bluuebunny/crossref_metadata_2025 huggingface dataset:
Delay of Rotating Stall in Compressors Using Plasma Actuators
Authors: Ashrafi Farzad , Michaud Mathias , Vo Huu Duc
Published: August 2015

Rotating stall is a well-known aerodynamic instability in compressors that limits the operating envelope of aircraft gas turbine engines. An innovative method for delaying the most common form of rotating stall inception using an annular DBD (Dielectric Barrier Discharge) plasma actuator had been proposed. A DBD plasma actuator is a simple solid-state device that converts electricity directly into flow acceleration through partial air ionization. However, the proposed concept had only been preliminarily evaluated with numerical simulations on an isolated axial rotor using a relatively basic CFD code. This paper provides both an experimental and a numerical assessment of this concept for an axial compressor stage as well as a centrifugal compressor stage, with both stages being part of a low-speed two-stage axial-centrifugal compressor test rig. The two configurations studied are the two-stage configuration with a 100 mN/m annular casing plasma actuator placed just upstream of the axial rotor leading edge, and the single-stage centrifugal compressor with the same actuator placed upstream of the impeller leading edge. The tested configurations were simulated with a commercial RANS CFD code (ANSYS CFX) in which was implemented the latest engineering DBD plasma model and dynamic throttle boundary condition, using single-passage multiple blade row computational domains. The CFD simulations indicate that in both types of compressors the actuator delays the stall inception by pushing the incoming/tip clearance flow interface downstream into the blade passage. In each case, the predicted reduction in stalling mass flow matches the experimental value reasonably well.
Evaluation of CFD Predictions Using Different Turbulence Models on a Film Cooled Guide Vane Under Experimental Conditions
Authors: Zhang Qingbo , Xu Huazhao , Wang Jianhua , Li Ge , Wang Lei , Wu Xiangyu , Ma Shiyan
Published: August 2015

This paper presents a numerical investigation of the conjugate heat transfer (CHT) to calculate the steady state aerodynamic and thermal characteristics of a film cooled gas turbine vane. The commercial code ANSYS FLUENT 15.0 is applied as the numerical tool. The turbine configuration selected from NASA Energy Efficient Engine program consists of 46 vanes with two impingement baffles in forward and aft cavities. The periodic boundary condition is used to reduce the calculation cost while maintaining a reasonable accuracy of the numerical results.

Using the commercial software ANSYS ICEM 15.0, steady simulations are based on a structured grid method with the finite volume technique. In the numerical simulations, two two-equation turbulence models, i.e. the Realizable k-epsilon (k-ε) and Shear Stress Transport k-omega (SST k-ω), and a four-equation turbulence model, i.e. the V2-F model, are used. To estimate the numerical strategy, the calculated results of the Mach number distributions obtained by the three turbulence models are compared with the experimental data of Timko (NASA CR-168289). Then the detailed flow and heat transfer characteristics, including the cooling effectiveness, heat transfer coefficient distributions on the vane’s surfaces, static pressure distributions along three span-wise lines and total pressure distributions in the cascade passage are predicted. Through the comparison of the numerical results obtained under adiabatic and CHT conditions, the influences of heat conduction on vane cooling effect are discussed.
Predicting Adiabatic Film Effectiveness of a Turbine Vane by Two-Equation Turbulence Models
Authors: Prapamonthon Prasert , Xu Huazhao , Wang Jianhua , Li Ge
Published: August 2015

The thermal efficiency of gas turbine engines increases with turbine inlet temperature (TIT) directly. However, the TIT is limited by the allowable temperature of current blade materials. Film cooling technique is an effective method to maintain turbine vane working smoothly under high TIT conditions. The adiabatic film effectiveness has been widely employed to understand film cooling mechanism. Therefore, the prediction of the adiabatic effectiveness of gas turbine engines under real operating conditions is essential. The showerhead film cooled turbine vane reported by L. P. Timko (NASA CR-168289) is adopted in the present study. There are two rows of film holes on the leading edge, three rows on the pressure side, and two rows on the suction side. All holes are cylindrical, which are placed at an angle of 45 degrees to the vane surface in the span-wise direction. This numerical investigation discusses the influences of free stream turbulence intensity on the adiabatic film effectiveness in the vane leading edge region and its vicinity. Five two-equation turbulence models based on Reynolds Averaged Navier-Stokes (RANS) are employed to predict the adiabatic film effectiveness under real operating conditions at a blowing ratio (BR) of 1.41 and three free stream turbulence intensities (Tu=3.3, 10, and 20%). The adiabatic film effectiveness on the vane surface at 8, 52.5, and 89% span in an x/C range between −0.4 and 0.4 is presented. Obviously, the numerical results predicted by all five models show that on the suction side, the increasing free stream turbulence intensity can reduce film effectiveness except at 8% span. On the pressure side, the RNG k-ε, Realizable k-ε and SST k-ω models predict the same trend of the adiabatic film effectiveness, especially the RNG k-ε and SST k-ω models. Those three models predict that the locally adiabatic film effectiveness (especially near film holes) can be improved when turbulence intensity increases. However, at a span of 89% within the x/C range between −0.4 and −0.2, all k-ε models and SST k-ω model predict that the increase of turbulence intensity can reduce the adiabatic film effectiveness. In addition, the film effectiveness contours show a significant variation of film effectiveness predicted by the five turbulence models on the leading edge when turbulence intensity increases. For the near-pressure side, all models except the Standard k-ω model predict that the high turbulence intensity can reduce the film spreading from film holes dramatically.
Adjoint-Based Optimization Method With Linearized SST Turbulence Model and a Frozen Gamma-Theta Transition Model Approach for Turbomachinery Design
Authors: Zhang Pengfei , Lu Juan , Wang Zhiduo , Song Liming , Feng Zhenping
Published: August 2015

In this paper, based on the grid node coordinates variation and Jacobian Matrices, the turbulent continuous adjoint method with linearized turbulence model is studied and developed to fully account for the variation of turbulent eddy viscosity. The corresponding adjoint equations, boundary conditions and the final sensitivities are formulated with a general expression. To implement the adjoint optimization of the transition flow, a flow solver combining the transition model with the turbulence model is employed, and an adjoint optimization framework with linearized SST turbulence model and a frozen Gamma-Theta transition model is established. In order to choose an appropriate objective for the transition flow optimization, four objectives are studied, including the entropy generation, the total pressure loss coefficient, the field integral of turbulent kinetic energy, the area ratio of transition and turbulent regions to the suciton side. And finally the entropy generation is adopted as the objective. Then, the derivation of the adjoint system for the entropy generation optimization is presented. To demonstrate the validity of the adjoint system for transition flow, four shape optimizations for the bypass transitions and the separation-induced transition are implemented. A 2D isentropic case for bypass transitions is conducted to compares the performances of the fully turbulent adjoint system and the frozen Gamma-Theta transition adjoint system, while the other isothermal case is performed to take the aerodynamic and heat transfer issues into account together. The case of separation-induced transition is performed and also consistent well with its flow mechanism. The four optimization results illustrate the effectiveness of the adjoint system for the transition flow optimization, which can improves the performance of overall cascades and the transition region.
Multi-Scale Measurements in Wind Farms in Complex and Flat Terrain
Authors: Zendehbad M. , Chokani N. , Abhari R. S.
Published: August 2015

Large-scale (that is over the kilometre scale of a whole wind farm) and small-scale (over the metre scale of an individual wind turbine) wind flow measurements are made with a mobile-based LIDAR system. The large-scale measurements detail the multiple wakes in the wind farm, including both single and double wakes, that result in up to 70% less power generation for a given wind direction, and 2.5% loss of the wind farm’s annual energy yield. The small-scale measurements show that there is a non-uniform work extraction of the turbine across the vertical extent of the wind turbine rotor. This non-uniform work extraction is accompanied by an upward pitching of the flow that is as much as 50° immediately downstream of the turbine and reduces to 10° two diameters downstream. Measurements with the mobile-based LIDAR system are made in both complex and flat terrains. A comparison of the wake profiles show that whereas in complex terrain the profiles are self-similar up to two-and-half rotor diameters downstream, this is not the case in flat terrain. It is shown that these measurements, which are made at the full-scale Reynolds number in the field, may be useful to support the development of wake flow prediction tools.
Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces
Authors: Yang Xing , Liu Zhao , Feng Zhenping
Published: August 2015

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.
Effect of Slot Injection and Effusion Array on the Liner Heat Transfer Coefficient of a Scaled Lean Burn Combustor With Representative Swirling Flow
Authors: Andreini Antonio , Becchi Riccardo , Facchini Bruno , Picchi Alessio , Turrini Fabio
Published: August 2015

International standards regarding polluting emissions from civil aircraft engines are becoming gradually even more stringent. Nowadays, the most prominent way to meet the target of reducing NOx emissions in modern aero-engine combustors is represented by lean burn technology. Swirl injectors are usually employed to provide the dominant flame stabilization mechanism coupled to high efficiency fuel atomization solutions. These systems generate very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that affect the distribution and therefore the estimation of heat loads on the gas side of the liner as well as the interaction with the cooling system flows.

The main purpose of the present work is to provide detailed measurements of Heat Transfer Coefficient (HTC) on the gas side of a scaled combustor liner highlighting the impact of the cooling flows injected through a slot system and an effusion array. Furthermore, for a deeper understanding of the interaction phenomena between gas and cooling flows, a standard 2D PIV (Particle Image Velocimetry) technique has been employed to characterize the combustor flow field.

The experimental arrangement has been developed within EU project LEMCOTEC and consists of a non-reactive three sectors planar rig installed in an open loop wind tunnel. Three swirlers, replicating the real geometry of a GE Avio PERM (Partially Evaporated and Rapid Mixing) injector technology, are used to achieve representative swirled flow conditions in the test section. The effusion geometry is composed by a staggered array of 1236 circular holes with an inclination of 30deg, while the slot exit has a constant height of 5mm. The experimental campaign has been carried out using a TLC (Thermochromic Liquid Crystals) steady state technique with a thin Inconel heating foil and imposing several cooling flow conditions in terms of slot coolant consumption and effusion pressure drop. A data reduction procedure has been developed to take into account the non-uniform heat generation and the heat loss across the liner plate.

Results, in terms of 2D maps and averaged distributions of HTC have been supported by flow field measurements with 2D PIV technique focussed on the corner recirculation region.
Sensitivity Analysis to Flutter for Front Stages Compressor Blades
Authors: Benvenuto Marcello , Silingardi Andrea , Astrua Pio , Cecchi Stefano
Published: August 2015

Heavy duty gas turbine front stages compressor blades aero-elastic behavior is deeply analyzed and investigated by means of an uncoupled, non-linear and time-accurate CFD URANS solver. The travelling-wave approach and the energy method have been applied in order to assess the aerodynamic damping (in terms of logarithmic decrement) for each inter blade phase angle (IBPA) and thus to localize the flutter stability region. The work is mainly focused on a sensitivity analysis with respect to blade operating conditions, eigen-mode shapes and frequency in order to improve the understanding of flutter mechanism and to identify the key parameters. Transonic, supercritical and subsonic blades are investigated at different operating conditions with their corresponding eigenmode and eigen-frequency (first and second flexural mode and first torsional). The results show that non-linear effects can be neglected for subsonic blades. Besides, the modal-shape and the shock structure, if any, are identified to play a key role for flutter stability.
Influence of Mainstream Turbulence Intensity on Heat Transfer Characteristics of a HP Turbine Stage With Inlet Hot Streak
Authors: Wang Zhiduo , Liu Zhaofang , Feng Zhenping
Published: August 2015

An unsteady computational study were carried out for the GE-E3 HP turbine at inflow turbulence intensities of 5%, 10% and 20% accompanying with inlet hot streak (HS) at two circumferential positions (impinging and non-impinging relative to vane leading edge) to analyze the interacted turbulence and HS influences. Several validation studies were performed to investigate the heat transfer prediction ability of shear stress transport (SST) turbulence model coupled with γ-θ transition model. Turbulence decay mechanisms in turbine passage were presented, and the airfoil heat transfer behaviors were explored by means of both time-averaged adiabatic wall temperature and heat transfer coefficient (HTC). The results indicate that increase of inflow turbulence leads to favorable turbine temperature distributions in general, and on the blade and tip surface in particular, especially for the non-impinging case and inflow turbulence increasing from 10% to 20%. While the vane and blade surface area-averaged temperatures are hardly changed, a maximum area-averaged temperature drop of 8.9 K is induced at the tip surface. Higher HTC is observed at vane, blade pressure surface, and suction surface mid region at higher turbulence. However, HTCs at endwall regions of blade suction surface and blade tip are insensitive to the turbulence effect, thus the heat load of these regions is not critical when the inflow turbulence intensity is increased. HS position not only affects the airfoil surface temperature variations, but also slightly affects the vane and blade midspan HTC for the variation of fluid driving temperature.
Comparison of Flame Dynamics at Stable and Near-LBO Conditions for Swirl-Stabilized Kerosene Spray Combustion
Authors: Zhang Chi , Zou Pengfei , Wang Bosen , Xue Xin , Lin Yuzhen , Sung Chih-Jen
Published: August 2015

An experimental investigation was conducted to characterize the flame structures and dynamics at stable and near-lean blowout (LBO) conditions. The current experiments were carried out using a laboratory-scale aero-combustor with an internally-staged dome. The internally-staged injector consisted of pilot and main swirlers, and the pilot swirler was fueled with Chinese kerosene RP-3 while the main injector was chocked. The resulting spray flame was confined within a quartz tube under atmosphere pressure. In the present study, the influence of swirl intensity of the pilot swirler was also investiagted. The OH* chemiluminescence of the flame was recorded by a high-speed camera at a frequency of 2000 Hz. From the high-speed OH* images, the reaction zone was marked and the fluctuation of the reaction zone along axial direction was observed, showing that it became stronger at near-LBO condition than at stable condition. Proper Orthogonal Decomposition (POD) analysis was further used to provide insights into the characteristics of flame dynamics. Based on the POD results, the difference of the flame dynamics between the stable and near-LBO combustion was distinct. While the major Mode l of the flame under stable condition was rotation representing the rotation motion in the swirl flame, at near-LBO condition the flame dynamics included three modes — vibration, rotation, and flame shedding. In addition, for swirl-stabilized kerosene spray combustion investigated herein, the fluctuation of the reaction zone in axial direction became stronger with decreasing equivalence ratio when approaching LBO, and the POD analysis indicated that the Mode l of flame dynamics transitions from the rotation mode to the vibration mode. Although the change of pilot swirl number was found to have little influence on the Mode l of flame dynamics, it was noted to vary the fluctuation energy of the flame.
Investigation on the Dynamic Response of Blades With Asymmetric Under Platform Dampers
Authors: Bessone Andrea , Toso Federico , Berruti Teresa
Published: August 2015

The paper presents the experimental activity about the dynamic response of the blades of a gas turbine for power generation carrying underplatform dampers. The final aim of the activity is to provide an experimental data base to validate the results of a numerical tool which calculates the response of the blades with underplatform dampers. The blades have fir tree attachments and an asymmetric damper is fitted between the blade platforms. The dynamic behavior of the blades is detected by an experimental campaign on two blades mounted in a test rig. Stepped sine measurements are performed with a closed-loop control system on the excitation amplitude. Different levels of excitation amplitude and centrifugal force on the damper are tested. The test campaign pointed out the presence of damping due both to the underplatform damper and to the blade attachment. The contribution of the different damping sources are discussed and analyzed. A method is suggested to identify the root damping which is not constant but proved to depend on the excitation force on the blades.
Experimental and Numerical Investigation of the Flow Inside the Return Channel of a Centrifugal Process Compressor
Authors: Rube C. , Rossbach T. , Wedeking M. , Grates D. R. , Jeschke P.
Published: August 2015

This paper presents the first detailed experimental performance data for a new centrifugal process compressor test rig. Additional numerical simulations supported by extensive pressure measurements at various positions allow an analysis of the operational and loss behavior of the entire stage and its components.

The stage investigated is a high flow rate stage of a single-shaft, multistage compressor for industrial applications and consists of a shrouded impeller, a vaneless diffuser, a U-bend and an adjoining vaned return channel. Large channel heights due to high flow rates induce the formation of highly three-dimensional flow phenomena and thus enlarge the losses due to secondary flows. An accurate prediction of this loss behavior by means of numerical investigations is challenging. The published experimental data offer the opportunity to validate the used numerical methods at discrete measurement planes, which strengthens confidence in the numerical predictions.

CFD simulations of the stage are initially validated with global performance data and extensive static pressure measurements in the vaneless diffuser. The comparison of the pressure rise and an estimation of the loss behavior inside the vaneless diffuser provide the basis for a numerical investigation of the flow phenomena in the U-bend and the vaned return channel. The flow acceleration in the U-bend is further assessed via the measured two-dimensional pressure field on the hub wall. The upstream potential field of the return channel vanes allows an evaluation of the resulting flow angle. Measurements within the return channel provide information about the deceleration and turning of the flow. In combination with the numerical simulations, loss mechanisms can be identified and are presented in detail in this paper.
Influence of Water Injection on Heat Release Distribution, Lean Blowout and Emissions of a Premixed Swirl Flame in a Tubular Combustor
Authors: Lellek Stephan , Sattelmayer Thomas
Published: August 2015

Water injection is often used to control NOx emissions and/or to increase the power output from non-premixed combustion of gaseous and liquid fuels to increase the power output. In non-premixed flames the drop of NOx generation due to water injection is associated with a strong effect on the heat release distribution, which often leads to a loss of combustion stability, if the amount of injected water exceeds a water to fuel ratio in the order of unity. Since premixed combustion dominates in large gas turbines for power generation fueled with natural gas, water injection for emission reduction is usually not an issue. However, the increasing share of fluctuating electricity from renewables stimulates R&D on the improvement of the operational flexibility of combined cycle power plants. One aspect in that context is power augmentation by injection of liquid water in premixed combustors without drawbacks regarding emissions and flame stability. An atmospheric single burner combustor test rig has been set up at the Lehrstuhl für Thermodynamik at Technische Universität München in order to investigate the effect on gas turbine combustion. For all investigations presented in the paper natural gas has been used as fuel. The test rig was operated at different preheating temperatures (T=573 … 673K) and different equivalent ratios (Φ=0.4 … 1.0). In contrast to approaches where steam is injected into the combustion chamber liquid water was used. Water injection has been realized using two-fluid nozzles with air as atomizing gas. The influence of varying amounts of water and atomizing air on blowout limits, flame shape and emissions was investigated by emission and OH*-chemiluminescence measurements. The results of the experimental study will be presented and they will be compared to experimental data of gas turbine combustors with steam injection taken from literature. At constant equivalence ratios a significant reduction of the NOx emissions was found for increasing amounts of injected water, whereas for measurements at constant adiabatic flame temperature reduction in NOx emissions was very small. In comparison to literature data for steam injected lean premixed flames a smaller operational window of the investigated configuration was detected. The effect of liquid water injection on the flame shape is similar compared to the effect of steam injection found in literature.
Design and Performance Measurements of a 6 kW High-Speed Micro Gas Turbine Prototype
Authors: Grönman Aki , Honkatukia Juha , Sallinen Petri , Backman Jari , Uusitalo Antti , Turunen-Saaresti Teemu , Jaatinen-Värri Ahti
Published: August 2015

Small portable electricity generating systems are suitable in remote locations where the access by vehicles is restricted or not even possible. These kind of places include for example catastrophic areas after earthquakes or tropical cyclones. Such machines can also be used as auxiliary power units in motor or sail boats. Gas turbine based electricity generation systems offer a good alternative for typical engine-generator units which are characterized by lower specific powers. It is suggested that the power to weight ratio of a 6 kW micro gas turbine can be more than eight times higher than that of the corresponding engine-generator unit. The biggest drawback is the higher specific fuel consumption; however, by introducing a recuperator, the specific fuel consumption can be improved.

In this article, the design process and experiments of a 6 kW micro gas turbine prototype are described and discussed in detail. The built non-recuperated prototype is based on a commercial, small jet engine originally designed to give thrust to radio controlled model airplanes. The jet nozzle of the jet engine was replaced by an axial power turbine which was directly connected to a small, high speed permanent magnet generator. The experiments showed the potential of the prototype.
Dynamics and Turbulence Characteristics of Wake-Boundary Layer Interaction in a Low Pressure Turbine Blade
Authors: Berrino M. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P. , Bertini F.
Published: August 2015

The paper analyzes the unsteady interaction between an impinging wake and the suction side boundary layer of a low pressure turbine cascade operating under unsteady inflow conditions. The instantaneous flow fields are obtained with Particle Image Velocimetry (PIV) for two different free-stream turbulence intensities (FSTI) and two orthogonal measurement planes (a blade-to-blade and a wall-parallel plane, respectively). The large data set has been post-processed by means of Proper Orthogonal Decomposition (POD) to provide a solid statistical interpretation of the physics of this complex unsteady interaction.

For the analysis of the blade-to-blade plane measurements, the paper takes advantage of the POD properties, which consist in splitting spatial (POD modes) and temporal (POD eigenvector) information. The phase identification of each PIV image within the wake passing period is then extracted from the eigenvectors of properly selected POD modes in order to reconstruct a phase-averaged velocity field. This post-processing allow us to separately account for the contribution to deterministic and stochastic unsteadiness as well as to have a look at the most significative scales of turbulence generating during the different phase of the wake-boundary layer interaction process.

The detailed analysis is completed by the measurements in a wall-parallel plane (aligned with the blade span). Instantaneous images and POD modes in this plane allow recognizing the presence of three-dimensional disturbances, induced by low and high speed travelling streaks (Klebanoff mode). These coherent structures have been shown to play a significant role in the unsteady transition process of the boundary layer at both low and elevated FSTI, and results reported in the paper further characterize their role in the transition process.
Damping Behavior of Blades From Small Radial Turbines
Authors: Hemberger David , Filsinger Dietmar , Bauer Hans-Jörg
Published: August 2015

Next to excitation forces and the dynamic properties of mistuned structures the damping behavior is a key feature to evaluate the dynamic turbine blade response and thus the HCF life of a bladed disk (blisk). Just as the determination of the mistuning properties and the assessment of the vibration excitation, the evaluation of damping is also subject to uncertainty especially considering the wide operating range of a small radial turbine of a turbocharger. Since the total damping is composed of material damping, structural damping and aerodynamic damping, which are affected by parameters, like the eigenform of the vibration, the magnitude of the vibration amplitude and aerodynamic properties, the total damping can be strongly dependent on the operating conditions.

The study at hand provides results from investigations that allow estimating the contribution of aerodynamic damping on the total damping. Experimental and numerical analysis of radial turbines from turbochargers for vehicular engines with variable turbine inlet vanes were performed. Measurements under different environmental conditions such as at rest and during operation, as well as unsteady CFD calculations and, coupled flow and structural calculations were carried out.

A change in total damping could be found depending on the density of the surrounding gas by vibration measurements in operation on the hot gas test bench. But it was also shown that the total damping is decisively influenced by the mistuning of the structure. On one side the structural damping is varied by the variation in mistuned blade vibration amplitudes and otherwise the aerodynamic damping is influenced by the different inter blade phase angles (IBPA ) due to the mistuning, which is a symptom of geometric differences and material inhomogeneity in the wheels.

Finally, the estimated total damping values were utilized in forced response calculations using a mistuned FE-model of a real turbine and excitation forces from unsteady CFD calculation. The magnitudes of the measured vibration amplitudes were compared with results from numerical analysis to validate the numerical model with focus on the investigation about the total damping. The deviation between the results was ±10% for different eigenforms and excitation orders.
Vacuum Spin Test Series of a Turbine Impeller With Focus on Mistuning and Damping by Comparing Tip Timing and Strain Gauge Results
Authors: Maywald Thomas , Beirow Bernd , Heinrich Christoph R. , Kühhorn Arnold
Published: August 2015

This paper describes preparation, execution and evaluation of a comprehensive bladed disk spin test series. At the example of an turbine impeller the effects of rotation and temperature are analyzed with special focus on mistuning and damping. The forced response is measured synchronously via 13 identical positioned strain gauges on each blade as well as via blade tip-timing. Subsequently it is possible to compare the results of both systems. During the test series rotational speed varies in the range from 10.000 up to 19.000 RPM. Simultaneously, the wheel is heated up to 820 K by an oven. A number of pre-selected natural frequencies, damping ratios and operating deflection shapes are evaluated and compared with respect to different rotational speeds and impeller temperatures.
Effects of Radial Loading Distribution on Partial Surge Initiated Instability in a Transonic Axial Flow Compressor
Authors: Pan Tianyu , Li Qiushi , Sun Tailu , Li Zhiping , Gong Yifang
Published: August 2015

Partial surge is a new type of instability inception in transonic axial flow compressors and occurs in the form of axisymmetric low-frequency disturbances localized in the hub region. In this study, the evolution of instability in a transonic axial flow compressor at different rotor speeds shows that at 65% of the design rotor speed, partial surge does not occur; at 78% of the design rotor speed and higher, partial surge occurs and leads to compressor instability. The result of RANS simulation of the same compressor then suggests that the level of blade loading in the hub region could be highly correlated to the occurrence of partial surge. Next, the radial distribution of blade loading near the stall point is varied by introducing inlet distortion — alternately mounting specially designed screens at the inlet of the compressor. The experimental results suggest that high hub loading near the stall point would lead to partial surge initiated instability. The general effects of radial loading distribution on the type of stall inceptions are also discussed.
Uncertainty Quantification of Hot Gas Ingestion for a Gas Turbine Nozzle Using Polynomial Chaos
Authors: Panizza Andrea , Bonini Alessio , Innocenti Luca
Published: August 2015

One of the most critical parameters in the design process of cooled hot gas components, is the Back Flow Margin (BFM). This dimensionless parameter quantifies the margin to hot gas ingestion through a cooled component wall. A correct evaluation of this parameter is crucial in order to avoid component failure. In presence of combustion chambers that exhibit low pressure losses, BFM becomes one of the most restrictive requirements in the thermal design of cooled components.

In this work, a conceptual BFM assessment of the first nozzle of an HP gas turbine is described. The component is subject to the highest thermal load; complex cooling systems are required to ensure an acceptable metal temperature and to match life time requirement. Due to manufacturing tolerances and fluid dynamic uncertainties, hot gas ingestion events are possible also for a nozzle that exhibits BFM higher than zero in nominal conditions, even if with a low probability. Here, the cooling scheme of the nozzle is modeled using an in-house fluid network tool that allows a quick and accurate computation of the equivalent cooling scheme and thus the occurrence of hot gas ingestion, corresponding to a negative flow rate in one of the cooling sub-models.

However, as the probability of hot gas ingestion is rather small, an accurate estimation of this event based on the standard Monte Carlo method requires a huge number of runs. A more efficient estimation of this probability can be obtained using stochastic expansion methods, such as the Polynomial Chaos Expansion. Pseudospectral approximations based on either a tensor-product expansion or the Sparse Pseudospectral Approximation Method (SPAM) are used, in order to estimate the probability of hot gas ingestion and the sensitivity to random parameters. The results are compared with those coming from Monte Carlo method, showing the superior accuracy of the stochastic expansion methods.
A Shape Memory Alloy-Based Morphing Axial Fan Blade: Part II — Blade Shape and CFD Analyses
Authors: Suman Alessio , Fortini Annalisa , Aldi Nicola , Merlin Mattia , Pinelli Michele
Published: August 2015

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper experimental and CFD numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed.

Starting from the experimental results proposed in the first part of this work, a morphing blade, made of Shape Memory Alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques.

After the analyses in the wind tunnel CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with non-activated blades and with activated blades.

The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan.

This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life thanks to a strong relationship between the engine thermal request and the cooling fan performance.
Radial Inflow Turbine Design Through Multi-Disciplinary Optimisation Technique
Authors: Barsi Dario , Perrone Andrea , Ratto Luca , Simoni Daniele , Zunino Pietro
Published: August 2015

Multidisciplinary design optimisation (MDO) is nowadays widely employed to obtain advanced turbomachines design. The aim of this work is to provide a complete tool for the aeromechanical design of a radial inflow gas turbine. The high rotational speed of such machines, especially if used for micro cogenerative power plants, coupled with high exhaust gas temperature, exposes blades to really high centrifugal and thermal stresses; thus the aerodynamics optimisation has to be necessarily coupled with the mechanical one. Such an approach involves two different computational tools: a fully 3D Reynolds Averaged Navier-Stokes (RANS) solver is used for the aerodynamic optimisation, while an open source Finite Element Analysis (FEA) solver is employed for the mechanical integrity assessment. The geometry parameterization is handled with a commercial tool that employs b-spline advanced curve for blades and vanes definition. The aerodynamic mesh generation is managed via dedicated tools provided by the CFD software and it is a fully structured hexahedral multi-block grid. The FEA mesh is built by means of a harmonic map approach, which is able to provide high quality second order unstructured grid preserving geometrical features starting from boundary surfaces of the fluid domain. The finite element calculation provides stresses, displacements and eigenmodes that are used for mechanical integrity assessments while the CFD solver provides performance parameters and local thermodynamic quantities. Due to the high computational cost of both these two solvers, a metamodel, such as an artificial neural network, is employed to speed up the process. The interaction between two codes, the mesh generation and the post processing of the results is obtained via in-house developed scripting modules. Results obtained are presented and discussed.
Overall Effectiveness and Flowfield Measurements for an Endwall With Non-Axisymmetric Contouring
Authors: Mensch Amy , Thole Karen A.
Published: August 2015

Endwall contouring is a technique used to reduce the strength and development of three-dimensional secondary flows in a turbine vane or blade passage in a gas turbine. The secondary flows locally affect the external heat transfer, particularly on the endwall surface. The combination of external and internal convective heat transfer along with solid conduction determines component temperatures, which affect the service life of turbine components. A conjugate heat transfer model is used to measure the non-dimensional external surface temperature, known as overall effectiveness, of an endwall with non-axisymmetric contouring. The endwall cooling methods include internal impingement cooling and external film cooling. Measured values of overall effectiveness show that endwall contouring reduces the impingement effectiveness alone, but increases the effectiveness of film cooling alone. Given the combined case of both impingement and film cooling, the laterally averaged overall effectiveness is not significantly changed between the flat and contoured endwall. Flowfield measurements indicate that the size and location of the passage vortex changes as film cooling is added and as the blowing ratio increases. Because endwall contouring can produce local effects on internal cooling and film cooling performance, the implications for heat transfer should be considered in endwall contour designs.
A Detailed Uncertainty Analysis of Adiabatic Film Cooling Effectiveness Measurements Using Pressure Sensitive Paint
Authors: Natsui Greg , Little Zachary , Kapat Jayanta S. , Dees Jason E. , Laskowski Gregory
Published: August 2015

Pressure sensitive paint (PSP) can be a powerful tool in measuring the adiabatic film cooling effectiveness. There are two distinct sources of error for this measurement technique; the ability to experimentally obtain the data and the validity of the heat and mass transfer analogy for the problem being studied. This paper will assess the experimental aspect of this PSP measurement specifically for film cooling applications.

Experiments are conducted in an effort to quantifiably bound expected errors associated with temperature non-uniformities in testing and photo-degradation effects. Results show that if careful experimental procedures are put in place, both of these effects can be maintained to have less than 0.022 impact on effectiveness.

Through accurate semi-in-situ calibration down to 4% atmospheric pressure, the near-hole distribution of effectiveness is measured with high accuracy. PSP calibrations are performed for multiple coupons, over multiple days. In addition, to reach a partial pressure of 0 the calibration vessel was purged of all air by flowing CO2.

The primary contribution of this paper lies in the uncertainty analysis performed on the PSP measurement technique. A thorough uncertainty analysis is conducted and described, in order to completely understand the presented measurements and any shortcomings of the PSP technique. This quantification results in larger, albeit more realistic, values of uncertainty, and helps provide a better understanding of film cooling effectiveness measurements taken using the PSP technique. The presented uncertainty analysis takes into account all random error sources associated with sampling and calibration, from intensities to effectiveness.

Adiabatic film cooling effectiveness measurements are obtained for a single row of film cooling holes inclined at 20 degrees, with CO2 used as coolant. Data is obtained for six blowing ratios. Maps of uncertainty corresponding to each effectiveness profile are available for each test case. These maps show that the uncertainty varies spatially over the test surface, high effectiveness corresponds to low uncertainty. The noise floors can be as high as 0.04 at effectiveness levels of 0. Day-to-day repeatability is presented for each blowing ratio and shows that laterally averaged effectiveness data is repeatable within 0.02 effectiveness.
Effect of Various Tip Clearance Squealer Design on Turbine Stage Efficiency
Authors: Lomakin Nikolay , Granovskiy Andrey , Shchaulov Vladimir , Szwedowicz Jaroslaw
Published: August 2015

This paper presents investigation of nine tip squealer design variants based on full 3D Navier-Stokes CFD calculations. In particular two main design features have been studied: the impact of relative squealer cavity rim extension and the impact of pressure side squealer cavity rim inclination on stage efficiency. All these cases have been compared for two values of relative radial gaps 0.6% and 1.36%. Obtained numerical results were validated against the experimental data measured on the E3 blade cascade test rig given in the open literature. As the overall outcome for these numerical investigations two zones with different vortex structures and different sealing features have been found. Moreover the size of these zones determines the level of the tip clearance leakage and losses for various tip squealer designs. The obtained loss values and corresponding change of the stage efficiency level as well as flow structure details were compared for all studied cases, providing insight into turbine stage aerodynamics with respect to minimal and maximal radial clearance.
Interval Analysis on Aero-Engine Rotor System With Misalignment
Authors: Wang Cun , Ma Yanhong , Zhang Dayi , Hong Jie
Published: August 2015

Misalignment is a usual phenomenon in rotating machines. The rotor centerlines are not collinear at the couplings and the rotors operate in incorrect axial positions in a multi-span rotor. The effects of misalignment of flexible rotor system are summarized as the variation of joint stiffness and additional misalignment excitation force based on the dynamic model established.

The variation of joints stiffness is difficult to describe, meanwhile the misalignment excitation and rotor unbalance changes with different assembly and operating conditions. The distributions of these parameters which have significant effect on rotor dynamics are unknown, but the intervals of uncertain parameters are usually easier to get. An interval analysis method based on Taylor expansion and direct integration, which solves the dynamic response of rotor system under complex excitations including misalignment and multi unbalance with different frequencies and excitation points is presented. The differential equation of rotor system is formulated by combination of the matrixes of an actual rotor system finite element model and interval excitation vectors. The responses of a single spool and two spools with misalignment and unbalance are calculated by the interval analysis method. The results indicate that the method is effective and reflects some dynamic influence of misalignment and unbalance on rotor system. Second harmonic frequency appears, and rotor orbit is irregular. The response reflects the uncertain interval distribution characteristics, and the frequency components on different locations of the rotor have different characteristics.
Acoustic Analysis of a Liquid Fuel Swirl Combustor Using Dynamic Mode Decomposition
Authors: Ghani Abdulla , Gicquel Laurent , Poinsot Thierry
Published: August 2015

The flame transfer function (FTF) of an aeronautical burner in a rectangular combustion chamber is determined using large eddy simulation (LES). The configuration contains an industrial swirling device placed in a laboratory combustor. The swirler comprises three air passages and liquid kerosene is injected through a pilot and a multipoint injection device including 24 injection holes. In order to reduce computational costs, the forcing process for FTF determination is limited to three forcing cycles. Application of the dynamic mode decomposition (DMD) allows to extract the coherent flow structures at the forcing frequency and to construct local flame response and time delay fields. In a next step, modal analysis is carried out with a Helmholtz solver where acoustic boundary conditions are utilized taking mean flow effects into account. The latter allows to model mean flow effects in a zero Mach number framework. Results are compared with experimental observations: stable and unstable combustion modes for different outlet impedances are correctly identified by this methodology. All results are validated against experimental data and show good agreement.