Le Rouzic Julian , Arghir Mihai 
Published: August 2017

Counter-rotation angled injection employed for aerostatic hybrid bearings reduces the cross coupling stiffness that may lead to whirl-whip instabilities at high rotation speeds. The benefits of counter-rotation injection have been known for years. Theoretical investigations were performed for water or air fed hybrid bearings but experiments were conducted only for water fed bearings. The present work is the first effort dedicated to angled injection in air fed hybrid bearings. The tests were performed for a simple rotor supported by two identical hybrid bearings. The hybrid bearings are provided with small size, shallow pockets and are fed with air via counter-rotation oriented orifice type restrictors. An impulse turbine fed with air entrains the rotor. An impact gun applies dynamic excitations and the rotordynamic coefficients are identified from the equations of motion of the rotor. Different air feeding pressures are tested as well as high rotational speeds.
Compared to the dynamic characteristics of radial injection hybrid bearings, the direct stiffness of counter-rotation injection bearings has slightly lower values and the direct damping is higher but the main impact is the drastic reduction of the cross-coupling stiffness that may have even negative values.
Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios
Authors: Li Zhigang , Li Jun , Feng Zhenping 
Published: August 2017

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor-stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines.
The paper deals with the leakage and static stability behavior of a fully-partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360° mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-Averaged Navier-Stokes (RANS) solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7 000 rpm, 11 000 rpm and 15 000 rpm) including the non-rotating condition, three pressure ratios (0.17, 0.35 and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions, no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal would be statically unstable.
Sliding Controller Design for Aero-Engines With the Rate Limitation of Actuators
Authors: Yang Shubo , Wang Xi 
Published: August 2017

With the relevant theories fully developed, sliding mode control (SMC), a kind of nonlinear control strategy having particularly strong robustness and disturbance rejection properties, has been applied in a considerable number of fields, such as robotic manipulator control, power generation control in wind turbines, robust stepper motor control, etc. For aero engines, remarkable progress of adopting SMC has been made. For instance, Richter has published his research of limit management in aircraft engine controls which suggests that replacing the linear regulators with sliding controllers can overcome the obstacle of traditional min-max approach.
It is revealed from publication that researchers who design sliding controller for aero engines have made every effort to focus on the sliding surface and control law of SMC while they seldom paid attention to the constraints in actuators, such as saturation and rate limitation. In practical engineering, the performance of the ideal controller is infeasible under the situation that unavoidable constraints exist. Although the actuator saturation can be avoided by introducing a velocity form controller, rate limitation can still degenerate the control performance severely.
In this paper, therefore, the design of a sliding controller for aero engines with rate limitation is discussed. A speed tracking problem is described based on the engine model simplified from a nonlinear system to a piecewise linear system at selected equilibrium points. A sliding surface is defined as the generalized tracking error, and a SMC law is designed with Lyapunov analysis of the closed loop system. Simulation results verify the stability of the closed-loop system, and show that the proposed sliding controller is capable of regulating a turbofan engine for large thrust commands in a stable fashion with proper tracking performance, which can mitigate the negative effect of actuator rate limitation.
Investigation of the Influence of Leakages on Non Axisymmetric Endwall Contouring Applied on 3D Steam Turbine Airfoils
Authors: Zimmermann Tobias W. , Wirsum Manfred , Fowler Andrew , Patel Kush 
Published: August 2017

Tangential endwall contouring is intended to improve the blading efficiency in turbomachinery. The present paper focusses on the influence of leakage flows on the performance of non-axisymmetric endwall contouring.
All tests were conducted on a 2 stage axial turbine test rig at the Institute of Power Plant Technology, Steam and Gas Turbines (IKDG) of RWTH Aachen University. The test rig is driven with air. Two sealing setups are applied to create two different leakage mass flows. Four operating points are investigated that represent the design point as well as over load and part load conditions.
The endwall contouring is applied on both hub and casing sides. Three configurations are compared. A baseline design without endwall contouring, contoured stator vanes and non-contoured rotor blades as well as contoured vanes and blades.
At first, all configurations are investigated with a negligible leakage flow rate at the casing side. The results show that the vane contoured configuration performs best in stage 1 while the fully contoured set-up loses in efficiency for the design point and in part load compared to baseline. This trend is flipped in stage 2 as the full contoured version performs best and the vane contoured configuration loses significantly. This finding is suggesting that endwall contouring has the potential to increase the efficiency.
The second focus is put on the interaction of endwall contouring and leakage flow. These investigations show that neither the vane contoured nor the fully contoured set up show an increased efficiency at any operating point. The trends within the first stage are similar to the measurements with the low amount of leakage flow. In the second stage both contouring designs perform worse than the baseline leading to the assumption that the change in efficiency is mainly caused by the re-entering leakage mass flow upstream the contouring and not by the flow that is sucked into the cavities in front of the rotor contouring.
Analysis of Aerothermal Characteristics of Surface Micro-Structures
Authors: Kapsis M. , He L. 
Published: August 2017

Recent advances in manufacturing technologies, such as additive manufacturing, have raised the potential of choosing surface finish pattern as a design parameter. Hence, understanding and prediction of aerothermal effects of machined micro-structures (‘machined roughness’) would be of great interest. So far, however, roughness has been largely considered as a stochastic attribute and empirically modelled. A relevant question is: if and how would shape of the machined roughness elements matter at such fine scales?
In this paper, a systematic computational study has been carried out on the aerothermal behaviour and impact of some discrete micro-structures. Two shapes of micro-structure configurations are considered: hemispherical and rectangular elements for a Reynolds number range typical for those roughness elements (Re<5000). Several validation cases are studied as well as the turbulence modelling and grid sensitivities are examined to ensure the consistence of the numerical results. Furthermore, LES analyses are performed to contrast the behaviour in a well-established turbulent flow regime to a transitional one.
The present results reveal a distinctive common flow pattern change (from an ‘open separation’ to a ‘reattached separation’) associated with a drastic change of drag/loss correlation from a low to a high loss regime. The results also indicate a clear dependence of drag and heat transfer characteristics on the element pattern and orientation relative to the flow. The distinctive performance correlations with Reynolds number can be affected considerably by the element shape, for both a transitional and a turbulent flow regime. The results also consistently illustrate that conventional empirical stochastic roughness parameters would be unable to predict these trends.
Introducing a New Test Rig for Film Cooling Measurements With Realistic Hole Inflow Conditions
Authors: Fraas Marc , Glasenapp Tobias , Schulz Achmed , Bauer Hans-Jörg 
Published: August 2017

Further improvements in film cooling require an in-depth understanding of the influencing parameters. Therefore, a new test rig has been designed and commissioned for the assessment of novel film cooling holes under realistic conditions.
The test rig is designed for generic film cooling studies. External hot gas flow as well as internal coolant passage flow are simulated by two individual flow channels connected to each other by the cooling holes. Based on a similarity analysis, the geometry of the test rig is scaled up by a factor of about 20. It furthermore offers the possibility to conduct experiments at high density ratios and realistic approach flow conditions at both cooling hole exit and inlet. The operational range of the new test rig is presented and compared to real engine conditions. It is shown that the important parameters are met and the transfer-ability of the results is ensured.
Special effort is put onto the uniformity of the approaching hot gas flow, which will be demonstrated by temperature and velocity profiles. A first measurement of the heat transfer coefficient without film cooling is used to demonstrate the quality of the measurement principle.
Correlation Between Pressure Recovery of Highly Loaded Annular Diffusers and Integral Stage Design Parameters
Authors: Mimic Dajan , Drechsel Bastian , Herbst Florian 
Published: August 2017

Exhaust diffusers significantly enhance the available power output and efficiency of gas and steam turbines by allowing for lower turbine exit pressures. The residual dynamic pressure of the turbine outflow is converted into static pressure, which is referred to as pressure recovery. Since total pressure losses as well as construction costs increase drastically with diffuser length, it is more than favourable to design shorter diffusers with rather steep opening angles. However, those designs are more susceptible to boundary layer separation.
In this paper, the stabilising properties of tip leakage vortices generated in the last rotor row and their effect on the boundary layer characteristics are examined. Based on analytical considerations, for the first time a correlation between the pressure recovery of the diffuser and integral rotor parameters of the last stage, namely the loading coefficient, flow coefficient and reduced frequency, is established. Both, experimental data and scale resolving simulations, carried out with the SST-SAS method, show excellent agreement with the correlation.
Blade tip vortex strength predominantly depends on the amount of work performed in the rotor, which in turn is described by the non-dimensional loading coefficient. The flow coefficient influences mainly the orientation of the vortex, which affects the interaction between vortex and boundary layer. The induced velocity field accelerates the boundary layer, essentially reducing the thickness of the separated layer or even locally preventing separation.
High Aspect Ratio Blading in an Axial Compressor Stage
Authors: Schmidt Tobias , Peters Markus , Jeschke Peter , Matzgeller Roland , Hiller Sven-Jürgen 
Published: August 2017

This paper majorly aims to identify and understand the driving flow phenomena when the blading aspect ratio of a 1.5-stage axial compressor is increased so that its overall axial length is reduced. The blading is representative for a state-of-the-art high-pressure compressor (HPC) front-stage design. As part of the investigation steady-state RANS simulations are performed to evaluate the impact on its performance and operability. Moreover, an optimized high aspect ratio (HAR) design is introduced to recover performance penalties.
In order to achieve the desired reduction in axial stage length at constant blade row spacing and blade height, numerous possible combinations of increased rotor and stator aspect ratios exist. The impact on compressor efficiency and surge margin will be more or less severe, depending on the chord length reduction in rotor and stator. One intermediate combination of both changes in rotor and corresponding stator aspect ratio is analyzed in detail. The results show that by reducing rotor chord length, the compressor’s stability is predominantly compromised, whereas a shorter stator chord has a bigger impact on efficiency than the rotor. For each HAR configuration, profile loss is increased through a reduced blade chord Reynolds number and a higher profile edge thickness-to-chord ratio. Secondary loss is significantly reduced. However, this effect is extenuated by an increased endwall boundary layer thickness-to-chord ratio. Ultimately, this yields a diminished overall stage efficiency. In general, current HPC blade designs exhibit a lower initial rotor aspect ratio compared to the stator vanes. Consequently, an equivalent stage length reduction has a less crucial impact on Reynolds number — hence profile loss — for rotor blades than for stator vanes. Thus, regarding efficiency, there is an optimum of balancing rotor and stator chord length reduction yielding the least efficiency drop.
On the contrary, the stability margin for the compressor stage analyzed is primarily driven by the rotor’s clearance-to-chord ratio. Hence, at constant tip clearance an increase in the rotor’s aspect ratio is proportional to the resulting lack of stability. However, specific compressor design modifications are introduced in order to recover the stability margin without adversely affecting design point efficiency, such that the optimized HAR compressor stage exhibits at least the same performance specifications of the baseline design.
This study’s findings also encourage that increasing the blading aspect ratio is a feasible measure for reducing the compressor’s overall axial length aiming a compact design. An optimized HAR compressor allows additional design flexibility, which provides potential for performance improvements.