bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Combustor Geometry on Swirl Stabilized Premixed Methane-Air Flame
Authors: Tong Yiheng , Li Mao , Klingmann Jens
Published: September 2016

Flame structures, blowout limits and emissions of swirl-stabilized premixed methane-air flames were studied experimentally in a small atmospheric combustor rig. Combustion sections with rectangular cross section (30mm by 40mm) and circular cross section (inner diameter = 39mm) were used to investigate effects of combustor geometry on the flame’s performance. Flame structures and instabilities were obtained from CH* chemiluminescence captured by a high speed intensified CMOS camera. Maps of flame blowout limits (ΦBO) versus total mass flow rates ( ṁ = 70 ∼ 130 standard liter per minute, SLPM) were obtained with the combustor inlet flow temperature (Tin) kept at Tin = 397 ± 5K and a flow swirl number of S = 0.6. Emission data of mole fraction of CO in the exhaust gas versus equivalence ratio was obtained under the conditions of Tin = 293 ± 5K and S = 0.66. It is found that the flame became longer and more unstable with decreasing equivalence ratio or increasing total mass flow rates. A strong high-amplitude and low-frequency oscillation was found to be the reason for the flame blowout. A possible reason for flame instability and blowout is presented in the paper. Within the parameters investigated in this study, the equivalence ratio had the strongest impact on flame stabilities and CO emission. Both in the rectangular and circular combustors, when the flame length increased to a critical value (LIBO, which was approximately the same for these two combustors), flame could not be stabilized anymore and blowout occurred. Compared with the rectangular combustor, the circular one had lower blowout limits and was better in stabilizing the flame. Combustor geometry did not significantly affect CO emission in the current study.
Preliminary and Robust Design Analysis of a Solar Thermal Power Block
Authors: Persky Rodney , Sauret Emilie
Published: September 2016

Australia is endeavouring to expand the mix of power resources, and is investing heavily in the development of renewable generation methods such as concentrated solar thermal power. In these systems, the power block and turbine need to maintain high efficiency under non-ideal conditions away from the design point.

Literature shows that there is a clear relationship between the selection of fluids, the design of the operating cycle, the fluctuation in operating conditions and changes in power block performance. It is thus important for innovative power block designs to consider the performance of the system as a whole rather than by component, mainly turbine design, cycle development and economic analysis. However, there are few works that consider the coupling of multidisciplinary design and robust design to turbine-fluid selection and economic analysis for realistic systems. Furthermore, existing methodologies for robust optimisation often do not consider the effects of high-density gas properties on the performance of the power block. It is also critical that a power generation system produces ideal economic outcomes that meet a number of key performance indicators including levelised cost of electricity.

Therefore, this paper develops a preliminary multidisciplinary design and robust design approach applied to turbine-fluid selection and economic analysis of a solarthermal power block. In this work, an Organic Rankine Cycle using novel working fluids for a solarthermal power system is developed. Integrating robust optimisation into the development of the power block is key to push efficiency further and guarantee power block feasibility when running at non-ideal conditions. A preliminary multidisciplinary optimisation is applied to design the complete power block concept such that the power block operates at peak performance across multiple analysis approaches.
Numerical Analysis of the Dynamic Flame Response and Thermo-Acoustic Stability of a Full-Annular Lean Partially-Premixed Combustor
Authors: Innocenti Alessandro , Andreini Antonio , Facchini Bruno , Cerutti Matteo
Published: September 2016

A thermo-acoustic stability of a full-annular lean partially-premixed heavy-duty gas turbine combustor is carried out in the present paper. A sensitivity analysis is performed, varying the flame temperature for two operating conditions.

The complex interaction between the system acoustics and the turbulent flame is studied in Ansys Fluent, using Unsteady-RANS simulations with Flamelet-Generated Manifolds combustion model. Perturbations are introduced in the system imposing a broadband excitation as inlet boundary condition. The flame response is then computed exploiting system identification techniques. The identified flame transfer functions are compared each other and the results analysed in order to give more physical insight on the coupling mechanisms responsible for the flame dynamic response.

The effect of fuel mass flow fluctuations is then introduced as further driving input, describing the flame as a Multi-Input Single-Output system. Further in-depth studies are carried out on pilot flames aiming at replicating the dynamic response of the real flame and understanding the driving mechanism of thermo-acoustic instability onset as well.

The obtained results are implemented into a finite element model of the combustor, realized in COMSOL Multiphysics, to analyse the system stability.

Numerical model affordability has been assessed through comparisons with results from full-annular combustor experimental campaign carried out by GE Oil & Gas since the early phases of the design and development of a heavy-duty gas turbine. This allowed the discussion of the model ability to describe the stability properties of the combustor and to catch the instabilities onset as detected experimentally.

Valuable indications for future design optimization were also identified thanks to the obtained results.
Highly Resolved LES of a Linear HPT Vane Cascade Using Structured and Unstructured Codes
Authors: Pichler Richard , Kopriva James , Laskowski Gregory , Michelassi Vittorio , Sandberg Richard
Published: September 2016

Conventionally meridian, RANS or URANS simulations are used in design. However, their accuracy is not always satisfactory. Higher order methods like direct and large eddy simulation have shown improved results for various case. While traditionally many direct numerical simulation (DNS) and large eddy simulation (LES) studies have been conducted using highly tailored research codes. These codes often use high order methods with both low numerical dissipation and dispersion often in conjunction with structured grids. While these features allow for high efficiency and accuracy they require a considerable effort to obtain appropriate grids. The ongoing rapid increases in available computer power have allowed commercial software packages to also include LES using lower order methods and unstructured grids. These are more flexible and robust to apply but it is not clear how they compare to the higher accuracy research solvers. In this work an initial comparison between a structured research code and an unstructured commercial code is presented.

To that end, the paper compares compressible LES conducted with a high-resolution research code and with a commercial code of a statistically 2D linear transonic high pressure turbine vane cascade. The geometry investigated is that of Arts and Rouvroit [1] at isentropic exit Reynolds number approximately 590,000 and isentropic exit Mach number 0.93 with a target inlet turbulence intensity of 4%. The results are also compared to Direct Numerical Simulation results, published by Wheeler et al. [2], for boundary layer and wake development for low levels of freestream inlet turbulence. In the research code inlet turbulence is generated synthetically while the turbulence grid comprised of bars is simulated in the commercial code. While the flow around the blade is in good agreement differences are present in the wake data.
The Effects of Periodic Wakes on Boundary Layer Separation of Low-Pressure Turbine Using Large Eddy Simulation
Authors: Wu Xiaodi , Chen Fu , Wang Yunfei
Published: September 2016

For low-pressure turbine, the unsteady disturbances are dominated by relative motions between rotors and stators and the unsteady flow is closely associated with aerodynamic efficiency of low-pressure turbine and engine performance. One of its most important manifestations is the boundary layer separation on the turbine blades by the passing wakes produced by upstream rows of blades. Hence, accurate prediction of the flow physics at low Reynolds number conditions is required to effectively implement flow control techniques which can help mitigate separation induced losses. The present paper concentrates on simulations for boundary layer separation of low-pressure turbine cascade under periodic wakes. In this paper, a multiblock computational fluid dynamics (CFD) code of compressible N-S equations is developed for predicting the phenomenon of boundary layer separation, transition and reattachment using large eddy simulation (LES) in the field of turbomachinery. The large-scale structures can be directly obtained from the solution of the filtered Naiver-Strokes equations and the small-scale structures are modeled by dynamic subgrid-scale model of turbulence. Firstly, unsteady boundary layer separation on a flat plate with adverse pressure gradient is simulated under periodic inflow. The time-averaged field, the phase-averaged field and the instantaneous flow field are presented and analyzed. The separation bubble becomes unstable and the location of transition moves back and forth due to vortex shedding. Secondly, a stator of turbomachinery which is influenced by wakes periodically passing is simulated. The results of the numerical simulations are discussed and compared with experimental data. For the instantaneous flow field, it seems that the spanwise vortices induced by upstream wakes are the primary reason of the initial roll-up of the shear layer and the Kelvin-Helmholtz instability plays an important role in the transition to turbulence which is observed in the separated flow.
Development and Performance Measurements of a Beta-Type Free-Piston Stirling Engine Along With Dynamic Model Predictions
Authors: Sim Kyuho , Kim Dong-Jun
Published: September 2016

This paper presents the development and performance measurements of a beta-type free-piston Stirling engine (FPSE) along with dynamic model predictions. A test FPSE, composed of two pistons and spring elements, is designed by drawing root locus trajectories from linear eigenvalue analysis. Piston springs are developed by using finite element stress analyses and validated through static load-deflection tests. An experimental test rig for a manufactured FPSE includes ceramic heater, water cooler, and external dashpot. Tests are conducted with the atmospheric air at increasing heater temperatures under no load and external load conditions. Firstly, no load tests at increasing heater temperatures show significant increases in both piston stroke and pressure amplitude, but negligible changes in working frequency. Pressure-volume (P-V) power and thermal efficiency also increase significantly. Interestingly, dynamic discontinuities occur during continuous variations of heater temperature, demonstrating sudden increases in engine performance as well as operation uncertainty. Besides, cooling flow rate is found to have minimal influence on engine performance. Secondly, external load tests for increasing damping loads demonstrate considerable decreases in piston stroke, pressure amplitude and P-V power, but negligible changes in working frequency; while shaft power increases then decreases having an optimal operating load. Finally, the test FPSE is turned out to adapt itself to variations in heater temperatures and external loads by changing piston strokes and their phase angle.
Research on Characteristics of a New Marine Gas Turbine Exhaust Ejector Device
Authors: Sun Tao , Sun Lanxin , Luan Yigang , Sun Peng
Published: September 2016

Naval ships, as well as commercial ships, are exposed to more risks than before with the development of IR-guided threats. IR Suppress System (IRSS) is used to reduce or eliminate the infrared signatures of exhaust system of the ship. In order to optimize the structure of exhaust ejector and shorten the cycle of research, it is essential to study the successful experiences on exhaust ejectors by scholars abroad. In this article two structure innovations are introduced: an improved structure of nozzle and multi-stage diffuser; A new type of exhaust ejector for marine gas turbine is designed. Through simplifying the ejector model, numerical simulation is applied to forecast the characteristics of both the single-stage ejector and the multistage ejector. Result indicates the effects of structural parameters on the performance parameters. This research result has certain reference value for marine gas turbine exhaust ejector design and performance optimization.
Optimization of Reinforcing Ribs of a Hollow Fan Blade Using Metamodel-Based Optimization Algorithm
Authors: Ma Ying , Xu Shengli , Liu Haitao , Wang Xiaofang
Published: September 2016

With the development of aero-engine technology, the demand for fan blade with light weight and better structural performances is urgent. This paper focuses on the weight optimization of a hollow fan blade through changing the thickness and distribution of the inner triangular reinforcing ribs under the constraints of equivalent stress, displacement, bending and torsional frequencies. A finite element analysis process was established in the paper, considering the load of centrifugal force and gas pressure. In the CAD-based model parameterization, to avoid possible interference problems brought by design parameters, the relative locations of control points are applied to determine the locations of control points on the vane profile curves. A metamodel-based global optimization scheme is employed for improving the optimization efficiency. An optimal design with about 13.7% weight reduction is finally obtained by the above optimization procedure. The triangular reinforcing ribs of hollow fan blade were rearranged with the constraints of the stress, displacement and natural frequencies satisfied.
Aeroacoustic Optimization of Radial Fans for Medical Applications
Authors: Stadler Michael , Grilliat Julien , Laufer Wolfgang , Schmitz Michael B.
Published: September 2016

In recent years there is a growing number of patients suffering from pneumonia, chronic obstructive pulmonary disease or asthma. In these situations, the application of Continuous Positive Airway Pressure (commonly known as CPAP) is indicated by clinicians. It is a noninvasive means of healthcare used widely. As a more advanced technique, the positive airway pressure may follow a time-cycled change between two preset pressure values. This technique is known as BPAP (Bi-level Positive Airway Pressure).

The devices are used mainly during sleep at home. Hence the aeroacoustic requirements are critical. In addition the devices must be portable and compact. Furthermore, the high frequency of pressure change required in BPAP devices poses additional demands on the design. Due to the complexity of the overall design problem, it may be solved efficiently by multi objective optimization.

The pressure head in these devices is generated by radial fans. For the aerodynamic optimization, we utilize a RANS solver. For the aeroacoustic optimization we use the Lattice-Boltzmann Method (LBM). Both are operating on a parametric geometric model of the fan and housing. For the propagation of sound waves into the far-field, we develop algorithmic strategies for using the Ffowcs Williams-Hawkings (FW-H) equation with the LBM. The constrained multi objective optimization is driven by a variant of the NSGA-II algorithm.

We outline the complete optimization procedure for a BPAP device. Our numerical results are compared with physical tests. To analyze the contribution of selected geometric features to the emitted sound pressure, we perform a sensitivity study. The new algorithmic arrangement has shown to drastically cut development costs and time.
Modelling of Gas Turbine NOx Emissions Based on Long-Term Operation Data
Authors: Rudolf Christian , Wirsum Manfred , Gassner Martin , Zoller Benjamin Timo , Bernero Stefano
Published: September 2016

The continuous monitoring of gas turbines in commercial power plant operation provides long-term engine data of field units. Evaluation of the engine performance from such data is challenging since, apart from variations of operating points and ambient conditions, the state of the engine is subject to change due to ageing of engine components. The installed measurement devices influence the analysis due to their accuracy, which may itself alter with time. Furthermore, the available measurements usually do not cover all necessary information for assessment of the engine performance. To overcome these issues, this paper describes a method to systematically evaluate long term operation data without the incorporation of engine design models that depict the design state of the engine, but do not cover performance changes when components are ageing. Key focus of the methodology is thereby to assess long-term emission performance in the most reliable manner.

The analysis applies a data reconciliation method to long-term operating data in order to model the engine performance including non-measured variables and to account for measurement inaccuracies. This procedure relies on redundancies in the data set due to available measurements and the identification of suitable additional constituting equations that are independent of component ageing. The resulting over-determined set of equations allows for performing a data set optimization with respect to a minimal cumulated deviation to the measurement values, which represents the most probable, real state of the engine. The paper illustrates the development and application of the method for analysing emission performance with long-term operating data of a commercial gas turbine combined cycle power plant.
Thermo-Economic Evaluation of Novel Flexible CAES/CCPP Concept
Authors: Herrmann Stephan , Kahlert Steffen , Wuerth Manuel , Spliethoff Hartmut
Published: September 2016

This paper presents the results of a thermodynamic and economic evaluation of a novel hybrid combination of a compressed air energy storage and a combined cycle power plant. The new cycle is modeled on basis of a GE LM6000 gas turbine model, an adiabatic compressor model, an air expander and a conventional dual pressure HRSG configuration. Furthermore, a detailed design of the recuperator is presented. With the simulated components, a storage efficiency of 60% is reached. In CHP configuration the total efficiency of the plant reaches up to 86.2%. The thermodynamic and economic performance is compared to a conventional LM6000 combined cycle. For the economic evaluation the German electricity day-ahead prices and average gas price of the year 2014 are used. Overall it is found that the CAES/CCPP concept exhibits far more operation hours per year and a higher profit margin than the compared CCPP. Taking into account the investment and operational costs, especially with steam extraction the net present value of the novel cycle is higher than that of the combined cycle, despite the challenging market environment for storage technologies in Germany.
Assessment of Solar Steam Injection in Gas Turbines
Authors: Kalathakis C. , Aretakis N. , Roumeliotis I. , Alexiou A. , Mathioudakis K.
Published: September 2016

The concept of solar steam production for injection in a gas turbine combustion chamber is studied for both nominal and part load engine operation. First, a 5MW single shaft engine is considered which is then retrofitted for solar steam injection using either a tower receiver or a parabolic troughs scheme. Next, solar thermal power is used to augment steam production of an already steam injected single shaft engine without any modification of the existing HRSG by placing the solar receiver/evaporator in parallel with the conventional one.

For the case examined in this paper, solar steam injection results to an increase of annual power production (∼15%) and annual fuel efficiency (∼6%) compared to the fuel-only engine. It is also shown that the tower receiver scheme has a more stable behavior throughout the year compared to the troughs scheme that has better performance at summer than at winter. In the case of doubling the steam-to-air ratio of an already steam injected gas turbine through the use of a solar evaporator, annual power production and fuel efficiency increase by 5% and 2% respectively.
Numerical Study on the Passive Control of the Aeroelastic Response in Large Axial Fans
Authors: Castorrini A. , Corsini A. , Sheard A. G. , Rispoli F.
Published: September 2016

The morphing geometry concept finds interesting applications in load reduction and performance increasing for wings and rotor blades in off-design conditions. Here we report a numerical study on the effect that a passive morphing system (made by an elastic-low stiffness surface) has on the sectional load and flowfield, when it is applied to the trailing edge of an axial fan. We obtain the results extracting the section of the fan blade and test it in the 2D cascade, with and without the elastic device, in different operating conditions. Keeping in mind the two-dimensional approximation, it will be possible to observe how the tested device could reduce the load in off-design and high angle of attack conditions, while the same solution could introduce vibrations in design conditions. All the simulations imply the solution of the fluid-structure interaction between the incompressible, turbulent flow and the elastic structure. This solution is obtained using a finite element based, strongly coupled solver, applied to the periodic 2D domain of the section in the cascade.
Investigation of the Combustion Performance in a Three-Nozzle RQL Combustor
Authors: Ge Bing , Ji Yongbin , Zang Shusheng , Yuan Yongwen , Xin Jianhua
Published: September 2016

RQL (Rich-burn/Quick-quench/Lean-burn) is a candidate to support fuel flexible stationary power generation. The equivalence ratio of rich-burn zone (Φr) and the quench air flow are paramount for implantation of the whole process. In this paper, an experimental test stand with multi-sector model combustor was established. Rich premixed combustion were used in rich zone. The experiments which pay attention to the impacts of Φr and quench air flow on the combustion performance and emission are conducted. The results show that the flame in RQL combustor is segmented when Φr >1.4, presenting flameless combustion in rich zone and a pale blue flame in lean zone. Axial temperature distribution is M-type. Two peaks appear at the head and tail of the combustion chamber, and the valley is located in the quench zone. The concentration of CO decreases rapidly in quench zone because of the injection of quench air. However, the concentration of NOx increases quickly at the same time. The outlet emissions of CO and NOx in RQL combustor are maintained at low level (<20ppm@15%O2). With a decrease of Φr from 1.4 to 1.2, the emission of NOx increases, and the emission of CO decreases. With jet-to-mainstream mass-flow ratio increases from 1.28 to 2.22., the concentration of NOx in outlet declines gently, but the CO emission increase. The average exhaust temperature depresses gradually, and the uniformity coefficient of exhaust temperature increases.
Role of Shear Layer Instability in Driving Pressure Oscillations in a Backward Facing Step Combustor
Authors: Kirthy Srinivas K. , Hemchandra Santosh , Hong Seunghyuck , Shanbhogue Santosh , Ghoniem Ahmed F.
Published: September 2016

This paper presents a global hydrodynamic stability analysis of flow fields in a backward facing step combustor, assuming weakly non-parallel flow. The baseline experiments in a ‘long’ combustor of length of 5.0 m shows the presence of two combustion instability states characterized by coherent low and high amplitude acoustic pressure oscillations. The analysis is performed for Propane-air mixtures at three values of ϕ = 0.63, 0.72 and 0.85 which correspond to quiet, low amplitude and high amplitude instability states in the long combustor experiments. Base flow velocity and density fields for the hydrodynamic stability analysis are determined from time averaged PIV measurements made after the length of the duct downstream of the step has been shortened to eliminate acoustic pressure oscillations. The analysis shows that the shear layer mode is self-excited for the ϕ = 0.72 case with an oscillation frequency close to that of the long combustor’s fundamental acoustic mode. We show from an analysis of the weakly forced, variable density Navier-Stokes equations that self-excited hydrodynamic modes can be weakly receptive to forcing — suggesting that the low amplitude instability in the long combustor is due to semi-open loop forcing of heat release oscillations by the shear layer mode. At ϕ = 0.85 the flow is hydrodynamically globally stable but locally convectively unstable. Spatial amplification of velocity disturbances by the convectively unstable flow causes high amplitude combustion instability in the long combustor case. These results show that combustion instability can be sustained by acoustic and hydrodynamic modes being either strongly coupled, resulting in fully closed loop forcing, or weakly coupled, resulting in semi-open loop forcing of the flame by a self-excited hydrodynamic mode.
Thermal Investigation of Integrated Combustor Vane Concept Under Engine-Realistic Conditions
Authors: Jacobi Simon , Rosic Budimir
Published: September 2016

This paper presents a thermal investigation of the Integrated Combustor Vane concept for power generation gas turbines with individual can combustors. This concept has the potential to replace the high-pressure turbine’s first vanes by prolonged combustor walls. Experimental measurements are performed on a linear high-speed cascade consisting of two can combustors and two integrated vanes. The modularity of the facility allows for the testing at engine-realistic high turbulence levels, as well as swirl strengths with opposing swirl directions. The heat transfer characteristics of the integrated vanes are compared to conventional nozzle guide vanes. The experimental measurements are supported by detailed numerical simulations using the inhouse CFD code TBLOCK. Experimental as well as numerical results congruently indicate a considerable reduction of the heat transfer coefficient (HTC) on the integrated vanes surfaces and endwalls caused by a differing state of boundary layer thickness. The studies furthermore depict a slight, non-detrimental shift in the heat transfer coefficient distributions and the strength of the integrated vanes secondary flows as a result of engine-realistic combustor swirl.
Experimental Investigation of a Non-Ideal Expansion Flow of Siloxane Vapor MDM
Authors: Spinelli Andrea , Cozzi Fabio , Dossena Vincenzo , Gaetani Paolo , Zocca Marta , Guardone Alberto
Published: September 2016

Nozzle flows of siloxane fluid MDM (C8H24O2Si3, octamethyltrisiloxane) expanding to supersonic speeds in non-ideal conditions are observed experimentally for the first time in the Test-Rig for Organic Vapors (TROVA) at Politencnico di Milano. The TROVA is a blow-down facility for investigating non-ideal compressible flows of organic vapors typical of Organic Rankine Cycle (ORC) applications. Total conditions in the settling chamber are subcritical and superheated, with total presssure 3.15 bar and total temperature 246 °C. In these conditions, the thermodynamic model predicts a value of the compressibility factor and of the fundamental derivative of gasdynamics equal to Z = 0.884 < 1 and Γ = 0.885 < 1, respectively. The total pressure and temperature are monitored during the test runs, together with the static pressure at selected stations along the nozzle axis. A double-passage Schlieren is used to visualize the density gradients within the nozzle. The nozzle is a convergent-divergent planar nozzle with a throat area of 16.8 mm (height) × 18.7 mm (width). Differently from dilute gas conditions, for a constant total-to-ambient expansion ratio, the static-to-total pressure ratio measured at the geometrical throat is observed to slightly depend on the reservoir conditions.
Investigation of Steady and Unsteady Film-Cooling Using Immersed Mesh Blocks With New Conservative Interface Scheme
Authors: Jiang Y. , He L. , Capone L. , Romero E.
Published: September 2016

Advanced development of high pressure turbines requires accurate predictions of film cooling flow. However, the length scales inherent to film cooling flows produce a large disparity compared to those of the mainstream flow field. To address this computational modelling challenge, an immersed mesh block (IMB) methodology has been initiated (Lad and He, 2011) which uses the much refined mesh around cooling holes to be mapped into the base mesh which tends to be much coarser for blade aerodynamic designs. Both the base mesh flow field and that of the IMB are solved simultaneously. By employing a simultaneous two-way coupling, the flow physics in and around cooling holes is able to interact with the mainstream, hence the length scales of both types of flow, as well as their interactions, are appropriately captured and resolved. The present work is aimed to develop a new numerical scheme for enforcing conservation at the interfacing boundary between the immersed cooling block and the base mesh, as well as, carry out a systematic validation and application of the IMB method for some well-established film-cooling experimental configurations (cylindrical and fan-shaped holes) at different blowing ratios. During the validation process, the mesh counts/resolution requirements for consistent cooling predictions for design analyses are established. The method is then applied to a transonic HPT stage. Its steady and unsteady flows are investigated. The results consistently demonstrate the effectiveness and applicability of the conservative IMB method, and indicate, for the first time, some interesting and relevant unsteady film-cooling behaviour.
The Use of Eddy Current Sensors for the Measurement of Rotor Blade Tip Timing: Development of a New Method Based on Integration
Authors: Chana K. S. , Sridhar V. , Singh D.
Published: September 2016

The advent of tip-timing systems makes it possible to assess turbomachinery blade vibration using non-contact systems. The most widely used systems in industry are optical. However, these systems are still only used on developmental gas turbine engines, largely because of contamination problems from dust, dirt, oil, water etc. Further development of these systems for in-service use is problematic because of the difficulty of eliminating contamination of the optics. Eddy current sensors are found to be a good alternative and are already being used for gas turbine health monitoring in power plants. Experimental measurements have been carried out on three different rotors using an eddy current sensor developed in a series of laboratory and engine tests in-house to measure rotor blade arrival times. A new tip-timing algorithm for eddy current sensors based on integration has been developed and is compared with two existing tip-timing algorithms: peak-to-peak and peak-and-trough. Among the three, the integration method provided the most promising results in the presence of electrical noise interference. The main aim of this work is to develop an algorithm that can be used to build a simple, robust, real-time and low cost analogue electronic circuit for use in-service health monitoring of engines.
Film Cooling Effectiveness Measurements on Trailing Edge Cutback Surface and Lands Following Novel Cross Corrugated Slot Geometry
Authors: Wong T. H. , Ireland P. T. , Self K. P.
Published: September 2016

The trailing edge of the high pressure turbine blade presents significant challenges to the turbine cooling engineer. A novel cooling design using cross corrugated slots for the trailing edge has been proposed. This geometry allows blade designers to finely tune pressure loss and consequently coolant flow through the slot, but potentially results in poor film cooling performance downstream of the slot exit, an effect that could be mitigated with exit shaping. The current study is focused on comparing film cooling effectiveness on the cutback surface and lands with a plain rectangular slot under the same conditions. A set of nine cross corrugated internal slot geometries has been investigated in a large scale model of the trailing edge pressure side ejection slot exit. Four geometries used a 90° included angle with variations to the channel alignment at slot exit. Four used a 120° included angle, with the same variations to the exit alignment. The final geometry used a 90° included angle with exit shaping. Pressure sensitive paint was used to measure adiabatic film cooling effectiveness at five blowing ratios ranging from 0.6 to 1.4 in increments of 0.2. High resolution 2D distributions of film cooling effectiveness both on the cutback surface and the top of the lands were recorded. It was found that unmodified cross corrugated slots do result in poor film effectiveness on the cutback surface compared to a plain rectangular slot. However, land cooling is slightly improved, and applying exit shaping to the cross corrugated slot results in effectiveness levels at the trailing edge on par with or even superior to the rectangular slot at blowing ratios of 0.8 or below. Therefore, in this respect, the novel cross corrugated slot design proposed is a viable candidate for blade design, provided exit shaping is used and low blowing ratios are expected.
Laboratory Infra-Red Thermal Assessment of Laser-Sintered High-Pressure Nozzle Guide Vanes to De-Risk Engine Design Programmes
Authors: Kirollos Benjamin , Povey Thomas
Published: September 2016

The continuing maturation of metal laser-sintering technology (DMLS) presents the opportunity to de-risk the engine design process by experimentally down-selecting HPNGV cooling designs using laboratory tests of laser-sintered — instead of cast — parts to assess thermal performance. Such tests could be seen as supplementary to thermal-paint-test engines, which are used during certification to validate cooling system designs.

In this paper, we compare conventionally cast and laser-sintered titanium alloy parts in back-to-back experimental tests at engine-representative conditions over a range of coolant mass flow rates. Tests were performed in the University of Oxford Annular Sector Heat Transfer Facility. The thermal performance of the cast and laser-sintered parts — measured using new infra-red processing techniques — is shown to be very similar, demonstrating the utility of laser-sintered parts for preliminary engine thermal assessments.

We conclude that the methods reported in this paper are sufficiently mature to make assessments which could influence engine development programmes.
Numerical Study on Effects of Jet Nozzle Angle and Number on Vortex Cooling Behavior for Gas Turbine Blade Leading Edge
Authors: Du Changhe , Li Liang , Chen XiuXiu , Fan Xiaojun , Feng Zhenping
Published: September 2016

Vortex cooling is a promising blade cooling technique for its excellent heat transfer and pressure loss control behavior. In this paper, the proper vortex chamber model is utilized for vortex cooling mechanism analysis. Three dimensional viscous steady Reynolds Averaged Navier-Stokes (RANS) equations are adopted to explore the influences of jet nozzle angle and number on vortex cooling flow and thermal performance. Turbulence model verification and grid independence analysis are conducted to determine the suitable turbulence model and mesh number for calculations. Results show that due to obvious mass flux enhancement downstream, stronger axial impact effect will generate, leading to the high Nusselt number region downstream deflection towards outlet. As jet nozzle angle increases from α=60° to α=120°, the static pressure ratio increases for the upstream region and decreases for the downstream region, and the total pressure loss ratio increases. The rotation movement and heat transfer intensity will decrease when jet nozzle angle changes away from α=90°. The air jetting velocity decreases and the static pressure ratio increases with the increasing jet nozzle number. When jet nozzle angle increases from 1 to 11, the total pressure loss ratio decreases and the heat transfer intensity increases at first and then decreases.
Design of Compressor Endwall Velocity Triangles
Authors: Auchoybur Kiran , Miller Robert J.
Published: September 2016

Near the endwalls of multi-stage compressor blade rows, there is a spanwise region of low momentum, high entropy fluid which develops due to the presence of annulus walls, leakage flows and corner separations. Off-design this region, known as the endwall flow region, often grows rapidly and in practice sets the compressor’s operating range. By contrast, over the operating range of the compressor, the freestream region of the flow is not usually close to its diffusion limit and has little effect on overall range. In light of these two distinct flow regions within a bladerow, this paper considers how velocity triangles in the endwall region should be designed to give a more balanced spanwise failure across the blade span.

In the first part of the paper, the sensitivity of the operating flow range of a single blade row to variations in realistic multistage inlet conditions and endwall geometry is investigated. It is shown that the operating range of the blade row is largely controlled by the size and structure of the endwall ‘repeating stage’ inlet boundary layer and not the detailed local geometry within the blade row.

In the second part of the paper the traditional design process is ‘flipped’. Instead of redesigning a blade’s endwall geometry to cope with a particular inlet profile into the blade row, the endwall region is redesigned in the multi-stage environment to ‘tailor’ the inlet profile into downstream blade rows. This is shown to allow an extra degree of freedom not usually open to the designer. This extra degree of freedom is exploited to balance freestream and endwall operating range, resulting in a compressor having an increased operating range of ∼20%. If this increased operating range is traded with reduced blade count, it is shown that a design efficiency improvement of Δη∼0.5% can be unlocked.
Influence of the Coriolis Force on the Flow in a Low Pressure Turbine Cascade T106
Authors: Baum Oliver , Koschichow Denis , Fröhlich Jochen
Published: September 2016

The paper presents numerical investigations of a model setup conceived to investigate the influence of the Coriolis force on the secondary flow in a low pressure turbine cascade. It addresses the question in which sense and by how much results in a linear cascade may differ from the situation in a rotating cascade. For this purpose highly resolved Direct Numerical Simulations of the flow within a T106A passage close to the endwall were conducted for two cases with and without rotation and hence with and without Coriolis force at a Reynolds number of 20,000. Comparing non-rotating and rotating turbine passage, several effects are detected: First, the Coriolis force causes transition of the horseshoe vortices, so that the region between the blades becomes much more turbulent and an explanation for the destabilization is provided. Second, the strong radial flow caused by the Coriolis force suppresses the laminar separation of the boundary flow at the suction side. Third, in the case with rotation, the large-scale secondary motion creates higher stagnation pressure loss than in the reference case and is responsible for a complete redistribution of the flow field in the passage. An additional test case with opposite rotation was computed for completeness.
Study of Geometric Parameter Influence on Fishtail Pipe Diffuser Performance
Authors: Han Ge , Lu Xingen , Zhang Yanfeng , Zhao Shengfeng , Yang Chengwu , Zhu Junqiang
Published: September 2016

Centrifugal compressor stages with pipe diffusers are characterized by their high efficiency, especially under high pressure ratio conditions. Although it is believed that pipe diffuser scallop leading edge formed by the intersection of two pipes is a critical point in pipe diffuser design, there is another crucial and influential point, which is how to guide and decelerate the flow from pipe diffuser throat to the inlet of combustor chamber, with minimum loss and maximum outflow uniformity. Fishtail pipe diffuser passage is employed by Pratt&Whitney to connect impeller exit and combustor chamber inlet due to its improved performance characteristics. However, only a few comprehensive results have been published describing the complex flow patterns in the fishtail diffuser. Therefore, in the present work fishtail pipe diffusers with several different geometries were designed for a pressure ratio 8.3 centrifugal compressor stage used on a small turbo engine, aiming at providing detailed understanding of geometric parameter influence on fishtail pipe diffuser performance and flow mechanisms in complex fishtail passages. Cone length, streamwise area distribution and centerline shape are critical parameters of a fishtail pipe diffuser. Hence, parametric studies on fishtail pipe diffuser of this high pressure ratio centrifugal compressor by varying cone length, area distribution and centerline shape of the diffuser passage were performed using a state-of-the-art multi-block flow solver. These three parameters were changed respectively, while keeping other parameters unchanged. Detailed analysis was done to identify the influence on flow field in fishtail diffuser passage when these parameters were changed. It was found that increase of fishtail diffuser cone length could alleviate separation in diffuser passage, thus compressor performance is improved. And linear area distribution along passage centerline could build a more efficient fishtail pipe diffuser. A trumpet-shaped or bell-shaped passage is more likely to make flow separate. The centerline is of vital importance for a fishtail passage and it was built by two lines tangent to an ellipse in this work. It was modified by changing major and minor axes of the ellipse. Stage total pressure ratio and adiabatic efficiency maps for varying fishtail passage centerlines were obtained by numerical method, which indicate that there is an optimum range for both axes to make the fishtail pipe diffuser have a better performance. Through these works, the geometric parameter influence on fishtail diffuser performance was uncovered and physical insight into complex flows in fishtail pipe diffuser passage was obtained to give some guidelines on diffusing system design with fishtail pipe diffuser.
Investigations of the Actuation Effect of a Single DBD Plasma Actuator for Flow Separation Control Under Simulated Low-Pressure Turbine Blade Conditions
Authors: Pescini Elisa , Marra Fedele , De Giorgi Maria Grazia , Francioso Luca , Ficarella Antonio
Published: September 2016

The present study intends to investigate the potentiality of the single dielectric barrier discharge plasma actuators (SDBDPAs) to reattach the separated flow, occurring at low Reynolds numbers. For this aim, a curved wall plate, which profile shape was designed to reproduce the suction surface of a low-pressure turbine (LPT) blade, was installed in the test section of a closed loop wind tunnel and a SDBDPA was placed in a groove made over it, at the front of the adverse pressure gradient region. The flow behavior in absence of actuation has been experimentally investigated by particle image velocimetry (PIV) and laser Doppler velocimetry measurements (LDV). Moreover, sinusoidal voltage excitation with amplitude of 8 kV and frequency of 2 kHz was applied to the SDBDPA and PIV measurements were also performed in presence of actuation. The applied voltage and the discharge current have also been recorded simultaneously, and they have been used for the determination of the device dissipated power.

Different wind tunnel free stream velocities were investigated, both in absence and presence of actuation. The effect of the active flow control was then studied in the entire measurement domain by analyzing the velocity fields, the turbulence intensity (Tu) values, the momentum coefficient (cμ) and the boundary layer shape factor (H12). In absence of actuation, a large reverse flow and a turbulence intensity up to ≈60% was observed in the separation region. Good agreement was found between the flow results obtained by the two velocity measurement techniques. Considering the actuated cases, it was found that, in all the tested operating conditions, actuation implied a reduction of the separated region and the turbulence intensity, even if a low flow control effect was noticed at the highest tested velocity.
Aero-Thermal Performance of a Nozzle Vane Cascade With a Generic Non Uniform Inlet Flow Condition: Part I — Influence of Non Uniformity Location
Authors: Perdichizzi A. , Abdeh H. , Barigozzi G. , Henze M. , Krueckels J.
Published: September 2016

In this paper, the modifications induced by the presence of an inlet flow non uniformity on the aerodynamic performance of a nozzle vane cascade are experimentally assessed. Tests were carried out in a six vane linear cascade whose profile is typical of a first stage nozzle guide vane of a modern heavy duty GT. An obstruction was located in the wind tunnel inlet section to produce a non uniform flow upstream of the leading edge plane. The cascade was tested in an atmospheric wind tunnel at an inlet Mach number Ma1 = 0.12, with a high turbulence intensity (Tu1 = 9%) and variable obstruction tangential and axial positions, as well as tangential extension. The presented results show that an inlet flow non uniformity influences the stagnation point position when it faces the vane leading edge from the suction side. A relevant increase of both 2D and secondary losses are observed when the non uniformity is aligned to the vane leading edge. When it is instead located in between the passage it does not affect the stagnation point location, in the meanwhile allowing a reduction in the secondary loss.
Hydrogen Enriched Combustion Testing of Siemens SGT-400 at High Pressure Conditions
Authors: Lam Kam-Kei , Parsania Nishant
Published: September 2016

Following successful testing of the SGT-400 combustion system at atmospheric conditions with hydrogen enriched natural gas, a high pressure combustion test campaign was carried out at the Siemens test facility in Lincoln UK. Combustion performance at full engine operating conditions was studied, with the aim of demonstrating the capability of the standard SGT-400 combustion hardware to fire fuels with increased hydrogen content. Measurements consisted of: a pilot tip thermocouple to monitor the risk of flashback; pressure sensors to capture the combustion dynamics signature; and emissions instrumentation measuring NOx and CO. The combustor was also instrumented with thermocouples to monitor both the distribution of wall temperatures and potential locations of flashback when utilizing the highly reactive hydrogen enriched gas. The current paper reports the findings of the high pressure tests and compares with the atmospheric results that had been documented previously. Combustion behavior at full engine pressure and temperature was found to be consistent with atmospheric conditions. Pilot tip temperature increased with the hydrogen gas content due to the higher flame speed. Combustion dynamics shifted to a higher frequency for the hydrogen enriched gas, and heat release fluctuations increased. NOx emission also increased with the hydrogen blending due to the enhanced fuel reactivity. The high pressure tests demonstrated that the SGT-400 standard DLE combustion system can operate without risk of flashback for up to 20% vol hydrogen content. The next phase of the hydrogen program is to test a production engine using enriched gas and confirm its full operational characteristics. Extending the operational envelope of the standard DLE combustion system to hydrogen contents above 20% vol is also of interest.