bluuebunny/crossref_metadata_2025 huggingface dataset:
Eddy Current Damper for Turbine Blading: Electromagnetic Finite Element Analysis and Measurement Results
Authors: Laborenz Jacob , Krack Malte , Panning Lars , Wallaschek Jo¨rg , Denk Markus , Masserey Pierre-Alain
Published: May 2012

In the dynamics of turbomachinery the mechanical damping of the blading is in the focus of research for the last decades to improve the dynamic performance in terms of high cycle fatigue issues. Besides that an increased mechanical damping can produce a higher flutter safety margin such that stable operation conditions are achievable in a bigger range. Hence, novel damping techniques are considered besides the well known friction based damping devices. In this paper an extended analysis of the eddy current based damping device for a last stage steam turbine blading presented in GT2009-59593 is conducted. A transient electromagnetic finite element analysis of the eddy current damper is performed and the resulting damping forces are compared to their analytical solution. Parameter studies are carried out and equivalent damping factors are calculated. Furthermore, for the validation of the finite element model a test rig was built which allows for the direct measurement of damping forces when forcing a sinusoidal relative motion. Forced response measurements and simulations are used to demonstrate its dynamic performance and predictability.
Interaction of Vortex Shedding and Transverse High-Frequency Pressure Oscillations in a Tubular Combustion Chamber
Authors: Schwing Joachim , Sattelmayer Thomas , Noiray Nicolas
Published: May 2012

Intense research on the thermoacoustic stability of premixed gas turbine combustors in the past two decades has led to an improved understanding of instabilities of longitudinal modes in the sub-kHz range and predictive tools for thermoacoustic stability analysis have also been developed. Circumferential modes in annular combustors have been studied in the past as well, even though to a much lower extent due to the high experimental effort. Combined experimental-numerical methods for the low-frequency regime (i.e. acoustically compact flames) are widely used. However, such experimental and numerical approaches with predictive capability have to be developed to also address the high-frequency (HF) regime. An experimental study of HF thermoacoustic coupling is presented in this paper. A fully premixed swirl-stabilized flame at atmospheric condition in a cylindrical combustion chamber is investigated. The test rig is equipped with several dynamic pressure transducers to identify and reconstruct the acoustic field in the combustion chamber. Planar information about the flame front location is obtained from Mie-scattering and the flow field is measured with particle image velocimetry (PIV). In the tests the first transverse mode of the combustion chamber exhibits instability for a particular operating condition, which leads to sustained limit-cycle pulsations. Mie-scattering images reveal periodic vortex shedding at the outlet of the burner. PIV results provide quantitative information on the strength of these coherent shear layer vortices.
Gas Turbine Nozzle Life Assesment due to Thermal Fatigue
Authors: Mazur Z. , Pe´rez-Herna´ndez E. B. , Garcia-Illescas R.
Published: May 2012

Available fatigue models are analyzed to assess gas turbine nozzle life due to thermal fatigue cycles experienced in operation. A nozzle retired from service made of cobalt base alloy FSX-414 experienced fatigue cracks during its operation period. Nozzle thermal stresses and strains generated during gas turbine transitions; startups and shut downs, determined in previous investigations are used for fatigue analysis and life assessment. A specialized software nCode was used for fatigue analysis and the Rainflow method to account for fatigue cycles. The fatigue life models of Manson-Coffin-Basquin, Morrow and Smith-Watson-Topper were compared assessing nozzle life in different critical zones of the vane and its union to the internal and external shrouds. Some similarities and deviations found among fatigue models are analyzed. Diagrams of nozzle life distribution within its body are provided. It was found that the nozzle zones having shortest life are located in the vane cooling ducts and transitions/unions between vane and shrouds.
Inverse Fin Arrangement in a Low Pressure Turbine to Improve the Interaction Between Shroud Leakage Flows and Main Flow
Authors: Mahle Inga , Schmierer Roman
Published: May 2012

The paper deals with the geometry of the shroud cavities in low pressure gas turbines and presents a design which helps to reduce the losses that arise when the shroud leakage flows interact with the main flow. The fins in low pressure gas turbines are usually attached to the shroud of the blades. They are therefore rotating while the non-rotating honeycomb or abrasive coating is mounted into the casing. The shroud leakage flow, after passing the rear fin, is decelerated in the rear cavity chamber and enters the main flow path with an axial velocity that is smaller than the axial velocity of the main flow. This difference in axial velocity, together with differences in the circumferential velocity, leads to increased turbulence, mixing losses and an unfavorable incidence of the subsequent vane row in the wall region. Contrarily to the usual configuration, the inverse fins in the turbine presented in the paper are attached to the casing while the honeycomb is mounted onto the rotating blades. This arrangement results in the location of the gap between the fin and the honeycomb being very close to the position of re-entry of the leakage flow into the main flow. Therefore, the leakage flow keeps a high velocity resulting from the narrow fin gap until re-entry which reduces the velocity difference with respect to the main flow. Consequently, the mixing losses and subsequent row losses are reduced. Due to the favorable position of the gap and a particular shaping of the honeycomb, the leakage flow is kept close to the surface of the shroud and enters the main flow with little perturbations. The paper presents numerical results of steady 3D simulations of a three-stage low pressure turbine. Results with an ideal flow path (no cavities), with shroud cavities with conventionally rotating fins and with shroud cavities with inverse fins are compared.
Numerical Investigation of Heat Transfer and Pressure Drop Characteristics for Different Hole Geometries of a Turbine Casing Impingement Cooling System
Authors: Ben Ahmed F. , Tucholke R. , Weigand B. , Meier K.
Published: May 2012

A representative part of an active clearance control system for a low pressure turbine has been numerically investigated. The setup consisted of a cylindrical plenum with 20 inline arranged impinging jets at the bottom side discharging on a flat plate. The study focused on the influence of the nozzle geometry on the flow as well as heat transfer characteristics at the impingement plate and the discharge pressure drop. CFD (Computational Fluid Dynamics) simulations were performed for a constant Reynolds number ReD = 7,500 and different mean jet Mach numbers up to 0.7. Different length-to-diameter ratios of the jet holes (L/D) and various hole shapes (cylindrical, elliptic, convergent and divergent conical) were investigated to evaluate the performance of the impingement cooling configurations. The predictions showed a significant influence of the length-to-diameter ratio of the orifice bores on the heat transfer and the pressure losses. For L/D = 2 no suction of the ambient air in the nozzles was observed. In comparison to the configuration with L/D = 0.25 an improvement of the discharge coefficient of 9% for Ma = 0.7 and 20% for Ma = 0.17 was achieved. However, the highest heat transfer was observed for the smallest L/D-ratio of 0.25. The shape variation showed that only the elliptic jet holes with a ratio of AR = 0.5 enhanced the overall heat transfer and simultaneously reduced the pressure losses because of discharging onto the target plate. This result was found to be valid for all investigated jet Mach numbers. Additionally, for both elliptic jet aspect ratios of 0.5 and 2 the axis-switchover phenomenon of the flow was observed.
Improved Trench Film Cooling With Shaped Trench Outlets
Authors: Oguntade Habeeb Idowu , Andrews Gordon E. , Burns Alan , Ingham Derek B. , Pourkashanian Mohammed
Published: May 2012

This paper presents the influence of the shaped trailing edge of trench outlets on film cooling effectiveness and aerodynamics. A 90° outlet wall to a trench will give a vertical slot jet into the cross flow and it was considered that improvements in the cooling effectiveness would occur if the trailing edge of the trench outlet was bevelled or filleted. CFD approach was used for these investigations which started with the predictions of the conventional sharp edged trench outlet for two experimental geometries. The computational predictions for the conventional sharp edged trench outlet were shown to have good agreement with the experimental data for two experimental geometries. The shaped trailing edge of the trench outlet was predicted to improve the film cooling effectiveness. The bevelled and filleted trench outlets were predicted to further suppress vertical jet momentum and give a Coanda effect that allowed the cooling air to attach to the downstream wall surface with a better transverse spread of the coolant film. The new trench outlet geometries would allow a reduction in film cooling mass flow rate for the same cooling effectiveness. Also, it was predicted that reducing the coolant mass flow per hole and increasing the number of holes gave, for the same total coolant mass flow, a much superior surface averaged cooling effectiveness for the same cooled surface area.
A Novel Bulk-Flow Model for Improved Predictions of Force Coefficients in Grooved Oil Seals Operating Eccentrically
Authors: San Andre´s Luis , Delgado Adolfo
Published: May 2012

Oil seals in centrifugal compressors reduce leakage of the process gas into the support bearings and ambient. Under certain operating conditions of speed and pressure, oil seals lock, becoming a source of hydrodynamic instability due to excessively large cross coupled stiffness coefficients. It is a common practice to machine circumferential grooves, breaking the seal land, to isolate shear flow induced film pressures in contiguous lands, and hence reducing the seal cross coupled stiffnesses. Published tests results for oil seal rings shows that an inner land groove, shallow or deep, does not actually reduce the cross-stiffnesses as much as conventional models predict. In addition, the tested grooved oil seals evidenced large added mass coefficients; while predictive models, based on classical lubrication theory, neglect fluid inertia effects. This paper introduces a bulk-flow model for groove oil seals operating eccentrically and its solution via the finite element method. The analysis relies on an effective groove depth, different from the physical depth, which delimits the upper boundary for the squeeze film flow. Predictions of rotordynamic force coefficients are compared to published experimental force coefficients for a smooth land seal and a seal with a single inner groove with depth equaling 15 times the land clearance. The test data represent operation at 10 krpm and 70 bar supply pressure, and four journal eccentricity ratios (e/c = 0, 0.3, 0.5, 0.7). Predictions from the current model agree with the test data for operation at the lowest eccentricities (e/c = 0.3); discrepancies increasing at larger journal eccentricities. The new flow model is a significant improvement towards the accurate estimation of grooved seal cross-coupled stiffnesses and added mass coefficients; the later previously ignored or largely under predicted.
Numerical Study on Heat Transfer Characteristics in Rectangular Ducts With Pin-Fins
Authors: Wang Xinjun , Bai Xiaowei , Wu Jiangbo , Liu Rui , Zhu Ding , Liao Gaoliang
Published: May 2012

By using the CFX software, three-dimensional flow and heat transfer characteristics in rectangular cooling ducts with in-line and staggered array pin-fins of gas turbine blade trailing edge were numerically simulated. The effects of in-line and staggered arrays of pin-fins, flow Reynolds number as well as density of cylindrical pin-fins in flow direction on heat transfer characteristics were analyzed. Both in the cases of in-line and staggered arrays of pin-fins, the results show that the pin-fin surface averaged Nusselt number increases with the increasing of Reynolds number. In the case of the same Reynolds number, the mean Nusselt number of pin-fin surface decreased with the increasing of X/D (the ratio of streamwise pin-pitch to pin-fin diameter) value. The Nusselt number increases gradually before the first pin-fin row and then reached the fully developed value at fourth or fifth row. The pin-fin Nusselt number at flow direction is larger than that at back flow direction. Along the height direction of pin-fin, the Nusselt number in middle area is larger.
Improved Multiple Point Non-Linear Genetic Algorithm Based Performance Adaptation Using Least Square Method
Authors: Li Y. G. , Abdul Ghafir M. F. , Wang L. , Singh R. , Huang K. , Feng X. , Zhang W.
Published: May 2012

At off-design conditions, engine performance model prediction accuracy depends largely on its component characteristic maps. With the absence of actual characteristic maps, performance adaptation needs to be done for good imitations of actual engine performance. A non-linear multiple point Genetic Algorithm based performance adaptation developed earlier by the authors using a set of non-linear scaling factor functions has been proven capable of making accurate performance prediction over a wide range of operating conditions. However, the success depends on searching the right range of scaling factor coefficients heuristically, in order to obtain optimum scaling factor functions. Such search ranges may be difficult to obtain and in many off-design adaption cases, it may be very time consuming due to the nature of trial and error process. In this paper, an improvement on the present adaptation method is presented using a Least Square method where the search range can be selected deterministically. In the new method, off-design adaptation is applied to individual off-design point first to obtain individual off-design point scaling factors. Then plots of the scaling factors against the off-design conditions are generated. Using the Least Square method, the relationship between each scaling factor and the off-design operating condition is generated. The regression coefficients are then used to determine the search range of the scaling factor coefficients before multiple off-design points performance adaptation is finally applied. The developed adaptation approach has been applied to a model single-spool turboshaft engine and demonstrated a simpler and faster way of obtaining the optimal scaling factor coefficients compared with the original off-design adaptation method.
Experimental and Numerical Analysis of High Temperature Gas Turbine Nozzle Vane Convective and Film Cooling Effectiveness
Authors: Krivonosova Victoria , Lebedev Alexander , Simin Nicolay , Zolotogorov Michael , Kortikov Nicolay
Published: May 2012

This paper presents the results of experimental and numerical investigations of cooling effectiveness of the film cooled turbine nozzle. The nozzle is with two internal cavities. Front cavity of the nozzle is fed with high pressure cooling air from compressor diffuser with minimal losses of pressure for ensuring film cooling of the leading edge. Rear cavity is with impingement tube for high effective convective cooling. Experimental measurements of cooling flow capacity and cooling effectiveness were carried out on experimental facility of OSC “NPO CKTI”. Investigations included isothermal internal flow tests and hot tests with internal flow and metal temperature measurements. Test results were compared with flow and thermal field CFD predictions. Temperature fields of body and platforms of nozzle were predicted by conjugate heat transfer simulation. Computation domain includes vane-to-vane path flow, vane solid body with shrouds and holes for cooling air injection. Heat transfer conditions inside vane were calculated with one dimension internal flow model. Isothermal internal flow test results were used to validate one dimension internal flow model. Comparison of the experimental and simulation results enabled to modify calculation models to obtain good agreement. Turbine vane temperature fields calculations in different operation conditions were carried out with validated numerical models.
Distributed Network System for Real-Time Model Based Control of Industrial Gas Turbines
Authors: Panov V.
Published: May 2012

This paper describes the development of a distributed network system for real-time model based control of industrial gas turbine engines. Distributed control systems contribute toward improvements in performance, testability, control system maintainability and overall life-cycle cost. The goal of this programme was to offer a modular platform for improved model based control system. Hence, another important aspect of this programme was real-time implementation of non-linear aero-thermal gas turbine models on a dedicated hardware platform. Two typical applications of real-time engine models, namely hardware-in-the-loop simulations and on-line co-simulations, have been considered in this programme. Hardware-in-the-loop platform has been proposed as a transitional architecture, which should lead towards a fully distributed on-line model based control system. Distributed control system architecture offers the possibility of integrating a real-time on-line engine model embedded within a dedicated hardware platform. Real-time executing models use engine operating conditions to generate expected values for measured and non-measured engine parameters. These virtual measurements can be used for the development of model based control methods, which can contribute towards improvements in engine stability, performance and life management. As an illustration of model based control concept, the example of gas turbine transient over-temperature protection is presented in this study.
Experimental Characterization of Low NOx Micromix Prototype Combustors for Industrial Gas Turbine Applications
Authors: Funke H. H.-W. , Boerner S. , Krebs W. , Wolf E.
Published: May 2012

The use of renewable discontinuous energy sources, such as wind- or solar-energy, raises the question of ensuring the continuous demand for energy. For future energy storage scenarios, hydrogen combustion systems play an important role. This offers new opportunities for alternative combustion processes with regard to efficient, safe and low NOx combustion of hydrogen. In addition hydrogen combustion technology will be in need of gas turbine technology for future IGCC power plant concepts. Against the background of ensuring a secure and low NOx combustion of hydrogen, the micromix burning principle is developed since years and was first investigated for the use in aircraft jet engines to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen and burns in multiple miniaturized diffusion type flames. The two advantages of this principle are the inherent safety against flash back and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames. The paper presents an experimental in depth analysis of the combustion principle with regards to low NOx-emissions for higher energy densities. Therefore several geometric variations were investigated and the burning principle was scaled and tested for higher energy densities up to 15 MW/(m2bar). For the different geometries and energy densities, combustion stability, flame anchoring behavior and associated NOx-emissions are tested under preheated atmospheric conditions. The experimental results show the successful scaling of the micromix principle for high energy densities. The general mapping of the test burners demonstrates a wide operating range. Flow phenomena influencing the flame lifting and flame anchoring position with respect to the resulting NOx-emission are analyzed. The investigations highlight further potential for NOx-reduction in industrial gas turbine applications.
Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 1—Externally-Induced Ingress
Authors: Sangan Carl M. , Zhou Kunyuan , Owen J. Michael , Pountney Oliver J. , Wilson Mike , Lock Gary D.
Published: May 2012

This paper describes a new research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. Measurements of CO2 gas concentration in the rim-seal region and inside the cavity are used to assess the performance of two generic (though engine-representative) rim-seal geometries in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs this externally-induced (EI) ingestion, was obtained from steady pressure measurements downstream of the vanes and near the rim seal upstream of the rotating blades. Although the ingestion through the rim seal is a consequence of an unsteady, three-dimensional flow field and the cause-effect relationship between pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a previously published orifice model. The data illustrate that, for similar turbine-stage velocity triangles, the effectiveness can be correlated using a non-dimensional sealing parameter, Φo. In principle, and within the limits of dimensional similitude, these correlations should apply to a geometrically-similar engine at the same operating conditions. Part 2 of this paper describes an experimental investigation of rotationally-induced (RI) ingress, where there is no mainsteam flow and consequently no circumferential variation of external pressure.
DNS of Stagnation Point Heat Transfer Affected by Varying Wake-Induced Turbulence
Authors: Venema Lars , von Terzi Dominic , Bauer Hans-Jo¨rg , Rodi Wolfgang
Published: May 2012

In the present study a tandem cylinder setup is simulated by means of embedded DNS. The influence of wake turbulence on the heat transfer in the stagnation region of the rear cylinder is investigated. The oncoming flow is varied by increasing the distance between the two cylinders, causing a change of the turbulent wake characteristics and the heat transfer. The data of both simulations show good agreement with an existing experimental correlation in the literature. For the small wake generator distance, a clear shift of the maximum heat transfer is observed away from the stagnation line. This shift is less pronounced for the larger distance.
High Frequency Pressure Measurements With an Uncooled Fast Insertion Probe at Turbine Exit in a Turbojet Engine
Authors: Lubbock R. J. , Oldfield M. L. G.
Published: May 2012

This paper concerns the development and testing of a novel high frequency pressure probe for high temperature turbomachinery flow measurements. The probe has a measurement bandwidth from DC to 100 kHz and has been demonstrated in conditions of up to 6 bar and 1900 K. The 4 mm diameter probes are uncooled whilst in the flow and employ a fast insertion traverse to limit immersion times to of the order of 0.1 seconds. The probe was calibrated against a hot wire anemometer in a known turbulent flow. Data acquired downstream of the turbine in a turbojet engine is presented. The unsteady pressure data is decomposed into periodic and random components. Power spectra, turbulence intensity and length scale are derived. Short duration gas turbine measurements using fast insertion techniques have been under development for some years at the University of Oxford. The current fast-insertion probe is more compact and robust than previous designs. The present work demonstrates that it can resolve useful flow parameters in hostile gas turbine flows. These can be difficult or impossible to obtain using other methods. The rapid probe insertion technique should add to the armoury of diagnostic tools used by the gas turbine developer.
Novel Dynamic Rotor and Blade Deformation and Vibration Monitoring Technique
Authors: Pfister Thorsten , Gu¨nther Philipp , Dreier Florian , Czarske Ju¨rgen
Published: May 2012

Monitoring rotor deformations and vibrations dynamically is an important task for improving both the safety and the lifetime as well as the energy efficiency of motors and turbo machines. However, due to the high rotor speed encountered in particular at turbo machines, this requires concurrently high measurement rate and high accuracy, which is hardly possible to achieve with currently available measurement techniques. To solve this problem, in this paper, we present a novel non-incremental interferometric optical sensor that measures simultaneously the in-plane velocity and the out-of-plane position of laterally moving objects with micrometer precision and concurrently with microsecond temporal resolution. It will be shown that this sensor exhibits the outstanding feature that its measurement uncertainty is generally independent of the object velocity, which enables precise deformation and vibration measurements also at high rotor speed. Moreover, this sensor does not require an in situ calibration and it allows a direct measurement of blade velocity variations in contrast to BTT systems. For application under harsh environmental conditions such as high temperatures, a robust and miniaturized fiber-optic sensor setup was developed. To demonstrate the capability of this sensor, measurements of tip clearance changes and rotor blade vibrations at varying operating conditions of a transonic centrifugal compressor test rig at blade tip velocities up to 600 m/s are presented amongst others.
Improvement in Efficiency and Stall Margin of Centrifugal Blower Impeller by Multi-Objective Optimization
Authors: Hiradate Kiyotaka , Nishioka Takahiro , Kanno Toshio , Sugimura Kazuyuki , Shinkawa Yasushi , Joukou Satoshi
Published: May 2012

We investigated a multi-objective optimization technique that can control a trade-off relationship between the efficiency and the stall margin of two-dimensional impellers using only a calculation result at the design flow rate. The suction flow coefficient at the design flow rate of the impeller we designed was 0.04. We used a multi-objective genetic algorithm and three-dimensional steady Reynolds Averaged Navier-Stokes (RANS) simulation with a blade-to-blade passage in the optimization. To determine a flow field index that can evaluate the stall margin of an impeller, the inner flows of two impellers were investigated. Results showed that the throat deceleration ratio correlates with the inception flow rate of the flow separation that occurs on the blade suction surface in the shroud side near the throat surface. Here, the throat deceleration ratio means a ratio of the relative velocity at the inlet to that at the throat surface in the shroud side of the impeller. We selected the adiabatic efficiency and the throat deceleration ratio at the design flow rate as the objective functions and performed an optimization. A 1.8% improvement in the efficiency and a 5% improvement in the stall margin were demonstrated in the optimized impeller from the detailed calculations. Moreover, it was found that an additional objective function was required to control the flow separation caused by the excessive increase of the blade loading in the rear part of the impeller.
Investigation of Passage Flow Features in a Transonic Compressor Rotor With Casing Treatments
Authors: Mu¨ller M. W. , Schiffer H.-P. , Voges Melanie , Hah Chunill
Published: May 2012

An experimental investigation on casing treatments in a one-stage transonic compressor is presented. The reference case consists of a radially staggered blisk and six circumferential grooves. Speedlines show that this axisymmetric treatment already provided a substantial increase in operating range with relatively small losses in efficiency. Since the onset of rotating stall in tip-critical high-speed compressors is always linked to the tip-leakage flow and the build-up of blockage within the blade passage. High-resolution measurement techniques have been employed to investigate the corresponding effects. Results with Particle Image Velocimetry show that the interaction between the tip leakage vortex and the shock front cause a blockage area. When throttled further, the blockage increases. The shock structure changes similar to the phenomena of vortex breakdown described by different researchers in the past, but a stagnation point is not present. Before reaching the stability limit, the interface line between the incoming flow and the blocked area moves towards the inlet plane of the rotor indicating spike-type stall inception. Wall pressure measurements confirmed this theory for the smooth wall, but with circumferential grooves applied, a part span stall cell develops prior to the stability limit. In order to assess the performance of circumferential grooves, two additional configurations are presented. The corresponding measurements addressed the questions whether circumferential grooves also provide an operating range extension when applied to an optimized rotor design with higher initial stall margin. Therefore, an identical casing treatment is applied to a forward swept rotor. The second question is, how circumferential grooves perform in direct comparison to a non-axisymmetric endwall structure. Axial slots have been applied to the radially staggered rotor. While the stall margin exceeds all other configurations, detrimential effects in efficiency are observed. A detailed anaylsis of probe data shows the changes of the radial profile at the rotor outlet which allows recommendations for more efficient CT designs. Parameters allowing to evaluate the CT influence are presented.
Simulations and Measurements of the Flow and Noise in Hot Supersonic Jets
Authors: Morris Philip J. , McLaughlin Dennis K. , Du Yongle , Kuo Ching-Wen
Published: May 2012

This paper describes a combined computational and experimental study of the noise of exhaust jets with operating conditions typical of high performance military aircraft engines. The numerical simulations use a hybrid RANS/LES approach for the turbulence modeling. Structured multiblock grids with non-matching interfaces are used to enable details of the nozzle geometry to be included. Dual time-stepping is used to advance the solution in time and multigrid and implicit residual smoothing is used to accelerate the convergence of the sub-iterations. The acoustic field is determined by integration over an acoustic data surface based on solutions to the Ffowcs Williams–Hawkings equation. Both the near and far acoustic fields are determined. Baseline nozzles and nozzles with chevrons for noise reduction are simulated. To simulate the effect of the chevrons, without using a body-fitted grid, an immersed boundary method is used. The companion experiments, whose measurements are used to assess the quality of the numerical simulations, are performed in an anechoic jet facility. The facility includes a forward flight stream and uses helium-air mixtures to simulate the effects of jet heating. Flow and noise measurements are described for both baseline and chevron nozzles. Comparisons are made between the numerical predictions and the measurements.
Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor: Part III—Tandem Vanes
Authors: Oh JongSik , Buckley Charles W. , Agrawal Giri L.
Published: May 2012

As Part III, following the authors’ previous studies, the aerodynamic performance of two different tandem LSDs (Low Solidity Diffusers), Tandem (A) and (B), in a high-pressure centrifugal compressor was numerically investigated over flow rates from impeller choke to minimal flows available in computation. Tandem (A) was of conventional design where the first row came directly from the authors’ previous studies (Part I and Part II), selected as the highest efficiency vane at design flow, and the second row was designed to be added considering flow conditions at the exit of the first row vane. Tandem (B) followed a creative patent-pending concept where the number of the first row vanes was doubled with much smaller vane chord keeping a low solidity. A position parameter of RCP (Relative Circumferential Position) was introduced to see the effect of the relative location of the second row vane. Using an in-house Navier-Stokes solver with finite volume time marching methods, overall performance was predicted to be compared with each other. Detailed investigation on the behavior of the static pressure recovery and the total pressure loss coefficient in both diffuser designs helps determine why Tandem (A) design is better and the case of RCP = 0.3 gives the best performance.
Fuel Flexibility in LM2500 and LM6000 Dry Low Emission Engines
Authors: Blouch John , Li Hejie , Mueller Mark , Hook Richard
Published: May 2012

The LM2500 and LM6000 dry-low-emissions (DLE) aeroderivative gas turbine engines have been in commercial service for 15 years and have accumulated nearly 10 million hours of commercial operation. The majority of these engines utilize pipeline quality natural gas predominantly comprised of methane. There is, however, increasing interest in nonstandard fuels that contain varying levels of higher hydrocarbon species and/or inert gases. This paper reports on the demonstrated operability of LM2500 and LM6000 DLE engines with nonstandard fuels. In particular, rig tests at engine conditions were performed to demonstrate the robustness of the dual-annular counter-rotating swirlers (DACRS) premixer design, relative to flameholding with fuels containing high ethane, propane, and N2 concentrations. These experiments, which test the ability of the hardware to shed a flame introduced into the premixing region, have been used to expand the quoting limits for LM2500 and LM6000 gas turbine engines to elevated C2+ levels. In addition, chemical kinetics analysis was performed to understand the effect of temperature, pressure, and fuel compositions on flameholding. Test data for different fuels and operating conditions were successfully correlated with Damkohler number.
Breakup of Liquid Jets Emerging From Elliptic Orifices
Authors: Amini Ghobad , Dolatabadi Ali
Published: May 2012

Passive control can result in increasing fuel efficiency and reducing combustion instabilities of gas turbine spray combustors. Through the use of geometric modifications of the conventional circular nozzles, this method potentially enhances mixing which is responsible for entraining the bulk air necessary for combustion. Several studies show that elliptic jets have higher mass entrainment and spreading rate compared to the equivalent circular jets [1]. The majority of these works have been limited to gaseous jets. The present study focuses on a liquid spray discharging into still ambient air from a single-hole injector with elliptic cross-section. The primary breakup is investigated using a theoretical approach. Characteristics of elliptic orifice jet are compared with circular orifice jet under different breakup regimes and various nozzle geometries.
Performance Evaluation of an Unsteady Turbine Driven by a Pulsed Detonation Combustor
Authors: Rouser Kurt P. , King Paul I. , Schauer Frederick R. , Sondergaard Rolf , Hoke John L.
Published: May 2012

Replacing a Brayton cycle near constant-pressure combustor with a pulsed detonation combustor (PDC) may take advantage of potential performance improvements from low-entropy, pressure-gain heat addition. In this paper, the radial turbine of a Garrett automotive turbocharger is coupled to a hydrogen fueled PDC. Unsteady turbine power is obtained with a conventional dynamometer technique. Sampling frequencies greater than 10 kHz resolve rapid flowfield transients of confined detonations which occur in less than a millisecond and include peak gas pressures exceeding 4 MPa and peak gas temperatures greater than 2,400 K. Results include 6 ms time histories of turbine inlet and exit temperature, pressure, mass flow, and enthalpy during blowdown of a PDC. The unsteady inlet flowfield included momentary reverse flow, which was not observed at the turbine exit. Full pulsed detonation cycle time histories of turbine power, rotor speed, rotational energy and net shaft torque are included to describe the turbine response to detonations. Rotor speed is periodic and net shaft torque oscillates in response to a detonation. Results are shown for fill fractions ranging from 0.5 to 1.0 with a 0.5 purge fraction. PDC operating frequencies in this study range from 10 Hz to 25 Hz.
Study of Unforced and Modulated Inclined Film-Cooling Jets Using Proper Orthogonal Decomposition: Part I—Unforced Jets
Authors: Bidan Guillaume , Vezier Clementine , Nikitopoulos Dimitris E.
Published: May 2012

The effects of jet flow-rate modulation were investigated in the case of a 35° inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records and large eddy simulations (LES). An unforced jet study was conducted over a wide range of blowing ratios to provide a baseline for comparison to the pulsed results. The two distinct and well known steady jet regimes (attached jet with high film cooling performance for BR<0.4 and detached jet with poor film cooling performance for BR>1.0) were related to the dynamics of characteristic vortical structures, significant in the transition from one regime to the other. Similarity of the inclined jet results with a past vertical jet study are also put in perspective when comparing wall adiabatic effectiveness results. 3D Proper Orthogonal Decomposition (3D-POD) was performed on LES results of an unforced case at BR = 0.15 to provide an analysis of dominant modes in the velocity and temperature fields. Error calculations on the reconstructed fields provided an estimation of the number of modes necessary to obtain satisfactory reconstruction while revealing some of the shortcomings associated with POD.
Roughness Modeling for Turbomachinery
Authors: Fiala Andreas , Ku¨geler Edmund
Published: May 2012

Fundamental concepts for roughness modeling have been further explored and advanced. A basic understanding of the effect of distributed roughness on fully developed turbulent boundary layer, its possible influence on transition, and the mechanism of local spanwise roughness on transition has been achieved. Predictions with a refinement around a spanwise roughness element have been conducted in comparison to TATMo’s turbine cascade investigated at VKI. 3d-computations document the status in comparison to the T106C measurements with spanwise roughness for all Reynolds-numbers with two different transition models. Additional validation work shows the reproduction of accurate behavior of influence of height, location, and shape of the roughness element on pitchwise averaged loss and exit angle at midspan. Beside the correct reproduction of flow quantities for the spanwise roughness element, the right assessment of distributed roughness on surfaces of an industrial configuration is important. Because a high grid resolution very near the wall on all surfaces is not always possible, the problem can be solved with the help of wall-functions. The results of the application document the significance of rough wall-function modeling for tubomachinery.
Design of Two Counter-Rotating Fan Types and CFD Investigation of Their Aerodynamic Characteristics
Authors: Yang Xiao-He , Shan Peng
Published: May 2012

The design information and numerical investigation are presented for two kinds of counter-rotating fans. The fans, both vaneless and non-aspirated, are intended for a civil aviation engine with a bypass ratio of 8 and for a military engine with a bypass ratio of 0.5 respectively. The pressure ratios are respectively 1.60 and 3.50, and the tip speeds are (300 m/s, −222 m/s) and (500 m/s, −391 m/s). The design rotating speed ratio of the front to the aft rotor is discussed based on one-dimensional analysis. The variations in pressure ratios, isentropic efficiencies, diffusion losses and shock losses at mean-line with the design rotating speed ratios are studied. The flow fields of the two contra-stages are numerically simulated and the detailed flow physics is investigated at both design and off-design conditions. The simulations reveal that the two stages both perform well. The civil engine contra-stage test fans are still conventional transonic rotors due to the low pressure ratio and low tip speeds. For the military engine contra-stage, the aft rotor differs from the conventional transonic front rotor. It is a full-span relative supersonic rotor in which both the leading edge shock and the passage shock extend from the casing to the hub. At the stall point, for the low pressure ratio civil test fan, both the front and aft rotors are stalled and the shocks detached. In the corresponding high pressure ratio military fan, only the aft rotor is stalled which determines the stage stall point.
Local Heat Transfer Characteristics in Channels With Pin Fin and Pin Fin-Dimple Arrays
Authors: Rao Yu , Wan Chaoyi , Xu Yamin , Zang Shusheng
Published: May 2012

A comparative study was conducted to investigate the spatially-resolved local heat transfer characteristics of air turbulent flow in rectangular channels with pin fin and pin fin-dimple arrays. The spatially-resolved Nusselt numbers on the endwall surface of the pin fin and pin fin-dimple channels have been obtained and compared with each other. Compared with the pin fin channel, the pin fin-dimple channel shows distinguishing heat transfer characteristics on the wall beneath the main flow and the wake flow region. Due to the presence of the dimples in the pin fin arrays, additional strong vortex flows are generated near the wall beneath the main flow region, which distinctively increase the heat transfer rates there; however the turbulent mixing in the wake of the pin fins is reduced appreciably, which leads to decreased heat transfer rates in the wake.
Detailed Heat Transfer Distributions and Pressure Drop Measurements for a Rotating Parallelogram Channel With Radially Outward Flow
Authors: Chang S. W. , Liou T.-M. , Lee T.-H.
Published: May 2012

This experimental study examines the pressure drop coefficients (f) and the detailed Nusselt numbers (Nu) distributions over two opposite leading and trailing walls roughened by 45° ribs for a rotating parallelogram channel with radially outward flow. For the first time the isolated effects of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers on local and area averaged Nusselt numbers (Nu and Nu) measured from the infrared thermography method were successfully examined at the parametric conditions of 5000≤Re≤15000, 0≤Ro≤0.3 and 0.001≤Bu≤0.23 for the single-pass parallelogram channel. A set of selected heat transfer data illustrates the Coriolis and rotating-buoyancy effects on the detailed Nu distributions and the area-averaged heat transfer performances of the rotating parallelogram channel. With the consideration of the f data generated at the isothermal conditions, the thermal performance factors (η) for this radially rotating channel were evaluated. The Nusselt numbers obtained from the leading and trailing walls of the rotating test channel fall in the respective ranges of 0.78–1.34 and 1.09–1.38 times of the stationary levels; while the η factors are in the range of 0.979–1.575 for the present test conditions.
Effect of Turbine Tip Leakage Flows on Exhaust Diffuser Performance
Authors: Babu Mohan , Bhatia Dinesh , Shukla Ram Krishna , Pradeep A. M. , Roy Bhaskar
Published: May 2012

This paper describes numerical simulation of the effect of turbine exhaust flows on typical exhaust diffuser geometries. The study has been carried out on three different diffuser geometries. These diffusers have varying degrees of diffusion in the annular section. The studies were carried out at a Reynolds number of 7.7 × 105 based on the diffuser inlet hydraulic diameter. The performance of the diffusers was assessed in terms of total pressure loss and static pressure coefficient across the diffuser. The turbine exhaust flow was simulated by combining an injection scheme from the casing in to the main flow that changes the uniform diffuser inlet velocity profile to that of a typical turbine exhaust flow profile. It was observed that the presence of a realistic exhaust flow influences the diffuser performance compared to an axial inlet flow. The effect of the real flow seems to be to make it more resistant to adverse pressure gradients. The exit flow of the diffusers, studied earlier, with uniform axial inlet flow, showed massively separated regions at the diffuser delivery. The diffuser performances improved significantly with realistic simulation of turbine exhaust flow. The present study also reinforces the fact that the diffuser performance is highly sensitive to the quality of the inlet flow.
The Approach to the Development of the Next Generation Gas Turbine and History of Tohoku Electric Power Company Combined Cycle Power Plants
Authors: Nishimura Yoshiaki , Ohno Sadahiro , Ishikawa Shinya , Masada Junichiro , Takata Kazumasa
Published: May 2012

As global warming becomes increasingly serious, Japan has committed to reduce the CO2 emission by 25% from 1990 levels in Japan with preconditions by the end of 2020. To reach such the difficult target, resources and energy utilizations should be more efficient than before. Tohoku Electric Power Company, Inc. (Tohoku-EPCO) has been adopting the cutting-edge gas turbines for combined cycle power plants to contribute to the reduction of energy consumption and pollutant emission. Now Tohoku-EPCO and Mitsubishi Heavy Industries, Ltd. (MHI) have started a study of next generation gas turbines to further improve the gas turbine combined cycle (GTCC) power plants efficiency. Tohoku-EPCO and MHI have invented a “closed circuit air cooling system” and a trial design of the closed circuit air cooled combustor is now being conducted as a collaborative project. Besides, the material technology development is being conducted for the further increase in the turbine Row 1 vane inlet temperature (TIT) in future.
Unsteady Flow Analysis of Interaction Between Jet-Wake Flow and Blades of Low Solidity Cascade Diffuser in a Centrifugal Blower
Authors: Sakaguchi Daisaku , Murakami Tengen , Ueki Hironobu , Ishida Masahiro , Hayami Hiroshi
Published: May 2012

A low solidity cascade diffuser (LSD) shows features of a wide operating range and a high pressure ratio in centrifugal compressors and blowers. According to the steady flow analysis results shown previously by the authors, the noise could be reduced effectively without deterioration of the LSD performance by means of a small blade tip-groove located at the shroud side, and a high blade loading could be achieved without stall even at the angle of attack as large as 15 deg. The high LSD performance at low flow rates was achieved by both formations of the stable and intense vortex in the shroud tip-groove and of the secondary flow moving circumferentially along the shroud wall toward the impeller exit. In the present study, the influence of the rotating jet-wake flow discharged from the impeller on the vortex in the shroud tip-groove and on the secondary flow moving circumferentially along the shroud wall were investigated by comparing the simulation results between the unsteady flow analysis and the steady flow one. It is clearly shown that the lift force of the LSD blade fluctuates periodically with the blade passing frequency, however, the flow behaviors of the vortex in the shroud tip-groove and the secondary flow on the shroud wall are little affected by the rotating jet-wake in the vaneless space.