bluuebunny/crossref_metadata_2025_split huggingface dataset:
Clocking in Low-Pressure Turbines
Authors: Evans K. R. , Longley J. P. 
Published: September 2016

The effect of stator clocking has been experimentally and computationally investigated using a low-speed, two-stage, Low-Pressure Turbine which was specifically designed to maximise the clocking potential by aligning the Stator 1 wake segments with the Stator 2 leading edge along the span. It was verified that the wake segments are aligned to within 10% of stator pitch across the span. The measured clocking effect on the work extraction is 0.12% and on efficiency is 0.08%. Although the effect of clocking is small, it is repeatable, periodic across four stator pitches and consistent between independent measurements. Furthermore, factors to consider for a reliable clocking investigation are discussed.
The measurements revealed that the majority of the clocking effect on the work extraction occurs in Stage 2 and it originates at Stator 2 exit. This indicates that the flow is being processed differently within Stator 2. There is also an effect on the Stage 1 work. In each blade row the measured clocking effect on the lost work is similar across the span.
The computations with meshed cavities do not capture any clocking effects in Stage 1. This indicates that an unsteady viscid phenomenon within Rotor 1 is not captured by the fully turbulent calculation e.g. unsteady transition. However, the computations do capture the measured clocking effect on the Stage 2 work extraction.
It is hypothesised that the clocking effect on Stator 2 flow turning is dominated by a steady, inviscid process.
Accounting for Eccentricity in Compressor Performance Predictions
Authors: Young Anna M. , Cao Teng , Day Ivor J. , Longley John P. 
Published: September 2016

It is known that the tip-clearance gap plays a pivotal role in determining the performance of an aero-engine compressor, both in terms of stability and pressure rise. However, the exact effect of tip-clearance size on stall margin over the range of clearances experienced during engine operation is not known, and most designers substitute rules of thumb for real knowledge when developing new compressors.
Eccentricity in the tip-clearance is also known to affect compressor performance, though again little work has been done to quantify the penalties. It is generally assumed that the stall margin of an eccentric machine will be approximately equal to that of a concentric machine with a clearance equal to the maximum eccentric clearance. Results given in this paper show a stabilising effect of the small tip-clearance sector of an eccentric compressor on the large tip-clearance sector, so the penalty on stall margin is not as large as commonly assumed. It is shown that the stall margin penalty in a single-stage eccentric machine is only 50–60% of that which a concentric compressor with clearance equal to the maximum clearance would exhibit. In addition, the effect of eccentricity is shown to diminish as the average clearance is increased.
In this paper, experiments and computational modelling are used to examine the effects of eccentric tip-clearance on flowfield redistribution and compressor performance. In particular, the three-dimensional nature of the flowfield generated by an eccentric gap is shown for the first time. The purpose of this work is not to provide ‘hard-and-fast’ design rules for eccentric compressors (this cannot be done on the basis of single-stage measurements), but to provide a starting point for a better physical understanding of the problem.
Numerical and Experimental Investigation of Noise Radiation for Double-Suction Centrifugal Fans of Air-Conditioner Indoor Unit
Authors: Zhao Xifeng , Sun Jinju , He Youwei , Lin Kang 
Published: September 2016

Aerodynamic performance and noise level of AC (Air-Conditioner) indoor unit fan system has always been receiving much concern. But most previous studies have been focused on aerodynamic performance and noise level, and less attention is paid to the noise radiation problem. It is essential to identify and quantify the noise radiation, so as to control and reduce the noise level effectively.
The objective of the present investigation is to identify the influential factors of the Blade Passing Frequency (BPF) noise radiation and investigate noise directivity distribution of two double-suction centrifugal flow fans with different fan blades used in AC indoor unit. A hybrid numerical approach is developed for predicting the unsteady fan flow and noise radiation. Unsteady fan flow is solved by Detached Eddy Simulation (DES) method. Then the areoacoustic calculation is performed based on the predicted unsteady flow field, and the obtained results are used as dipole source inputs in acoustic Finite Element Model (FEM) for predicting the noise radiation of the centrifugal fans.
Experimental tests of aerodynamic and aeroacoustic performance are conducted respectively for the fan. A comparison is made between the experimental and measured results. It is demonstrated that the predicted aeroacoustic and noise radiation both agree with the measured ones and the fan blade geometry is much influential to acoustic prediction. Finally, directivity of BPF noise radiation to noise level is evaluated for two different fans.
A One-Dimensional Analytical Method for Turbine Blade Preliminary Cooling Design
Authors: Li Chen , Liu Jian-jun 
Published: September 2016

The turbine blade cooling design is a complex procedure including one-dimensional preliminary cooling design, detailed two-dimensional design and fluid network analyses, and three-dimensional conjugate heat transfer and FEM predictions. Frequent alteration and modification of the cooling configurations make it unpractical to obtain all of three-dimensional design results quickly. Preliminary cooling design deals mainly with the coolant requirements and can be knitted into fluid network to look up the expected cooling structural style to promote three-dimensional geometry design.
Previous methods to estimate the coolant requirements of the whole turbine blade in the preliminary cooling design were usually based on the semi-empirical air-cooled blade data. This paper combines turbine blade internal and external cooling, and presents a one-dimensional theoretical analytical method to investigate blade cooling performance, assuming that the coolant temperature increases along the blade span. Firstly, a function of non-dimensional cooling mass flow rate is derived to describe the new relationship between adiabatic film cooling effectiveness and overall cooling effectiveness. Secondly, a new variable related to film cooling is found to estimate the required adiabatic film cooling effectiveness without using the empirical correlations. Finally, a theoretical calculation about the relationship between non-dimensional cooling mass flow rate and overall cooling effectiveness well corresponds to semi-empirical air-cooled blade data within regular range of cooling efficiency.
The currently proposed method is also a useful tool for the blade thermal analysis and the sensitivity analysis of coolant requirements to various design parameters. It not only can provide all the possible options at the given gas and coolant inlet temperatures to meet the design requirement, but also can give the third boundary conditions for calculating the blade temperature field. It’s convenient to use the heat transfer characteristic of internal cooling structures to estimate the coolant mass flow rate and the channel hydraulic diameter for both convection cooling and film cooling.
Assessment of Grid Resolution Requirements for Accurate Simulation of Disparate Scales of Turbulent Flow in Low-Pressure Turbines
Authors: Pichler R. , Sandberg R. D. , Michelassi V. 
Published: September 2016

Direct numerical simulations (DNS) on different grids for two Reynolds numbers of the T106A turbine cascade have been conducted to understand the influence of resolution on the solution. The work was motivated by different resolutions used in previously published studies that could not only be explained by different numerical methods. Most of these published studies used mean blade pressure distribution and wake loss profiles for validation and grid convergence purposes. DNS for canonical cases in general use more stringent criteria based on turbulence statistics considering that those require higher resolution.
Therefore, in this study the influence of grid resolution on disparate scales of DNS is discussed. It is discussed that mean blade pressure distribution and mean wake loss already show good agreement with experiments for large eddy simulations (LES) provided a sufficient part of the turbulence kinetic energy is resolved. However, to avoid modelling uncertainties of turbulence quantities, DNS is required as LES only resolves part of the turbulence kinetic energy. It is found that in order to achieve grid convergence for turbulence dissipation a six times larger resolution and more than 10 times the computational cost is required than if grid convergence was required for turbulence kinetic energy.
Flow Pattern Evolution and Energy Decomposition of Flows at Different Operating Conditions in a Hydrodynamic Torque Converter
Authors: Wei Wei , Huang Mingxing , Li Yu , Yan Qingdong 
Published: September 2016

Power loss and flow blockage in turbomachinery such as hydrodynamic torque converter are usually caused by jet flow, second flow and flow separation. In this paper, the velocity vector and the pressure distribution of the internal flow field in hydrodynamic torque converter were reduced by the method of the Proper Orthogonal Decomposition (POD) to find the main flow structures and the energy decomposition in the passages of pump, turbine and stator. In order to find their evolutionary processes and energy decompositions, oil flow visualizations were conducted at different speed ratios from 0 to 0.8, including stall condition and design operating condition.
The results showed that the first few modes containing the majority of energy could provide enough accuracy to predict flow behavior and flow structure in flow passages. Especially when the energy percentage of the first mode was majority, its vortex structures could be recognized easily. But the flow patterns of other modes were different from each other and they made the flow more turbulent and complex, which increases the energy loss in the process of power transmission. Besides that, the change of pressure gradient had a direct influence to velocity vector. The results also indicated that the observed fluid pattern of vortex structure became extensive while the influence of secondary flow decreased in the flow passage of pump with the increase of speed ratio. But the situation is just reversed in turbine, that is, the vortex disappeared gradually and the irregular turbulent flow appeared as the increase of speed ratio. In stator, the vortex structure emerged gradually when the speed ratio increased. So the method of snapshots is a very useful way to analyze the complex flow flied in depth and to predict the trend of development.
Solid Element Rotordynamic Modeling of a Rotor on a Flexible Support Structure Utilizing MIMO Support Transfer Functions
Authors: Hu Lingnan , Palazzolo Alan 
Published: September 2016

The accurate modeling of a rotor system is essential for effective design and troubleshooting in rotating machinery. The beam-type finite element (FE) may be inadequate for modeling a rotor or support structure with complex shapes. In addition, the isolated support impedance methods may be inaccurate for modeling the support structure that has modes that are highly coupled between bearings and directions at the bearing locations. The solid FE method is a good replacement of the beam FE and support impedance approaches. However, a drawback for this method is the significant amount of computation time required to obtain accurate solutions due to the large number of nodes in the solid FE analysis.
The authors present an improved approach to analyze the coupled rotor-support dynamics, by modeling the rotor with solid elements and utilizing transfer functions (TFs) to represent the flexible support. A state-space model is then employed to perform general rotordynamic analyses. The solid FE rotor model includes the gyroscopic effects and the asymmetric and cross-coupled stiffness coefficients of the bearing. A series of rational TFs are used to simulate dynamic characteristics of the support structure, including the cross-coupling between degrees of freedom (DOFs). These TFs are derived by curve-fitting the frequency response functions (FRFs) of the solid FE support model at the bearing locations. The impact of the polynomial degree of the TF on the unbalance response analysis is discussed, and a general rule is proposed to select an adequate polynomial degree.
To validate the proposed modeling approach, a comprehensive comparison among the complete solid FE rotor-support model and the solid FE rotor model with the TFs representing the flexible support (the reduced state-space model) are presented. Comparisons are made between natural frequencies, critical speeds, unbalance response, logarithmic decrement (log dec), and computation time. The results of these comparisons show that the reduced state-space rotor-support model provides a dynamically accurate approximation of the solid FE rotor-support model in terms of general rotordynamic analyses. Moreover, the computation time for the proposed modeling approach is reduced to 2.5 minutes, compared to 14 minutes for the complete solid FE modeling. The reduction of the computation time may vary with different number of DOFs of the rotor model and the support structure model.
In addition, the modes up to 100,000 cpm are compared among the beam rotor with the solid FE support model, the solid FE rotor with the super-element support model, and the reduced state-space model. The results show that the reduced state-space model is more accurate in predicting high-frequency modes than the beam rotor-support and super-element support models. Further, the proposed approach with the state-space model is useful for applications in vibration control and active magnetic bearing (AMB) systems.
Modeling for Tip Clearance Effects on Stall-Onset Condition in Transonic Axial Compressors
Authors: Ye Shubo , Zhao Qingjun , Xiang Xiaorong , Xi Guang , Xu Jianzhong 
Published: September 2016

Rotating stall is a primary limit to compressor performance, and the reasonable estimation of stall-onset point is very useful in compressor design. Extensive investigations have been conducted in the past few decades to develop analytical models and numerical methods for stall-onset prediction, and much progress has been made in the understanding of flow mechanism for rotating stall. In spite of the robust prediction ability of stall-onset condition, the unsteady 3-D computations are still time-consuming for industrial applications. Analytical models are able to provide a fast estimation of compressor stall onset. However, empirical correlations are usually needed in the analytical models, which leads to a decrement in the accuracy and application scope of the models. Especially for high speed compressors, tip clearance effects hasn’t been evaluated reasonably in the previous analytical models, which actually plays a very important role in determining the stall-onset point. Therefore, new analytical models accounting for tip clearance effects will be promising in estimating the stall-onset more precisely. It’s the requirement for a new analytical model that motivates the present work.
In the present work, the unsteady flow simulation of a transonic compressor rotor at near stall condition was performed to clarify the relations between tip clearance flow oscillations and compressor stall-onset in transonic axial compressor rotors. The interaction between tip clearance and incoming flow is simplified to a 2-D analogy of free-stream and counter-flow wall jet interaction. Momentum balance analysis is applied to identify the position of tip clearance/incoming flow interface, together with a prediction method of tip leakage vortex core trajectory. The effects of the in-passage shock on tip clearance/incoming flow interaction is taken into account by applying an upstream deflection of the interface, and this deflection is also observed in the computational flow field at near stall conditions. As a combination of the above-mentioned aspects, a model is proposed to define the critical point for tip clearance flow spillage from blade leading edge, which corresponds to the stall-onset point on compressor performance curves. Validations against numerical results prove that the model is capable of including tip clearance effects on stall-onset point. Parametric study of the model shows that blade tip offloads with increasing tip clearance, reducing the inverse momentum flux of tip clearance flow. As a result, the stalling flow coefficient appears to be less sensitive to tip clearance variation, which accords with the published experimental results.
Preliminary and Robust Design Analysis of a Solar Thermal Power Block
Authors: Persky Rodney , Sauret Emilie 
Published: September 2016

Australia is endeavouring to expand the mix of power resources, and is investing heavily in the development of renewable generation methods such as concentrated solar thermal power. In these systems, the power block and turbine need to maintain high efficiency under non-ideal conditions away from the design point.
Literature shows that there is a clear relationship between the selection of fluids, the design of the operating cycle, the fluctuation in operating conditions and changes in power block performance. It is thus important for innovative power block designs to consider the performance of the system as a whole rather than by component, mainly turbine design, cycle development and economic analysis. However, there are few works that consider the coupling of multidisciplinary design and robust design to turbine-fluid selection and economic analysis for realistic systems. Furthermore, existing methodologies for robust optimisation often do not consider the effects of high-density gas properties on the performance of the power block. It is also critical that a power generation system produces ideal economic outcomes that meet a number of key performance indicators including levelised cost of electricity.
Therefore, this paper develops a preliminary multidisciplinary design and robust design approach applied to turbine-fluid selection and economic analysis of a solarthermal power block. In this work, an Organic Rankine Cycle using novel working fluids for a solarthermal power system is developed. Integrating robust optimisation into the development of the power block is key to push efficiency further and guarantee power block feasibility when running at non-ideal conditions. A preliminary multidisciplinary optimisation is applied to design the complete power block concept such that the power block operates at peak performance across multiple analysis approaches.
Numerical Analysis of the Dynamic Flame Response and Thermo-Acoustic Stability of a Full-Annular Lean Partially-Premixed Combustor
Authors: Innocenti Alessandro , Andreini Antonio , Facchini Bruno , Cerutti Matteo 
Published: September 2016

A thermo-acoustic stability of a full-annular lean partially-premixed heavy-duty gas turbine combustor is carried out in the present paper. A sensitivity analysis is performed, varying the flame temperature for two operating conditions.
The complex interaction between the system acoustics and the turbulent flame is studied in Ansys Fluent, using Unsteady-RANS simulations with Flamelet-Generated Manifolds combustion model. Perturbations are introduced in the system imposing a broadband excitation as inlet boundary condition. The flame response is then computed exploiting system identification techniques. The identified flame transfer functions are compared each other and the results analysed in order to give more physical insight on the coupling mechanisms responsible for the flame dynamic response.
The effect of fuel mass flow fluctuations is then introduced as further driving input, describing the flame as a Multi-Input Single-Output system. Further in-depth studies are carried out on pilot flames aiming at replicating the dynamic response of the real flame and understanding the driving mechanism of thermo-acoustic instability onset as well.
The obtained results are implemented into a finite element model of the combustor, realized in COMSOL Multiphysics, to analyse the system stability.
Numerical model affordability has been assessed through comparisons with results from full-annular combustor experimental campaign carried out by GE Oil & Gas since the early phases of the design and development of a heavy-duty gas turbine. This allowed the discussion of the model ability to describe the stability properties of the combustor and to catch the instabilities onset as detected experimentally.
Valuable indications for future design optimization were also identified thanks to the obtained results.
Highly Resolved LES of a Linear HPT Vane Cascade Using Structured and Unstructured Codes
Authors: Pichler Richard , Kopriva James , Laskowski Gregory , Michelassi Vittorio , Sandberg Richard 
Published: September 2016

Conventionally meridian, RANS or URANS simulations are used in design. However, their accuracy is not always satisfactory. Higher order methods like direct and large eddy simulation have shown improved results for various case. While traditionally many direct numerical simulation (DNS) and large eddy simulation (LES) studies have been conducted using highly tailored research codes. These codes often use high order methods with both low numerical dissipation and dispersion often in conjunction with structured grids. While these features allow for high efficiency and accuracy they require a considerable effort to obtain appropriate grids. The ongoing rapid increases in available computer power have allowed commercial software packages to also include LES using lower order methods and unstructured grids. These are more flexible and robust to apply but it is not clear how they compare to the higher accuracy research solvers. In this work an initial comparison between a structured research code and an unstructured commercial code is presented.
To that end, the paper compares compressible LES conducted with a high-resolution research code and with a commercial code of a statistically 2D linear transonic high pressure turbine vane cascade. The geometry investigated is that of Arts and Rouvroit [1] at isentropic exit Reynolds number approximately 590,000 and isentropic exit Mach number 0.93 with a target inlet turbulence intensity of 4%. The results are also compared to Direct Numerical Simulation results, published by Wheeler et al. [2], for boundary layer and wake development for low levels of freestream inlet turbulence. In the research code inlet turbulence is generated synthetically while the turbulence grid comprised of bars is simulated in the commercial code. While the flow around the blade is in good agreement differences are present in the wake data.