bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of Heat Transfer Coefficients in Gaseous Flow: First Test of a Recent Sensor Concept for Stationary and Oscillating Flow
Authors: Eschmann Gunter , Kuntze Alexander , Uffrecht Wieland , Odenbach Stefan 
Published: September 2014

Heat transfer coefficients are very important for the design of the various flow paths found in turbomachinery. An accurate measurement of heat transfer is difficult considering gaseous flow in combination with good thermal conductivity of the boundaries along the flow path. The majority of the measurement methods applied frequently have at least one of the following problems. The measurement setup as for instance a heat flux sensor is a thermal barrier or introduces, for measurement reasons, a lot of heat into the object of interest. In both cases the main error results from the modification of the system, which is critical for the investigation of any sensitive flow condition. Furthermore, insufficient fluid reference temperature and/or heat flux with changing sign corrupts any attempt to calculate reasonably heat transfer coefficients.
Recent research and development activities are often focused on non-stationary effects as for instance caused by blade passing and combustor noise or any other source of transient or non-stationary flow in turbomachinery. This is not limited to the main gas path. A lot of attention is also paid to these effects for the internal air system for example the intensification of heat transfer by usage of non-stationary effects is very interesting for efficient cooling along the hot gas path. Therefore, the measurement of heat transfer coefficients becomes even more important for transient/non-stationary flow conditions.
This contribution presents a new test rig and an experimental investigation of local heat transfer coefficients in oscillating and superposed stationary and oscillating gaseous flow with metallic boundaries. The measurements presented are based on a novel measurement/sensor concept tested first time in non-stationary flow. The measurement setup features miniaturized sensor dimensions, low energy consumption, low backlash of the measurement on the flow and improved resolution compared to other concepts for the conditions addressed.
Furthermore, measurements of the radial distribution of the heat transfer coefficient on a flat plate in front of an oscillating and superposed stationary and oscillating free jet are presented. For the continuous jet, the air flows through a cavity and a nozzle for stationary conditions. The oscillating or so called synthetic jet is a zero mass flow jet through a nozzle generated by a pulsating diaphragm. Additionally, the superposition of continuous and synthetic jet results in the pulsed jet. All jets described are examined in an orthogonal impingement setup for Reynolds between 1000 and 9000. The nozzle-to-plate distances are varied between 0.5 and 7 nozzle diameters covering a flow region from stagnation point up to five nozzle diameters off the jet axis. Additionally a comparison with correlations found in literature as well as a discussion of the results is included.
Modeling the GTE Under Its Dynamic Heating Conditions
Authors: Yepifanov Sergiy V. , Zelenskyi Roman L. , Loboda Igor 
Published: September 2014

A modern gas turbine engine (GTE) is a complex non-linear dynamic system with the mutual effect of gas-dynamic and thermal processes in its components. The engine development requires the precise real-time simulation of all main operating modes.
One of the most complex operating modes for modeling is “cold stabilization”, which is the rotors acceleration without completely heated up the turbine elements. The dynamic heating problem is a topical practical issue. Solving the problem requires coordinating a gas-path model with heat and stress models, which is also a significant scientific problem.
The phenomenon of interest is the radial clearances change during engines operation and its influence on engines static and dynamic performances. To consider the clearance change, it is necessary to synthesize the quick proceeding stress-state models (QPSSM) of a rotor and a casing for the initial temperature and dynamic heating.
The unique feature of the QPSSM of GTEs is separate equation sets, which allow the heat exchange between structure elements and the gas (air) and the displacements of the turbine rotor and the casing. This ability appears as a result of determining the effect of each factor on different structural elements of the engine. The presented method significantly simplifies the model identification, which can be performed based on a precise calculation of the unsteady temperature fields of the structural elements and the variation of the radial clearance.
Thus, the present paper addresses a new method to model the engine dynamics considering its heating up. The method is based on the integration of three models: the gas-path dynamics model, the clearance dynamics model and the model of the clearance effect on the efficiency. The paper also comprises the program implementation of the models. The method was tested by applying to a particular turbofan engine.
Forward and Backward Mode Excitation of Flexible Rotor Supported by Tilting Pad Bearings: Numerical and Experimental Investigation
Authors: Wang Weimin , Li Qihang , Gao Jinji , Dimond Timothy , Allaire Paul 
Published: September 2014

Understanding rotor modal excitations is crucial for high performance centrifugal compressors and other rotating machines. Assuring low vibration levels of such machines at operating conditions before delivery is important both for original equipment manufacturers (OEMs) and end users. In this paper, transient simulations of a full scale test rig rotor subject to sine sweep excitations are performed to investigate the forward and backward rotor whirling response. The applied sine sweep excitations are circular forward, circular backward, and elliptical forward, respectively. The effects of excitation force amplitude are also investigated to determine the minimum force required to accurately identify the rotor system modal parameters.
The transient simulation results are then used to investigate a forward and backward mode system identification method for rotating machinery stability based on sine-sweep excitations. Both simulations and experimental testing on a full size rotor with an electromagnetic actuator were performed to verify and validate the method. The traditional Multiple Input Multiple Output (MIMO) Frequency Response Function (FRF) is transformed into a directional Frequency Response Function (dFRF) form. This transformation recasts the real number field into complex number field via a transformation matrix. This transformation separates the MIMO FRFs into forward and backward components, which improves the accuracy of the identified results. This method is used to identify the first forward bending modal parameters to estimate rotor stability. The rational polynomial method is used to fit and identify both the dFRFs. Excellent correlation was obtained between simulation results and the identification experiments. The results of this paper provide new insights for avoidance of rotor instability in centrifugal compressors.
Stall Margin Improvement in Three-Stage Low Pressure Compressor by Use of Slot Type Casing Treatments
Authors: Gelmedov F. Sh. , Mileshin V. I. , Kozhemyako P. G. , Orekhov I. K. 
Published: September 2014

The Central Institute of Aviation Motors (CIAM) has been engaged in the development of methods and technologies extending the range of stable operation for GTE axial compressors on the basis of systematic experimental and theoretical investigations of processes before and after flow disturbances for many years. The general sources of experimental data were stage models of various types. They are first supersonic stages with 0.3–0.45 hub ratio and subsonic stages with 0.75 hub ratio, as well as high-loaded stages with low aspect ratio.
As a result of these investigations, a structural configuration of the casing treatment (CT) was designed to prevent local flow separation on flow passage surfaces of a compressor stage.
The CT structure includes the following components:
- Slotted spacer installed above the inlet rotor section;
- Attached ring covering the slotted spacer.
An approximate procedure for selecting the optimal CT geometric parameters and their interrelations was developed for CT designing. Using this procedure, special investigations were completed and detected the CT effects on operation of the axial compressor.
These effects are:
- Effect of air back and forward leakage through slots between the blade tips and the inlet rotor section;
- Effect of stall deceleration in the stage flow passage;
- Pulsation damping at the stage tip when flowing around the CT slotted spacer.
Based on this methodology, CT prototypes were developed and tested in various single-stage and multi-stage compressors. As an example of CT advantages, we can show test results for a three-stage low-pressure compressor (LPC) designed by CIAM.
The LPC in take-off conditions provides the following design parameters:
- Pressure ratio: 3.4;
- Corrected tip speed: 418 m/s;
- Stall margin: 20% … 21% within 0.5–1.0 corrected RPM.
According to experimental investigations, the use of CT results in a considerable increase in LPC stall margin without losses in other design parameters. Additionally, the results of 3D viscous flow calculation are shown for compressor performance analysis.
Structural Analysis of a Small H-Darrieus Wind Turbine Using Beam Models: Development and Assessment
Authors: Bianchini Alessandro , Cangioli Francesco , Papini Susanna , Rindi Andrea , Carnevale Ennio Antonio , Ferrari Lorenzo 
Published: September 2014

In the present wind energy research, Darrieus-type vertical-axis wind turbines are increasingly appreciated, especially in small installations. In particular, H-shaped turbines can provide attractive spaces for novel design solutions, aimed at reducing the visual impact of the rotors and then at improving their degree of integration with several installation contexts (e.g. a built environment); moreover, novel small rotors are thought to be able in the near future to make large use also of new and cheaper materials (e.g. plastic or light alloys) which could notably reduce the final cost of the produced energy. As a consequence, the structural analysis of the rotors becomes more and more important: a continuous check between the design solutions needed to maximize the aerodynamic performance of the blades and the structural constraints must be provided. In addition, the requirements of international standards for certification encourage the development of proper numerical tools, possibly with low computational costs for the manufacturers.
In this study, the structural analysis of a novel three-helix-bladed Darrieus turbine is presented; the turbine is a real industrial machine almost entirely produced with plastic with a new complex aesthetic design. In detail, a structural modeling based on beam elements has been developed and assessed in comparison to more complex models, as it was thought to provide a notable reduction of the computational cost of the simulations with an acceptable decrease of the accuracy.
Moreover, the 1D structural model was exploited to verify the capabilities of a novel software, able to verify the dynamic response of the wind turbine in real functioning, i.e. with mechanical loads and interactions with the wind flow.
Benefits and drawbacks of the proposed modeling approach are finally discussed by analyzing both the calculation time and the accuracy of the simulations.
Analysis of the Rotordynamic Response of a Centrifugal Compressor Subject to Aerodynamic Loads due to Rotating Stall
Authors: Biliotti Davide , Bianchini Alessandro , Vannini Giuseppe , Belardini Elisabetta , Giachi Marco , Tapinassi Libero , Ferrari Lorenzo , Ferrara Giovanni 
Published: September 2014

In the current industrial research on centrifugal compressors, manufacturers are showing increasing interest in the extension of the minimum stable flow limit in order to improve the operability of each unit. The aerodynamic performance of a compressor stage is indeed often limited before surge by the occurrence of diffuser rotating stall. This phenomenon generally causes an increase of the radial vibrations, which, however, is not always connected with a remarkable performance detriment.
In case the operating curve has been limited by a mechanical criterion, i.e. based on the onset of induced vibrations, an investigation on the evolution of the aerodynamic phenomenon when the flow rate is further reduced can provide some useful information. In particular, the identification of the real thermodynamic limit of the system could allow one to verify if the new load condition could be tolerated by the rotordynamic system in terms of radial vibrations.
Within this context, recent works showed that the aerodynamic loads due to a vaneless diffuser rotating stall can be estimated by means of test-rig experimental data of the most critical stage. Moreover, by including these data into a rotordynamic model of the whole machine, the expected vibration levels in real operating conditions can be satisfactorily predicted.
To this purpose, a wide-range analysis was carried out on a large industrial database of impellers operating in presence of diffuser rotating stall; the analysis highlighted specific ranges for the resultant rotating force in terms of intensity and excitation frequency. Moving from these results, rotordynamic analyses have been performed on a specific case study to assess the final impact of these aerodynamic excitations.
Some Guidelines for the Experimental Characterization of Vaneless Diffuser Rotating Stall in Stages of Industrial Centrifugal Compressors
Authors: Bianchini Alessandro , Biliotti Davide , Giachi Marco , Belardini Elisabetta , Tapinassi Libero , Ferrari Lorenzo , Ferrara Giovanni 
Published: September 2014

An accurate estimation of rotating stall is one of the key technologies for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit.
With particular reference to the vaneless diffuser stall, much research has been directed at investigating the physics of the phenomenon, the influence of the main design parameters and the prediction of the stall inception. Few of them, however, focused attention on the evaluation of the aerodynamic unbalance due to the induced pressure field in the diffuser, which, however, could provide a valuable contribution to both the identification of the actual operating conditions and the enhancement of the compressor operating range by a suitable choice of the control strategy.
Although advanced experimental techniques have been successfully applied to the recognition of the stall pattern in a vaneless diffuser, the most suitable solution for a wider application in industrial test-models is based on dynamic pressure measurements by means of a reduced number of probes. Within this context, a procedure to transpose pressure measurements into the spatial pressure distribution was developed and validated on a wide set of industrial test-models.
In this work, the main guidelines of the procedure are presented and discussed, with particular reference to signals analysis and manipulation as well as sensors positioning.
Moreover, the prospects of using a higher number of sensors is analyzed and compared to standard solutions using a limited probes number.
Pore-Level Numerical Simulation of Open-Cell Metal Foams With Application to Aero Engine Separators
Authors: de Carvalho Thiago Piazera , Morvan Hervé P. , Hargreaves David 
Published: September 2014

In aero engines, the oil and air interaction within bearing chambers creates a complex two-phase flow. Since most aero engines use a close-loop oil system and releasing oil out is not acceptable, oil-air separation is essential. The oil originates from the engine transmission, the majority of which is scavenged out from the oil pump. The remainder exits via the air vents, where it goes to an air oil separator called a breather. In metal-foam-style breathers separation occurs by two physical processes. Firstly the largest droplets are centrifuged against the separator walls. Secondly, smaller droplets, which tend to follow the main air path, pass through the metal foam where they ideally should impact and coalesce on the material filaments and drift radially outwards, by the action of centrifugal forces. Although these devices have high separation efficiency, it is important to understand how these systems work to continue to improve separation and droplet capture.
One approach to evaluate separation effectiveness is by means of Computational Fluid Dynamics. Numerical studies on breathers are quite scarce and have always employed simplified porous media approaches where a momentum sink is added into the momentum equations in order to account for the viscous and/or inertial losses due to the porous zone [1]. Furthermore, there have been no attempts that the authors know of to model the oil flow inside the porous medium of such devices.
Normally, breathers employ a high porosity open-cell metal foam as the porous medium. The aim of this study is to perform a pore-level numerical simulation on a representative elementary volume (REV) of the metal foam with the purpose of determining its transport properties. The pore scale topology is represented firstly by an idealized geometry, namely the Weaire-Phelan cell [2]. The pressure drop and permeability are determined by the solution of the Navier-Stokes equations. Additionally, structural properties such as porosity, specific surface area and pore diameter are calculated. The same procedure is then applied to a 3D digital representation of a metallic foam sample generated by X-ray tomography scans [3]. Both geometries are compared against each other and experimental data for validation. Preliminary simulations with the X-ray scanned model have tended to under predict the pressure drop when compared to in-house experimental data. Additionally, the few existing studies on flow in metal foams have tended to consider laminar flow; this is not the case here and this also raises the question that Reynolds-averaged turbulence models might not be well suited to flows at such small scales, which this paper considers.
Time-Resolved Heat Transfer and Surface Pressure Measurements for a Fully-Cooled Transonic Turbine Stage
Authors: Nickol Jeremy B. , Mathison Randall M. , Malak Malak F. , Rana Rajiv , Liu Jong S. 
Published: September 2014

The flow field in axial gas turbines is driven by strong unsteady interactions between stationary and moving components. While time-averaged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in high-speed turbomachinery requires time-accurate measurements that capture this unsteady behavior. Towards this end, time-accurate measurements are presented for a fully cooled transonic high-pressure turbine stage operating at design-corrected conditions. The turbine is run in a short-duration blowdown facility with uniform, radial, and hot streak vane-inlet temperature profiles as well as various amounts of cooling flow. High frequency response surface-pressure and heat-flux instrumentation installed in the rotating blade row, stator vane row, and stationary outer shroud provide detailed measurements of the flow behavior for this stage. Previous papers by Haldeman et al. [1, 2] have reported the time-averaged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heat-flux measurements from double-sided heat-flux gauges cover three span-wise locations on the blade pressure and suction surfaces. In addition, there are two instrumented blades with the cooling holes blocked to isolate the effect of just blade cooling. The stage can be run with the vane and blade cooling flow either on or off. High-frequency pressure measurements provide a picture of the unsteady aerodynamics on the vane and blade airfoil surfaces, as well as inside the serpentine coolant supply passages of the blade. A time-accurate CFD simulation is also run to predict the blade surface pressure and heat-flux, and comparisons between prediction and measurement are given.
It is found that unsteady variations in heat-flux and pressure are stronger at low to mid-span and weaker at high span, likely due to the impact of secondary flows such as the tip leakage flow. Away from the tip, it is seen that the unsteady fluctuations in pressure and heat-flux are mostly in-phase with each other on the suction side, but there is some deviation on the pressure side. The flow field is ultimately shown to be highly three-dimensional, as the movement of high heat transfer regions can be traced in both the chord and span-wise directions. These measurements provide a unique picture of the unsteady flow physics of a rotating turbine, and efforts to better understand and model these time-varying flows have the potential to change the way we think about even the time-averaged flow characteristics.
Investigation of 3D Blading and Non-Axisymmetric Hub Endwall Contouring to a Dual-Stage Counter-Rotating Compressor in Multistage Environment
Authors: Zhang Peng , Liu Bo , Zhang Guochen , Na Zhenzhe 
Published: September 2014

3D blading technique is an effective way to mitigate flow separation and improve the performance of turbomachinery. Non-axisymmetric endwall contouring technique is widely used to reduce transverse secondary flows near the endwall region in turbines, while the application of non-axisymmetric endwall contouring to compressors is rare.
The investigation rig is the Northwestern Polytechnical University dual-stage counter-rotating compressor. In order to further improve the aerodynamic performance of the compressor, 3D blading optimization of the two rotors and outlet guide vane (OGV) was done in multistage environment at near stall condition. After 3D blading optimization, the radial secondary flows of the two rotors and the separation vortex at the tip of OGV are obviously reduced. However, the transverse secondary flows at the hub endwalls of the two rotors are scarcely improved. Based on the 3D blading optimization, non-axisymmetric hub endwall contouring optimization of the two rotors was carried out afterwards and the circumferential secondary flow losses of the two rotors are reduced effectively. The efficiency of the counter-rotating compressor on optimization point increases and the aerodynamic performance is improved largely after 3D blading and non-axisymmetric hub endwall contouring optimization.
A Simple Format for the Definition of Safety Factors for LCF
Authors: Beretta S. , Foletti S. , Sanguineti A. 
Published: September 2014

Turbine components are heavy duty mechanical parts that are usually designed onto safe-life approach, where the low-cycle fatigue analysis is based onto design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion of the case of LCF.
In this paper, we firstly define a simple lognormal format for calculation of reliability for a given fatigue life under LCF conditions. Then, the partial safety factor to be applied to ε–Nf curve are then obtained for different COV’s of the applied load. The so defined design ε–Nfcurve for a rotor steel is then adopted for a complex analysis of a notched component under LCF, whose life has been estimated by an elasto-plastic analysis.