bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the Steady Wake-Tip Clearance Vortex Interaction in a Compressor Cascade: Part I — Experimental Investigations
Authors: Krug Andreas , Busse Peter , Vogeler Konrad
Published: September 2014

An important aspect of the aerodynamic flow field in the tip region of axial compressor rotors is the unsteady interaction between the tip clearance vortex and the incoming stator wakes. In order to gain an improved understanding of the mechanics involved, systematic studies need to be performed. As a first step towards the characterisation of the dynamic effects caused by the relative movement of the blade rows, the impact of a stationary wake-induced inlet disturbance on a linear compressor cascade with tip clearance will be analysed. The wakes were generated by a fixed grid of cylindrical bars with variable pitch being placed at discrete pitchwise positions.

Part I of this two-part paper focuses on experimental studies conducted at the newly designed low-speed cascade wind tunnel in Dresden. The general tunnel configuration and details on the specific cascade setup will be presented. Steady state flow field measurements were carried out using five-hole probe traverses up- and downstream of the cascade and accompanied by static wall pressure readings. 2D-PIV measurements complemented these results by visualizing the blade-to-blade flow field. Hence, the structure of the evolving secondary flow system is evaluated and compared for all tested configurations.
T100 Micro Gas Turbine Converted to Full Humid Air Operation: Test Rig Evaluation
Authors: De Paepe Ward , Montero Carrero Marina , Bram Svend , Contino Francesco
Published: September 2014

Micro Gas Turbines (mGTs) are very cost effective in small-scale Combined Heat and Power (CHP) applications. By simultaneously producing electric and thermal power, a global CHP efficiency of 80 % can be reached. However the low electric efficiency of 30 % makes the mGT profitability strongly dependent on the heat demand. This makes the mGT less attractive for applications with a non-continuous heat demand like domestic applications. Turning the mGT into a micro Humid Air Turbine (mHAT) is a way to decouple the power production from the heat demand. This new approach allows the mGT to keep running with water injection and thus higher electric efficiency during periods with no or lower heat demand. Simulations of the mHAT predicted a substantial electric efficiency increase due to the introduction of water in the cycle. The mHAT concept with saturation tower was however never tested experimentally. In this paper, we present the results of our first experiments on a modified Turbec T100 mGT. As a proof of concept, the mGT has been equipped with a spray saturation tower to humidify the compressed air. The primary goal of this preliminary experiments was to evaluate the new test rig and identify its shortcomings. The secondary goal was to gain insight in the mHAT control, more precisely the start-up strategy. Two successful test runs of more than 1 hour with water injection at 60 kWe were performed, resulting in stable mGT operation at constant rotation speed and pressure ratio. Electric efficiency was only slightly increased from 24.3 % to 24.6 % and 24.9 % due to the limited amount of injected water. These changes are however in the range of the accuracy on the measurements. The major shortcomings of the test rig were compressor surge margin reduction and the limited energy transfer in the saturation tower. Surge margin was reduced due to a pressure loss over the humidification unit and piping network, resulting in possible compressor surge. Bleeding air to increase surge margin was the solution to prevent compressor surge, but it lowers the electric efficiency by approximately 4 % absolute. The limited energy transfer was a result of a low water injection temperature and mass flow rate. The low energy transfer causes the limited efficiency increase. The first experiments on the mHAT test rig indicated its shortcomings but also its potential. Stable mGT operation was obtained and electric efficiency remained stable. By increasing the amount of injected water, the electric efficiency can be increased.
Computational Investigation of Flows and Pressure Fields Associated With Spur Gear Meshing
Authors: Al Baydu C. , Simmons Kathy , Morvan Herve P.
Published: September 2014

The efficiency of power transmission systems is increasingly targeted with a view to reducing parasitic losses and improving specific fuel consumption (SFC). One of the effects associated with such parasitic losses is the successive compression and expansion of fluid within the cavities between teeth of a meshing gear pair as they rotate. This process is cyclic and there are multiple cavities compressed and expanded at the same time.

During the meshing process the volume of the cavity between the teeth suddenly contracts and as a result pressure rises. The fluid is therefore expelled primarily in the axial direction (for spur gears) since this area is considerably larger compared to the backlash area. Once the cavity starts to expand fluid is drawn into the cavity between the teeth by the negative pressure. Besides the air flow in the gear box, the meshing point is of particular interest to the oil flow, since oil is typically injected at or upstream of the meshing point. Good understanding of such flows can be used to balance lubrication needs with the need to minimise the required oil volumes and parasitic losses.

This paper proposes the use of Computational Fluid Dynamics (CFD) as a means to investigate the phenomenon. A simplified two-dimensional CFD approach has been developed to study flows and pressure fields associated with spur gear meshing. The influence of the rotational speed has been investigated. Good validation is shown for the transient pressure variation within the tooth space. The limitations and potential applications of the modelling strategy are then discussed.
ABS NVR Type Approval of the Rolls-Royce Naval Marine Model MT5S Gas Turbine Engine and the RR4500 Generator Set
Authors: Lahm Peter , Halsey Jack
Published: September 2014

This treatise examines the activities required to Type Approve the MT5S gas turbine engine and RR4500 generator set to the American Bureau of Shipping Naval Vessel Rules (ABS NVR). Detailed accounts of the various phases of the approval process and challenges encountered therein are presented. The methods utilized to achieve ABS design assessment and the process of Type Approval testing is presented. Design assessment and Type Approval test results are summarized. A discourse containing lessons learned and corrective measures for future Type Approval efforts is included.
A 3-Dimensional Computational Study of Pulsating Flow Inside a Double Entry Turbine
Authors: Newton Peter , Martinez-Botas Ricardo , Seiler Martin
Published: September 2014

The double entry turbine contains two different gas entries, each feeding 180° of a single rotor wheel. This geometry can be beneficial for use in turbocharging and is uniquely found in this application. The nature of the turbocharging process means that the double entry turbine will be fed by a highly pulsating flow from the exhaust of an internal combustion engine, most often with out of phase pulsations in each of the two entries.

Until now research on the double entry turbine under pulsating flow conditions has been limited to experimental work. Although this is of great value in showing how pulsating flow will affect the performance of the double entry turbine, the level of detail with which this can be studied is limited. This paper is the first to use a 3 dimensional computational analysis to study the flow structures within a double entry turbine under conditions of pulsating flow. The analysis looks at one condition of pulsating flow with out of phase pulsations. The computational results are validated against experimental data taken from the turbocharger test facility at Imperial College and a good agreement is found.

The analysis first looks at the degree of mass flow storage within different components of the turbine and discusses the effect on the performance of the turbine. Each of the volute limbs is found to be subject to a large degree of mass storage throughout a pulse cycle demonstrating a definite impact of the unsteady flow. The rotor wheel shows a much smaller degree of mass flow storage overall due to the pulsating flow, however each rotor passage is subject to a much larger degree of mass flow storage due to the instantaneous flow inequality between the two volute inlets. This is a direct consequence of the double entry geometry.

The following part of the analysis studies the loss profile within the turbine under pulsating flow using the concept of entropy generation rate. A significant change in the loss profile of the turbine is found throughout the period of a pulse cycle showing a highly changing flow regime. The major areas of loss are found to be due to tip leakage flow and mixing within the blade passage.
Liquid Jets in Subsonic Air Crossflow at Elevated Pressure
Authors: Song Jinkwan , Cain Charles Cary , Lee Jong Guen
Published: September 2014

The breakup, penetration, droplet size and size distribution of a Jet A-1 fuel in air crossflow has been investigated with focus given to the impact of surrounding air pressure. Data has been collected by Particle Doppler Phased Analyzer (PDPA), Mie-Scattering with high speed photography augmented by laser sheet, and Mie-Scattering with ICCD Camera augmented by nano-pulse lamp. Nozzle orifice diameter, do, was 0.508 mm and nozzle orifice length to diameter ratio, lo/do, was 5.5. Air crossflow velocities ranged from 29.57 to 137.15 m/s, air pressures from 2.07 to 9.65 bar and temperature held constant at 294.26 K. Fuel flow was governed to provide a range of fuel/air momentum flux ratio q from 5 to 25 and Weber number from 250 to 1000. From the results, adjusted correlation of the mean drop size has been suggested using drop size data measured by PDPA as follows; (1)D0D32=0.267Wea0.44q0.08ρlρa0.30μlμa-0.16This correlation agrees well and shows roles of aerodynamic Weber number, Wea, momentum flux ratio, q, and density ratio, ρl/ρa. Change of the breakup regime map with respect with surrounding air pressure has been observed and revealed that the boundary between each breakup modes can be predicted by a transformed correlation induced from above correlation. In addition, the spray trajectory for the maximum Mie-scattering intensity at each axial location downstream of injector was extracted from averaged Mie-scattering images. From these results correlations with the relevant parameters including q, x/do, density ratio, viscosity ratio, and Weber number are made over a range of conditions. According to spray trajectory at the maximum Mie-scattering intensity, the effect of surrounding air pressure becomes more important in the farfield. On the other hand, effect of aerodynamic Weber number is more important in the nearfield.
A Preliminary Design System for Turbine Discs
Authors: Ouellet Yannick , Garnier François , Roy François , Moustapha Hany
Published: September 2014

In order to improve product development cycle, design engineers use multi-disciplinary analysis tools which allow better productivity. This paper covers the development of new tools to improve the preliminary design phase of turbine disc, being a critical part of aircraft engines. First, a new single platform D&A (Design & Analysis) tool integrating commercial CAD (Computer Aided Design) and FEA (Finite Element Analysis) software processing in batch mode is presented. This integrated architecture leads to a real improvement enabling a cohesive single integrated simulation environment that offers significant time reduction on user manipulation and execution. An optimization of disc geometry is then performed by using different optimization algorithms and configurations for a given disc parameterized model. The results show potential improvement over the current preliminary rotor discs for life and burst limited design. Finally, optimal curves obtained by developing HPT (High Pressure Turbine) disc reference charts, indicate how to get the minimum weight for given mechanical performance without running any structural analysis. These new tools supporting disc design have allowed improvement of disc life and durability leading to reduction of preliminary design phase duration.
An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate: Part 2 — Two-Phase Flow Measurements and Droplet Dynamics
Authors: Ragab Reda , Wang Ting
Published: September 2014

A Phase Doppler Particle Analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of a typical coolant film layer and a wider droplet layer. The droplet layer is identified by a wedge-shaped enclosure prescribed by the data rate (droplet number per second) distribution. The apex of the enclosure, depicting by the maximum data rate, roughly indicating the core region of the coolant film. The upper boundary of the film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. Thanks to higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant layer, resulting in a wider droplet layer than the cooling film layer.

With the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part 1 are reexamined. The 3-D droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explains the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole’s centerline as demonstrated in the case using the cylindrical holes.
Experimental Investigation of Leading Edge Impingement Under High Rotation Numbers With Racetrack Shaped Jets
Authors: Harmon Weston V. , Elston Cassius A. , Wright Lesley M.
Published: September 2014

The effect of rotation on leading edge jet impingement is experimentally investigated in this study. Cooling air travels radially outward through a square supply channel, turns 90° into a cross-over hole, and impinges on a semi-circular surface. To eliminate the effect of jet cross-flow, regionally averaged heat transfer coefficients are measured on the surface surrounding a single jet. The heat transfer performance of a round jet is compared to that afforded by a 2:1 racetrack shaped jet. Two jet Reynolds numbers were investigated, Rejet = 15,000 and Rejet = 25,000. This, in addition to a varying rotational speed, allows for the consideration of rotation numbers varying from 0.0–0.076 (based on the jet velocity and jet hydraulic diameter). The results obtained are benchmarked against stationary results to highlight enhancement due to rotation. It is shown that as the rotation number increases, the heat transfer is enhanced on all regions of the semi-circular target surface. For rotation numbers of less than 0.030, enhancement due to rotation is marginal. Once rotation numbers breach this value, heat transfer begins to increase significantly on all surfaces. Additionally, it was shown that a racetrack shaped jet consistently out performs a round jet at an equivalent rotation number. The racetrack jet offers better and more consistent coverage of the leading edge surface, yielding higher average heat transfer enhancement.
Probabilistic Analysis of the Secondary Air System of a Low-Pressure Turbine
Authors: Brack Stefan , Muller Yannick
Published: September 2014

The present investigation aims at performing a probabilistic analysis of the secondary air system of a three-stage low-pressure turbine rotor in a jet engine. Geometrical engine to engine variations due to the tolerance of the different parts as well as the variation of engine performance parameters are taken into account to analyse the impact on the aerodynamic behaviour of the secondary air system. Three main functions of the secondary air system have been investigated at one engine condition — take-off. At first the variation of the turbine rotor cooling flow consumption was studied. Secondly the axial bearing loads were considered and finally the system was analysed with regard to its robustness towards disc space hot gas ingestion.

To determine the uncertainty in the accomplishment of these tasks and to identify the major variation drivers, a Latin Hypercube sampling method coupled with the correlation coefficient analysis was applied to the 1D flow model. The incapability of the correlation coefficient analysis to deal with functional relationships of not monotonic behaviour or strong interaction effects was compensated by additionally applying in such cases an Elementary Effect analysis to determine the influential variables. As the 1D flow model cannot consider thermal and centrifugal growth effects, a simple mathematical model was deduced from the physical dependencies enhancing the 1D flow model to approximately capture the impact of these effects on the labyrinth seals.

Results showed that the cooling mass flow and axial bearing load are both normally distributed while their uncertainties are mainly induced by the uncertainties of the state variable of the primary air system. The investigated chamber temperature ratio to analyse the hot gas ingestion showed a not normally distributed histogram and a strong influence of interaction terms. Therefore the results of the correlation coefficient analysis were complemented with the results of an Elementary Effect analysis.
Study on the Stiffness Loss and the Dynamic Influence on Rotor System of the Bolted Flange Joint
Authors: Wang Cun , Zhang Dayi , Zhu Xiaobin , Hong Jie
Published: September 2014

The bolted flange joint is a kind of widely used joint structure in the rotor system. Its discontinuous mechanical characteristics result from the existing of the contact surface, which will slide and deform when the spool deforms. As a consequence, the joint’s stiffness is always smaller than that of fixed configuration, which affects rotor’s stiffness distribution and the rotor’s dynamics further.

The objective of this study is to investigate the mechanical characteristics of the bolted flange joint, the affecting factors and the influence on rotor’s dynamics.

According to the characteristics of structure and mechanical state, using the existing equivalent axial spring-bending beam model to describe the tension and compression stiffness of bolted flange joint section, then the bending stiffness model of whole bolted flange joint is established based on that. The results show that there is a significant effect of the bolted flange joint on the local stiffness of the rotor, the loss of local bending stiffness reach a high level when the number of bolts is few. The mathematical description between stiffness loss and structure size, load and assembling condition is obtained through the analytical results.

A bolted flange joint simulation model, taking the characteristics of the contact into account, is built by the nonlinear finite element method. The trends of numerical results agree with the analytical conclusion, and show the stiffness of bolted flange joint is smaller than that of the fixed configuration. The stiffness of bolted flange joint decreases a small amount with the increasing moment. When the number and the pretension force increases, the stiffness increases nonlinearly.

Based on the mechanism of stiffness loss, the equivalent stiffness is used to replace the fixed configuration stiffness on the location of bolts in finite element model of high pressure rotor system. The results of dynamic analysis shows that the stiffness loss has a greater impact on bending modes than the rigid modes while the static analysis shows that the stiffness loss has a small negatively effect on clearances.

The study shows that, the stiffness loss of bolted flange joint has a close relationship with the load and assembling conditions. The results show the effectiveness in controlling the mechanical and dynamic properties of the rotor with bolted flange joints by careful adjusting of structural parameter, load parameter and assembling parameter during designing.
Hybrid RANS/LES of Flow in a Rib-Roughened Rotating Channel
Authors: Kubacki Slawomir , Rokicki Jacek , Dick Erik
Published: September 2014

The aim of the present study is to verify the ability of a hybrid RANS/LES model, based on the newest version of the RANS k-ω model of Wilcox (2008), in reproducing the flow in a rib-roughened rotating channel. The numerical results are compared to experimental data by Coletti and Arts (2011), and Coletti et al. (2012). Results obtained with the basic RANS k-ω model are analysed as well, with and without the correction term for frame rotation by Hellsten (1998). It is demonstrated that the hybrid RANS/LES k-ω model produces accurate results for the rotating ribbed duct flow. However, the RANS model with the correction term for frame rotation produces quite good results as well for mean velocity profiles, although not as good as with the hybrid model. Further, the RANS model has lower quality in the representation of the small-scale fluctuations.
Experimental Study on Heat Transfer Characteristics to Supercritical Hydrocarbon Fuel in a Horizontal Micro-Tube
Authors: Fu Yanchen , Tao Zhi , Xu Guoqiang , Deng Hongwu , Jia Zhouxia
Published: September 2014

Supercritical hydrocarbon fuel experimental loop was constructed at Beihang University to study the heat transfer characteristics to supercritical hydrocarbon fuel. The test section, a stainless tube (1.86mm I.D., 2.26mm O.D., 1Cr18Ni9Ti) with the length of 300mm, was placed horizontally above the ground and the local heat transfer coefficients of the test section were systematically measured at fixed supercritical pressure of 5MPa. The mass flux varied from 786.5 to 1573 kg/ (m2 ·s), with the uniform heat flux from 180 to 450kW/m2 and the inlet fuel temperature ranged from 373 to 673K. The experimental investigation was confined to supercritical flows with heat addition only. Hence, heat losses were measured to be taken into consideration for every experimental condition.

The experimental results were analyzed that heat transfer enhances at the reduced temperature Tb/Tpc rising from 0.95 to 1.04 and deteriorates when Tb/Tpc is larger than 1.04. The criterions of Shitman and Jackson were selected to judge the heat transfer characteristics in a horizontal micro-tube. The results indicated that buoyancy effects are ignored as the K<0.01 for the micro-scale tube and thermal acceleration is the main factor for the heat transfer characteristics. By direct comparison with an assortment of experimental data, a new correlation was proposed to be more accurate than others in predicting heat transfer phenomena for Chinese RP-3 hydrocarbon fuel in a horizontal micro-tube.
An Approximate Method to Obtain Thermodynamic Gas Properties for Use in Gas Turbines
Authors: Cumpsty N. A. , Marquis A. J.
Published: September 2014

The calculation of the performance of gas turbines, turbochargers, compressors and turbines requires the thermodynamic properties of the gases. Tables of properties exist which are effectively exact, but using these tables is tedious and far from practical in computer-based calculations. Representing tabulated results with polynomial approximations is inconvenient and prone to error in implementation. For teaching and simple calculations simple approximations, such as γ = 1.4 for unburned air and γ = 1.3 for combustion products, are sometimes used, but this is far from wholly satisfactory. This paper describes and discusses a simple empirical approach which will give adequate accuracy for many purposes but is simple enough to be used as part of an educational course.
Quantifying the Economic Benefits of Wind Turbine Condition Monitoring
Authors: Williams Richard , Crabtree Christopher , Hogg Simon
Published: September 2014

This paper presents a cost benefit analysis for wind turbine condition monitoring systems. It is widely acknowledged that performing proactive maintenance actions can reduce the number and severity of wind turbine failures. However, the use of condition monitoring systems to determine the health of the system is often viewed as costly and of little financial benefit. In this analysis the increased costs associated with condition monitoring were offset by the positive effect of early fault detection, with faults being detected before they reach a critical stage. The continual growth in turbine output and the emergence of far-offshore wind farm sites make the economic case for cost of energy reduction from timely and accurate fault detection ever stronger.

An assessment of the capability of the monitoring system was undertaken through allowance for the true to false condition monitoring detection ratio and the ability of the system to detect the severity of a fault. The analysis also compared onshore and offshore assets where the access availability can severely influence the downtime.

The results show a clear financial justification for wind turbine condition monitoring and indicate the successful detection ratio required before a condition monitoring system can offer a financial benefit.
Effect of Unguided Turning Angle and Trailing Edge Shape on Cooled Blade Loss
Authors: Granovskiy Andrey , Kostege Mikhail , Vassiliev Vladimir
Published: September 2014

A significant part of the overall loss in modern gas turbines is the trailing edge loss. This loss is, more strongly than other constituents, affected by operation, because the trailing edge can significantly change its shape due to degradation. Also by manufacturing of new parts and reconditioning the same tolerances as in other parts of blade lead to higher deviations of aerodynamic characteristics. Therefore the understanding of trailing edge loss generation mechanisms is of utmost importance for a sound blade design. In this work the results of combined experimental and numerical investigation of the trailing edge impact on the transonic cooled blade loss are presented.

This study comprises the investigation of the unguided flow angle and the trailing edge shape on the profile losses and a base pressure. The unguided flow angle characterizes the curvature distribution on the aerofoil suction side. The numerical and experimental investigation of transonic cooled turbine cascades have shown that the increase of the unguided flow angle results in loss reduction due to increase of the base pressure downstream of the trailing edge. At the same time the deviation of the trailing edge from a round shape has detrimental effect on performance and conducted investigations allow quantification of this effect.

The measurements were performed in a transonic wind tunnel and numerical simulations were done using in-house 2D Navier-Stokes code. The comparison of calculations with measurements showed that they are in reasonable agreement.

The validated numerical procedure has been used for demonstration of possibility to reduce loss in aerofoil with thick trailing edge by tuning of the unguided flow angle. The use of the thick trailing edges at HP cooled turbines reduces restriction on tolerances, improves of manufacturability and reduces cost.
Experimental Investigation of a Leading Edge Cooling System With Optimized Inclined Racetrack Holes
Authors: Carcasci Carlo , Facchini Bruno , Tarchi Lorenzo , Ohlendorf Nils
Published: September 2014

An experimental survey of a leading edge cooling scheme was performed to measure the Nusselt number distribution on a large scale test facility simulating the leading edge cavity of an high pressure turbine blade. Test section is composed by two adjacent cavities, a rectangular supply channel and the leading edge cavity. The cooling flow impinges on the concave leading edge internal walls, by means of an impingement array located between the two cavities, and it is extracted through showerhead and film cooling holes. The impingement geometry is composed by a double array of circular or shaped holes. The aim of the present study is to investigate the heat transfer performance of two optimized impingement schemes in comparison with a standard one with circular and orthogonal holes. Both the optimized arrays have inclined racetrack shaped holes and one of them has also a converging shape. Measurements were performed by means of a transient technique using narrow band Thermo-chromic Liquid Crystals (TLC). Jet Reynolds number was varied in order to cover the typical engine conditions of these cooling systems (Rej = 15000–45000). Results are reported in terms of detailed 2D maps, radial and tangential averaged Nusselt numbers.
All-Mach Number Density Based Flow Solver for OpenFOAM
Authors: Heinrich Martin , Schwarze Rüdiger
Published: September 2014

A density-based solver for turbomachinery application is developed based on the central-upwind schemes of Kurganov and Tadmor using the open source CFD-library OpenFOAM. Preconditioning of Weiss and Smith is utilized to extend the applicability down to the incompressibility limit. Implicit residual averaging, bulk viscosity damping and local time stepping are employed to speed up the simulations. A low-storage 4-stage Runge-Kutta scheme and dual time-stepping are used for time integration.

The presented solver is compared with results from ANSYS Fluent 13.0 and measurement data. Three different test cases are conducted to analyze different flow conditions: The circular bump for low and high speed inviscid flows and computational performance assessment, the two-dimensional VKI turbine guide vane for viscous flows and the the three-dimensional DLR high speed centrifual compressor validating the performance for rotating turbo-machinery. All three test cases show a very good agreement between OpenFOAM and ANSYS Fluent.
CFD Investigation of a Fluidic Device for Modulation of Aero-Engine Cooling Air
Authors: Koli Bharat , Chew John W. , Hills Nick J. , Scanlon Timothy
Published: September 2014

The quantity of cooling air delivered by the secondary air system to various engine components is usually fixed by cooling requirements at the most arduous operating condition in the flight cycle. Modulation of cooling air would allow optimization of cooling supply at different flight cycle conditions, giving significant performance benefits. Switched vortex valves (SVV) have been proposed for control of air systems [1]. An important characteristics of this device is the absence of any moving part. This offers advantages compared to other systems. This report discusses the numerical study of a typical SVV. The study includes comparison of predicted results with available experimental data and prediction of switching characteristics of the device. In this study two turbulence models namely the Spalart-Allmaras model (SA) and Reynolds stress model (RSM) were used. The RSM showed a good agreement with measured mass flow rate and qualitative agreement with other experimental observations.
Study of Particles Deposition in Gas Turbine Blades in Presence of Film Cooling
Authors: Borello Domenico , D’Angeli Luca , Salvagni Alessandro , Venturini Paolo , Rispoli Franco
Published: September 2014

Exhaust entering the gas turbine is usually fed with solid particles produced in the combustion of hydrocarbons (ashes, unburned char, etc.). Then, the interaction between the particles motion and the film cooling jets must be properly addressed.

Here an integrated approach based on an Eulerian-Lagrangian scheme for particle-laden flow was applied to a real turbomachinery case. The code was preliminary assessed by simulating two simplified test cases: a) 3-D cooling jet in a channel; b) 2-D turbine cascade with film cooling. These cases were selected to separately validate the main effects here considered: a) interaction of particles trajectories and 3D cooling jets; b) effect of the cooling jets on surface temperature and particles trajectory and possibly on particle deposition, in comparison with the non-cooled case.

Finally, 3D simulation of the particle-laden flow around a real E3 gas turbine vane with and without film cooling was performed. Flow features, particles trajectories and deposit on the blade are presented.

The compressible flow field was simulated using the OpenFOAM code obtaining credible predictions of the velocity and temperature field.

Then the P-Track code developed by the authors was applied for tracking the particles trajectories and determining the deposit on the solid surface. As the temperature are relatively high, the sticking probability method, that is strongly dependent on the temperature itself, was used here.

The results showed that the presence of the cooling jets affect deeply the deposit following two main causes: the influence of the jets in removing the fluid from the close-to-the-wall region and the reduction of temperature along the blade.
Probabilistic Validation of Complex Engineering Simulations With Sparse Data
Authors: Subramaniyan Arun K. , Chennimalai Kumar Natarajan , Wang Liping
Published: September 2014

The challenges of validating expensive simulations with very sparse experimental data are addressed in this article. The effects of uncertainties in simulations and test data and their impact on validation are highlighted using several examples. Bayesian methods for calibration and tool validation are presented as the primary techniques for performing probabilistic validation. The applicability of the methods to complex engineering problems is discussed. The effect of prior assumptions on calibration and validation are explained through simple illustrative examples. Guidelines for planning simulations and experiments for validation are also provided.
Spatial Analysis on Forced Heat Release Response of Turbulent Stratified Flames
Authors: Han Zhiyi , Balusamy Saravanan , Hochgreb Simone
Published: September 2014

The local equivalence ratio distribution in a flame affects its shape and response under velocity perturbations. The forced heat release response of stratified lean-premixed flames to acoustic velocity fluctuations are investigated via chemiluminescence measurements and spatial Fourier transfer analysis. A laboratory scale burner and its boundary conditions were designed to generate high-amplitude acoustic velocity fluctuations in flames. These flames are subject to inlet radial equivalence ratio distributions created via a split annular fuel delivery system outfitted with a swirling stabilizer. Simultaneous measurements on the oscillations of inlet velocity and heat release rate were carried out via a two-microphone technique, and OH* chemiluminescence. The measurements show that, for a given mean total power and equivalence ratio (ϕg = 0.60), the flame responses vary significantly depending on forcing frequency, equivalence ratio split and velocity fluctuation amplitude, showing significant non-linearities with respect to forcing amplitude and stratification ratio. Furthermore, the spatial Fourier transfer analysis shows the underlying changes in the rate of heat release, including the direction and speed of the perturbation within the flame.
Helical Flow Disturbances in a Multi-Nozzle Combustor
Authors: Aguilar Michael , Malanoski Michael , Adhitya Gautham , Emerson Benjamin , Acharya Vishal , Noble David , Lieuwen Tim
Published: September 2014

This paper describes an experimental investigation of a transversely forced, swirl stabilized combustor. Its objective is to compare the unsteady flow structures in single and triple nozzle combustors and determine how well a single nozzle configuration emulates the characteristics of a multi-nozzle one. The experiment consists of a series of velocity field measurements captured on planes normal to the jet axis. As expected, there are differences between the single and triple-nozzle flow fields, but the differences are not large in the regions upstream of the jet merging zone. Direct comparisons of the time averaged flow fields reveal a higher degree of non-axisymmetry for the flowfields of nozzles in a multi-nozzle configuration. Azimuthal decompositions of the velocity fields show that the transverse acoustic forcing has an important influence on the dynamics, but that the single and multi-nozzle configurations have similar forced response dynamics near the dump plane. Specifically, the axial dependence of the amplitude in the highest energy axisymmetric and helical flow structures is quite similar in the two configurations. This result suggests that the hydrodynamic influence of one swirling jet on the other is minimal and, as such, that jet-jet interactions in this configuration do not have a significant influence on the unsteady flow structures.
Investigation of Hydrogen Enriched Natural Gas Flames in a SGT-700/800 Burner Using OH PLIF and Chemiluminescence Imaging
Authors: Lantz Andreas , Collin Robert , Aldén Marcus , Lindholm Annika , Larfeldt Jenny , Lörstad Daniel
Published: September 2014

The effect of hydrogen enrichment to natural gas flames was experimentally investigated at atmospheric pressure conditions using flame chemiluminescence imaging, planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and dynamic pressure monitoring. The experiments were performed using a 3rd generation dry low emission (DLE) burner used in both SGT-700 and SGT-800 industrial gas turbines from Siemens. The burner was mounted in an atmospheric combustion test rig at Siemens with optical access in the flame region. Four different hydrogen enriched natural gas flames were investigated; 0 vol.%, 30 vol.%, 60 vol.% and 80 vol.% of hydrogen. The results from flame chemiluminescence imaging and OH PLIF show that the size and shape of the flame was clearly affected by hydrogen addition. The flame becomes shorter and narrower when the amount of hydrogen is increased. For the 60 vol.% and 80 vol.% hydrogen flames the flame has moved upstream and the central recirculation zone that anchors the flame has moved upstream the burner exit. Furthermore, the position of the flame front fluctuated more for the full premixed flame with only natural gas as fuel than for the hydrogen enriched flames. Measurements of pressure drop over the burner show an increase with increased hydrogen in the natural gas despite same air flow thus confirming the observation that the flame front moves upstream towards the burner exit and thereby increasing the blockage of the exit. Dynamic pressure measurements in the combustion chamber wall confirms that small amounts of hydrogen in natural gas changes the amplitude of the dynamic pressure fluctuations and initially dampens the axial mode but at higher levels of hydrogen an enhancement of a transversal mode in the combustion chamber at higher frequencies could occur.
Numerical Analysis and Validation of the Rotor Blade Vibration Response Induced by High Pressure Compressor Deep Surge
Authors: Giersch Thomas , Figaschewsky Felix , Hönisch Peter , Kühhorn Arnold , Schrape Sven
Published: September 2014

The following paper presents a numerical analysis of a deep surge cycle of a 4.5 stage research compressor. The resulting unsteady loads are used to determine the response of two particular rotor blade rows that are then compared to strain gauge data from measurements. Within a deep surge cycle the compressor experiences a rapid change of the flow field from forward to reversed flow. This rapid breakdown is linked to a new mean blade load. Hence, the rapid change in blade loads are able to excite fundamental blade modes similar to an impulse load. The resulting vibration magnitudes might reach critical levels. This paper demonstrates two different approaches to evaluate the unsteady flow during a surge cycle.

The first uses a three dimensional, time accurate finite volume solver for viscid compressible flows to calculate the transient surge cycle of the compressor. The compressor itself is represented by a multi-blade-row sector model. The second approach makes use of the same solver and compressor domain to determine steady state characteristics of the HPC in forward, stalled and reversed flow. Based on these characteristics an one dimensional finite volume solver for inviscid compressible flows was developed to determine the transient compressor behavior. The one dimensional solver represents the compressor by source terms that are linked to the previously determined steady state characteristics.
Study of Rotor Blades Vibration Behavior of Counter Rotating Fan Models
Authors: Stepanov A. , Fateev V. , Mileshin V.
Published: September 2014

Three test campaigns were carried out at CIAM C-3A test facility (Turaevo, Russia) with the aim of investigating aerodynamic and acoustic performances of three counter rotating fan models under the European VITAL project [1–3]. The second fan configuration CRTF2a [2] differs from the reference fan configuration CRTF1 by thickened blades profiling designed for simulation the composite blades. The third version of counter rotating fan model CRTF2b [4] was manufactured according to “blisk” technology to simulate composite blades. Along with studies of aerodynamic and acoustic performances of fan models, the C-3A test facility provides an opportunity to investigate and estimate the rotor blades vibration behavior. The rotor blade as the most loaded fan component, experiences the impact of various types of flow disturbances leading to its resonance vibrations and sometimes creating conditions for initiation of flutter at rotor blade natural frequencies. This is the reason for extending the information content of the measurements, improvement the measurement tools and methodology. The contactless method of blade vibration measurements (tip-timing) was used on the basis of MIC-DPM equipment («Mera» Research and Production Enterprise, Russia) [5,6] in combination with a traditional technique of strain gauges installation for determination of counter rotating fan rotor blades vibration behavior. This work presents the description of applied methodologies for measurements of rotor blades vibration parameters. Additionally, the paper presents the measurement results of rotor blades vibration behavior for three counter rotating fan models studied by means of a strain gauges technique and a contactless blade tip-timing method as well as the comparison analysis of numerical and experimental results in relation to vibration behavior of tested fan models.
Exploitation of Acoustic Effects in Film Cooling
Authors: Collins Matthew , Povey Thomas
Published: September 2014

There have been numerous studies of the behavior of shaped film cooling holes for turbine applications. It is known that the introduction of coolant is an unsteady process, and a handful of studies have described and characterized the unsteadiness. To the authors’ knowledge there are no studies in which unsteady acoustic effects have been actively exploited such that they have led to novel designs with improved cooling performance.

This paper discusses the fundamental mechanism of pressure wave propagation through cooling holes, and describes systems in which holes which have been acoustically shaped have led to a direct improvement in film cooling hole performance. The mechanism relies on sequential pressure wave reflection within an acoustically shaped hole, and is therefore applicable in regions where the external surface is subject to large pressure wave fluctuations at high frequency. The principle is developed analytically, and then demonstrated with a number of CFD simulations. We demonstrate that a desired temporal mass flow rate profile can be achieved by appropriate acoustic shaping of the cooling hole.

The purpose of this paper is to describe the fundamental design considerations relevant to acoustic shaping. The discussion is developed with reference to a film cooling system for the over-tip region of an un-shrouded rotor. The performance benefit of the system in terms of modulation of unsteady mass flux and ingestion characteristics is quantified. It is believe that this is the first time this significant effect has been exploited in film cooling design.
Experimental and Numerical Investigation of Temperature Fields in a Radial Turbine Wheel
Authors: Diefenthal Mathias , Tadesse Hailu , Rakut Christian , Wirsum Manfred , Heuer Tom
Published: September 2014

Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase.

To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the turbine wheel is essential.

To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the turbine wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results.

In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.
Aerodynamic Design and Analysis of a Multistage Vaneless Counter-Rotating Turbine
Authors: Zhao Wei , Wu Bing , Xu Jianzhong
Published: September 2014

Multistage vaneless counter-rotating turbines eliminate vanes between rotors, which reduces the weight of the turbine pronouncedly and avoids viscous losses associated with vanes. As a result, a gas turbine engine employing such a turbine would have greater thrust to weight ratio and smaller specific fuel consumption. This paper presents aerodynamic design and analysis for a multistage vaneless counter-rotating turbine, named as a 4*1/2 turbine, which consists of a rotating frame and four rotors without any vanes. The first rotor and the third rotor drive a single-shaft compressor with a pressure ratio of 11.8, and the second rotor and the forth rotor deliver a total shaft power of around 2MW. Stage loading and flow axial acceleration in blades and ducts are selected to provide sufficient inlet swirl for downstream vaneless rotor to produce required power output with acceptable performance. The stage work coefficients of each rotor are 0.95, 2.9, 1.4 and 1.0, respectively. Non-uniform radial circulation distributions and tapered blades are also used to maximize the turbine power output. Centrifugal forces in the outer rotor of the turbine are captured by carrying out a finite element analysis to validate the aerodynamic design results. Three dimensional viscous numerical results show that an adiabatic total-to-total efficiency of 91.5% with a pressure ratio of 9.8 at design condition is obtained and achieves the initial design objective very well. Entropy creation associated with the tip leakage and secondary flow in each rotor is also illustrated for understanding the origins and effects of losses in such turbines. Pressure ratios and efficiency at speed combinations of the 80% to 100% design speeds of the inner and outer rotors are discussed to reveal the turbine characteristics at off-design conditions.