bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Numerical Combustion Models for Hydrogen and Hydrogen-Rich Syngas Applied for Dry-Low-NOx-Micromix-Combustion
Authors: Funke H. H.-W. , Beckmann N. , Keinz J. , Abanteriba S.
Published: September 2016

The Dry-Low-NOx (DLN) Micromix combustion technology has been developed as low emission combustion principle for industrial gas turbines fueled with hydrogen or syngas. The combustion process is based on the phenomenon of jet-in-crossflow-mixing. Fuel is injected perpendicular into the air-cross-flow and burned in a multitude of miniaturized, diffusion-like flames. The miniaturization of the flames leads to a significant reduction of NOx emissions due to the very short residence time of reactants in the flame.

In the Micromix research approach, CFD analyses are validated towards experimental results. The combination of numerical and experimental methods allows an efficient design and optimization of DLN Micromix combustors concerning combustion stability and low NOx emissions.

The paper presents a comparison of several numerical combustion models for hydrogen and hydrogen-rich syngas. They differ in the complexity of the underlying reaction mechanism and the associated computational effort.

For pure hydrogen combustion a one-step global reaction is applied using a hybrid Eddy-Break-up model that incorporates finite rate kinetics. The model is evaluated and compared to a detailed hydrogen combustion mechanism derived by Li et al. including 9 species and 19 reversible elementary reactions. Based on this mechanism, reduction of the computational effort is achieved by applying the Flamelet Generated Manifolds (FGM) method while the accuracy of the detailed reaction scheme is maintained.

For hydrogen-rich syngas combustion (H2-CO) numerical analyses based on a skeletal H2/CO reaction mechanism derived by Hawkes et al. and a detailed reaction mechanism provided by Ranzi et al. are performed.

The comparison between combustion models and the validation of numerical results is based on exhaust gas compositions available from experimental investigation on DLN Micromix combustors.

The conducted evaluation confirms that the applied detailed combustion mechanisms are able to predict the general physics of the DLN-Micromix combustion process accurately. The Flamelet Generated Manifolds method proved to be generally suitable to reduce the computational effort while maintaining the accuracy of detailed chemistry.

Especially for reaction mechanisms with a high number of species accuracy and computational effort can be balanced using the FGM model.
A Practical Approach for Evaluation of Equivalent Linear Damping From Measurements of Mistuned and/or Non-Linear Stages and Forced Response Validation
Authors: Hartung Andreas , Hackenberg Hans-Peter
Published: September 2016

The equivalent linear damping is an important parameter for the design of blades and vanes. This parameter will normally be used based on experience and worst case considerations. In this paper, a practical approach for the evaluation of the equivalent linear damping of blade and vane stages from measurements is proposed. The method can especially be used for mistuned and/or non-linear systems as well as in case of non-satisfying quality of the measurement signals. Based on the approach developed, a way for the validation of the forced response analysis is presented.
Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors
Authors: Jenny Philipp , Bidaut Yves
Published: September 2016

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high cycle fatigue. In addition to the well-established high frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes, the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing high cycle fatigue during the design phase. The unsteady fluid-structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries, therefore they are not critical and confirm a robust and reliable design.
Automatic Detection of Defects in a Swirl Burner Array Through an Exhaust Jet Pattern Analysis
Authors: Hartmann Ulrich , Hennecke Christoph , Dinkelacker Friedrich , Seume Joerg R.
Published: September 2016

A significant challenge in improving the regeneration process of jet engines is the reduction of engine down-time during inspection. As such, early defect detection without engine disassembly will speed up the regeneration process. Defects in the engines hot-gas path (HGP) influence the density distribution of the flow and lead to irregularities in the density distribution of the exhaust jet which can be detected with the optical Background-Oriented Schlieren (BOS) method in a tomographic set-up.

The present paper proposes a combination of tomographic BOS measurements and supervised learning algorithms to develop a methodology for an automatic defect detection system. In a first step, the methodology is verified by analyzing the exhaust jet of a swirl burner array with a non-uniform fuel-supply of single burners with tomographic BOS measurements. The measurements are used to implement a Support Vector Machine (SVM) pattern recognition algorithm.

It is shown that the reconstruction quality of tomographic BOS measurements is high enough to be combined with pattern recognition algorithms. The results strengthen the hypothesis, that it is possible to automatically detect defects in jet engines with tomographic BOS measurements and pattern recognition algorithms.
A New Three-Dimensional Viscous Inverse Design Method for Axial Compressor Blade
Authors: Liu Zhaowei , Wu Hu
Published: September 2016

A recently developed aerodynamic inverse design method for axial compressor is presented in this paper. The inverse design method is based on solving the three-dimensional Reynolds-averaged Navier-Stokes equations. Blade surface static pressure distribution is prescribed before the design procedure. A new inverse design boundary condition is established based on the conservation of Riemann invariant on the blade surface. Blade profile is constantly modified by a virtual wall velocity which is obtained from the difference between the current and prescribed static pressure. The dynamic mesh theory is used to update the computation mesh where the shape of the blade is changing during the design process. The design procedure finishes after the prescribed static pressure distribution on the blade surface is satisfied. The method is first validated by a blade recovery test. It is then used to redesign the NASA Rotor 67.
Comparison of 2D and 3D Airfoils in Combination With Non Axisymmetric End Wall Contouring: Part 1 — Experimental Investigations
Authors: Zimmermann Tobias W. , Curkovic Oliver , Wirsum Manfred , Fowler Andrew , Patel Kush
Published: September 2016

Tangential end wall contouring is intended to improve turbomachinery blading efficiency. This paper is the first of a series of two papers. It summarizes the experimental investigation of a test turbine with end wall contoured vanes and blades. Constant section airfoils as well as optimized 3D high pressure steam turbine blading in baseline and end wall contoured configurations have been examined in a 2 stage axial turbine test rig at the Institute of Power Plant Technology, Steam and Gas Turbines (IKDG) of RWTH Aachen University.

The test rig is driven with air. Brush seals are implemented within the casing sided cavities to minimize the leakage flow near the tip end walls, where the contouring is also applied. The pressure and temperature data that is recorded in three axial measuring planes are plotted to visualize the change in flow structure. This has shown that the efficiency is increased for 2D airfoils by means of end wall contouring, which is caused by a homogenized inflow to the second stage. However the efficiency of the first stage suffers, the end wall contouring is beneficial for the performance of the engine.

Both phenomena (an efficiency loss in stage one and an improvement of the performance in stage two) have also been measured for the optimized 3D configurations thus it can be expected that end wall contouring has also a beneficial impact on the performance of multi row turbines.

The second part of this paper presents the results of numerical investigations of end-wall contoured blades. It will demonstrate how the secondary flow phenomena are influenced by end-wall contours. The simulations are validated with measured data from the test rig.
CFD Analysis of the Unsteady Flow in a Two-Stage Axial Turbine
Authors: Pan Yang , Yuan Qi , Chen Qian , Ge Qing , Ji Dawei
Published: September 2016

Partial admission, which has the advantage of avoiding large losses while the turbine at low load operations, is widely used in regulating the power of turbomachinery. However, partial admission causes prominent unsteady flow, additional exciting forces and extra losses. Thus, it has great significance to investigate the characteristics of partial admission turbines. In this paper, efficiency and unsteady flow performance of a small two-stage subsonic axial turbine with partial admission are analyzed.

Firstly, a 3-D model with four discontinuous equally-distributed nozzle blocks was built, and the computational grid, which only consisted of hexahedral mesh, was generated. Reynolds Averaged Navier-Stokes equations were solved by commercial software ANSYS-CFX and the RNG k-ε turbulence model was adopted. Secondly, to investigate the influence of admission modes, two partial admission modes (A-two diagonal valve opening; B-two adjacent valves opening) were analyzed separately and compared with the full admission situation (Mode C). Finally, the turbine performances in Mode A and B at other speeds (75% and 110% of rated speed) were analyzed and pressure distributions at three different heights (10%, 50% and 90% of the blade height) were investigated in detail.

The results indicated that partial admission could cause extra mixture losses and lead to lower efficiency. Among these kinds of modes, full admission (Mode C) performed best in efficiency, and Mode B performed better than Mode A under partial admission conditions. Furthermore, strong non-uniformity was found in circumferential direction and large pressure drop occurred at the gap between two admission blocks due to expansion effects. The computational results also showed that the flow parameter fluctuations attenuated evidently in the downstream stages and the pressure vibration mainly occurred after nozzle stages. Strong vortices and backflow can be noticed at the pressure side of the active nozzle boxes. Additionally, the rotational speed has a great influence on the performance of turbine. Higher rotational speed led to bigger efficiency and smoother pressure distribution. And the alteration trend becomes slow at high speed.
Fan-Intake Interaction Under High Incidence
Authors: Cao Teng , Vadlamani Nagabhushana Rao , Tucker Paul G. , Smith Angus R. , Slaby Michal , Sheaf Christopher T. J.
Published: September 2016

In this paper, we present an extensive numerical study on the interaction between the downstream fan and the flow separating over an intake under high incidence. The objectives of this investigation are twofold: (a) to gain qualitative insight into the mechanism of fan-intake interaction and (b) to quantitatively examine the sensitivity of the flow distortion (in terms of distortion coefficient DC60), to the key design parameters of the intake (Length, L / Diameter, D).

Both steady and unsteady Reynolds Averaged Numerical Simulations (RANS) were carried out. For the steady calculations, a low order fan model has been used while a full 3D geometry has been used for the unsteady RANS. The numerical methodology is also thoroughly validated against the measurements for the intake-only and fan-only configurations on a high bypass ratio turbofan intake and fan respectively. To systematically study the effect of fan on the intake separation and explore the design criteria, a simplified intake-fan configuration has been considered. In this fan-intake model, the ratio of the intake length to diameter (L/D) can be conveniently altered without affecting other parameters.

The key results indicate that, depending on L/D, the fan has either suppressed the level of the post separation distortion or increased the separation-free operating range. At the lowest L/D (∼ 0.17), around a 5° increase in the separation-free angle of incidence was achieved. This delay in the separation-free angle of incidence decreased with increasing L/D. At the largest L/D (∼ 0.44), the fan was effective in suppressing the post-separation distortion rather than entirely eliminating the separation. Isentropic Mach number distributions over the intake lip for different L/D’s revealed that the fan accelerates the flow upstream of the fan face, thereby decreasing the distortion level in the immediate vicinity. However, this acceleration effect decayed rapidly with increasing upstream distance from the fan-face.
An Aero-Thermal Coupled Throughflow Method for Convective Cooled Turbines
Authors: Gu Chunwei , Li Haibo , Ba Wei , Ren Xiaodong
Published: September 2016

Cooling technologies have been widely applied to protect the turbine blades at high inlet temperature, which also makes the aero-thermal coupled phenomenon more remarkable. Nevertheless, the aero-thermal phenomenon had not been considered in traditional throughflow methods and led to challenges of cooled turbine design. This paper proposes a new cooling model for the aero-thermal coupled throughflow method which was first proposed by the same author. The cooling model considers the variation of the temperature caused by air cooling both along the stream and span direction to improve the heat flux calculation accuracy. The impacts of heat transfer on mainstream enthalpy and entropy are further studied in this paper. The equivalent blade thickness and the estimation method of the heat exchange area were also introduced into the cooling model. The cooling model is validated with experimental data of the Mark II profile. This paper applies the method in the design of a high-pressure axial turbine, of which the first stator is cooled with convective cooling. With the prescribed blade temperature limitation, the flow field properties and the coolant requirement are predicted. The three dimensional CHT analysis is performed to validate the aerothermal coupled throughflow method, and the aerodynamic parameter predicted by the throughflow method is in accordance with the 3-D CHT analysis.
Advanced Aero-Engines Technology Enablers: An Overview of the European Project E-BREAK
Authors: Silva Manuel , Tantot Nicolas , Selezneff Serge , Walsh Mike , Nyatando Rose , Johann Erik , Klauke Thomas , Coppola Michele , Kando André
Published: September 2016

This paper describes research carried out in the European Commission co-funded project E-BREAK (Engine BREAK through components and subsystems) focused on development of generic enabling technologies for new aero-engines.

A global market forecast (2015–2034) from Airbus [1], depicts an average growth rate of 4.6% per year. Air traffic is forecasted to double in the next 15 years. It is expected, to triple in the next 20 years, according to the speech given by RRUK CEO during the Aerodays 2015 in London [2]. This high level of growth in demand for air travel represents huge opportunities as well as significant challenges for the aerospace industry. Research and Technology through collaborative European projects addresses the environmental penalties of air traffic. Europe’s aviation industry therefore faces a huge challenge to satisfy the demand whilst guaranteeing competitiveness, safety and more environmentally friendly air travel. Innovative engine configurations consequently need to be investigated in order to reduce significantly the pollutant emissions (15 to 20% for fuel consumption and CO2 and 80% reduction for NOx). Such reductions can only be achieved by considering innovative components that could be integrated and optimized in new engine configurations.

In response to the above demands, aero-engine manufacturers are constantly aiming to improve gas turbine efficiency for two main reasons: to reduce environmental impact and to minimize operating costs.

The E-BREAK project is aimed at the development of generic enabling technologies needed to address the challenges for future engines with higher overall pressure ratios (OPR) and bypass ratio (BPR). These technologies are developed at subsystem and component level and validated in test rigs which are equivalent to Technical Readiness Level (TRL) 5. The utility of the developed technologies are assessed using four standard study powerplants. These are turboshaft, regional turbofan, mid-size open rotor, and large turbofan, covering most of the expected future commercial aero-engine market.

This article describes the technical approach followed in E-BREAK for the various technologies being investigated, these are:

• Advanced sealing to reduce oil and air leakages

• Variability control to ensure stability of thermodynamic cycle

• High temperature resistant material and abradables to prevent fast degradation at high temperatures

• Light material to prevent significant mass increase

• Health monitoring system to anticipate sub-systems degradation

The envisaged outcomes from E-BREAK are enablers to other EU-funded research projects focused on module maturation progress, such as LEMCOTEC dealing with high OPR modules and ENOVAL dealing with high BPR LP components.
Development and Design of a Two-Stage Contraction Zone and Test Section of an Organic Rankine Cycle Wind Tunnel
Authors: Passmann Maximilian , Reinker Felix , Hasselmann Karsten , aus der Wiesche Stefan , Joos Franz
Published: September 2016

This contribution presents the development and design of a two-stage contraction zone and modular test section for a closed loop Organic Rankine Cycle (ORC) wind tunnel. The first contraction consists of four truncated cones, whose length and angle of inclination are derived from a two-stage optimization procedure, with the objective to minimize flow deviation and to avoid boundary-layer separation. The geometrical optimization yields a profile with minor deviation to the ideal polynomial shape, whereas the flow optimized shape minimizes flow separation at the break-points between the single conical pieces.

The second contraction has to perform two major tasks, namely the acceleration of the flow up to a Mach number of Ma = 0.8 for organic fluids and the transformation of the circular inlet to a rectangular outlet cross-sectional shape, required by the working section. The circular-to-rectangular transition is accomplished by variation of the generalized ellipse, also known as Lamé curve. Smooth polynomials are then used to define the reduction of cross-sectional area. A comprehensive number of contraction geometries with fixed contraction ratio, variable length, and different points of inflection are analyzed with regards to minimum flow deviation, the avoidance of flow separation, as well as a uniform velocity field at the contraction outlet. A semi-analytical approach based on a potential flow solution in combination with the Stratford criterion is the basis for evaluating boundary-layer separation.

The design of a two-part modular diffuser, based on the concept of a dumped diffuser, as commonly encountered in gas turbine design, is presented. The numerical results are compared with analytical findings and special characteristics of the different designs are explained. Finally, the overall design concept of the test section is presented.
Flow Visualization of Unsteady and Transient Phenomena in a Mixed-Flow Multiphase Pump
Authors: Serena Alberto , Bakken Lars E.
Published: September 2016

The flow inside of turbomachines rotating channels, when operating away from the design point, is intrinsically unsteady; two-phase flow and part-load operation further complicate the analysis, introducing additional challenges.

Transient phenomena, linked to the typical unsteadiness of multiphase flows (bubble formation, coalescence or breakdown, segregation and gas locking) and to variable inlet flow compositions, as in case of slug flow, require advanced analysis tools which can reveal the local flow mechanisms responsible for performance degradation and instabilities. General trends can be outlined, but the air accumulation zones and two-phase flow patterns are highly dependent on the machine design.

The flow regimes vary from a homogeneous distribution of fine bubbles, evenly dispersed and carried away by the main flow, to more complex flow patterns, especially when the phases separate or the bubbles coalesce forming a gas pocket which adheres to a wide portion of the channel wall.

Tests are performed on a multiphase pump laboratory, recently installed at the Norwegian University of Science and Technology, which allows a complete optical access to the pump channels and fine adjustments in the inlet configuration and the tip clearance gap; the air can be injected from different locations producing transient regimes too.

A high speed camera provides an interesting insight into the transient flow phenomena.

This paper focuses on these specific ones:

- Irregular backflow and swirl at the inlet section

- Gas accumulation zones and contribution of the tip leakage to mixing

- Flow pattern shift to phase segregation, as the relative flow is reduced

- Origin of pump blockage, when increasing gas contents cannot be carried away by the water phase

- Flow and machine parameters response to a variation in the inlet flow

Tests are performed at various operating conditions — rotational speed, mixture composition and impeller tip clearance.

The study is completed with the time and frequency domain analysis of the pressure pulsations at surging and during specific transient events.
Application of Humpback Whale Flippers in an Annular Compressor Cascade
Authors: Zheng Tan , Qiang Xiaoqing , Teng Jinfang , Feng Jinzhang
Published: September 2016

Humpback whales possess bumpy tubercles on the leading edge of their flippers. Due to these leading edge tubercles, the whales are able to perform complex underwater maneuvers agilely. Inspired by the flippers, this paper applies sinusoidal-like tubercles to the leading edge of the blade in an annular compressor cascade, and presents a numerical investigation to explore the effects of tubercles with the aim of controlling the corner separation and reducing losses.

A preliminary study by steady 3D RANS simulations is performed. The aerodynamic performance and the behavior of the corner separation are investigated in the baseline compressor cascade. Subsequently, cascades with leading edge tubercles are numerically simulated. A crucial geometry parameter of the tubercles, wavelength, is varied to obtain different configurations. The influence of the parameter is concluded from the comparison of the performance attained by these configurations. Also, several configurations, which are typical in loss characteristics, are selected for further DES simulations so as to obtain more flow details, especially at the separation region. Flow visualizations show that leading edge tubercles could induce the formation of counter-rotating streamwise vortices. The interaction between the streamwise vortices and corner separation is emphatically investigated. By analysis of all the results obtained, this paper tries to figure out the mechanism of leading edge tubercles in loss reduction and separation delay in an annular compressor cascade.
Influence of a Shroud Axisymmetric Slot Injection on a High Pressure Turbine Flow
Authors: Tang Etienne , Philit Mickaël , Leroy Gilles , Trebinjac Isabelle , Ngo Boum Ghislaine
Published: September 2016

This paper focuses on an axisymmetric slot injecting cooling air at the casing between the stator and the rotor in a one-stage unshrouded transonic high pressure turbine. This configuration has been studied with the help of unsteady RANS computations with and without the slot. Special care has been taken to model and describe the interaction induced unsteady mechanisms. It has been found that the cooling air is ejected from the axisymmetric slot at a fixed position with respect to the stator vanes, with a much lower incidence angle than the main stream. The flow through the rotor passage is highly modified and reveals an unsteady behaviour which highlights the necessity of using unsteady simulations in order to accurately model such a configuration. The effect on the efficiency and on the repartition of loss generation has been determined. As several different definitions of the efficiency can be used for cooled turbine cases, this choice is discussed. In particular, Young & Horlock’s “Weighted Pressure” definition, which takes into account some unavoidable mixing losses in the definition of the ideal process, is evaluated. With this definition, the slot does not yield any significant decrease in overall efficiency.
Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters
Authors: Clark Christopher , Pullan Graham , Curtis Eric , Goenaga Frederic
Published: September 2016

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge).

For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.
Limitations of a State-of-the-Art Numerical Modelling Framework for Two-Phase Flow in Aero-Engine Air/Oil Separators
Authors: Piazera de Carvalho Thiago , Morvan Hervé P. , Hargreaves David , Cordes Laura , Höfler Corina
Published: September 2016

The development and limitations of a numerical modelling framework applied to an aero-engine air/oil separator are presented here. Oil enters the device in the form of dispersed droplets and primary separation occurs by centrifuging larger droplets towards the outer walls, whereas secondary separation occurs by partially coalescing and centrifuging smaller droplets within a porous material, namely an open-cell metal foam. The work described here is part of a study led jointly by the University of Nottingham (UNott) and the Karlsruhe Institute of Technology (KIT) in the Engine Breakthrough Components and Subsystems (E-BREAK) project. The main objectives for UNott have been to define a CFD methodology able to provide an accurate representation of the air flow behaviour and a qualitative assessment of the oil capture within the air/oil separator. The feasibility of using the current state-of-the-art modelling framework is assessed. Experimental measurements of the overall pressure drop and oil capture performed at KIT are used to validate the simulations. The methodology presented here overcomes some limitations and simplifications present in previous studies. A novel macroscopic model for the secondary oil separation phenomena within metal foams is presented. Experiments and simulations were conducted for three different separator configurations, one without a metal foam, and two with metal foams of different pore sizes. For each configuration, a variation of air flow, shaft speed and droplet size was conducted. The focus was on the separation of droplets with a diameter smaller than 10 μm. Single-phase air flow simulation results showed that overall pressure drop increases with both increased shaft speed and air flow, largely in agreement with the experiments. Oil capture results proved to be more difficult to be captured by the numerical model. One of the limitations of the modelling set-up employed here is not capable of capturing droplet re-entrainment due to accumulation of oil inside the metal foam, which is believed to play a significant role in the separation phenomena.
Numerical Study on the Effects of the Upstream Wake Generator on the Aerodynamic Performance of a High-Lift Low Pressure Turbine Blade
Authors: Bigoni Fabio , Vagnoli Stefano , Arts Tony , Verstraete Tom
Published: September 2016

The aim of the present paper is to analyze and discuss in detail the effects of the upstream incoming wakes on both the aerodynamic loading and the evolution of the laminar separation bubble developing along the suction side of the high-lift T106-C low pressure turbine blade at engine similar Reynolds and Mach numbers, but at a low free stream turbulence level. The investigation is carried out numerically by means of steady and unsteady RANS simulations for two different Reynolds numbers (100,000 and 140,000), employing the SST turbulence model coupled to the γ–Re~θt transition model. The numerical results are compared with the experimental data provided by the von Karman Institute in terms of variation of losses and blade loading between steady and unsteady inflow conditions. In general, the incoming wakes have a crucial effect both on the reduction of the separation bubble and on the modification of the blade loading. This is analyzed in detail, in order to separate these contributions.
Impact of the Expansion Ratio on the Unsteady Aerodynamics and Performance of a HP Axial Turbine
Authors: Gaetani P. , Persico G. , Spinelli A. , Mora A.
Published: September 2016

In the frame of the European research project RECORD, the flow field within a HP axial-flow turbine model was investigated experimentally for several operating conditions. A number of studies on stator-rotor interaction in HP turbines for subsonic as well as transonic/supersonic conditions were proposed in the last decades, but none of them compared different conditions for the same geometry. In this paper, the transonic condition is investigated and compared to three subsonic ones, in the frame of an entirely new experimental campaign. The research was performed at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy), where a cold-flow, closed-loop test rig is available for detailed studies on turbines and compressors. The boundary conditions resulted in keeping constant both the turbine inlet temperature and the stage outlet absolute flow direction; so far, while the expansion ratio was varied, the rotational speed was also modified accordingly.

The analysis was performed by means of a conventional five hole probe in the stator – rotor axial gap and by a fast response aerodynamic probe downstream of the rotor. The local time-averaged and phase-resolved flow field was then derived and used to analyze the stage aerodynamics and performance.

Results show that the stage expansion ratio has a dramatic impact on both the rotor aerodynamics and stage performance. In particular, Mach number effects are recognized in the stator cascade that passes from transonic to low subsonic conditions. On the rotor cascade the reduction of expansion ratio reduces significantly the Mach and Reynolds numbers and increases the incidence angle as well; the rotor loss mechanics as well as the vane-rotor interaction are greatly amplified. Correspondingly a significant variation of stage overall efficiency is recorded.
Evaluation of Kinetic Mechanisms for Direct Fired Supercritical Oxy-Combustion of Natural Gas
Authors: Coogan Shane , Gao Xiang , McClung Aaron , Sun Wenting
Published: September 2016

Existing kinetic mechanisms for natural gas combustion are not validated under supercritical oxy-fuel conditions because of the lack of experimental validation data. Our studies show that different mechanisms have different predictions under supercritical oxy-fuel conditions. Therefore, preliminary designers may experience difficulties when selecting a mechanism for a numerical model. This paper evaluates the performance of existing chemical kinetic mechanisms and produces a reduced mechanism for preliminary designers based on the results of the evaluation.

Specifically, the mechanisms considered were GRI-Mech 3.0, USC-II, San Diego 204-10-04, NUIG-I, and NUIG-III. The set of mechanisms was modeled in Cantera and compared against the literature data closest to the application range. The high pressure data set included autoignition delay time in nitrogen and argon diluents up to 85 atm and laminar flame speed in helium diluent up to 60 atm. The high carbon dioxide data set included laminar flame speed with 70% carbon dioxide diluent and the carbon monoxide species profile in an isothermal reactor with up to 95% carbon dioxide diluent.

All mechanisms performed adequately against at least one dataset. Among the evaluated mechanisms, USC-II has the best overall performance and is preferred over the other mechanisms for use in the preliminary design of supercritical oxy-combustors. This is a significant distinction; USC-II predicts slower kinetics than GRI-Mech 3.0 and San Diego 2014 at the combustor conditions expected in a recompression cycle. Finally, the global pathway selection method was used to reduce the USC-II model from 111 species, 784 reactions to a 27 species, 150 reactions mechanism. Performance of the reduced mechanism was verified against USC-II over the range relevant for high inlet temperature supercritical oxy-combustion.
Contoured Endwall Flow and Heat Transfer Experiments With Combustor Coolant and Gap Leakage Flows for a Turbine Nozzle Guide Vane
Authors: Saxena Reema , Alqefl Mahmood H. , Liu Zhao , Moon Hee-Koo , Zhang Luzeng , Simon Terrence W.
Published: September 2016

Flow in a high pressure gas turbine passage is complex, involving systems of secondary vortex flows and strong transverse pressure gradients. This complexity causes difficulty in providing film cooling coverage to the hub endwall region, which is subjected to high thermal loading due to combustor exit hot core gases. Therefore, an improved understanding of these flow features and their effects on endwall film cooling is needed to assist designers in developing efficient cooling schemes. The experimental study presented in this paper is performed on a linear, stationary, two-passage cascade representing the first stage nozzle guide vane of a high-pressure gas turbine. The sources of film cooling flows are the upstream combustor liner coolant and the leakage flow from the combustor-nozzle guide vane interfacial gap. Measurements are performed on an axisymmetrically-contoured endwall passage under conditions of various leakage mass flow rates to mainstream flow ratios (MFR= 0.5%, 1.0%, 1.5%). Flow migration and mixing are documented by measuring passage thermal fields and adiabatic effectiveness values over the endwall. It is found that, compared to our previous studies with a rotor inlet leakage slot geometry, the thin slot geometry of the nozzle leakage path gives a more uniform coolant spread over the endwall with significant coverage reaching the downstream and pressure-side regions of the passage. Interestingly, the coverage is seen to be only weakly dependent on the leakage mass low ratio and even reduce slightly with an increase in mass flow ratio above 1%, as indicated by lowered endwall adiabatic effectiveness values.
Experimental Study on Instability Characteristics of Low-Swirl Flames in a Multi-Nozzle Combustor With Different Swirling Arrays
Authors: Liu Weijie , Ge Bing , Tian Yinshen , Zang Shusheng , Weng Shilie , Li Mingjia , Xu Wenyan
Published: September 2016

This paper presents experimental study on self-excited combustion instability characteristics of premixed low-swirl flames in a multi-nozzle can combustor with counter-swirl and co-swirl arrays. Experiments were carried out over a wide range of inlet velocity from 4 m/s to 15.5 m/s and equivalence ratio from 0.5 to 0.85. Phase-locked OH planar laser-induced fluorescence was employed to measure flame shape and identify heat release rate. Four operation regions: stable combustion region, unstable combustion region, flashback region and extinguish region are observed for both array burners. The stable operating window for counter-swirl array is wider compared to the co-swirl array. Pressure fluctuation amplitude for co-swirl burner is larger than the counter-swirl arrangement at the same operating condition. In the unstable combustion region, the counter-swirl flames trigger the 2L mode of the combustion system while co-swirl flames incite three longitudinal modes with the highest amplitude near 3L. Rayleigh index distribution reveals neighboring flame interaction results in thermoacoustic coupling for multi-nozzle flames. Additionally, for counter-swirl array, thermoacoustic couplings in flame base region and shear region are also the main reasons for inducing self-excited combustion instabilities. For co-swirl array, the instability driving zones also locate at the lip region and the tail of center flame.
Investigation of a Novel Fuel Injector for Dry Low NOx Combustor
Authors: Hamza Mahmoud , Kumaran Arul , Li Jianing , Bhayaraju Umesh , Jeng San-Mou
Published: September 2016

In the present investigation, a novel fuel injection concept is developed for Dry Low NOx combustors. A multi-injector block is used for fuel-air mixing and flame stabilization. The injectors in the multi-injector block are equally spaced in a rectangular grid of 3×3. Each injector of the multi-injector block has a porous concentric tube through which fuel is injected into the annular space around the porous tube. The porous tube is made up of stainless steel with 30 μm porosity. Air enters the annular space around the porous tube through eight tubes that surround the porous tube. The fuel and air mix in the annular space between the injector wall and the porous tube.

A CO2 mixing technique is adopted to investigate the fuel-air mixing quality under non-reacting atmospheric conditions. CO2 is used to simulate the fuel. The CO2 concentrations are converted to fuel mass fractions for comparison. The experiments are carried out at pressure drop of 4% across the injector. The fuel mass fraction contours show an annular ring of low fuel concentration downstream of the individual injectors with a high concentration in the Central Toroidal Recirculation zone (CTRZ). Furthermore, PIV measurements are conducted to study the injector aerodynamics under the same operating conditions. The PIV measurements also show CTRZ downstream of the individual injector. The jet emanating from the injectors expands gradually downstream. An outer weak recirculation zone (ORZ) is also observed between the jets. Preliminary combustion experiments are carried out to observe the flame shape and heat release distribution. The flame shape follows the velocity contours. The combustion studies show that the flame length is longer. The long flame length is due to the high velocities at the exit of the injector. A probability density function (pdf) is generated for the fuel mixture fraction. The pdf is based on the mixture fraction and velocity data obtained at the exit of the injector block. Chemkin analysis is carried out to estimate the emissions based on the experimentally obtained pdfs.
A Comparative Study on the Dynamic Characteristics of Bladed Disks With Piezoelectric Network and Piezoelectric Shunt Circuit
Authors: Liu Jiuzhou , Li Lin , Deng Pengcheng , Li Chao
Published: September 2016

This paper is meant to contribute a further investigation of the dynamic characteristics of the bladed disks with piezo-network and piezo-shunt circuit. The non-engine-order (NEO) excitation is taken into account from a practical point of view, and the mechanisms of vibration suppression of the two electromechanical systems are explained by means of the modal analysis and the energy analysis. First of all, the dynamic equations are derived based on a lumped parameter electromechanical model, and a normalizing process is used to make the analysis results more general. After the modal analysis of the electromechanical systems, the vibration suppression effect is analyzed when the bladed disk is excited by the engine-order (EO) excitation and the NEO excitation respectively. Then, an energy analysis of the electromechanical systems is performed to understand the dynamic behaviors of the systems better. Finally, the effect of reducing the amplitude magnification of the mistuned bladed disk is investigated. The research results turn out that the electrical natural frequencies (induced by electrical elements) of the system with piezo-shunt circuit are dense, while those of the system with piezo-network are not. When the system is excited by an EO excitation, the energy dissipated by resistors in the shunt circuit is slightly more than that in the network. However, the former is much less than the latter when the system is excited by an NEO excitation. A statistical analysis has been performed and proved that both the piezo-shunt circuit and the piezo-network can compensate the amplitude magnification of the forced response induced by mistuning, and the piezo-network has a better performance when the bladed disk is excited by an NEO excitation.
Active Flow Control on a Highly Loaded Compressor Stator Cascade With Synthetic Jets
Authors: Qin Yong , Wang Ruoyu , Song Yanping , Chen Fu , Liu Huaping
Published: September 2016

Numerical investigations on the control effects of synthetic jets are conducted upon a highly loaded compressor stator cascade. The influence of forcing parameters including actuation frequency, jet amplitude and slot location are analyzed in detail with the single-slit synthetic jet. Besides, a new slot arrangement is put forward for the purpose of effectively controlling flow separation.

Simulation results validate the remarkable effectiveness of the single-slit synthetic jet on controlling flow separation. Owing to the coupling effect between the jet and the main flow, the actuation appears to be most efficient under the characteristic frequency of the main flow passing through the airfoil. Additionally, with the increase of jet momentum coefficient, the control effect is enhanced at first and then decreased, depending on the two aspects: the improvements of aerodynamic performance by momentum injection and the additional flow losses caused by the jet. Compared to other actuator configurations, the segment synthetic jet with three sections can more effectively deflect the end-wall cross flow and thus impede the development of corner vortex, which helps to restrain the accumulation of low momentum fluid towards the corner, emphasizing the importance of slot arrangement. Accordingly, under the optimum condition, the total pressure loss coefficient gains a 15.8% reductions and the static pressure rise coefficient is increased by 5.01%.
Experimental Study on the Film Cooling Characteristics of the Cylindrical Holes Embedded in Sine-Wave Shaped Trench
Authors: Wei Jian-sheng , Zhu Hui-ren , Liu Cun-liang , Song Hui , Liu Cong , Meng Tong
Published: September 2016

Experimental investigation has been performed to study the film cooling performance of the cylindrical holes embedded in sine-wave shaped trench. The sine-wave shaped trench is got by changing the trailing edge of the transverse trench into sine-wave shape; the holes are located next to the peaks of the wave. The sine-wave shaped trench hole is expected to get a wider spread of the cooling jet in the span-wise direction. The film cooling effectiveness and discharge coefficient of the sine-wave shaped trench hole configurations with different trench depths (0.75D, 1D) and wave peaks (1D, 2D) have been measured using the transient thermal liquid measurement technique. The blowing ratio covers a range from 0.5 to 2.0. The transverse trench hole was also investigated as a basis of comparison. Thermal and hydrodynamic fields were investigated numerically using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment. Results show that downstream the sine-wave shaped trench, the film cooling effectiveness is higher in the region between the holes. That’s due to the jet spread wider under the influence of the anti-counter-rotating vortices which caused by the sine-wave shape. With the increasing blowing ratio, the film cooling effectiveness of the sine-wave shaped trench hole increases. The larger trench depth produces higher film cooling effectiveness in the region between the holes. With the increasing wave peak, the film cooling effectiveness is increased in the region between the holes due to that more of the jet flows to the wave valley. The discharge coefficients of the sine-wave shaped trench configurations are higher than the transverse trench which means that the sine-wave shape trench has lower flow resistance.
Modelling of Axial Fan and Anti-Stall Ring on a Virtual Test Rig for Air Performance Evaluation
Authors: Bonanni Tommaso , Corsini Alessandro , Delibra Giovanni , Volponi David , Sheard Anthony G.
Published: September 2016

Market requests for higher performance fans and legal requirements to meet minimum efficiency grades drive industrial fan designers for tunnel and metro applications to study or re-think stall control solutions. This paper, therefore, focuses on how anti-stall rings work and provides a robust and fast numerical methodology to evaluate and improve their efficiency and effectiveness. Here we present a numerical study validated against available experiments on the fitting of an anti-stall ring on an axial fan for tunnel and metro operations. The study synthetizes the effects of the anti-stall ring with an actuator disk coupled to a frozen rotor model for the fan, significantly reducing the computational load required and validating the methodology. Such approach can be implemented to easily derive fan performance with different geometries of the anti-stall ring plenum as well as its fins.