bluuebunny/crossref_metadata_2025 huggingface dataset:
Film Cooling Modelling for Gas Turbine Nozzles and Blades: Validation and Application
Authors: Andrei Luca , Innocenti Luca , Andreini Antonio , Facchini Bruno , Winchler Lorenzo
Published: August 2015

The use of Computational Fluid Dynamics (CFD) for modern turbine blade design requires the accurate representation of the effect of film cooling. However, including complete cooling hole discretization in the computational domain requires a substantial meshing effort and leads to a drastic increase in the computing time. For this reason, many efforts have been made to develop lower order approaches aiming at reducing the number of mesh elements and therefore computational resources. The simplest approach models the set of holes as a uniform coolant injection, but it does not allow an accurate assessment of the interaction between hot gas and coolant. Therefore higher order models have been developed, such as those based on localized mass sources in the region of hole discharge.

It is here proposed an innovative injection film cooling model (FCM), embedded in a CFD code, to represent the effect of cooling holes by adding local source terms at the hole exit in a delimited portion of the domain, avoiding the meshing process of perforations. The goal is to provide a reliable and accurate tool to simulate film-cooled turbine blades and nozzles without having to explicitly mesh the holes.

The validation campaign of the proposed model is composed of two phases. During the first one, results obtained with the film cooling model are compared to experimental data and to numerical results obtained with the full meshing of the cooling holes on a series of test cases, ranging from single row to multi row flat plate, at varying coolant conditions (in terms of blowing and density ratio). Though details of the flow structure downstream of the holes cannot be perfectly captured, this method allows an accurate prediction of the overall flow and performance modifications induced by the presence of the cooling holes, with a strong agreement to complete hole discretization results. In the second phase, a complete film-cooled vane test case has been studied, in order to consider a real injection system and flow conditions. In this case, film cooling model predictions are compared to an in-house developed correlative approach and full CHT 3D-CFD results.

Finally, a comparison between film cooling model predictions and experimental data was performed on an actual nozzle of a GE Oil & Gas heavy-duty gas turbine as well, in order to prove the feasibility of the procedure.

The presented film cooling model proved to be a feasible and reliable tool to evaluate adiabatic effectiveness, simplifying the design phase avoiding the meshing process of perforations. Also, refining the mesh near the hole exit, FCM results well approximate the solution coming from a full CHT calculation.
Performance Testing of Centrifugal Compressors: Schultz Compressibility Factors
Authors: Taher Matt
Published: August 2015

ASME PTC-10 [2009] recognizes inaccuracies involved in using the generalized charts to calculate Schultz compressibility factors for real gas compression. However, it neither addresses a method to develop the compressibility factors, nor does it specify when to use calculated compressibility factors rather than using generalized values. Using inaccurate generalized values for Schultz compressibility factors may lead to erroneous calculation of polytropic exponents and polytropic work.

This paper employs the LKP equation of state to directly calculate Schultz compressibility factors for a mixture of hydrocarbons typically found in natural gas. The results are compared with the values of compressibility factors from the generalized compressibility charts.
Engineering Approach for LCF Assessment of Porous Alloys
Authors: Bednarz Piotr , Szwedowicz Jaroslaw
Published: August 2015

Most components used in gas and steam turbines are metallic parts produced by either casting or forging processes. Although process control works to eliminate defects, there can be variation in micro-porosity from component to component. Previously this micro-porosity was only able to be detected destructively using metallography. Using Computer Tomography (CT), one can find voids in the range of a few tenths of a millimeter and know the location of the voids with high precision. This allows one to map the defects present in each component onto the stress and temperature fields for that component. However, there is not yet universal agreement upon a consistent method to evaluate the effect of these small porosities on a component’s lifetime. Having a robust analysis tool to understand the impact of micro-porosity would decrease development costs, decrease the time to bring a product to market, and increase the likelihood of failure-free operation.

This paper presents an approach using equivalent LCF material properties which avoids the need to explicitly model the morphology of the microstructure in the region of the micro-porosity. The homogenization methodology calculates new LCF curves depending on porosity ratios in material. This approach uses Morrow’s correlation factor of LCF cycles to crack initiation regarding energy amount dissipated in stable cycling (shake-down) and ultimate strain energy under monotonic loading. The paper generalizes Morrow’s postulate and formulates the hypothesis that energy stored and dissipated in the material under shake-down conditions corresponds directly to the number of LCF cycles to crack initiation. The paper demonstrates that the reduction of LCF life based on the porosity ratio agrees well with the experimental results. These results also show that the methodology is very sensitive to the void orientation and loading direction.
Numerical Characterization of a Jet Impingement Cooling System Using Coupled Heat Transfer Analysis
Authors: Kaçar E. Nadir , Erbay L. Berrin
Published: August 2015

In this study jet impingement cooling method is investigated with coupled analysis. Total cooling rate is observed for the specific jet impingement configuration using both finite volume and finite element methods. The specific configuration contains single row of jets of separate four rowed impingement cooling system. This single row is placed at the suction side of vane near trailing edge. For the observation, finite volume analysis is carried out via Fluent program. CFD model, which uses constant hot wall (target surface) temperature, is validated using the test case available in the literature. Constant wall temperature is 1250 K and hot gas of system is at 1500 K with 800 kPa. Moreover, conditions of cooling air are 500 K and 400 kPa. All conditions are determined to simulate specifications of a vane of middle class engine. The coupled solution is performed to calculate realistic heat transfer coefficient (htc) values. It involves concurrent execution of finite element analysis and finite volume analysis for aero-thermal optimization. Iterations are carried out via exchanging heat transfer coefficient values for finite element analysis and metal temperature values for finite volume analysis. At the end of three iterations, 8.1% decrease of htc values is obtained and optimum metal temperature values for the specified cooling configuration are calculated.
Development of Laminated Seals for Stator-Stator Sealing in Gas Turbines
Authors: Sarawate Neelesh , Morgan Victor , Weber David
Published: August 2015

This paper describes the development of laminated seals for stator-stator sealing in gas turbines. Cloth seals were introduced as stator-stator seals in the 1990’s and resulted in a significant improvement in sealing performance over the rigid seals then in service. Laminated seals presented here are proposed as an improvement to the existing cloth seals. They demonstrate improved leakage performance over cloth seals in aligned and offset conditions. Several versions of laminated seals were developed and tested before arriving at a seal geometry that satisfied the leakage, manufacturability and assembly requirements. These seals therefore provide an alternative to cloth seals that leak less and are durable, cost-effective and robust in assembly.
Effects of Unsteady Flow Interactions on the Performance of a Highly-Loaded Transonic Compressor Stage
Authors: Hah Chunill
Published: August 2015

The primary focus of this paper is to investigate the loss sources in an advanced GE transonic compressor design with high reaction and high stage loading. This advanced compressor has been investigated both experimentally and analytically in the past. The measured compressor efficiency is significantly lower than the efficiency calculated with various existing tools based on RANS and URANS. The general understanding is that some important flow physics in this modern compressor design are not represented in the current tools. To pinpoint the source of the efficiency miss, an advanced test with detailed flow traverse was performed for the front one and a half stage at the NASA Glenn Research Center. In the present paper, a Large Eddy Simulation (LES) is employed to determine whether a higher-fidelity simulation can pick up any additional flow physics that can explain past efficiency miss with RANS and URANS. The results from the Large Eddy Simulation were compared with the NASA test results and the GE interpretation of the test data. LES calculates lower total pressure and higher total temperature on the pressure side of the stator, resulting in large loss generation on the pressure side of the stator. On the other hand, existing tools based on the RANS and URANS do not calculate this high total temperature and low total pressure on the pressure side of the stator. The calculated loss through the stator from LES seems to match the measured data and the GE data interpretation. Detailed examination of the unsteady flow field from LES indicates that the accumulation of high loss near the pressure side of the stator is due to the interaction of the rotor wake with the stator blade. The strong rotor wake interacts quite differently with the pressure side of the stator than with the suction side of the stator blade. The concave curvature on the pressure side of the stator blade increases the mixing of the rotor wake with the pressure side boundary layer significantly. On the other hand, the convex curvature on the suction side of the stator blade decreases the mixing and the suction side blade boundary layer remains thin. The jet velocity in the rotor wake in the stator frame seems to magnify the curvature effect in addition to inviscid redistribution of wake fluid toward the pressure side of the blade.
Estimation of Burner-Can Induced Excitation Response of an Industrial Low Pressure Turbine Blade: Validation Against Prototype Test Data
Authors: Mayorca Maria A. , Torres Albert , Kharyton Vsevolod , Bladh Ronnie
Published: August 2015

Discovering vibration problems after engine prototype tests translates in increased costs and limited re-design space. For this reason numerical tools are more and more being applied to help taking correct decision in the early design. This paper presents the estimation of the vibration levels induced by hot-streaks from burner-cans in the last blade of an industrial gas turbine. The aerodynamic forcing was obtained from full wheel time marching unsteady computational fluid dynamics calculation. The results are compared with a previous calculation of a scaled sector model. Determination of different sources of damping is achieved by the use of an unsteady aerodynamics harmonic solver and a friction damping harmonic balance method. Results show that the fatigue risk due to the first burner-can harmonic could be predicted with a fairly good accuracy from both scaled and full wheel model when compared with the strain gage prototype test data. The presence of various engine orders in the test spectral maps are commented and related to the calculations.
Effect of Higher-Than-Rated-Speed Rotordynamic Modes on Rotor Balancing
Authors: Yu John J. , Ashar Siddharth
Published: August 2015

It was surprisingly reported that a generator rotor could not be balanced to an acceptable vibration level by weights at two balance planes at the drive end (DE) and the non-drive end (NDE) fan rings. Both real measured vibration data and rotordynamic calculations indicate that the rotor at rated speed of 3600 rpm appears to run just above the 2nd critical speed (couple or conical mode). However, couple weights (same weights placed at both DE and NDE with 180-degree-out-of-phase) have little effect on 1X vibration response. A third balance plane had to be utilized to effectively reduce vibration. This paper uses measured data and rotordynamic modelling to explain these findings. It is found that the 4th mode could affect synchronous vibration response at rated speed significantly besides the 3rd mode. The two fan ring balance planes appear to be near the nodal points of the 4th mode, which explains ineffectiveness of the couple weights to vibration response at rated speed in the field. Measured data from real machines including influence vectors are presented from third balance planes such as the coupling and the exciter ends, besides the fan ring wheels. The 3rd and 4th rotordynamic modes are also given along with unbalance response studies.
Implicit Heterogeneous 1D/2D Coupling for Aero-Thermo-Mechanical Simulation of Secondary Air Systems
Authors: Ganine Vlad , Hills Nick , Miller Matt , Barnes Chris , Curzons Steve , Turner Lynne , Smout Peter
Published: August 2015

The paper presents a computational procedure for heterogeneous coupled analysis of 1D flow network models of air engine secondary air systems and 2D/3D solid thermo-mechanical finite element models of engine components. We solve an unsteady heat transfer problem over solid domain coupled to a sequence of structural static and steady flow problems using a quasi-steady state approximation. Strong coupling is achieved at each time step by a fixed-point iteration, based on the successive solution of the fluid and the solid sub-problems. The procedure is applied to a 2D axisymmetric finite element model of an intermediate pressure turbine assembly coupled to a flow network model of whole engine secondary air system simulated through a square cycle. The simulation results are compared to reference stand-alone predictions showing important non-negligible coupled effects and component interactions of a multidisciplinary multi-physical nature resolved in an efficient and automatic fashion.
Gasification of Agro-Industrial Wastes for Electricity Cogeneration
Authors: Sarmiento A. L. E. , Maya D. M. Y. , Chejne F. , Lora E. E. S.
Published: August 2015

The purpose of this paper is to report studies on agricultural residual biomass gasification to power cogeneration. The classification was determined by availability and feedstock for thermochemical conversion of waste materials of flower industry in Colombia. Firstly, it was made an inventory of the main species of flowers produced, they were evaluated from the point of view of energy proximate and ultimate analysis of the available biomass[1]–[4] [5].

As a result of this work, the waste types with higher residual biomass per unit area were classified, they generate on average 665.59 Kg/ha of dry residual biomass. The elemental analysis (CHON) was expressed to be: C:35,47%, H:4,50%, O:52,24 % and N:2,291% and a calorific value of 3248,30 cal/kg. Experimental tests were conducted in a gasification updraft reactor using air as gasifying agent, steam and a mixture of air and steam at 850°C. The yields and gas composition were analyzed, in this case the values of CO, H2, CO2, N2 and CH4 have been on average 21.9%, 44.8%, 24.4%, 5.9% and 3.1% respectively [1], [2], [4], [6]–[10]. With the experimental test data was fed zero dimensional model in Aspen Plus® software, which highlights that 20% of energy from biomass producer gas is carried to later becoming electricity, it concludes that for each kilogram of biomass with 11% humidity fed to the process will provide 0.66 kW of electric power to the motor generator.
Validation of a Modified Parallel Compressor Model for Prediction of the Effects of Inlet Swirl on Compressor Performance and Operability
Authors: Floyd Reginald S. , Davis Milton
Published: August 2015

Engine inlet distortion complications have plagued the turbine engine development community for decades, and engineers have developed countless methods to identify and combat the harmful effects of inlet distortion. One such type of distortion that has gained much attention in recent years is known as inlet swirl, which results in a significant flow angularity at the face of the engine. This flow angularity can affect the pressure rise and flow capacity of the fan or compressor, and subsequently affect compressor and engine performance.

Previous modeling and simulation efforts to predict the effect inlet swirl can have on fan and compressor performance have made great strides, yet still leave a lot to be desired. In particular, a one-dimensional parallel compressor model called DYNTECC (Dynamic Turbine Engine Compressor Code) has been used to analyze the effects of inlet swirl on fan and performance operability of the Honeywell F109 turbofan engine. However, when compared to experimental swirl data gathered at the United States Air Force Academy (USAFA), the model predictions were found to be inaccurate.

This paper documents work done to compare the initial predictions generated by DYNTECC to the latest set of experimental swirl data, analyze the potential shortcomings of the initial model, and modify the existing model to more accurately reflect test data. Extensive work was completed to create a methodology that can calibrate the model to existing clean inlet fan map data. In addition, an in depth study of fan/compressor stalling criteria was conducted, and the model was modified to use an alternate stalling criteria that more accurately predicted the point of stall for various swirl inlet conditions. The prediction of the fan stall pressure ratio for all inlet swirl conditions tested is within 2% of the ground test stall point at the same referred fan speed and referred mass flow.
Adjoint Optimization of an Internal Cooling Channel U-Bend
Authors: Willeke Sebastian , Verstraete Tom
Published: August 2015

This paper addresses the optimization of a two-dimensional U-bend passage of an internal serpentine cooling channel for reduced total pressure loss by means of a steepest-descent method. A steady-state incompressible flow is considered at a Reynolds number of 40,000 based on the bulk velocity at the domain inlet. The two-equation k-ε model is used for primal turbulence modeling. After only 30 design iterations, the gradient-based optimization results in a reduction of total pressure loss by 46% compared to the baseline geometry.

To obtain the required objective gradients efficiently, a continuous adjoint approach is implemented in the OpenFOAM environment. Adjoint governing equations and boundary conditions are derived from state equations for steady-state, incompressible, turbulent flows under the assumption of frozen turbulence. Two different methods are proposed for modifying the shape of internal and external curves defining the duct geometry. The first method makes use of direct displacement of boundary grid points, allowing for a wide design space. The second, novel parameterization utilizes a projection of the surface sensitivities to an underlying Bézier curve. In this case, the Bézier control points are used as design variables. A comparison of both methods demonstrates a slightly lower performance improvement by the Bézier-based approach due to the reduced design freedom. This approach has, however, several practical advantages.

Previous studies already addressed this optimization problem using gradient-free methods, but were limited in the degrees of freedom given to the shape variation. The present gradient-based optimization allows for a much larger design space and hence is used to compare the different methodologies. It shows that both optimizations result in similar shapes, although the gradient-based method allows for a slightly larger reduction in pressure loss due to the wider design space, while converging faster towards the optimum.
Experimental Rotordynamic Parameter Study at Turbochargers With Hydrodynamic Journal Bearing Systems
Authors: Hummel Alexander T. , Rott Michael , Schneider Christoph , Kuschnertschuk David , Stelzner Günther , Müller Markus , Leweux Johannes
Published: August 2015

This paper presents an evaluation of various rotordynamic parameters at commercial vehicle turbochargers, which are operated supercritically in full-floating hydrodynamic journal bearing systems. The evaluation is conducted by using an experimental approach to determine the performance of the rotor-bearing-system in a real-life assembly at a hot gas test bench. This takes support stiffness, external heating and the excitation by seals, thrust bearings and gas forces into account, while Engine-specific excitation is not present. The system’s ability to carry additional unbalance load at different oil support pressures without the occurrence of mixed friction throughout a complete run-up is assessed. By executing this assessment for multiple assemblies with different bearings, rotors and oil types, the influence of main design and boundary parameters on the effective journal bearing performance of turbochargers is quantified.
Innovative Ram Air Turbine for Airborne Power Generation
Authors: Haid Daniel , Justak John
Published: August 2015

An innovative high power density and low drag ram air turbine for airborne power generation has been developed. Future systems on military and commercial aircraft will require greater electrical power. Unfortunately, expanding the capacity of the electrical systems on current aircraft and ones in development can result in costly design changes, require recertification, and significantly impact performance. Powering these systems locally with batteries is often considered. However, operation time is limited by the battery and the additional weight can limit aircraft range. The innovative ram air turbine design configuration described here has a power density that can be significantly higher than batteries and a lower drag and greater integration flexibility than conventional ram air turbines. Unlike batteries, which have a finite specific energy, the ram air turbine is only limited by the flight time of the vehicle. This system has a ducted turbine located in a pod or fuselage interior, unlike current ram air turbines that are externally mounted and require direct exposure to the free-stream flow. The internally mounted ram air turbine contributes less to overall aerodynamic drag than current ram air turbines, allows for more power to be extracted in an equivalent design space, and offers reduced radar signature compared to present externally-bladed turbines. Computational analyses along with wind tunnel testing have been conducted in support of this design. A 25-inch (0.635 m) diameter turbine demonstrated 110 kW of electrical power over a wide range of Mach numbers and simulated altitudes.
UHEGT: The Ultra-High Efficiency Gas Turbine Engine With Stator Internal Combustion
Authors: Schobeiri Meinhard T. , Ghoreyshi Seyed M.
Published: August 2015

The current article introduces a physics based revolutionary technology that enables energy efficiency and environmental compatibility goals of future generation aircraft and power generation gas turbines. An Ultra-High Efficiency Gas Turbine technology (UHEGT) is developed, where the combustion process is no longer contained in isolation between the compressor and turbine, rather distributed in three stages and integrated within the first three HP-turbine stator rows. The proposed distributed combustion results in high thermal efficiencies, which cannot be achieved by conventional gas turbine engines. Particular fundamental issues of aero-thermodynamic design, combustion, and heat transfer are addressed in this study along with comprehensive CFD simulations. The aero-thermodynamic study shows that the UHEGT-concept improves the thermal efficiency of gas turbines 5–7% above the current most advanced high efficiency gas turbine engines, such as Alstom GT24. Multiple configurations are designed and simulated numerically to achieve the optimum configuration for UHEGT. CFD simulations include combustion process in conjunction with a rotating turbine row. Temperature and velocity distributions are investigated as well as power generation, pressure losses, and NOx emissions. Results show that the configuration in which fuel is injected into the domain through cylindrical tubes provides the best combustion process and the most uniform temperature distribution at the rotor inlet.
Development of Advanced Material Systems for Future Gas Turbine Applications
Authors: Alvin M. A. , Anderson I. , Heidloff A. , White E. , Bhatt R. , Grady J. , McMordie B. , Warnes B.
Published: August 2015

Advanced coating systems in conjunction with novel internal airfoil cooling configurations continue to be a critical research focus to provide enhanced oxidation protection and cooling of commercial metal alloys as future land-based gas turbines are being designed for inlet gas temperature operations of >1300–1400°C. With the application of densified oxide dispersion strengthened (ODS) coatings on cast near surface embedded micro-channel (NSEMC) airfoil surfaces, improvements of >50–70% in heat removal capabilities are projected over that of conventional, smooth-channeled, internally-cooled, airfoil configurations. For turbine inlet and airfoil surface design temperatures exceeding 1400–1600°C, oxide-coated, silicon carbide-based ceramic matric composites (CMCs) have been developed. In this paper we will review our recent advancements that have been made with respect to ODS coating development and the oxidation stability of CMCs during bench-scale laboratory testing.
A Study of the Mean and Dynamic Behavior of the Swirling Flow Generated by a Counter Rotating Radial-Radial Swirler Using a Water Test Rig
Authors: Estefanos Wessam , Tambe Samir , Jeng San-Mou
Published: August 2015

An experimental investigation has been conducted to study the mean and unsteady behavior of the non-reacting swirling flow using a water test rig. Water was used as the flow medium as for a given Reynolds number (Re), the flow dynamics are slowed down by about 18 times compared to atmospheric air making it easier to investigate the flow dynamics. The flow was examined using a 3X model of a counter rotating radial-radial swirler. 2D high speed Particle Image Velocimetry (PIV) measurements were employed to study the instantaneous and the mean velocity fields. Tests were conducted at Re values corresponding to an air pressure drop of 4%, 2.8%, 1.8% and 1% of atmospheric pressure for the corresponding 1X model of the swirler under atmospheric test conditions. The use of water to test the unsteady behavior of the swirling flow was validated by conducting tests on the same 3X model in the same test rig using air at the same Re values. The mean and turbulent behavior of the swirling flow in water and air showed excellent agreement over the range of Re tested. For this swirler, the normalized mean and RMS velocities did not change significantly with Re for the range of Re tested. Strong flow instability was observed at the exit of the swirler. This instability was created by a precessing vortex core (PVC). For air and water tests, the dominant frequency of this instability increased linearly with the increase in Re. For all Re investigated, the dominant frequency of water flow was 18 times less than that of air at the same Re. The Strouhal number was found to be nearly identical for air and water testing for all Re values. Maximum Turbulent Kinetic Energy (TKE) was found to exist on the boundaries of strong shear layers. The TKE decayed quickly downstream due to the quick decay of the PVC. The phase angle difference between the high TKE regions was 3.14 radians indicating a circumferential mode of instability. The results obtained demonstrate that water testing is an accepted method for studying the unsteady flows.
Non-Linear Time-Transient Rotor Dynamic Analyses of Geared Systems
Authors: Kaplan Jason A. , Fittro Roger L. , Untaroiu Alexandrina , Wood Houston G.
Published: August 2015

The ability to accurately predict the response of rotating machinery to external forces and to assess system-level stability for different modes is crucial from a reliability and preventive maintenance perspective. Geared systems, in particular, contain many complexities, which may lead to instability and even chaotic vibration behavior. No methods for determining the effects of the dynamic meshing forces on the vibrations of complete shaft/bearing systems have been proposed in the literature. Several time-transient and steady-state models for analyzing gear forces and deflections have been proposed, but they focus primarily on the dynamics of the gearbox itself and neglect vibration transmission through the remainder of the drive-train. Models that do incorporate other components of the drive-train propose simplified lumped-parameter models for the shafts and bearings. Recent models have used the finite element method to couple the lateral, torsional, and axial degrees-of-freedom of geared shaft systems to the forces and moments exchanged between the gears via stiffness matrices. Other models in literature capture the backlash non-linearity and the state-varying mesh stiffness and observe the time-transient response of the gearbox and simplified shaft/bearing structure. A finite element formulation of complete geared systems, which couples the axial, lateral, and torsional degrees-of-freedom, is developed in which the shaft is modeled with Timoshenko beam elements and captures the forces and moments due to gyroscopic effects, and rotational accelerations due to start-up. It includes the capability of modeling non-linear contact loss due to backlash clearance and parametric excitations resulting from the state-varying mesh stiffness and solves the time-transient state equations for the displacements and velocities of the shafts using the direct Runge-Kutta method.
Measured Heat Transfer in a Transonic Fan Rig at Casing With Implications on Performance
Authors: Turner Mark G. , Nemnem Ahmed , Gannon Anthony J. , Hobson Garth V. , Sanz Wolfgang
Published: August 2015

A highly loaded transonic fan with a splittered rotor and maximum pressure ratio of 2 has been tested at the Naval Post-graduate School. Temperatures on the casing outer wall have been measured using thermocouples in order to assess the heat transfer. An axisymmetric heat transfer analysis has shown that the heat transfer downstream of the rotor through the casing leads to an overstatement of the experimental efficiency by 0.36% and 0.29% for 100% and 90% speed respectively. Just above the rotor is an abradable material that can be considered adiabatic. Thus heat escapes only aft of the rotor and upstream of the total pressure and total temperature probes. For rotors without an adiabatic casing, the effect would be considerably higher. This has a large effect on the exit total temperature profiles which are often not matched well with CFD using an adiabatic boundary condition. In addition, heat transfer coefficients have been determined that can be used to assess other compressor applications.
Mechanical Design Features of a Small Gas Turbine for Power Generation in Unmanned Aerial Vehicles
Authors: Cunningham Caleb S. , Ransom David , Wilkes Jason , Bishop John , White Benjamin
Published: August 2015

As part of the Intelligence Advanced Research Projects Activity (iARPA) Great Horned Owl (GHO) program, Southwest Research Institute® (SwRI®) developed and tested a small gas turbine for power generation in Unmanned Aerial Vehicles (UAV). This development program focused on advancing the state of the art in UAV power systems by meeting key metrics in weight, fuel efficiency, and noise generation.

Design, assembly, and testing of the gas turbine were completed in-house at SwRI. Fundamental mechanical design features of the gas turbine include an integrated 7 kW motor-generator, minimal oil lubrication system, cantilevered compressor/turbine assembly, and can combustor with air-atomizing fuel nozzles. The compressor/turbine assembly is cantilevered directly off of the motor-generator shaft, which spins on hybrid ceramic bearings. Due to potential rotor natural frequencies in the design operating range, the rotor-dynamic design of this configuration was a special design challenge. The outboard rotor bearing is softly supported on O-rings to provide compliance and drive shaft natural frequencies below the operating range.

The lube oil system is another interesting design feature of the GHO gas turbine. It is based on a minimal oil lubrication system previously used at SwRI. The minimal oil lubrication system relies on low oil flow rates and cooling air to pull droplets of oil through the bearing. The oil passes through the machine and is consumed during combustion. This system eliminates traditional oil recirculation hardware for simplicity and weight savings.

The can combustor features a modular design and uses additive manufacturing techniques to facilitate easy and cost effective prototyping. All combustor components are manufactured from Inconel 718 using direct metal laser sintering (DMLS) with additional post-machining. These parts are particularly challenging for DMLS because of their thin walls and high aspect ratio. The custom air-atomizing fuel nozzles also highlight one of the exciting advantages of the DMLS process. Each nozzle would be difficult to machine using traditional techniques because of the tight internal flow passages; however, they are simple to construct using additive manufacturing.

The GHO turbine developed by SwRI demonstrates interesting design features including a minimal oil lubrication system, a cantilever shaft with softly supported bearing, and combustor components built using additive manufacturing techniques. This design provides a platform for further development, testing, and demonstration of small gas turbine technology for UAV power generation.
Modelling Non-Uniform Bleed in Axial Compressors
Authors: Grimshaw S. D. , Pullan G. , Hynes T. P.
Published: August 2015

The coupling between the bleed system and the flowfield of a downstream compressor stage is studied using two approaches.

In the first, three-dimensional, full annulus, unsteady computations simulate the flow in a low speed research compressor with non-uniform bleed extraction. Comparisons with experimental data show that the flow prediction in the main annulus is accurate to within 0.005 of flow coefficient and 0.5° of flow angle. The CFD is then used to provide a description of flow within the bleed system itself.

In the second approach, a two-dimensional mean radius model, similar to that adopted by Hynes and Greitzer in previous work on compressor stability, is used to simulate the response of the compressor to non-uniform bleed. This model is validated against experimental data for a single stage compressor and despite the inherent assumptions (two dimensional flow and simplified compressor response) provides a satisfactory prediction of the flow for preliminary design purposes with orders of magnitude less computational cost than full 3D CFD. The model is then used to investigate the effect of different levels of bleed non-uniformity and of varying the axial distance between the bleed and the downstream stage. Reducing bleed non-uniformity and moving the stage away from the bleed slot are predicted to reduce the circumferential non-uniformity of the flow entering the stage.
Simplified Protrusion Drag and Heat Transfer Modelling of Bolts on a Rotating Disc
Authors: Mohamed Sulfickerali Noor , Chew John W. , Hills Nick J.
Published: August 2015

The main objective of the present work was to develop a porous media based axi-symmetric bolt protrusion drag and heat transfer model for fast and efficient aero-thermal coupling of a rotor-stator cavity with rotor mounted bolts. Traditionally, detailed non axisymmetric features like bolts, holes etc. are either approximated through windage correlations or ignored which could result in significant difference in disc temperature prediction. Protrusion drag and windage work terms are introduced into the bolt porous zone in an axisymmetric model to simulate non axisymmetric effects of protrusions. The drag, tangential velocity and adiabatic disc surface temperature results from the simplified axisymmetric model are compared with 3D CFD model predictions and experimental data for a range of rotational and throughflow Reynolds numbers. The simplified porous media based models are found to predict the drag and windage heat transfer with reasonable accuracy compared to 3D sector CFD results. However, 3D sector CFD under-predicts the high core flow swirl and mixing of the hot fluid withinthe rotor-stator cavity and also under-predicts the adiabatic disc surface temperature inboard of the bolt, compared to experimental data, particularly for the rotationally dominated flow case. The comparison of disc temperature with measurements for the through flow dominated case of λT=0.2 and Cw = 105 is satisfactory.
Unsteady Wet Steam Flow Field Measurements in the Last Stage of Low Pressure Steam Turbine
Authors: Bosdas Ilias , Mansour Michel , Kalfas Anestis I. , Abhari Reza S. , Senoo Shigeki
Published: August 2015

Modern steam turbines need to operate efficiently and safely over a wide range of operating conditions. This paper presents a unique unprecedented set of time-resolved steam flowfield measurements from the exit of the last two stages of a low pressure (LP) steam turbine under various volumetric massflow conditions.

The measurements were performed in the steam turbine test facility in Hitachi city in Japan. A newly developed fast response probe equipped with a heated tip to operate in wet steam flows was used. The probe tip is heated through an active control system using a miniature high-power cartridge heater developed in-house.

Three different operating points, including two reduced massflow conditions, are compared and a detailed analysis of the unsteady flow structures under various blade loads and wetness mass fractions is presented. The measurements show that at the exit of the second to last stage the flow field is highly three dimensional. The measurements also show that the secondary flow structures at the tip region (shroud leakage and tip passage vortices) are the predominant sources of unsteadiness at 85% span. The high massflow operating condition exhibits the highest level of periodical total pressure fluctuation compared to the reduced massflow conditions at the inlet of the last stage. In contrast at the exit of the last stage, the reduced massflow operating condition exhibits the largest aerodynamic losses near the tip. This is due to the onset of the ventilation process at the exit of the LP steam turbine. This phenomenon results in 3 times larger levels of relative total pressure unsteadiness at 93% span, compared to the high massflow condition. This implies that at low volumetric flow conditions the blades will be subjected to higher dynamic load fluctuations at the tip region.
Thin-Film Flow Over a Rotating Plate: An Assessment of the Suitability of VOF and Eulerian Thin-Film Methods for the Numerical Simulation of Isothermal Thin-Film Flows
Authors: Kakimpa B. , Morvan H. P. , Hibberd S.
Published: August 2015

An isothermal thin-film flow over a rotating plate has been simulated using the depth-averaged Eulerian Thin-Film modelling (ETFM) approach. The model setup is based on published experimental and numerical Volume of Fluid (VOF) CFD studies of the same problem to allow for model validation. A range of controlled film inlet heights and mass flow rates are explored together with varied plate rotational speeds ranging from a stationary plate (50rpm) to 200 rpm. While the VOF model has previously been shown to accurately reproduce film thickness, the Eulerian thin-film model is shown to provide predictions of comparable accuracy at a much lower computational cost. The model is also shown to be able to reproduce the film solution’s sensitivity to variations in fluid properties due to changes in inlet temperature. A full 3D domain has been used in this study and the ETFM model is also shown to be able to reproduce azimuthal film thickness variations and surface features similar to those previously observed in experiments.
Capabilities of Thermal Wall Functions to Predict Heat Transfer on the NGVs of a Gas Turbine With Multiple Can Combustors
Authors: Mazzoni Cosimo Maria , Luque Salvador , Rosic Budimir
Published: August 2015

Modern gas turbine combustion systems are characterised by enhanced air/fuel mixing and this results in more diffused and redistributed hot streaks leading to higher thermal loads established on the vane surface and endwalls. Thus, a detailed aero-thermal characterization of the near-wall region has become crucial both for the analysis of turbine performances and for the subsequent design of special features, such as the use of advanced materials and/or novel efficient cooling concepts. In order to investigate complex combustor-turbine flow interactions high fidelity experimental facilities and numerical tools are required.

In particular, detailed prediction of heat transfer at the gas turbine hot walls is computationally very demanding since it requires fully resolved boundary layers and very fine computational meshes. The present work investigates the capabilities of computationally less demanding near wall treatments (thermal wall functions) to predict heat transfer in gas turbine first stage vanes. This paper first summarizes the recent progress in the implementation of heat transfer capabilities into the CFD solver TBLOCK, by describing the near-wall treatments for forced thermal convection adopted in combination with standard turbulence models and aerodynamic wall functions. In order to assess the capabilities of the flow solver TBLOCK to predict heat transfer under engine realistic conditions an experimental cascade is then modelled numerically. The test case is the new linear cascade built at Oxford’s Osney Thermofluids Laboratory to simulate combustor-vane interactions in gas turbines for power generation; it consists of four first stage vane passages downstream a contracting inlet duct divided in two by a transition splitter that acts as the wall between two can combustors. Both aerodynamic and heat transfer numerical results are compared with available experimental data.

Numerical predictions show good agreement with experiments and well reproduce the aero-thermal influence of the combustor wall, showing the reliability of standard CFD tools in simulating these flow regimes without demanding CPU costs.
Effects of the Main Gas Path Pressure Field on Rim Seal Flows in a Stationary Linear Cascade
Authors: Gibson Jeffrey , Thole Karen , Christophel Jesse , Memory Curtis
Published: August 2015

Rim seals in the turbine section of gas turbine engines aim to reduce the amount of purge air required to prevent the ingress of hot mainstream gas into the under-platform space. A stationary, linear cascade was designed, built, and benchmarked to study the effect of the interaction between the pressure fields from an upstream vane row and downstream blade row on hot gas ingress for engine-realistic rim seal geometries. The pressure field of the downstream blade row was modeled using a bluff body designed to produce the pressure distortion of a moving blade. Sealing effectiveness data for the baseline seal indicated that there was little to no ingress with a purge rate greater than 1% of the main gas path flow. Adiabatic endwall effectiveness data downstream in the trench between the vane and blade showed a high degree of mixing. Extending the seal feature associated with the vane endwall indicated better sealing than the baseline design. Steady computational predictions were found to overpredict the sealing effectiveness due to underpredicted mixing in the trench.
Experimental Study of Non-Reacting Low NOx Combustor Simulator for Scaled Turbine Experiments
Authors: Hall Benjamin F. , Povey Thomas
Published: August 2015

This paper presents the first experimental characterisation of a fully annular combustor simulator incorporating both swirl and temperature pattern. The simulator has been designed to non-dimensionally replicate the conditions of next-generation low NOx combustors, with high swirl and high near wall temperature gradients, making it suitable for use in fully scaled (correct Re, M, N/√T, TG/TW) turbine facilities, to investigate combustor turbine interaction effects.

In reacting combustor flows with high swirl, combustion has a significant influence on vortex stability and therefore flow structure. In non-reacting simulators, with approximately isothermal flow, it is common to find instabilities that are not present in the equivalent reacting flow. Where this is the case, artificial methods must be used to stabilise the vortex core. It has previously been shown numerically and in simple experimental studies that a low-momentum axial jet at the vortex centre suppresses precession of the vortex core.

This paper reports experimental data for highly swirling flows both with and without stabilizing jets. This investigation is the first of its type, and the results have implications for the design of simulators for next-generation scaled turbine experiments both in industry and academia.
Swirling Premixed Combustor Simulation Using a Parameterized Stochastic Model
Authors: Mattick Stephen J. , Calhoon William H. , Menon Suresh
Published: August 2015

An LES subgrid modeling formulation based on a parameterization of the linear-eddy model (LEM) has been employed to assess the sensitivity of model predictions on strain rate effects within a model premixed combustor configuration. This subgrid model directly includes strain rate effects through the application of the LEM to a counter flow configuration. This allows for the estimation of the turbulent flame speed as a function of resolved scale strain rate, as well as for the prediction of turbulent flame extinction limits. Tractability and efficiency of the modeling formulation is achieved through a database driven approach where the LEM is used to perform off-line simulations which are used to populate a database. This database is then deployed within the LES flow solver. This subgrid formulation was applied to a model combustor configuration to parametrically investigate the effects of strain rate and inflow turbulence specification on model predictions. This case was found to be highly dependent of the inflow turbulence specification illustrating the need for highly controlled and comprehensive experimental measurements of the boundary conditions. Strain effects within the context of the inflow turbulence specification were found to significantly affect the predictions as well.
Improving Lifetime and Manufacturability of an RQL Combustor for Microturbines: Design and Numerical Validation
Authors: Laranci Paolo , Bidini Gianni , D’Alessandro Bruno , Zampilli Mauro , Forcella Fabio , Fantozzi Francesco
Published: August 2015

A new annular RQL combustion chamber of an 80 kWel Elliott TA80R micro gas turbine was designed and built with a modified geometry to overcome known failures at low running hours (around 2500 hrs) caused by overheating. Design considered simplified manufacturability and flow optimization to reduce emission while maintaining similar temperatures and efficiencies. A preliminary geometry was analyzed and also built to verify manufacturability and economics. It was easily built with overall brute costs around 3000 €. It has also run continuously for over 27.000 hrs.

An optimized geometry, however, guaranteed similar TIT with respect to the original geometry with a considerable reduction in CO and NOx emissions.

Given the installation of the mGT at the IRP (Integrated Pyrolysis Regenerated Plant) the modified geometry was tested through CFD analysis on syngas from biomass thermochemical processes. The results show that further modifications of the liner are required for optimal operation and to reach adequate values for Turbine Inlet Temperature.