bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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%.
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.
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.