bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part II: Two-Phase Flow Measurements and Droplet Dynamics
Authors: Ragab Reda , Wang Ting
Published: August 2017

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 two layers: a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. With the results of PDPA measurements and the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part I are re-examined, and the fundamental mist-flow physics are analyzed. The three-dimensional (3D) 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 explain 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.
Enhanced Flow Boiling Using Radial Open Microchannels With Manifold and Offset Strip Fins
Authors: Recinella Alyssa , Kandlikar Satish G.
Published: August 2017

The increasing demand for designing effective cooling solutions in high power density electronic components has resulted in exploring advanced thermal management strategies. Over the past decade, phase-change cooling has received widespread recognition due to its ability to dissipate large heat fluxes while maintaining low temperature differences. In this paper, a radial flow boiling configuration through a central inlet was studied. This configuration is particularly suited for chip cooling application. Two heat transfer surfaces with (a) radial microchannels, and (b) offset strip fins were fabricated and their flow boiling performance with distilled water was obtained. Furthermore, the effect of the liquid flow rate on the boiling performance and enhancement mechanisms was also investigated in this study. At a flow rate of 240 mL/min, a maximum heat flux of 369 W/cm2 at a wall superheat of 49 °C and a pressure drop of 59 kPa was achieved with the radial microchannels, while the offset strip fins achieved a maximum heat flux of 618 W/cm2 at a wall superheat of 20 °C. Increasing the flow rate to 320 mL/min resulted in a heat flux of 897 W/cm2 demonstrating the potential of using a radial configuration for enhancing the boiling performance. The increase in flow cross-sectional area was shown to be responsible for the reduced pressure drop when compared to straight microchannel configurations. The high-speed imaging incorporated in each test provided valuable insight and understanding into the flow patterns and underlying mechanism in these geometries. With the ease of implementation, highly stable flow, and further optimization possibilities with different microchannel and taper configurations, the radial geometry is expected to provide significant performance enhancement well beyond a critical heat flux (CHF) of 1 kW/cm2.
Process Control for Compression Systems
Authors: Kurz Rainer , Brun Klaus
Published: August 2017

The paper discusses the interaction between a centrifugal compressor and the process, and as a result, the control requirements for centrifugal compressor packages. The focus is on variable speed, upstream and midstream applications. The impact of the interaction between system characteristics and compressor characteristics, both under steady state and transient conditions is explained. Also considered are concepts to optimize and control the units. Special attention is given to the issue of surge avoidance.

Additionally, the impact of the process and how the process dynamics interact with the compressor is analyzed, categorized, and explained.
Characterising the Influence of Impeller Exit Recirculation on Centrifugal Compressor Work Input
Authors: Stuart Charles , Spence Stephen , Filsinger Dietmar , Starke Andre , Kim Sung In
Published: August 2017

Impeller recirculation is a loss which has long been considered in 1 D modelling, however the full extent of its impact on stage performance has not been analysed. Recirculation has traditionally been considered purely as a parasitic (or external) loss, i.e. one which absorbs work but does not contribute to total pressure rise across the stage. Having extensively analysed the impact of recirculation on the impeller exit flow field, it was possible to show that it has far reaching consequences beyond that of increasing total temperature. The overall aim of this package of work was to apply a much more physical treatment to the impact of impeller exit recirculation (and the aerodynamic blockage associated with it), and hence realise an improvement in the 1 D stage performance prediction of a number of turbocharger centrifugal compressors.

The factors influencing the presence and extent of this recirculation are numerous, requiring detailed investigations to successfully understand its sources and to characterise its extent. A combination of validated 3 D Computational Fluid Dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. In order to capture the variation of the blockage presented to the flow with both geometry and operating condition, an approach involving the impeller outlet to inlet area ratio and a novel flow coefficient term were employed. The resulting data permitted the generation of a single equation to represent the impeller exit blockage levels for the entire operating map of all six compressor stages under investigation.

With an understanding of the extent of the region of recirculating flow realised, and the key drivers leading to its creation identified, it was necessary to comprehend how the resulting blockage influenced compressor performance. Consideration was given to the impact on impeller work input through modification of the impeller exit velocity triangle, incorporating the introduction of the concept of an “aerodynamic meanline” to account for the reduction in the size of the active flow region due to the presence of blockage. The sensitivity of the stage to this change was then related back to the level of backsweep applied to the impeller. As a result of this analysis, the improvement in the 1 D performance prediction of the six compressor stages is demonstrated. In addition, a number of design recommendations are presented to ensure that the detrimental effects associated with the presence of impeller exit recirculation can be minimised.
Numerical Study of the Flow Past an Axial Turbine Stator Casing and Perspectives for its Management
Authors: Kadhim Hakim T. K. , Rona Aldo , Obaida Hayder M. B. , Gostelow J. Paul
Published: August 2017

The interaction of secondary flow with the main passage flow results in entropy generation; this accounts for considerable losses in turbomachines. Low aspect ratio blades in an axial turbine lead to a high degree of secondary flow losses. A particular interest is the reduction in secondary flow strength at the turbine casing, which adversely affects the turbine performance. This paper presents a selective review of effective techniques for improving the performance of axial turbines by turbine end wall modifications. This encompasses the use of axisymmetric and non-axisymmetric end wall contouring and the use of fences. Specific attention is given to non-axisymmetric end walls and to their effect on secondary flow losses. A baseline three-dimensional steady RANS k-ω SST model, with axisymmetric walls, is validated against experimental measurements from the Institute of Jet Propulsion and Turbomachinery at the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Germany, with comparative solutions generated by ANSYS Fluent and OpenFOAM. The predicted performance of the stator passage with an axisymmetric casing is compared with that from using a contoured casing with a groove designed using the Beta distribution function for guiding the groove shape. The prediction of a reduced total pressure loss coefficient with the application of the contoured casing supports the groove design approach based on the natural path of the secondary flow features. This work also provided an automated workflow process, linking surface definition in MATLAB, meshing in ICEM CFD, and flow solving and post-processing OpenFOAM. This has generated a casing contouring design tool with a good portability to industry, to design and optimize new turbine blade passages.
Influence of Aerodynamic Mistuning and Aerodynamic Coupling on Vibration Behavior of Mistuned Small Radial Turbine Wheels
Authors: Hemberger David , Filsinger Dietmar , Bauer Hans-Jörg
Published: August 2017

The study at hand analyzes the influence of aerodynamic mistuning and aerodynamic coupling on the vibration behavior of mistuned small radial turbine wheels. The aerodynamic mistuning is caused by angular non uniformity of the variable turbine guide vanes. Variable turbine guide vanes are state of the art in exhaust gas turbochargers for automotive diesel engines. Aerodynamic coupling describes the coupling of the turbine blades through the flow. It can influence the mistuned vibration behavior of the turbine wheel due to varying operation conditions, in which the turbine pressure ratio and the pressure distribution over the turbine wheel surface is changed.

It was analyzed whether the aerodynamic mistuning and aerodynamic coupling must be considered for small radial turbine wheel designs. The basis for this investigation were blade vibration measurements under standstill conditions with a laser vibrometer as well as blade vibration measurements during operation with a tip timing system. The mistuned turbine eigenforms were analyzed and compared at various ambient conditions using these measurement results.

By means of forced response calculations — unsteady 3D CFD and 3D FEA —, the influence of aerodynamic mistuning on the ideal tuned turbine was examined to be able to separate the aerodynamic mistuning from the mistuning of the structure. Furthermore, the superimposed effect of the aerodynamic mistuning and the mistuning of the structure on the turbine eigenforms and the amplitude amplification was analyzed using a mistuned 3D FE model and a population of samples with varying aerodynamic mistuning.

It was found, that the aerodynamic coupling and aerodynamic mistuning have a negligible effect on the mistuned vibration behavior for a small radial turbine with variable turbine guide vanes. These two parameters must not be considered when designing such a turbine wheel.
An Investigation of the Stability Enhancement of a Centrifugal Compressor Stage Using a Porous Throat Diffuser
Authors: Galloway Lee , Spence Stephen , Kim Sung In , Rusch Daniel , Vogel Klemens , Hunziker René
Published: August 2017

The stable operating range of a centrifugal compressor stage of an engine turbocharger is limited at low mass flow rates by aerodynamic instabilities which can lead to the onset of rotating stall or surge. There have been many techniques employed to increase the stable operating range of centrifugal compressor stages. The literature demonstrates that there are various possibilities for adding special treatments to the nominal diffuser vane geometry, or including injection or bleed flows to modify the diffuser flow field in order to influence diffuser stability. One such treatment is the porous throat diffuser. Although the benefits of this technique have been proven in the existing literature, a comprehensive understanding of how this technique operates is not yet available.

This paper uses experimental measurements from a high pressure ratio compressor stage to acquire a sound understanding of the flow features within the vaned diffuser which affect the stability of the overall compression system and investigate the stabilising mechanism of the porous throat diffuser. The non-uniform circumferential pressure imposed by the asymmetric volute is experimentally and numerically examined to understand if this provides a preferential location for stall inception in the diffuser. The following hypothesis is confirmed: linking of the diffuser throats via the side cavity equalizes the diffuser throat pressure, thus creating a more homogeneous circumferential pressure distribution, which delays stall inception to lower flow rates. The results of the porous throat diffuser configuration are compared to a standard vaned diffuser compressor stage in terms of overall compressor performance parameters, circumferential pressure non-uniformity at various locations through the compressor stage and diffuser sub-component analysis. The diffuser inlet region was found to be the element most influenced by the porous throat diffuser and the stability limit is mainly governed by this element.
Species Dependency of the Compositional Indirect Noise Mechanism
Authors: O’Brien Jeffrey D. , Ihme Matthias
Published: August 2017

Indirect combustion noise is a growing concern for aviation engine designers. It is typically associated with the distortion of “hot spots” (entropy structures) and vortical structures that generate excess noise as they are convected by an accelerating mean flow. Recently, it has been shown theoretically that fluctuations in a gas’s chemical composition can act as an additional source of indirect noise in aviation engines. This work examines this composition noise mechanism, focusing on the underlying chemical effects that drive this source of indirect noise. Since the mechanism has yet to be confirmed experimentally, this paper begins by applying the theory to inert mixtures of noble gases and air, in an attempt to guide experimentalists by identifying the set of operating conditions that will produce the strongest acoustic response. Turning from non-reacting to reacting flows, the paper next examines the sensitivity of the compositional noise mechanism to fuel type, testing several common fuels. It is found that, while there is a substantial difference between hydrogen and hydrocarbon fuels, overall noise levels vary only slightly between different hydrocarbon fuels. Additionally, there appears to be a common underlying structure to the response of a product-gas mixture generated by burning a fuel, which is explained through linearized theory and confirmed with numerical results. Lastly, the physics of composition noise is examined at the species-specific level, attempting to provide a link between individual combustion products and changes in a mixture’s propensity to generate indirect noise. The sensitivity of individual species can be explained by a combination of differences between the species and mixture’s Gibbs free energy and strong gradients in product gas concentration with mixture fraction. However, by analyzing the species dependency of combustion products at several different mean mixture fractions, it is found that no single species dominates the noise generation over the combustor’s entire range, but rather the most acoustically active species varies strongly with local stoichiometry.
Heat Transfer in the Core Compressor Under Ice Crystal Icing Conditions
Authors: Bucknell Alexander , McGilvray Matthew , Gillespie David R. H. , Jones Geoff , Reed Alasdair , Buttsworth David R.
Published: August 2017

It has been recognised in recent years that high altitude atmospheric ice crystals pose a threat to aircraft engines. Instances of damage, surge and shutdown have been recorded at altitudes significantly greater than those associated with supercooled water icing. It is believed that solid ice particles can accrete inside the core compressor, although the exact mechanism by which this occurs remains poorly understood.

Development of analytical and empirical models of the ice crystal icing phenomenon is necessary for both future engine design and this-generation engine certification. A comprehensive model will require the integration of a number of aerodynamic, thermodynamic and mechanical components. This paper studies one such component, specifically the thermodynamic and mechanical processes experienced by ice particles impinging on a warm surface.

Results are presented from an experimental campaign using a heated and instrumented flat plate. The plate was installed in the Altitude Icing Wind Tunnel (AIWT) at the National Research Council of Canada (NRC). This facility is capable of replicating ice crystal conditions at altitudes up to 9 km and Mach numbers up to 0.55 [1]. The heated plate is designed to measure the heat flux from a surface at temperatures representative of the early core compressor, under varying convective and icing heat loads.

Heat transfer enhancement was observed to rise approximately linearly with both total water content and particle diameter over the ranges tested. A Stokes number greater than unity proved to be a useful parameter in determining whether heat transfer enhancement would occur. A particle energy parameter was used to estimate the likelihood of fragmentation. Results showed that when particles were both ballistic and likely to fragment, heat transfer enhancement was independent of both Mach and Reynolds numbers over the ranges tested.
Boundary Layer Flashback in Premixed Hydrogen-Air Flames With Acoustic Excitation
Authors: Hoferichter Vera , Sattelmayer Thomas
Published: August 2017

Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback.

This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0 to 36 % of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.
Non-Axisymmetric Stator Design for Boundary Layer Ingesting Fans
Authors: Gunn E. J. , Hall C. A.
Published: August 2017

In a Boundary Layer Ingesting (BLI) fan system the inlet flow field is highly non-uniform. In this environment, an axisymmetric stator design suffers from a non-uniform distribution of hub separations, increased wake thicknesses and casing losses. These additional loss sources can be reduced using a non-axisymmetric design that is tuned to the radial and circumferential flow variations at exit from the rotor.

In this paper a non-axisymmetric design approach is described for the stator of a low-speed BLI fan. Firstly sectional design changes are applied at each radial and circumferential location. Next, this approach is combined with the application of non-axisymmetric lean. The designs were tested computationally using full-annulus unsteady CFD of the complete fan stage with a representative inlet distortion. The final design has also been manufactured and tested experimentally.

The results show that a 2D sectional approach can be applied non-axisymmetrically to reduce incidence and diffusion factor at each location. This leads to reduced loss, particularly at the casing and midspan, but it does not eliminate the hub separations that are present within highly distorted regions of the annulus. These are relieved by non-axisymmetric lean where the pressure surface is inclined towards the hub. For the final design, the loss in the stator blades operating with BLI was measured to be 10% lower than for the original stator design operating with undistorted inflow. Overall, the results demonstrate that non-axisymmetric design has the potential to eliminate any additional loss in a BLI fan stator caused by the non-uniform ingested flow-field.
Total Temperature Based Correction of the Turbulence Production in Hot Jets
Authors: Truemner Jens , Mundt Christian
Published: August 2017

Comparisons with experiments have shown that RANS models tend to underpredict the mixing process in shear layers with strong temperature gradients. In the modeling of jet engine’s exhaust systems this leads to an overpredicted potential core length and underestimated turbulence intensity in the free jet. In addition, the calculated efficiency gain is lower than indicated by measurements in mixed turbofan engines. Based on the findings from scale-resolving simulations a correction to the turbulence production term is proposed and compared with two NASA-experiments on hot jets. This correction is implemented in a Reynolds-stress and a k-ε model. The results are in very good agreement with the experimental data.
Measurement of the Mean Flow Field in a Smooth Rotating Channel With Coriolis and Buoyancy Effects
Authors: You Ruquan , Li Haiwang , Tao Zhi , Wei Kuan
Published: August 2017

The mean flow field in a smooth rotating channel was measured by particle image velocimetry under the effect of buoyancy force. In the experiments, the Reynolds number, based on the channel hydraulic diameter (D) and the bulk mean velocity (Um), is 10000, and the rotation numbers are 0, 0.13, 0.26, 0.39, 0.52, respectively. The four channel walls are heated with Indium Tin Oxide (ITO) heater glass, making the density ratio (d.r.) about 0.1 and the maximum value of buoyancy number up to 0.27. The mean flow field was simulated on a 3D reconstruction at the position of 3.5<X/D<6.5, where X is along the mean flow direction. The effect of Coriolis force and buoyancy force on the mean flow was taken into consideration in the current work. The results show that the Coriolis force pushes the mean flow to the trailing side, making the asymmetry of the mean flow with that in the static conditions. On the leading surface, due to the effect of buoyancy force, the mean flow field changes considerably. Comparing with the case without buoyancy force, separated flow was captured by PIV on the leading side in the case with buoyancy force. More details of the flow field will be presented in this work.
High Humidity Aerodynamic Effects Study on Offshore Wind Turbine Airfoil/Blade Performance Through CFD Analysis
Authors: Yu Xue , Yan Liu
Published: August 2017

Damp air with high humidity combined with foggy, rainy weather as well as icing in winter weather often found to cause turbine performance degradation, and it is more concerned with off-shore wind farm development. To address and understand the high humidity effects on wind turbine performance, our study has been conducted with spread sheet analysis on damp air properties investigation for air density and viscosity, then CFD modeling study using Fluent were carried out on Airfoil and Blade aerodynamic performance effects investigation due to water vapor partial pressure of mixing flow and water condensation around leading edge and trailing edge of airfoil. It is found that the high humidity effects with water vapor mixing flow and water condensation thin film around airfoil may have insignificant effect directly on airfoil/blade performance; however the indirect effects such as blade contamination and icing due to the water condensation may have significant effects on turbine performance degradation. Also found the foggy weather with micro water droplet (including rainy weather) may cause higher drag that lead to turbine performance degradation. It is found that at high temperature, the high humidity effect on air density cannot be ignored for annual energy production calculation. As qualitative validation, the CFD result was compared and correlated with field observation in foggy day of cold weather. The blade contamination and icing phenomenon need to be further investigated in the future study, and blade surface properties such as high surface energy coating effects on water condensation and icing will be investigated for anti-icing coating agent development.
Mixed Helical Labyrinth Groove Seal Optimization Using Computational Fluid Dynamics
Authors: Paudel Wisher , Watson Cori , Wood Houston G.
Published: August 2017

Non-contacting annular seals are used in rotating machinery to reduce the flow of fluid across a pressure differential. Helical and labyrinth groove seals are two types of non-contacting annular seals frequently used between the impeller stages in a pump. Labyrinth seals have circumferential grooves cut into the surface of the rotor, the stator, or both. They function to reduce leakage by dissipating kinetic energy as fluid expands in the grooves and then is forced to contract in the jet stream region. Helical groove seals have continuously cut grooves in either or both of the rotor and stator surfaces. Like labyrinth seals, they reduce leakage through dissipation of kinetic energy, but have the added mechanism of functioning as a pump to push the fluid back towards the high pressure region as it tries to escape. Previous work has shown that both labyrinth and helical groove seals with grooves on both the rotor and the stator have lower leakage than seals with grooves on just one surface. The goal of this work is to analyze seals with helical grooves on one surface and labyrinth grooves on the other. Designs for both helical stator, labyrinth rotor and labyrinth stator, helical rotor will be simulated and the performance of each configuration will be compared. The primary variables considered for the designs of the seals include the width, depth, and the number of grooves for labyrinth seal and the width, depth, and the angle of the grooves for helical. The designs to simulate will be chosen using a Kennard-stone algorithm to optimally space them within the design space. Then, for both configurations, multi-factor quadratic regression models will be generated. Backward regression will be used to reduce the models to only statistically significant design parameters. From there, the response surfaces will be created to demonstrate the effects of each design parameter on the performance of the seal. Finally, optimal designs will be produced based on the regression models. These designs will be simulated to show the predictive power of the regression models. The simulations for this work will be run in ANSYS CFX for each seal type and configuration will be used to compare solutions for the two different types of designs to previous studies. The findings from this study is expected to show substantial decrease in leakage for a mixed helical-labyrinth seal in comparison to the seal with either helical or labyrinth grooves on both surfaces and thus will provide useful results needed to minimize amount of leakage and therefore improve the efficiency of the machine.
A Discussion on the Advancement of Blade Tip Timing Data Processing
Authors: Kharyton Vsevolod , Dimitriadis Grigorios , Defise Colin
Published: August 2017

The Blade Tip Timing method (BTT) is a well-known approach permitting individual blade vibration behavior characterization. The technique is becoming increasingly popular among turbomachinery vibration specialists. Its advantages include its non-intrusive nature and its capability of being used for long-term monitoring, both in on-line and offline analysis. However, the main drawback of BTT is frequency aliasing.

Frequency aliasing effects in tip timing can be reduced by means of the application of different methods from digital signal analysis that can exploit the non-uniform nature of the data sampled by BTT. This non-uniformity is due to the fact that an optimization of the circumferential distribution of BTT probes is usually required in order to improve the data quality for targeted modes of blade vibration and/or orders of excitation.

The BTT data analysis methods considered in this study are the non-uniform Fourier transform, the minimum variance spectrum estimator approach, a multi-channel technique using in-between samples interpolation, the Lombe-Scargle periodogram and an iterative variable threshold procedure. These methods will be applied to measured data representing quite a large scope of events occurring during gas-turbine compressor operation, e.g. synchronous engine order resonance crossing, rotating stall, suspected limit-cycle oscillations.

Finally, the frequency estimates obtained from all these methods will be summarized.
Numerical Approach for Real Gas Simulations: Part II — Flow Simulation for Supercritical CO2 Centrifugal Compressor
Authors: Saxena Swati , Mallina Ramakrishna , Moraga Francisco , Hofer Douglas
Published: August 2017

This paper is presented in two parts. Part I (Tabular fluid properties for real gas analysis) describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate and robust tabular representation of the RefProp CO2 properties. Part II (this paper) presents numerical simulations of a low flow coefficient supercritical CO2 centrifugal compressor developed for a closed loop power cycle. The real gas tables presented in part I are used in these simulations. Three operating conditions are simulated near the CO2 critical point: normal day (85 bar, 35C), hot day (105 bar, 50 C) and cold day (70 bar, 20C) conditions. The compressor is a single stage overhung design with shrouded impeller, 155 mm impeller tip diameter and a vaneless diffuser. An axial variable inlet guide vane (IGV) is used to control the incoming swirl into the impeller. An in-house three-dimensional computational fluid dynamics (CFD) solver named TACOMA is used with real gas tables for the steady flow simulations. The equilibrium thermodynamic modeling is used in this study. The real gas effects are important in the desired impeller operating range. It is observed that both the operating range (minimum and maximum volumetric flow rate) and the pressure ratio across the impeller are dependent on the inlet conditions. The compressor has nearly 25% higher operating range on a hot day as compared to the normal day conditions. A condensation region is observed near the impeller leading edge which grows as the compressor operating point moves towards choke. The impeller chokes near the mid-chord due to lower speed of sound in the liquid-vapor region resulting in a sharp drop near the choke side of the speedline. This behavior is explained by analyzing the 3D flow field within the impeller and thermodynamic quantities along the streamline. The 3D flow analysis for the flow near the critical point provides useful insight for the designers to modify the current compressor design for higher efficiency.
Numerical Investigation of a Centrifugal Compressor With a Single Circumferential Groove in Different Types of Diffusers
Authors: Chen Xuefei , Ai Zijian , Ji Yunfeng , Qin Guoliang
Published: August 2017

Enhancing compressor stall and surge has a great importance for the development of turbo compressors. The application of casing treatment is an effective measure to expand the stall margin and stable operation range. Numerical investigations were conducted to predict the performance of a low flow rate centrifugal compressor with circumferential groove casing treatment in diffuser. Numerical cases with different radial location, radial width and axial depth of a circumferential single groove in different types of diffusers (vaned diffuser, half-vaned diffuser, vaneless diffuser) were carried out to compare the results. The computational fluid dynamics analyses results show that the centrifugal compressor with circumferential groove in vaned diffuser can extend stable range by about 9.1% while the efficiency over the whole operating range decreases by 0.2 to 1.7%; the results with half-vaned diffuser and vaneless diffuser can improve stable range less and the efficiency decreases more. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor’s stall margin and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analyzed. The flow transport across the tip gap in the smooth wall and the circumferential grooves were compared.
Preliminary Design, Ignition, and Fuel Injection for a High Temperature Recuperated Microturbine Combustor
Authors: Tuttle Steven , Hinnant Katherine , Vick Michael
Published: August 2017

Recuperation and high turbine inlet temperatures could enable miniature (<20 kW) gas turbines to match the fuel efficiency and installed weight of current internal combustion (IC) engines. However, these strategies create unusual challenges for combustor development. As the engine transitions from ignition to steady state, changes in the preheated air temperature, fuel/air mixture, evaporation, and chemical timescales make operability difficult with a fixed-geometry combustor at all operational states. The flame must also be exceptionally clean in all conditions because any soot will foul the recuperator. Furthermore, preheated air is less effective for cooling, potentially creating extreme thermal loads on the liner, especially during transients, and any ignition device that protrudes into the unusually hot primary zone could melt.

This paper describes the preliminary design of a combustor being developed to meet these challenges, and reviews the late progress on subsystem testing and experiments. The combustor is a single-can type with a radial swirler and single atomizer nozzle at one end. An optically accessible burner is being used to explore fundamental aspects of swirler aerodynamics, ignition strategies, liner cooling, and lean blow off behavior. Particle image velocimetry (PIV) is enabling quantitative velocity measurements of swirler jet decay and interaction with the liner wall. Two different methods for projecting an ignition source into the primary zone from outside the liner, a micro-torch and a conventional spark igniter, have been tested.
Sand Transport and Deposition in Rotating Two-Passed Ribbed Duct With Coriolis and Centrifugal Buoyancy Forces at Re=100,000
Authors: Dowd Cody , Tafti Danesh , Yu Kuahai
Published: August 2017

The paper investigates the transport of sand particles in the two-pass internal cooling duct of a turbine blade under rotation. The size range is representative of Fine Arizona Road Test Dust from Powder Technology Inc., corresponding to 50% of injected particles being less than 4 microns in diameter, with 90% being less than 50 microns, The geometry consists of a U-bend with 17 ribs in each pass. The ribs are staggered with an e/Dh = 0.1 and a P/e = 10. LES simulation is used with a Reynolds number, Re = 100,000, a Buoyancy parameter, Bo = 0.5, and a rotation number, Ro = 0.2. Deposition and impingement patterns are investigated for three different wall temperatures, 950, 1000, and 1050°C under rotating and stationary conditions. In the first pass, rotation results in much higher levels of impingement and deposition along the trailing wall in comparison to the leading wall and the stationary duct leading and trailing walls. This is due to the action of Coriolis forces which push the particles towards the trailing wall on entry into the rotating duct resulting is a high level of interaction with the trailing duct surface and ribs. Roughly 0.5% of the impacting particles deposit. As a result of this about 84% of the particles deposit in the first pass compared to only 27% in the stationary duct. It is found that temperature effects in the range of wall temperatures from 950–1050°C had no significant effect on deposition. This is because the particle temperatures remained below 900°C, much below the softening temperature of 1120 °C, to have any significant impact on the deposition dynamics. Thus most of the deposits are theorized to be caused by multiple collisions which eventually lead to deposition.
Stall Inception Analysis of Transonic Compressors With Chordwise and Axial Sweep
Authors: Chen He , Dakun Sun , Xiaofeng Sun
Published: August 2017

This paper concentrates on the stall inception analysis of transonic compressors with chordwise and axial sweep. A new prediction approach of stall inception is developed based on global stability analysis and immersed boundary theory, which makes it possible to takes both the concrete blade geometry and complicated base flow into consideration. The prediction of stall inception boils down to an eigenvalue problem. Spectral collocation method is adopted to discretize the eigenvalue equations and the eigenvalues are solved by using singular value decomposition method. The developed prediction approach is validated on two different typical transonic compressors, a single stage compressor and an isolated-rotor compressor, which shows a good agreement with the experimental data. The latter is adopted as a baseline rotor for the investigation of chordwise and axial sweep. By adjusting the stacking line of the baseline rotor, a series of swept rotors are modelled and the stall inception behavior of them are predicted by using the developed approach. The comparison of stall inception behaviors between these rotors is presented, and in combination with steady flow analyses, the effects of sweep features on the stall inception in transonic compressors are discussed.
Long-Term NOx Emission Behavior of Heavy Duty Gas Turbines: An Approach for Model-Based Monitoring and Diagnostics
Authors: Lipperheide Moritz , Weidner Frank , Wirsum Manfred , Gassner Martin , Bernero Stefano
Published: August 2017

Accurate monitoring of gas turbine performance is a means to an early detection of performance deviation from the design point and thus to an optimized operational control. In this process, the diagnosis of the combustion process is of high importance due to strict legal pollution limits as aging of the combustor during operation may lead to an observed progression of NOx emissions. The method presented here features a semi-empirical NOx formulation incorporating aging for the GT24/GT26 heavy duty gas turbines: Input parameters to the NOx-correlation are processed from actual measurement data in a simplified gas turbine model. Component deterioration is accounted for by linking changes in air flow distribution and control parameters to specific operational measurements of the gas turbine. The method was validated on three different gas turbines of the GE GT24/GT26 fleet for part- and baseload operation with a total of 374,058 long-term data points (5 min average), corresponding to a total of 8.5 years of observation, while only commissioning data was used for the formulation of the NOx correlation. When input parameters to the correlation are adapted for aging, the NOx prediction outperforms the benchmark prediction method without aging by 36.7, 54.0 and 26.7 % in terms of RMSE yielding a root-mean-squared error of 1.26, 1.81 and 2.99 ppm for the investigated gas turbines over a three year monitoring period.
Gas Turbine Model Combustor Emissions of Liquid Single-Component Fuels
Authors: Grohmann Jasper , Meier Wolfgang , Aigner Manfred
Published: August 2017

Alternative liquid fuels can contain hydrocarbons of different types and chain lengths and the fuel composition has an influence on combustion behavior. In this study, the influence of liquid single-component fuels on exhaust gas emissions of a gas turbine model combustor for swirl-stabilized spray flames was investigated under atmospheric pressure. The nozzle exhibited a dual-swirl geometry and a prefilming airblast atomizer. The spray was characterized by Phase Doppler Anemometry (PDA) and Mie scattering measurements and the flame CH* chemiluminescence was measured. Six single-component hydrocarbons were chosen: three linear alkanes (n-hexane, n-nonane, n-dodecane), one cyclic alkane (cyclohexane), one branched alkane (iso-octane) and one aromatic hydrocarbon (toluene). Kerosene Jet A-1 was used as a technical reference. Results show minor differences in CO emissions and significant differences in NOx emissions of the various fuels at comparable flow conditions and adiabatic flame temperatures. The measurements indicate a correlation between the nitric oxide emissions and the spray quality.
Asynchronous Response Analysis of Non-Contact Vibration Measurements on Compressor Rotor Blades
Authors: Krause Christoph , Giersch Thomas , Stelldinger Marco , Hanschke Benjamin , Kühhorn Arnold
Published: August 2017

Although the research in non-intrusive techniques for the measurement of vibration have made major progress since the beginning in the 1960’s, they are still mainly used as additional tool to the common strain gauges. Therefore, there is still a great deal of interest in the improvement of such non-contact vibration measurement techniques, to replace the intrusive ones with alternative techniques. One possibility to monitor all blades at once is blade tip-timing. The probes for a blade tip-timing measurement system are mounted circumferentially in the engine casing to log the passing times of the rotor blades. These logged time data will be compared with theoretically calculated passing times. The deviation between measured and calculated passing times can be transformed to blade displacement values. In recent years, several methods to analyse the acquired vibration data have been developed and improved. They are directed to evaluate synchronous and asynchronous blade vibration events. This paper focuses on the identification of asynchronous vibrations on rotor blades using blade tip-timing. Taking the data from all probes into account gives an opportunity to determine the vibration of each single blade. Due to the usage of a research test rig, all measurement data could be acquired in simulated real case operation scenarios. Analysis data were evaluated with a developed post processing routine based on a Fourier transformation algorithm coupled with a least square fitting procedure. Since compressor surge represents one of the most critical non synchronous events during compressor operation, in this paper a special interest is paid to the analysis of compressor surges. Vibration frequencies revealed during surge investigation will be compared with simultaneously measured strain gauge data to ensure the reliability of blade tip-timing measurement and analysis. To explain the results in more detail, the possibility of a blade damaged triggered shift of the blade characteristic frequency is shown. The most promising result of the analysis is the close correlation between the identified vibration frequencies of compressor surge events and the afterwards determined frequency mistuning and crack distributions. Blade damage becomes visible through increasing deviation between characteristic frequencies of different blades as result of multiple surge events. In addition, with the comparison of mean frequency records over each single surge among each other it is possible to restrict the blade damage time. Subsequently, the possibility to develop a process routine to predict blade damage during compressor test series could arise.
Evolution of Turbine Cooling
Authors: Bunker Ronald S.
Published: August 2017

Turbine cooling is a battle between the desire for greater hot section component life and the techno-economic demands of the marketplace. Surprisingly little separates the haves from the have nots. The evolution of turbine cooling is loosely analogous to that of the Darwinian theory of evolution for animals, starting from highly simplistic forms and progressing to increasingly more complex designs having greater capabilities. Yet even with the several generations of design advances, limitations are becoming apparent as complexity sometimes leads to less robust outcomes in operation. Furthermore, the changing environment for operation and servicing of cooled components, both the natural and the imposed environments, are resulting in new failure modes, higher sensitivities, and more variability in life. The present paper treats the evolution of turbine cooling in three broad aspects including the background development, the current state-of-the-art, and the prospects for the future. Unlike the Darwinian theory of evolution however, it is not feasible to implement thousands of small incremental design changes, random or not, to determine the fittest for survival and advancement. Instead, innovation and experience are utilized to direct the evolution.

Over the last approximately 50 years, advances have led to an overall increase in component cooling effectiveness from 0.1 to 0.7. Innovation and invention aside, the performance of the engine has always dictated which technologies advance and which do not. Cooling technologies have been aided by complimentary and substantial advancements in materials and manufacturing. The state-of-the-art now contains dozens of internal component cooling methods with their many variations, yet still relies mainly on only a handful of basic film cooling forms that have been known for 40 years. Even so, large decreases in coolant usage, up to 50%, have been realized over time in the face of increasing turbine firing temperatures. The primary areas of greatest impact for the future of turbine cooling are discussed, these being new engine operating environments, component and systems integration effects, revolutionary turbine cooling, revolutionary manufacturing, and the quantification of unknowns. One key will be the marriage of design and manufacturing to bring about the concurrent use of engineered micro cooling or transpiration, with the ability of additive manufacturing. If successful, this combination could see a further 50% reduction in coolant usage for turbines. The other key element concerns the quantification of unknowns, which directly impacts validation and verification of current state-of-the-art and future turbine cooling. Addressing the entire scope of the challenges will require future turbine cooling to be of robust simplicity and stability, with freeform design, much as observed in the “designs” of nature.