bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow Simulation Around a Rim-Driven Wind Turbine and in Its Wake
Authors: Kaiser Bryan E. , Poroseva Svetlana V. , Snider Michael A. , Hovsapian Rob O. , Johnson Erick 
Published: November 2013

A relatively high free stream wind velocity is required for conventional horizontal axis wind turbines (HAWTs) to generate power. This requirement significantly limits the area of land for viable onshore wind farm locations. To expand a potential for wind power generation and an area suitable for onshore wind farms, new wind turbine designs capable of wind energy harvesting at low wind speeds are currently in development.
The aerodynamic characteristics of such wind turbines are notably different from industrial standards. The optimal wind farm layout for such turbines is also unknown. Accurate and reliable simulations of a flow around and behind a new wind turbine design should be conducted prior constructing a wind farm to determine optimal spacing of turbines on the farm.
However, computations are expensive even for a flow around a single turbine. The goal of the current study is to determine a set of simulation parameters that allows one to conduct accurate and reliable simulations at a reasonable cost of computations. For this purpose, a sensitivity study on how the parameters variation influences the results of simulations is conducted. Specifically, the impact of a grid refinement, grid stretching, grid cell shape, and a choice of a turbulent model on the results of simulation of a flow around a mid-sized Rim Driven Wind Turbine (U.S. Patent 7399162) and in its near wake is analyzed. This wind turbine design was developed by Keuka Energy LLC.
Since industry relies on commercial software for conducting flow simulations, STAR-CCM+ software [1] was used in our study. A choice of a turbulence model was made based on the results from our previous sensitivity study of flow simulations over a rotating disk [2].
Faster Design of Gas Turbine Parts Using Rapid Prototype Models for Verification of Coolant Flow Characteristics
Authors: Sedlov Andrey , Bauer Andreas , Mozharov Alexey , Gritsch Michael , Kostege Valery 
Published: November 2013

One of the keys to successful time-to-market introduction of a gas turbine blading upgrade package is fast-track development. Cooled turbine blades should match the designed coolant mass flow from the first iteration, otherwise, lengthy and expensive wax or core die rework has to be done.
Use of rapid prototyping for cooled components allows verification of their flow characteristics during the design phase and the check/calibration of flow predictions, prior to manufacturing. The present paper discusses features of the rapid prototyping process (selective laser sintering) in their application to plastic models of hot gas path components of modern heavy-duty gas turbines. A tailored sintering process was developed and successfully applied also to film cooled parts. Rapid prototype models were flow tested and then design changes were made to achieve the required levels of cooling air flow. Wax and core dies were produced, taking the design changes into account. Coolant flow characteristics of cast and machined parts were compared with those of rapid prototype models and with the design intent for a wide set of configurations and flow conditions. Comparison demonstrates good agreement in flow characteristics between prototyped and production parts, and thus confirms the applicability and reliability of this approach. Use of rapid prototype models significantly reduced the project duration, eliminated rework cost for casting tooling, and ultimately lead to a higher quality end product.
Grid Stability: Gas Turbines for Primary Reserve
Authors: DiCampli James , Schulke William 
Published: November 2013

Power grids are continually subjected to variations in load demand, leading to imbalances between generation and consumption. Such imbalances have an impact on the frequency level, requiring ongoing frequency control. Timely response of sufficient magnitude is critical to ensure grid stability. Without appropriate controls, variation in frequency levels can compound, leading to trips or even blackouts.
Primary Frequency Control (PFC) and Regulation Margin Control (RMC) have recently become a requirement for gas turbine generators (GTG) by many transmission grid authorities. PFC provides grid stability by allowing the gas turbine to automatically increase (or decrease) load when a grid frequency deviation occurs outside of a frequency band, and maintains this increased (or decreased) load while the deviations persist. RMC is used to ensure that a percentage of the GTG generating capability is reserved for use when grid frequency excursions occur.
There are different grid control regulations for different countries and regions. For example, the European Grid Code requires enough Primary Reserve set aside to support a +/−200 mHz grid frequency deviation with associated response times. The GTG must keep a percentage of the unit’s power capacity, or Primary Reserve, available for this purpose. The size of Primary Reserve power contributed by the grid frequency deviation is determined by the RMC Margin and PFC Droop settings, and must be managed under a wide range of operating and ambient conditions.
This paper reviews field test results and lessons learned in developing an approach to meeting the grid requirements. This includes the PFC reserve power response to frequency deviations, associated tolerances, and additional controls required to optimize the spray-intercooling power augmentation system.
Experimental and Numerical Investigation of Near-Tip Flow Field in an Axial Flow Compressor Rotor: Part I — Flow Characteristics at Stable Operating Conditions
Authors: Wu Yanhui , Wu Junfeng , Zhang Haoguang , Chu Wuli 
Published: November 2013

Systematical casing pressure measurements were undertaken to supplement instantaneous experiment data to available database of a high-speed small-scale compressor rotor, which was crucial for understanding the flow mechanism of short-length scale stall inception. At the same time, improved full-annulus simulations were conducted to assist in interpretation of experimental observations. In Part I of current investigation, FFT (fast Fourier transformation) and STFT (short time Fourier transformation) analyses of instantaneous casing pressure signals were conducted to conclude flow characteristics near casing at stable operating conditions, and reasonable explanation of experimental observations was given in combination with the current and previous numerical results.
FFT analyses of casing pressure signals showed a characteristic hump with varying band lower than blade passing frequency (BPF) appeared at near-stall stable conditions. This indicated that an unsteady phenomenon emerged from the near-tip flow field for the test rotor. The variation in the amplitude of characteristic hump implied that underlying flow mechanism leading to the emergence of unsteady phenomenon originated from a location near leading edge and within passage. Further STFT analyses showed that the active frequency of this unsteady phenomenon varied with time, thus leading to the appearance of excitation band in FFT analysis results. FFT and STFT analyses of monitoring results of numerical probes arranged in absolute frame showed a similar unsteady phenomenon appeared in the simulated near-tip flow field. Detailed analyses of simulated instantaneous flow fields and comparison with measured flow characteristics indicated that the unsteady flow phenomenon observed in experiments was equivalent to rotating instability (RI) as far as non-uniform tip loading distribution was concerned, and the formation and activity of tip secondary vortex (TSV) was the flow mechanism of emergence of RI.
Experimental and Numerical Investigation of Near-Tip Flow Field in an Axial Flow Compressor Rotor: Part II — Flow Characteristics at Stall Inception Condition
Authors: Wu Yanhui , Wu Junfeng , Zhang Haoguang , Chu Wuli 
Published: November 2013

Systematical casing pressure measurements were undertaken to supplement instantaneous experiment data to available database of a high-speed small-scale compressor rotor, which was crucial for understanding the flow mechanism of short-length scale stall inception. At the same time, improved full-annulus simulations were conducted to assist in interpretation of experimental observations. In Part II of current investigation, original instantaneous casing pressure signals and STFT (short time Fourier transformation) analyses were conducted to conclude flow characteristics near casing at stall inception operating condition, and reasonable explanation of experimental observations was given in combination with numerical results.
The current experimental investigation showed the stall inception of the test rotor was triggered by a spike, propagating at about 66.7%, which evolved into a single fully-developed stall cell. STFF analysis of pressure signal detected by probe located at tip leading edge showed that frequency peaks with varied band, which already observed in near-stall stable flow condition in Part I, was still a dominant flow feature before spike emergence, though it was hardly perceived after spike emergence due to a sudden increase in the overall energy of pressure signal, which attributed to the interface of incoming and tip clearance flow beyond leading edge plane according to STFT results. Monitoring results of static pressures in the absolute frame from current simulation and the corresponding FFT and STFT analyses showed a similar flow field evolution process as those observed in experiment. The current investigation provided adequate experimental evidence to support the previous simulation results in which a viewpoint of formation and activity of tip secondary vortex (TSV) was proposed as the underlying flow mechanism of the origin of unsteadiness near casing at near-stall stable operating conditions, and emergence of spike during the transition of flow field into unstable state, and further verified that the unsteady flow phenomenon observed in near-stall stable flow condition was equivalent to rotating instability (RI), thus establishing the causal linkage between RI and stall inception for the test rotor.
Unsteady Simulation of a Two-Stage Cooled High Pressure Turbine Using an Efficient Non-Linear Harmonic Balance Method
Authors: Subramanian Venkataramanan , Custer Chad H. , Weiss Jonathan M. , Hall Kenneth C. 
Published: November 2013

The harmonic balance method is a mixed time domain and frequency domain approach for efficiently solving periodic unsteady flows. The implementation described in this paper is designed to efficiently handle the multiple frequencies that arise within a multistage turbomachine due to differing blade counts in each blade row. We present two alternative algorithms that can be used to determine which unique set of frequencies to consider in each blade row. The first, an all blade row algorithm, retains the complete set of frequencies produced by a given blade row’s interaction with all other blade rows. The second, a nearest neighbor algorithm, retains only the dominant frequencies in a given blade row that arise from direct interaction with the adjacent rows. A comparison of results from a multiple blade row simulation based on these two approaches is presented. We will demonstrate that unsteady blade row interactions are accurately captured with the reduced frequency set of the nearest neighbor algorithm, and at a lower computational cost compared to the all blade row algorithm.
An unsteady simulation of a two-stage, cooled, high pressure turbine cascade is achieved using the present harmonic balance method and the nearest neighbor algorithm. The unsteady results obtained are compared to steady simulation results to demonstrate the value of performing an unsteady analysis. Considering an unsteady flow through a single blade row turbine blade passage, it is further shown that unsteady effects are important even if the objective is to obtain accurate time-averaged integrated values, such as efficiency.
A Fluid-Structure Coupling Method for Rotor Blade Unrunning Design
Authors: Yang Hui , Zheng Yun 
Published: November 2013

This paper reports a numerical method for the design of a unrunning blade with the consideration of both nonlinear aerodynamic and centrifugal forces. Accurate prediction of blade manufacture shape in turbomachinery is crucial for performance, efficiency and aeroelastic stability. An iterative procedure starting from a given blade running shape is developed to predict the manufacture blade shape.
The model is based on a three-dimensional (3D) unsteady nonlinear Navier-Stokes Computational Fluid Dynamics (CFD) solver and the mode superposition structural dynamic theory in conjunction with a finite element structural model for the rotor blade. The manufacture profile of the blade (“Cold” blade) is estimated from the running blade shape (“Hot” blade). ANSYS finite element code is used to compute the deflection of the cold blade due to centrifugal loads. A finite volume based 3D nonlinear CFD code, coupled with a mode superposition structural dynamic modal method, is employed to determine the blade deflection due to unsteady aerodynamic loading. The difference between the computed blade profile and the targeted hot blade shape is used to predict a new cold blade for the next iteration if the convergence criterion is not met.
The method is applied to predict the manufacture blade shape of a large-scale propfan and a NASA rotor 67 fan. The predicted blade profile and the twist angle of the blade at various spans are presented. The results show that improvements of the manufacture blade profile can be made by including proper nonlinear aerodynamic effect on the blade deflection in the numerical model. The results also illustrate that aerodynamic nonlinear effects on structural deformation should be included for a better cold blade design.
Unsteady CFD Simulation of Control Valve in Throttling Conditions and Comparison With Experiments
Authors: Zanazzi Giorgio , Schaefer Ottmar , Sell Michael , Ridoutt Colin 
Published: November 2013

The operational flexibility of steam power plant is becoming more important as power generation becomes increasingly decentralized, with a growing contribution from renewable energy sources. In a power plant the control valve is a key component to guarantee the control of the plant of which is increasingly demanded to extend the operational capability.
At specific operating conditions, the control valve could experience vibrations. In this paper, the physical phenomena of the unsteady aerodynamic excitation force have been investigated by means of CFD techniques.
An in-house code was used to simulate the flow-induced vibration. Unsteady transonic 3D simulation generally requires huge computational effort. A novel unsteady quasi-3D approach has been developed and applied as pre-design tool to establish the qualitatively operational map of the valve and to detect the critical operational range, to reduce the number of detailed 3D simulations.
The numerical results are compared with experimental test undertaken in the Central Research Institute of Electric Power Industry [4] and full 3D simulation performed with the commercial tool CFX, using the Scale-Adaptive Simulation (SaS) turbulence model. Different pressure drops at certain lift have been selected from the operational map and reproduced numerically. Different modes have been identified, from stochastic behavior with wide width of frequency to periodic flow with one dominant frequency.
Results indicate good agreement between the predicted frequency and amplitude and benchmark experiments. The quasi-3D simulation is able to reproduce the principle behavior of the flow field for different drop of pressure and capture the different operational mode. Similar behaviour has been detected also for the selected operating condition in the full 3D analysis.
In addition, flutter calculation of the downstream pipe is carried out. It has demonstrated that the implementation of oscillating discharge piping influences the amplitudes and frequency of the upstream flow region.
Adaption of Giles Non-Local Non-Reflecting Boundary Conditions for a Cell-Centered Solver for Turbomachinery Applications
Authors: Robens Sebastian , Jeschke Peter , Frey Christian , Kügeler Edmund , Bosco Arianna , Breuer Thomas 
Published: November 2013

In contrast to external flow aerodynamics, where one-dimensional Riemann boundary conditions can be applied far up- and downstream, the handling of non-reflecting boundary conditions for turbomachinery applications poses a greater challenge due to small axial gaps normally encountered. For boundaries exposed to non-uniform flow in the vicinity of blade rows, the quality of the simulation is greatly influenced by the underlying non-reflecting boundary condition and its implementation. This paper deals with the adaptation of Giles’ well-known exact non-local boundary conditions for two-dimensional steady flows to a cell-centered solver specifically developed for turbomachinery applications. It is shown that directly applying the theory originally formulated for a cell-vertex scheme to a cell-centered solver may yield an ill-posed problem due to the necessity of having to reconstruct boundary face values before actually applying the exact non-reflecting theory.
In order to ensure well-posedness, Giles’ original approach is adapted for cell-centered schemes with a physically motivated reconstruction of the boundary face values, while still maintaining the non-reflecting boundary conditions. The extension is formulated within the original framework of determining the circumferential distribution of one-dimensional characteristics on the boundary. It is shown that, due to approximations in the one-dimensional characteristic reconstruction of boundary face values, the new approach can only be exact in the limiting case of cells with a vanishing width in the direction normal to the boundary if a one-dimensional characteristic reconstruction of boundary face values is used. To overcome the dependency on the width of the last cell, the new boundary condition is expressed explicitly in terms of a two-dimensional modal decomposition of the flow field. In this formulation, vanishing modal amplitudes for all incoming two-dimensional modes can easily be accomplished for a converged solution. Hence we are able to ensure perfectly non-reflecting boundary conditions under the same conditions as the original approach. The improvements of the new method are demonstrated for both a subsonic turbine and a transonic compressor test case.
Aerodynamic Design and Testing of an Axial Flow Compressor for the GT24/26 Gas Turbines
Authors: Novak Damir , Loetzerich Michael , Boese Matthias 
Published: November 2013

A 22-stage axial flow compressor with a pressure ratio 35:1 has been designed, built and successfully tested for a heavy-duty gas turbine application. Advanced technology and aero engine design tools have been used. The compressor has been designed using an “arbitrary” airfoil blading including 3D design features, like leading edge re-camber, lean, sweep and flowpath contouring.
The compressor performance and part load behavior have been improved by accurate stage matching based on whole compressor 3D analyses. The new compressor has been tested in a scaled down rig and validated in the Alstom Test Power Plant (ATPP).The compressor met all design objectives and demonstrated excellent performance.
This paper describes the aerodynamic design and test results.
Effect of Circumferential Static Pressure Non-Uniformity Caused by a Volute on Flow in High Pressure Ratio Centrifugal Compressor With Vaneless and Vaned Diffuser
Authors: Tamaki Hideaki , Unno Masaru , Zheng Xinqian , Zhang Yangjun 
Published: November 2013

Centrifugal compressors are deemed to have a wide operating range. Recirculation devices, which comprise a bleed slot, an upstream slot and an annular cavity connecting them, are often used particularly compressors for turbochargers. They remove low energy fluid at the inducer and improve the incidence angle of the impeller leading edge, i.e. the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. The impeller of a centrifugal compressor is often housed in a volute. Since the geometry of the volute is not axisymmetric, the impeller might be surrounded by an asymmetric flow field, hence there is the potential to enlarge the compressor operating range and improve efficiency using a recirculation device with an asymmetrically-distributed bleed slot, referred to here as a non-axisymmetric recirculation device.
The authors [1] applied non-axisymmetric recirculation devices to a compressor with a vaneless diffuser. The results showed the effectiveness of a non-axisymmetric recirculation device with a bleed slot partially channeled in the circumferential direction. They also showed that the surge line of the compressor characteristics, which is the line connecting the operational points of the smallest flow rates on all peripheral Mach numbers, was significantly affected by the change in the circumferential position of the bleed slot relative to the volute tongue. The tested compressor was originally designed to feature a vaned diffuser [2]. Enhancing the compressor operating range is the key for marine use turbochargers, integrally geared compressors, multistage compressors and gas turbines as well as automotive turbochargers. These compressors normally use vaned diffusers. In this study the authors tried to apply non-axisymmetric recirculation devices developed in their previous study [1] to compressors with a vaned diffuser. Moreover different circumferential positions of the bleed slot relative to the volute tongue were tested as well as the vanelss diffuser case. The change in the surge line of the compressor characteristics was much smaller compared to the compressor with the vaneless diffuser. The circumferential static pressure distributions in the compressors in combination with vaneless and vaned diffusers were measured to determine the above reason as well as conducting unsteady calculations with a simplified outlet boundary condition. These measurements and calculations showed that the impeller with the vaned diffuser was surrounded by a less distorted static pressure field than that with the vaneless diffuser. These results implied that the vaned diffuser depresses the spread of the circumferential static pressure non-uniformity effect caused by a volute to the impeller.