bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding of Secondary Loss Structures in a Multi-Stage Transonic Compressor Using DES
Authors: Kim Donghyun , Son Changmin , Kim Kuisoon
Published: September 2016

In the present study, a multi-stage transonic compressor has been analyzed to investigate secondary loss structures and flow interactions in the corner region where the hub endwall and blade suction surface meet. The Detached Eddy Simulation (DES) approach is used successfully with the Shear Stress Transport (SST) turbulence model to directly resolve the eddy structure in the separated region. The SST-DES results for a transonic three stage axial compressor are compared with a RANS analysis obtained using ANSYS CFX.

The present analysis indicates that the DES is better in simulating secondary losses and vortex structures than the RANS. With the DES, a large three-dimensional separation is predicted in the stator suction surface and hub endwall compared to the RANS prediction. The flow separation affects adversely the loss characteristics such as increases in the entropy and total pressure loss. The DES analysis indicates that the secondary flow phenomenon of the stator rows is apparent in all stages. It is observed to predict two distinct vortices induced by a three dimensional flow separation in the region adjacent to the suction surface and trailing edge of the last stage stator near the hub endwall. For the front two stages, the DES also predicts strong vortices and flow separation in the same corner region while the RANS analysis fails to predict them clearly.

The total pressure loss prediction is concerned, the DES analysis predicts significantly larger than the RANS analysis in the region where the hub corner separation occurs. The DES is also found to predict a periodic fluctuations in the entropy, leading to the instantaneous efficiency variations with maximum differences of about 10% compared with the RANS solutions.
Chemical Kinetic Models for Enhancing Gas Turbine Flexibility: Model Validation and Application
Authors: Güthe Felix , Gassner Martin , Bernero Stefano , Meeuwissen Thiemo , Wind Torsten
Published: September 2016

In recent years, market trends towards higher power generation flexibility are driving gas turbine requirements of operation at stable conditions and below environmental emission guarantees over a wide range of operating conditions, such as load, and for changing fuels. In order to achieve these targets, engine components and operation concept need to be optimized to minimise emissions (e.g. CO, NOx) and combustion instabilities, as well as to maximize component lifetime. Therefore the combination of field experience, experimental studies and theoretical modelling of flames with state of the art tools play a key role in enabling the development of such solutions.

For many applications the relative changes of reactivity due to changes in operation conditions are important thus in this report a few examples are shown, where chemical kinetics simulations are used to determine the reactivity and to predict engine behaviour. The predicted trends are validated by correlating them to validation data from high pressure test rigs and real gas turbine operational data. With this approach the full operational range from highest reactivity (flashback) to lowest reactivity (blow out or CO emission increase) are covered. The study is focused on the sequential combustor (SEV) of reheat engines and addresses both the safety margins with respect to highly reactive fuels and achievable load flexibility with respect to part load CO emissions.

The analysis shows that it is necessary to utilize updated kinetic mechanisms since older schemes have proved to be inaccurate. A version of the mechanism developed at NUI Galway in cooperation with Alstom and Texas A&M was used and the results are encouraging, since they are well in line with experimental test data and can be matched to GT conditions to determine, predict, and optimize their operational range.

This example demonstrates nicely how a development over several years starting from fundamental basic research over experimental validation finally delivers a product for power plants. This report therefore validates the kinetic model in combination with the approach to use modelling for guidance of the GT development and extending it fuel capabilities.

The GT24 / GT26 can not only be operated with H2 containing fuels, but also at very low part load conditions and with the integration of H2 from electrolysis (∼power to gas ∼PTG) the turndown capability can even be further improved. In this way the energy converted at low electricity prices can be stored and utilised at later times when it is advantageous to run the GT at lower loads increasing the overall flexibility. This development is well suited to integrate renewable energy at highly fluctuating availability and price to the energy provisioning by co-firing with conventional fuels.
Optimization of Robust Transonic Compressor Blades
Authors: Lejon Marcus , Andersson Niklas , Grönstedt Tomas , Ellbrant Lars , Mårtensson Hans
Published: September 2016

Surface degradation in an axial compressor during its lifetime can have a considerable adverse effect on its performance. The present study investigates how the optimized design of compressor blades in a single compressor stage is affected by considering a high level of surface roughness on a level representative of a long period of in-service use. It is shown that including surface roughness in the optimization process is of relatively little importance, however, matching of compressor stages is shown to require consideration as the rotational speed must be increased to reach the design point as surface quality decrease. An increased surface roughness in itself is shown to have a large effect on performance.

Two optimization approaches are compared. The first approach considers the compressor blades to be hydraulically smooth. The designs obtained from this approach are subsequently degraded by increasing the level of surface roughness. The compressor blades from the first approach are compared to designs obtained from a second optimization approach, which considers a high level of surface roughness from the outset.

The degraded compressor stages from the first approach are shown to be among the best performing designs in terms of polytropic efficiency and stability when compared to designs obtained with the second approach.
Numerical Investigation of Three-Dimensional Separation in an Axial Flow Compressor: The Influence of Free-Stream Turbulence Intensity and Endwall Boundary Layer State
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo
Published: September 2016

Regions of three-dimensional separations are an inherent flow feature of the suction surface - endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor’s efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources.

Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data is in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall.

Increasing the free-stream turbulence intensity (FST) changes the suction surface boundary layer transition mode from separation induced to bypass. However, it doesn’t significantly alter the transition location and therefore the corner separation size. Additionally, the FST doesn’t noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST.

The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear.
Laser-Based Investigation on a Dry Low Emission Industrial Prototype Burner at Atmospheric Pressure Conditions
Authors: Subash Arman Ahamed , Collin Robert , Aldén Marcus , Kundu Atanu , Klingmann Jens
Published: September 2016

Experiments were performed at atmospheric pressure conditions on the prototype 4th generation DLE burner. The combustion changes that occur for alteration of the operating conditions by changing the equivalence ratios (ϕ) for CH4 as fuel at different sections of the burner, were optically investigated. The burner assembly has three concentrically arranged premixed burner sections: an outer Main section, an intermediate section (Pilot) and a central pilot body or pre-chamber combustor, called RPL (Rich-Pilot-Lean) section. All sections are facilitated to vary equivalence ratios to achieve optimal combustion. Planar laser-induced fluorescence (PLIF) of OH radicals and flame chemiluminescence imaging were applied to study the local flame characteristics in order to investigate turbulence-flame interaction and formation of reaction zone at the burner exit. The results show that the position and shape of the flame are clearly affected by the variation of equivalence ratios at different sections of the burner. During the experiments, first the RPL, then the Pilot and the Main flame were added in a step wise manner keeping constant the total air flow for the global ϕ = 0.5 in order to understand the flame contributions from the different combustion sections. It is observed that for the RPL fuel lean conditions, the primary combustion starts and reaches completion before exiting the burner throat while for rich conditions, the residual fuel escapes out through the RPL exit with primary combustion products and starts secondary combustion along with the Pilot and Main combustion. At the global ϕ = 0.5, for changing the RPL ϕ from lean to rich conditions, the flame stabilization region moves downstream of the burner exit and the flame front fluctuation along inner shear layer increases. For increasing the global ϕ and increasing the Pilot fuel ratio (PFR) without changing the RPL and the global ϕ, the total extension of the flame becomes shorter and the flame stabilization region moves upstream.
Wall Modeled LES and its Impact on Rotor/Stator Cavity Unsteady Features
Authors: Bridel-Bertomeu Thibault , Gicquel Laurent Y. , Staffelbach Gabriel
Published: September 2016

Cavity flows are essential components of many aeronautical and spatial engines. For example, in gas turbines a network of cavities is calibrated and managed to divert part of the main cold stream which is then re-injected in the hot regions of the engine to shield walls from the hot combustion products. For pumps, cavities are naturally present at the junction of fixed and rotating parts. In both contexts, mastering the flow stability in rotor/stator cavities is essential to avoid imposing too large flow variations which could lead to miss-tuned operating conditions in the engine and a drastic loss of performance or life-span. Although stability of these flows has been widely studied in the literature, a lack of clear understanding of the triggering mechanisms from stable to unstable flow solutions remains, especially in the context of industrial applications where Reynolds numbers are very high and difficult to handle. To cope with such complex geometry, fully unsteady flows, the so-called Large Eddy Simulation (LES) approach appears as a very promising method. However and for such high Reynolds number industrial applications, wall modeling still remains a necessity to alleviate the computational cost of LES. Understanding the impact of such a strong modeling hypothesis on the mean flow features and unsteady energetic content is hence mandatory and the objective of the present discussion. To do so, the present paper studies LES flow solutions in an enclosed rotor-stator configuration with a stationary shroud. These simulations are performed using a two-steps Taylor-Galerkin finite-element scheme coupled to a WALE subgrid scale model giving a better prediction of the eddy viscosity in zones of strong shear. This allows capturing the unsteady structures known to be present in the boundary layers. Two sets of statoric boundary conditions are investigated: the dynamics of the boundary layer is either resolved using a fine mesh grid or modeled using a classic boundary layer law of the wall. It is shown that the modeling of the stationary disc layer induces an underestimation of the flow velocity at low radii and loss of accuracy in the radial description of the boundary layer structures. Despite these differences, the most energetic structures are found to have the same azimuthal organization as in the wall resolved configuration as well as the same pulsation, which in turn produces a boundary layer with the same spectral content as in the wall resolved test case.
Experimental Study and Vortex Analysis in a Linear Compressor Cascade With Active Flow Control
Authors: Tian Simeng , Wu Yangyang , Zhang Zhibo , Cheng Bangqin , Li Yinghong , Wu Yun
Published: September 2016

In this paper, experimental investigations of a linear compressor cascade have been performed with Reynolds number of 2.4×105 to analyze the flow mechanism of hub-corner separation with end-wall jet and suction control. The vortices are measured with a quasi-three dimensional test system in different axial planes consisting of vorticity distribution and secondary flow structure. The experimental results give detailed insight into the performance of the principle vortices with different flow control methods. Corner separation losses could remarkably decrease with the jets and suction position near the asymptotic line of separation lines on suction surface. The flow control position plays a great role in affecting the corner separation losses while it is a more sensitive factor in the case of jets rather than the suction. It is evidenced that the combined flow control would get a higher decrease in the total pressure loss coefficient while an additional benefit in the reduction of losses has been gained in the case of a combined actuator layout.
An Analytical Model of Flow-Induced Rotordynamic Forces in Shrouded Centrifugal Pump Impellers
Authors: Song Jieun , Song Seung Jin
Published: September 2016

Shrouded centrifugal pumps are widely used in industrial applications such as process machines, and they can suffer from rotordynamic instability. Eccentric shrouded impellers induce non-axisymmetric flow fields which, in turn, lead to rotordynamic forces. Therefore, a new analytical flow model for shrouded pump impellers (which considers non-axisymmetric flow fields in the upstream inlet duct, shrouded impeller, and downstream) has been developed using an actuator disk approach. The model can predict impeller rotordynamic stiffness values from pump geometry and operating conditions. When compared to the available pump test data [1], the new model’s predicted stiffness coefficients agree well with the measured data. The new model’s predictions show the strong influence of the non-axisymmetric shroud inlet flow on the rotordynamic stiffness forces. The shroud inlet flow non-axisymmetry, in turn, results from the non-axisymmetric flows upstream of and inside the impeller blade passage induced by impeller eccentricity.
Application of High-Resolution Large Eddy Simulation to Simplified Turbomachinery Flows
Authors: Teramoto Susumu , Ouchi Takuya , Sanada Hiroki , Okamoto Koji
Published: September 2016

Fully resolved large eddy simulation (LES) is applied to two simple geometry flowfields with well-defined boundary conditions. The LES results are compared with simulations based on a Reynolds-averaged Navier-Stokes (RANS) model with turbulence, and pros and cons of using high-resolution LES for turbomachinery flows are discussed. One flow is a linear compressor cascade flow composed of the tip section of GE rotor B at Rec = 4 × 105 with a clearance, and the other is a Mach 1.76 supersonic turbulent boundary layer at Reδ = 5000 that laminerizes through a 12-degree expansion corner. The grids are prepared fine enough to resolve the turbulent boundary layer through a grid sensitivity study. The liner cascade result shows that all the turbulent shear layers and boundary layers including those in the small tip clearance are well resolved with 800 million grid points. The Reynolds stress derived from the LES results are compared directly with those predicted from the Spalart-Allmaras one-equation RANS turbulence model. The two results agreed qualitatively well except for the shear layer surrounding the tip leakage vortex, demonstrating that the RANS model performs well at least for flowfields near the design condition. From the simulation of the turbulent boundary layer experiencing sudden expansion, noticeable decreases of both Reynolds stress and local friction coefficient were observed, showing that the turbulent boundary layer has relaminarized through the sudden expansion. The boundary layer downstream of the expansion exhibits a nonequilibrium condition and was different from the laminar boundary layer.
Aerodynamic Design of a Highly Loaded Axial Flow Fan Rotor Using a Novel One-Dimensional Design Method With its Numerical Simulation
Authors: Shahsavari Ali , Nili-Ahamadabadi Mahdi
Published: September 2016

This paper presents a novel one-dimensional design method based on the radial equilibrium theory and constant span-wise diffusion factor to redesign of NASA rotor 67 just aerodynamically with a higher pressure ratio at the same design point. A one-dimensional design code is developed to obtain the meridional plane and blade to blade geometry of rotor to reach the three-dimensional view of rotor blades. To verify the redesigned rotor, its flow numerical simulation is carried out to compute its performance curve. The experimental performance curve of NASA rotor 67 is used for validation of the numerical results. Structured mesh with finer grids near walls is used to capture flow field and boundary layer effects. RANS equations are solved by finite volume method for rotating zones and stationary zones. The numerical results of the new rotor show about 9% increase in its pressure ratio at both design and off design mass flow rate. The new rotor has a higher outlet velocity through its upper span improving bypass ratio of a turbofan engine. To prove the new fan ability of producing more bypass ratio, a thermodynamic analysis is conducted. The results of this analysis show 13% increase in bypass ratio and 5.7% decline in specific fuel consumption in comparison to NASA rotor 67.
Study of Film Cooling in the Trailing Edge Region of a Turbine Rotor Blade in High Speed Flow Using Pressure Sensitive Paint
Authors: Gurram Niharika , Ireland Peter T. , Wong Tsun Holt , Self Kevin P.
Published: September 2016

This research focuses on film cooling of the trailing edge of a scaled up turbine rotor blade with engine-representative Mach number distribution. Pressure sensitive paint was used to obtain high-resolution adiabatic film cooling effectiveness measurements in the trailing edge region of the scaled turbine blade. The large scale, high-speed experimental set-up consists of a Perspex test section for maximum visibility of the PSP coated blade. The test section was designed to recreate a single blade passage of a gas turbine with inlet Mach and Reynolds numbers matching the corresponding values in an engine. The test blade has a constant cross section, representative of the mid-span profile of the high pressure turbine rotor blade. It was manufactured from aluminium to minimize temperature gradients over the surface of the test blade. In the current research, pressure surface cooling slots at the trailing edge were examined and the effect of cutback surface protuberance, or ‘land’, shapes on trailing edge film cooling was studied. Nitrogen and air were used as coolant gases giving a coolant to mainstream density ratio close to 1. Two land geometries-straight and tapered-were studied for a set of 6 blowing ratios from 0.4 to 1.4 in steps of 0.2. Land taper has a benefit for film cooling near the slot exit but its advantage reduces close to the trailing edge. For both geometries, film effectiveness falls with blowing ratio from 0.4 to 0.8 and increases with blowing ratio in the 0.8 to 1.4 range. Crossflow causes the coolant film to be biased towards one side of the lands. Film effectiveness results are compared with data from a scaled up low speed flat plat model of the trailing edge to explain the effect of acceleration on film cooling.
Enhanced Convective Heat Transfer due to Dynamically Forced Impingement Jet Arrays
Authors: Haucke Frank , Nitsche Wolfgang , Peitsch Dieter
Published: September 2016

Within the framework of the German collaborative research centre “SFB1029”, dynamically forced impingement cooling is investigated experimentally. This will provide a contribution to compensate the critical effects of a turbine inlet temperature increase induced by innovative combustion concepts. The present study describes experimental investigations regarding dynamically forced heat transfer between a flat hot surface and an array of up to 7 by 7 circular impingement jets. Fast switching solenoid valves are used to periodically pulse each cooling jet separately by changing frequency, duty cycle and phasing. Depending on the excitation parameters, strong ring vortices can be generated around each single jet. Thereby the maximum velocity within the core zone of each single jet can be significantly increased. Simultaneously, the vorticity is increased, which induces higher local and temporal wall shear stress after impinging on the wall and thus enhanced forced convective heat transfer as well. Considering a multi nozzle arrangement, the vortex structures of each impingement jet will interfere with the adjacent ones, which strongly influences cooling effectiveness.
Parasitic Loss due to Leading Edge Instrumentation on a Low Pressure Turbine Blade
Authors: Ng Henry C.-H. , Coull John D.
Published: September 2016

During the testing of development engines and components, intrusive instrumentation such as Kiel head Pitot probes and shrouded thermocouples are used to evaluate gas properties and performance. The size of these instruments can be significant relative to the blades and their impact on aerodynamic efficiency must be considered when analysing the test data. This paper reports on such parasitic losses for instruments mounted on the leading edge of a stator in a low pressure turbine, with particular emphasis on understanding the impact of probe geometry on the induced loss.

The instrumentation and turbine blades have been modeled in a low Mach number cascade facility with an upstream turbulence grid. The cascade was designed so that the leading edge probes were interchangeable in-situ, allowing for rapid testing of differing probe geometries. RANS calculations were performed to complement the experiments and gain more understanding about the flow behaviour.

A horseshoe vortex-like system forms at the join of the probe body and blade leading edge, generating pairs of streamwise vortices which convect over the blade pressure and suction surfaces. These vortices promote mixing between the freestream and boundary layer fluid, and promote the transition of the boundary layer from laminar to turbulent flow.

The size and shape of the leading edge probes relative to the blade varies significantly between applications. Tests with realistic probe geometries demonstrate that the detailed design of the shroud bleed system can impact the loss. A study of idealised cylinders is performed to isolate the impact of probe diameter, aspect ratio and incidence.
Effect of Rib Density on Flow and Heat Transfer in an Internal Cooling Passage
Authors: Hagari Tomoko , Ishida Katsuhiko , Takeishi Kenichiro , Komiyama Masaharu , Oda Yutaka
Published: September 2016

Effect of rib density on mechanism of flow and heat transfer enhancement in an internally-cooled channel with rib turbulators have been investigated numerically. Based on the experimental setup in the previous study [32], flowfield and heat transfer coefficient distributions were predicted with LES approach. The rib pitch-to-height ratios were 3 and 11, and Reynolds number based on the channel hydraulic diameter and bulk velocity was set at 30,000. Comparison of time-averaged flow and heat transfer characteristics between numerical and experimental results showed that prediction accuracy of the present numerical setup was reasonable.

The previous study [33] suggested that, for higher rib density, low-frequency velocity fluctuation characterizes heat transfer. To investigate its flow and heat transfer mechanism, instantaneous velocity and temperature fields were compared. For smaller rib density, small vortices constantly occurred from each rib and were dissipated into the mainstream before reaching the next rib. On the other hand, for higher rib density, relatively large vortex occurs above the ribs in addition to smaller vortices inside the cavity between the ribs. The large vortex occurs intermittently behind the second rib of the channel, and increases its size by interacting with smaller vortex downstream. For each rib pitch, similar trend was observed in the measured result obtained using Particle Image Velocimetry. This unsteady vortex structure would contribute to enhancing the heat transfer of a cooling channel with densely-arranged rib turbulators.
Torsional Robustness of the Combined Cycle Power Train Arrangement: Application of Statistical Methods to Accelerate Shaft-Line Design Cycles
Authors: Golebiowski Mateusz , Ling John P. C. W. , Knopf Eric , Niedermeyer Andreas
Published: September 2016

This article presents the application of statistical methods to guide the rotordynamic design of a turbo-generator shaft-line. One of the basic requirements is all shaft components must survive the event of a short circuit at the terminals of the generator. This is typically assessed via a transient response simulation of the complete machine train (including generator’s electrical model) to check the calculated response torque against the allowable value. With an increasing demand of a shorter design cycle and competition in performance, cost, footprint and safety, the probabilistic approach is starting to play an important role in the power train design process.

The main challenge arises with the size of the design space and complexity of its mapping onto multiple objective functions and criteria which are defined for different machines. In the presented paper, the authors give an example demonstrating the use of statistical methods to explore (Design of Experiment) and understand (Surface Response Methods) the design space of the Combined Cycle Power Train with respect to the typically most severe constraint (fault torque torsional response), which leads to a quicker definition of a turbo-generator’s arrangement. Further statistical analyses are carried out to understand the robustness of the chosen design against future modifications as well as parameters’ uncertainties.
Suppression of Subsynchronous Vibrations in a 11 MW Steam Turbine Using Integral Squeeze Film Damper Technology at the Exhaust Side Bearing
Authors: Ferraro Riccardo , Catanzaro Michael , Kim Jongsoo , Massini Michela , Betti Davide , Livermore-Hardy Richard
Published: September 2016

The presence of high subsynchronous vibrations and other rotordynamic instabilities in steam turbines can prevent operation at full speed and/or full load. The destabilizing forces generating subsynchronous vibrations can be derived from bearings, seals, impellers or other aerodynamic sources. The present paper describes the case of an 11 MW steam turbine, driving a syngas centrifugal compressor train, affected by subsynchronous vibrations at full load.

After the occurrence of anomalous vibrations at high load and a machine trip due to the high vibrations, the analysis of data collected at the site confirmed instability of the first lateral mode. Further calculations identified that the labyrinth seal at the balance drum was the main source of destabilizing effects, due to the high pre-swirl and the relatively tight seal clearance.

The particular layout of the turbine, a passing-through machine with a combined journal/double thrust bearing on the steam admission side, together with the need for a fast and reliable corrective action limited the possible solutions. Based on the analyses performed, adjusting the clearance and preload of the journal bearings could not have ensured stable operation at each operating condition. The use of swirl brakes to reduce the steam pre-swirl at the recovery seal entrance would have required a lengthy overhaul of the unit and significant labor to access and modify the parts. The final choice was a drop-in replacement of only the rear bearing (on the steam exhaust side) with a bearing featuring integral squeeze film damper (ISFD) technology. In addition to being a time efficient solution, the ISFD technology ensured an effective tuning of stiffness and damping, as proven by the field results.

The analyses carried out to understand the source of the subsynchronous vibrations and to identify possible corrective actions, as well as the comparison of rotordynamic data before and after the application of the bearing with ISFD technology, are discussed.
Experimental and Numerical Study of Heat Transfer Performance for an Engine Representative Two-Pass Rotating Internal Cooling Channel
Authors: Wang Zhi , Corral Roque , Chedevergne Francois
Published: September 2016

This paper investigates, both experimentally and computationally, the heat transfer performance on an engine representative varying aspect ratio two-pass internal cooling channel, in both stationary and rotating conditions. The test geometry and design parameters were suggested by SNECMA as a representative HPT blade two-pass internal cooling channel. The cooling channel has radially outward flow in the first passage with an aspect ratio of 1:2.25 and after a 180 degree sharp turn, a radially inward flow in the second passage with an aspect ratio of 1:1.85. One side of the two passages is equipped with 45 degree angled rib turbulators with a rib spacing P/e=7 and blockage ratio e/Dh =0.116. The other side is smooth in order to have optical access for experiment.

The experiment was performed at three Reynolds numbers: 15,000, 25,000, and 35,000. Both forward and backward rotating directions were tested in order to study the heat transfer performance of the ribbed surface as trailing wall or leading wall individually. The tested Rotation numbers were Ro=±0.3 at Re=15,000 and Re=25,000, whereas the Rotation number was reduced to ±0.22 at Re=35,000, due to restrictions of the test facility. Infrared thermography technology is used to capture the temperature field for further evaluation of heat transfer performance.

Numerical simulations for all experimental cases were conducted using the same geometry including the air feeding system, applying the experimental wall temperature distribution in order to properly capture inlet and buoyancy effects, with the k–ω–SST turbulence model. Numerical results show overall agreement and similar trends than the experimental data. Numerical results also show that the rotation effects alter the internal flow significantly, resulting in different surface heat transfer distributions. Particularly, it is shown that heat transfer performance of the pressure side is not enhanced by the rotation in this study, which is a surprising result. This behavior was captured both in the experiments and the numerical predictions.
CFD Simulations of a Meshing Gear Pair
Authors: Burberi E. , Fondelli T. , Andreini A. , Facchini B. , Cipolla L.
Published: September 2016

Gearboxes are efficient systems for torque transmission, with an overall efficiency over 99 % if well designed. Nevertheless its use in high power applications lead to significant energy loss. Further improvement of efficiency can be reached analyzing in more detail the different sources of power losses within the transmission system. These losses can be classified into two groups, load-dependent and load-independent. Whereas the load-dependent power losses have been closely studied and predictive models have been already developed, on the contrary the fluid-dynamic losses require further analyses. There are many sources of such losses, but the primary ones are related to the windage, the oil squeezing due to the gear meshing and oil churning. The relative magnitude of these mechanisms varies depending on the application. The objective of this work is to study the meshing losses by means of CFD simulations. A gear pair has been analyzed, representing an experimental test available in literature. Transient RANS calculations have been performed, exploiting two different numerical approaches. The influence of the rotational speed on the fluid-dynamic resistant torque has been investigated, then the flow and pressure fields associated with the gears motion have been evaluated. The results are compared to experimental data in order to validate the most appropriate modelling.
Investigation of Fuel Distribution in Partially Premixed Swirled Burner With Pilot Flame
Authors: Matveev Sergey S. , Zubrilin Ivan A. , Orlov Mikhail Yu. , Matveev Sergey G. , Chechet Ivan V.
Published: September 2016

At this paper, results of investigation of influence fuel distribution for combustion efficiency in model gas turbine burner with central body are presented. The burner is used for burning partially premixed lean mixture. The first part of gaseous fuel is injected into the central body with pilot flame (first fuel inlet) and the second part into the swirler (second fuel inlet). Study was performed with using CDF and experimental measurement. Experimental measurement was carried out with using chromatography equipment for concentration of combustion products determination. Experiment was conducted two case with first fuel inlet mass flow rate of 20% and 50% of the total fuel mass flow rate. Total fuel consumption was a constant at all case, total equivalence ratio was φ=0.625. At inline heater provides preheated air up from 328K to 523K. Numerical simulation of the flow parameters was carried out using Reynolds Stress for turbulence modeling and Flamelet Generated Manifold approach for combusting modeling. CFD calculation was conducted first fuel inlet mass flow rate of 0 to 100% of the total fuel mass flow rate and with preheated air up from 328K to 1173K. Weight average emission pollutant and combustion efficiency were compared to experiment data. Optimal operation of the burner have been found by the study.
Analysis of Combustion Noise Using Locally Resolved Density Fluctuations and a Microphone Array
Authors: Peterleithner Johannes , Zerobin Stefan , Woisetschläger Jakob
Published: September 2016

For turbulent swirl-stabilized flames combustion noise can be directly calculated, if density fluctuations as a function of time and space are known. It is however not easily possible to assess the density fluctuations directly. Therefore, in the past, combustion noise has been expressed as a function of chemiluminescence, an approach bringing in more assumptions. Now, by using interferometry, density fluctuations in the flame can be measured quantitatively. The advantage of this technique is that it measures the time derivative of density fluctuations directly. In this work laser interferometric vibrometry (LIV) was used to scan a two dimensional field in the flame in order to calculate the sound power emitted by the flame. Sound intensity was measured in a half-hemisphere by pressure-pressure-probes in order to record the total sound power of the direct combustion noise emitted by the unconfined flame. The goal of this study was to compare the measured sound power exhibited by the flame with the sound power predicted due to fluctuations of density within the flame. By using a siren to generate linear excitation, it was possible to qualitatively predict combustion noise with good agreement in trend. A quantitative comparison between both measurement techniques showed a deviation of a factor of six.
Development of Requirements for Numerical Modeling of the Premixer Aerodynamic
Authors: Nazukin Vladislav A. , Avgustinovich Valery G.
Published: September 2016

The premixer is the most important part of DLN/DLE gas turbine combustion chambers because it is responsible for velocity and fuel concentration fields at the flametube inlet. Most currently used premixers were developed using long expensive experimental research efforts. At present, progress in high performance computing allows application of a new approach to the development process utilizing extensive numerical simulation up to the first tests of combustion chamber. However, it is necessary to be sure that the most important processes which take place inside premixers and downstream such as interaction of vane wakes with the main flow, fuel/air mixing, vortex breakdown and vortical structures generation are correctly predicted. In other words, verified methodology of the aerodynamic design of the premixers is required. The present work continues the previously performed analysis of non-reacting swirling flow inside premixers and it is directed towards more accurate determination the effect of different computational model parameters on the results of numerical simulation. In the first phase of this work, results of uncompressible swirling flow measurements were used. The effect of premixer geometry (full or simplified), grid resolution, turbulence model (k-e RNG, SST, SSG RSM, DES, SAS), number of timesteps and initial conditions on time-averaged flow parameters as well as flow structures such as precessing core were assessed. Some interesting features were found as the result of this work. For example, simplification of premixer geometry slightly effects on the results of RANS computations and entirely changes precessing core structure obtained in URANS modeling. In the second phase of this work compressible swirling flow measurements were used to compare the ability of DES and SST turbulence models to predict velocity and velocity fluctuation fields as well as vortical structures in a swirling flow. As the result of this work the main requirements for the computational fluid dynamics analysis of premixer aerodynamic were developed and validated. They specify parameters of computational model depending on the target flow parameters.
Alleviation of Shock-Wave Effects on a Highly Loaded Axial Compressor Through Novel Blade Shaping
Authors: John Alistair , Shahpar Shahrokh , Qin Ning
Published: September 2016

This paper describes the use of the Free-Form-Deformation [1] parameterisation method to create a novel blade shape for a highly loaded, transonic axial compressor. The novel geometry makes use of pre-compression (via an S-shaping of the blade around mid-span) to weaken the shock and improve the aerodynamic performance.

It has been known for some time that reducing the pre-shock Mach number of transonic compressors (via pre-compression) can improve their efficiency [2]. However, early attempts at this in the 60s [3] showed undesirable results (such as bi-stable operation), leading the design community to shy away from using pre-compression [4]. This issue is re-addressed here. It is shown that using modern simulation, optimisation and a 3D design, large amounts of pre-compression may be employed without the negative effects that plagued early attempts.

This paper shows how Free-Form-Deformation offers superior flexibility over traditionally used parameterisation methods. The novel design (produced via an efficient optimisation method) is presented and the resulting flow analysed in detail. The efficiency benefit is over 2%, surpassing other results in the literature for the same geometry. The pre-compression effect of the S-shape is analysed and explained, and the entropy increase across the shock (along the mid-blade line) is shown to be reduced by almost 80%. Adjoint surface sensitivity analysis of the datum and optimised designs is presented, showing that the S-shape is located in the region predicted to be most significant for changes in efficiency. Finally the off-design performance of the blade is analysed across the rotor characteristics at various speeds.
Effects of Inlet Swirl on Suction Side Phantom Cooling
Authors: Zhang Yang , Li Yifei , Yuan Xin
Published: September 2016

Though the temperature of the coolant injected from the endwall increases after the mixing process in the main flow, the injections moving from the endwall to the airfoil suction side still have the potential of second order cooling. This part of the coolant is called “Phantom cooling” in the paper. This paper is focused on the function of the coolant from fan-shaped holes on endwall surface which brought by passage vortex to the airfoil suction side. The test cascades are based on the profile of General Electric Energy Efficient Engine (GE-E3), with the inlet Mach number of 0.1 and Reynolds number of 1.46×105. The scale ratio of the test vanes is 1.95 and the film cooling effectiveness is tested with Pressure Sensitive Painting (PSP) Technology. Nitrogen is used to simulate the coolant which can provide a density ratio near 1.0. Two adjacent passages are investigated simultaneously by which the film cooling effectiveness can be compared in the same case on the suction side surface. The inlet rotating flow is simulated by an upstream swirler at the inlet, fixed at 5 different positions along the pitchwise direction. They are Blade 0 aligned, Passage 1 aligned, Blade 1 aligned, Passage 2 aligned and Blade 2 aligned. According to the experimental results, the inlet rotating flow can dominate the film cooling effectiveness distribution at the Suction Side. The averaged film cooling effectiveness changes substantially with the change in the swirler position. The inlet swirling flow effects are compared on the adjacent vanes at upstream and downstream regions. The research shows that the different pitchwise position of the inlet swirler is a significant factor which can change the phantom cooling phenomenon on the suction side. The relative position of inlet swirler cannot be ignored for Nozzle Guide Vane design.
Analytical Modeling and Experimental Validation of Heating at the Leaf Seal/Rotor Interface
Authors: Pekris Michael J. , Franceschini Gervas , Owen Andrew K. , Jones Terry V. , Gillespie David R. H.
Published: September 2016

The secondary air system of a modern gas or steam turbine is configured to satisfy a number of requirements, such as to purge cavities and maintain a sufficient flow of cooling air to key engine components, for a minimum penalty on engine cycle efficiency and specific fuel consumption. Advanced sealing technologies, such as brush seals and leaf seals, are designed to maintain pressures in cavities adjacent to rotating shafts. They offer significant reductions in secondary air parasitic leakage flows over the legacy sealing technology, the labyrinth seal. The leaf seal comprises a series of stacked sheet elements which are inclined relative to the radial direction, offering increased axial rigidity reduced radial stiffness, and good leakage performance.

Investigations into leaf seal mechanical and flow performance have been conducted by previous researchers. However, limited understanding of the thermal behavior of contacting leaf seals under sustained shaft contact has led to the development of an analytical model in this study, which can be used to predict the power split between the leaf and rotor from predicted temperature rises during operation. This enables the effects of seal and rotor thermal growth and, therefore, implications on seal endurance and rotor mechanical integrity to be quantified. Consideration is given to the heat transfer coefficient in the leaf pack. A dimensional analysis of the leaf seal problem using the method of extended dimensions is presented, yielding the expected form of the relationship between seal frictional power generation, leakage mass flow rate and rotor temperature rise. An analytical model is derived which is in agreement. Using the derived leaf temperature distribution formula, the theoretical leaf tip temperature rise and temperature distributions are computed over a range of mass flow rates and frictional heat values.

Experimental data were collected in high speed tests of a leaf seal prototype using the Engine Seal Test Facility at Oxford University. These data were used to populate the analytical model, and collapsed well to confirm the expected linear relationship. In this form, the thermal characteristic can be used with predictions of mass flow rate and frictional power generated to estimate leaf tip and rotor temperature rise in engine operation.
Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Experimental Investigation
Authors: Massini Daniele , Burberi Emanuele , Carcasci Carlo , Cocchi Lorenzo , Facchini Bruno , Armellini Alessandro , Casarsa Luca , Furlani Luca
Published: September 2016

A detailed aerothermal characterization of an advanced leading edge cooling system has been performed by means of experimental measurements. Heat transfer coefficient distribution has been evaluated exploiting a steady-state technique using Thermocromic Liquid Crystals (TLC), while flow field has been investigated by means of Particle Image Velocimetry (PIV). The geometry key features are the multiple impinging jets and the four rows of coolant extraction holes, which mass flow rate distribution is representative of real engine working conditions. Tests have been performed in both static and rotating conditions, replicating a typical range of jet Reynolds number (Rej), from 10000 to 40000, and Rotation number (Roj) up to 0.05. Different cross-flow conditions (CR) have been used to simulate the three main blade regions (i.e. tip, mid and hub). The aerothermal field turned out to be rather complex, but a good agreement between heat transfer coefficient and flow field measurement has been found. In particular, jet bending strongly depends on crossflow intensity, while rotation has a weak effect on both jet velocity core and area-averaged Nusselt number. Rotational effects increase for the lower cross-flow tests. Heat transfer pattern shape has been found to be substantially Reynolds-independent.
A Simple Model for Thermodynamic Properties of Air and Combustion Gases for Educational Purposes
Authors: Banjac Milan , Milic Srdjan , Petrovic Milan V.
Published: September 2016

A new, simple model for the thermodynamic properties of dry air and combustion gases is presented. The model has been developed mainly for educational purposes with the focus on gas turbine cycle calculations included in university courses. The equations used are short and easy to include in a student computer program. This ideal gas model is based on well-known correlations from the open literature and each equation is an approximated fit to an appropriate expression from the original reference. In the new concept, each relation is expressed using a simple algebraic formulation that has an explicit inverse function. Therefore, the numerical result of an inverse function can be obtained directly, without the involvement of any iterative procedure. This simplifies the programming of auxiliary subroutines for thermodynamic properties. It becomes an easy task and the use of complicated models, in basic university courses, is avoided. Long and complex subroutines which are treated as “black boxes” are now excluded from the code, and a program for thermodynamic cycle calculation is then completely written by a student, starting from the very beginning.