bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Study on Acoustic Features of Fan Model With Leaned Stators
Authors: Rossikhin Anton A. , Pankov Sergey V. , Khaletskiy Yuri D. , Mileshin Victor I.
Published: September 2014

Results of numerical calculations of fan tone noise for three variants of swept stator are presented. In the first variant the stator vanes are not leaned. In the second variant stator vanes are leaned on 30 degrees in the direction of rotor rotation and in the last variant the vanes are leaned on 30 degrees in the opposite direction. Calculations are carried out for approach fan operational conditions. These results are compared with the experimental data for the fan under consideration obtained in the Central Institute of Aviation Motors (CIAM) C-3A acoustic test facility. Comparison showed that the method can be used for qualitative estimation of tone noise variation with the change of stator lean.
Numerical Investigation of High Bypass Ratio Fan Tone Noise
Authors: Rossikhin Anton , Pankov Sergey , Brailko Igor , Mileshin Victor
Published: September 2014

Results of the high bypass ratio (>8) turbojet fan tone noise simulations in the cutback and sideline operating conditions are presented. Calculations are performed using the method of 3D unsteady numerical calculation of interaction between fan rows implemented in the 3DAS (3 Dimensional Acoustics Solver) CIAM in-house solver. The results of computations are compared with the experimental data for the fan under consideration, obtained in the anechoic chamber of CIAM C-3A acoustic test facility. Comparison was performed for first three harmonics of tone noise for each of conditions. It showed satisfactory qualitative and quantitative agreement between the results of the simulation and the experiment.
Numerical Simulation of Gas-Solid Two Phase Flow in Fouled Axial Flow Compressor
Authors: Yang Huadong , Xu Hong
Published: September 2014

Particles contained in air can deposit on the blade surface to cause fouling when lubricating oil and water steam are existed. Fouling changes blade geometry and blade surface roughness is increased, thus aerodynamic performance is affected. Many researchers simulated axial flow compressor fouling by adding constant surface roughness and modifying blade thickness which can’t reflect the real status of fouled compressor. In this paper, reverse technology is introduced to reconstruct the solid model of fouled compressor which is imported into fluid flow simulation software. The flow of gas phase and gas-solid coupling phase are implemented to reveal the nature of flow in fouled axial flow compressor. Based on Euler-Lagrange model, this paper made numerical simulation of gas-solid two phase flow in the axial flow compressor rotor cascade. Simulation result shows that fouling causes the decrease of effective flow area, thus thermodynamic performance is degraded. Gas-solid phase flow shows that particles are not uniformly deposited on the blade surface. When particle is smaller and rotor blade is rough, it is more easily deposited on the surface. And particle mass concentration is affected by ambient conditions such as inlet temperature, rotational speed, particle diameter, particle mass flow rate.
Blade Design Criteria to Compensate the Flow Curvature Effects in H-Darrieus Wind Turbines
Authors: Balduzzi Francesco , Bianchini Alessandro , Maleci Riccardo , Ferrara Giovanni , Ferrari Lorenzo
Published: September 2014

Darrieus wind turbines are experiencing a renewed interest in the wind energy scenario, in particular whenever small and medium-size installations are considered. In these contexts, the average wind speeds are generally quite low due to scale effects and therefore the most exploited design choices for the turbines are the H-shape configuration, as the entire blade can take advantage of the maximum rotational radius, and high chord to radius ratios, in order to ensure suitable Reynolds numbers on the airfoils. By doing so, the aerodynamic effects induced by the motion of the airfoils in a curved flowpath become more evident and the airfoils themselves have to be designed to compensate these phenomena if conventional design tools based on the BEM theory are used.

In this study, fully unsteady 2D simulations were exploited to analyze a three-bladed H-Darrieus wind turbine in order to define the real flow structure and its effects on the turbine performance; in detail, the influence of both the virtual camber and the virtual incidence were investigated.

CFD results were supported by experimental data collected on full-scale models reproducing two different airfoil mountings. Finally, the proper design criteria to compensate these phenomena are proposed and their benefits on a conventional simulation with a BEM approach are discussed.
Evaluation of Different Squealer Cavity Configurations in a HPT Blade Tip Region and its Influence on the Heat Transfer
Authors: da Silva Lucilene Moraes , Tomita Jesuino Takachi , Barbosa João Roberto , Bringhenti Cleverson
Published: September 2014

In high performance turbomachines the tip region is a key point to improve aiming at high pressure ratios without high penalties. In the case of HPT, several techniques are still in development by academic research laboratories and industry. Some geometrical configurations were created at the rotor tip region, as winglets and squealers geometries. In the case of squealers, the depth of their cavity is an important parameter to evaluate, because its values can cause different flow behavior on this region. Changing the heat transfer. In this work, the rotor blade of a HPT developed in the E3 program was changed, the aim is to study the influence of the squealer cavity depth variation on its performance. The flow within the turbine was calculated using a commercial CFD package. The details of the rotor geometrical changes, the differences between a simple flat rotor tip surface and squealer configurations are discussed and presented.
Progress in Smoothed Particle Hydrodynamics to Simulate Bearing Chambers
Authors: Kruisbrink A. Ch. H. , Morvan H. P. , Pearce F. R.
Published: September 2014

In this paper some novel Smoothed Particle Hydrodynamics (SPH) concepts are presented towards a feasibility study into the use of SPH for some aero-engine applications, e.g. for internal oil or fuel applications.

A first challenge is to develop a capability to model complex wall geometries, associated with two-phase flows in gear boxes and bearing chambers for example. A demonstration is made of how such complex (for SPH) geometries can be built together with an outline of some of the wall boundary condition concepts used, including moving walls. This is an important feature for the application of SPH to engineering. Other boundary conditions are needed such as inlets, outlets and pressure boundaries, and a proper treatment of the free surface. These are outlined in the context of the proposed application.

From an SPH flow simulation viewpoint, one of the challenges is to reduce the non-physical density variations arising from boundary conditions (at wall, free surface and interface), which are responsible for non-physical pressure variations and particle dynamics.

The flow regimes found in the engineering systems outlined above involve droplets, filaments and films. It is therefore important to be able to handle the merging of fluids, as it is to model their interaction with another phase, which calls for appropriate multi-fluid and surface tension models.

This paper introduces SPH, outlines a number of concepts listed above and presents some preliminary results towards the modeling of the KIT bearing chamber, as described by Kurz et al. [1]. This work builds on a number of numerical modeling communications made by the Nottingham team to SPHERIC, the ERCOFTAC Special Interest Group (SIG) for SPH.
Effect of Novel Casing Treatment on the Suppression of Stall Precursor in a Transonic Compressor
Authors: Sun Dakun , Sun Xiaofeng , Liu Xiaohua , Lin Feng , Qun Nie Chao
Published: September 2014

A kind of novel casing treatment is proposed to realize stall margin enhancement by suppressing stall precursor in turbomachinery. In view of its different configuration and mechanism, such casing treatment is named as stall precursor-suppressed casing treatment in the present work, or SPS casing treatment for short. In the present work, the experiments of SPS casing treatment are conducted in a transonic compressor J69 Rotor/Stage. The SPS casing treatment which consists of a backchamber and a perforated plate is designed according to a proposed theoretical model. It is noted that the open area ratio of the casing treatment is only 4–12%, which is much smaller than traditional casing treatments with over 50% open area ratio. The tests show that the SPS casing treatment can improve the stall margin by 8–12% for J69 Rotor, and 4–12% for J69 Stage. Meanwhile, the mechanism of stall margin improvement with such casing treatment will be revealed in this investigation. Comparing with the evolution of the precursors without casing treatments, the propagation of the stall inception waves will be suppressed and the non-linear development of the stall process will be delayed under the casing treatment case.
High Temperature Oxidation Behaviour of Detonation-Gun-Sprayed Cr3C2-NiCr-CeO2 Coatings on Inconel-718 at 900°C
Authors: Saladi Sekar , Menghani Jyoti V. , Prakash Satya
Published: September 2014

The high temperature oxidation behavior of detonation-gun sprayed Cr3C2-NiCr coatings with and without 0.4 wt. % CeO2 additive on Ni-based superalloy inconel-718 is comparatively discussed in the present study. Oxidation studies were carried out at 900°C for 100 cycles in air under cyclic heating and cooling conditions on bare and coated superalloys. The thermo-gravimetric technique was used to establish kinetics of oxidation. X-ray diffraction, SEM/EDAX and X-ray mapping techniques were used to analyze the oxidation products of bare and coated samples. The results indicate that Cr3C2-NiCr-CeO2 coated specimen showed better oxidation resistance. The overall weight gain and parabolic rate constant of Cr3C2-NiCr-CeO2 coated specimen was found to be lowest in the present study signifying that the addition of CeO2 in Cr3C2-NiCr powder has contributed to the development of adherent and dense oxide scale on the coating at elevated temperature.
Analysis of the Stiffness of Hirth Couplings in Rod-Fastened Rotors Based on Experimental Modal Parameter Identification
Authors: Liu Xin , Yuan Qi , Liu Yang , Gao Jin
Published: September 2014

Hirth couplings are widely used to transport torque between discs in turbine machinery for the advantages of precise centering, reliable positioning and excellent structural stability. However, the stiffness of the rotor segment with Hirth couplings is less than that of the integrated structure because it is weaken in the discontinuous structure. For the rotor segment with Hirth couplings, there are two types of contact status depending on the relationship between the separate stress and the compression stress. The first type is that the whole zone of Hirth couplings is in contact, where all of the Hirth couplings make contribution to the stiffness of the rotor segment. The second type of contact status is that some zones of the Hirth couplings are separated, where the equivalent stiffness of the rotor segment is only determined by the zones which are in contact. Obtaining accurate stiffness of Hirth couplings is of great significance in rotor dynamic performance analysis. In this study, the flexural stiffness of Hirth couplings of a gas turbine was calculated by three dimensional (3D) nonlinear contact Finite Element Method (FEM), and based on which the natural frequencies of a rod-fastened rotor were investigated. The stiffness modifying method which modifies the elasticity modulus of the material in the connection segment was used to conduct modal analysis in order to evaluate the effect of the stiffness weakening of the Hirth couplings. One experimental rotor with Hirth couplings and a central tie rod was designed to verify the theoretical and numerical analysis results. According to the results, the stiffness coefficient is constant when the load factor γ is less than 1.0, which means the stiffness of the Hirth couplings segment is almost constant when the pre-tightening force is large enough to keep the whole zone of the Hirth couplings in contact. The stiffness coefficient constant is about 0.32 (specific for the investigated model). And the stiffness coefficient drops dramatically when the load factor γ exceeds 1.0, which indicates that the stiffness of the Hirth couplings segment decreases dramatically since the pre-tightening force is insufficient and the Hirth couplings are separated. The Hirth couplings segment stiffness obtained by experimental modal parameter identification turned out to be consistent with the calculated results by FEM. The modified stiffness of the Hirth couplings segment were applied on the dynamic performance analysis of a real gas turbine rotor and the accuracy of calculating results was improved.
Aerodynamic Design of a Centrifugal Compressor Stage Using an Automatic Optimization Strategy
Authors: Barsi Dario , Costa Carlo , Cravero Carlo , Ricci Gianluca
Published: September 2014

In this paper a 3D optimization process for the aerodynamic design of a centrifugal multistage compressor stage is presented using the commercial software NUMECA/Design3D. The exercise, starting from a given single stage configuration with vaned diffuser, consists in the automatic design of the vaned diffuser with a return channel in order to obtain a repetitive compressor stage for multistage compressor architecture. The design process uses the meta-model approach coupled to 3D Navier-Stokes simulations; the optimization algorithm drives the automatic design process to minimize a prescribed goal function. Only the design condition has been considered and the effect of the starting DoE population on the optimization process has been investigated. In the paper a critical analysis on the design process using the meta-model approach is performed and the most crucial issues to set up a best practice for the effective use of such technology are discussed in some detail.
Probabilistic Optimization of Two-Phase Flow Using Bayesian Models
Authors: Miki Kenji , Subramaniyan Arun , Pai Madhusudan , Balasubramanyam Preetham
Published: September 2014

Gas-liquid two-phase flows are encountered in a variety of applications such as turbo-machinery flows, gas-turbines, ram-jet and scram-jets, automotive engines and aircraft engines. Designing systems to control such flows is enormously challenging owing to the addition of new non-dimensional groups that characterize the two-phase flow system compared to a single-phase flow. Additionally, two-phase flows can exhibit non-linear hydrodynamic instabilities that determine the overall behavior of the system.

In this study, we choose a generic two-phase flow configuration that exhibits known complexities in realistic two-phase flow systems. The goal of the study is to optimize the geometry of the two-phase flow configuration with minimal computational cost. We propose a probabilistic approach to model the stochastic system and optimize the two-phase flow system under uncertain inputs. The potential benefits of the approach are highlighted along with future directions for using probabilistic design techniques to optimize two-phase flow systems.
Unsteady Compressor Performance Assessment Using Euler Solvers
Authors: Zoppellari Serena , Pachidis Vassilios
Published: September 2014

Although the use of 3D CFD simulations has become common practice, 2D and quasi-3D through-flow tools are still used to quickly assess compressor performance. These tools rely on semi-empirical models and correlations to account for complex flow features such as flow deviation and losses. The purpose of this paper is to describe the methodology that led to the development of FENICE1-PC/2D (Fast Euler Numerical Integrator for Compressor Evaluation). FENICE-PC/2D is an unsteady Euler solver which allows the prediction of complete compressor maps (i.e. forward, stalled and reversed flow). The tool offers the user the choice to run as a 2D flow solver, or as a quasi-2D solver. The latter relies on the principles of the well-established ‘parallel compressors’ technique [1], with cross flow (mass flow exchange between sectors) for the modelling of asymmetric flow fields. In particular, this paper presents the capabilities of both versions of FENICE, highlighting advantages and limitations where appropriate. The tool has been implemented in FORTRAN and verified adopting different compressor geometries. The verification was performed by imposing inlet total pressure and total temperature distortions, to assess the effect of the circumferential mass redistribution on the compressor’s overall performance. For the specific case of total pressure distortion, a comparison against available 3D CFD results was also carried out to verify the circumferential trends of various flow properties. Moreover, the total pressure distortion was used as a trigger to force the C106 compressor into stall and investigate the stall region. The study has showed that both FENICE-PC and FENICE-2D can be used effectively during the compressor preliminary design and development phase to study asymmetric and axisymmetric phenomena, hence avoiding the complexity and computational overhead associated with full 3D CFD simulations.
Expander Models for a Generic 300 MW F Class Gas Turbine for IGCC
Authors: Cerri Giovanni , Chennaoui Leila , Giovannelli Ambra , Mazzoni Stefano
Published: September 2014

Gas Turbines (GTs) for large IGCC plants need some modifications because, usually, they have been developed to be fed with Natural Gas (NG) while the Syngas from the IGCC has a lower Low Heating Value (LHV). As a consequence, the larger flow in the expander raises the compressor exit pressure, producing some instability risks.

One of the possible options consists in the modification of the Expander Flow Functions to accommodate the input pressure in a safe range. The above option modifies also the hot surface blade wall temperature with no changes in cooling flows.

In this paper flow path data, average blade temperatures, cooling flows and global performance for the Reference GT (RGT) fed with CH4 and for the modified GT fed with syngas (H2R-GT) are reported and compared.

The changes in the stagger angles to accommodate the Expander Flow functions for stable GT conditions are presented and results widely discussed.
Numerical Analysis of Gas Turbine Inlet Fogging Nozzle Manifold Pressure Drop
Authors: Zhang Hai , Zheng Qun , Chaker Mustapha , Meher-Homji Cyrus
Published: September 2014

The air pressure drop over the nozzles manifolds of inlet fogging system and the flow resistance downstream of the nozzle array (manifold) have always been an area of concern and is the object of this paper. Fogging nozzles arrays (involving several hundred nozzles) are mounted on channels and beams, downstream of the inlet filters and affect the pressure drop. The water injection angle, nozzle injection velocities and the progressive evaporation of the water droplets evaporation all influence the inlet pressure seen at the gas turbine inlet. This paper focuses on a numerical simulation investigation of flow resistance (pressure drop) of inlet fogging systems.

In this research effort, the inlet duct is meshed in order to compute the pressure drop over the nozzles frames in fogging and non-fogging conditions. First, the resistance coefficients of an air intake filter are obtained by numerical and experimental methods, and then the coefficients are used for the simulation of the inlet duct by considering the filter as a porous media. Effects of nozzle spread pattern and water injection pattern are then modeled. The results indicate that injection velocity and arrangement of nozzles could have significant effects on the pressure drop and intake distortion, which will affect compressor performance. This paper provides a comprehensive analysis of the pressure drop and evaporation of inlet fogging and will be of value to gas turbine inlet fogging system designers and users.
Prediction of Heat Transfer With Cavity Flow Modeling for Engine Design
Authors: Sasaki Yukie , Hisaeda Koutarou , Matsuno Shinsuke , Nagao Takahisa , Kouwa Junya
Published: September 2014

In this paper, in order to improve temperature prediction, 2D axisymmetric CFD analysis has been implemented to determine the cavity flow network in Finite Difference Method (FDM) thermal analysis model. With this work process, for example, the complex recirculation of cavity flow can be considered in FDM thermal analysis.

In the beginning, the rig test of simplified cavity with rotating disk and PIV measurement are carried out to investigate the flow structure in the cavity and to validate CFD analysis. CFD result has matched well with the measurement data of PIV, and it has been found that SST k-ω turbulent model provides the most reliable result by the sensitivity study. The study result also helps to choose the most suitable scheme of discretization and the method of pressure correction. Then, the modeling of the cavity flow network based on CFD analysis result has been applied to the thermal analysis for the aero-engine. Compared with the measured data, the result with this modeling shows that temperature prediction has been well improved.
Numerical and Experimental Investigation of Micro-Jet on the Suction Side of a Supersonic Turbine Cascade
Authors: Liu Jian , Qiao Wei-Yang , Huang Peng , Chen Wei-Jie
Published: September 2014

This paper aims to numerically and experimentally analyze the effect of the micro-jet on the suction side (SS) of the transonic high-pressure turbine cascade, which could enable the possibility of the mass matching for turbine of the variable cycle engine (VCE) when it transforms working conditions according to flight demands. The experimental study had been conducted in a transonic and supersonic cascade wind tunnel to observe the influence of this kind of flow control technique on aerodynamic performance, operated at different exit Mach numbers. The nozzle guide vane with convergent-divergent passage was investigated in this paper. Two-dimensional steady simulations were performed to investigate the influence of the flow control method to exploit the potential of the application of this method in the design of high-pressure (HP) turbine for VCE.

Results of the numerical simulations and experiments indicated that micro-jet on the SS of the turbine blade would generate a separation zone near the jet slot, which would reduce the genuine throat area of the turbine passage and thus change the mass flow rate through the passage of the turbine cascade significantly. Also, velocity at the passage throat would be reduced due to the application of SS micro-jet, which would also contribute to the reduction of the mass flow rate through the turbine passage. However, extended total pressure loss was introduced with SS micro-jet.
A Thermodynamic Evaluation of GTCC/IGCC Based on a Quasi-One-Dimensional Turbine Cooling Model
Authors: Li Zhen , Zhao Lifeng , Wang Bo , Chi Jinling , Zhang Shijie , Xiao Yunhan
Published: September 2014

Developing an advanced gas turbine (GT) can have a significant impact on the thermodynamic performance of the GT combined cycle (GTCC) and the integrated gasification combined cycle (IGCC). Owing to the importance of system evaluation, it is essential to find ways to accurately predict the performance of state-of-the-art GTs through an accurate and reliable turbine cooling model. Thus, a quasi-one-dimensional (quasi-1D) turbine cooling model, which considers the film cooling and thermal barrier coating (TBC), is established and verified in this work. The model parameters, ηc,∞, ηt,∞, Z, rfc, Bitbc and Tbmx, which represent compressor and turbine efficiencies, convective cooling technology level, film cooling coefficient, Biot number of TBC and allowed maximal temperature of turbine blade, respectively, are confirmed. Reference is made to current advanced GTs during the modeling process. More importantly, the impacts of combustor exit temperature (Tcot), pressure ratio (PR), and cooling approaches on the thermodynamic performance of GTCC are all evaluated based on the quasi-1D turbine cooling model. Results show that the GTCC net efficiency does not always increase along with the increase of Tcot, under the premise of maintaining the cooling technology. The optimal PR, when the GTCC efficiency peaks, exists at each Tcot. In addition, the net efficiency of GTCC, which adopts a closed-loop steam cooling, is improved by about 2 to 3 percentage points compared with that of the conventional open-loop air cooling approach.

Furthermore, the IGCC thermodynamic performance potential is greatly affected by GTCC. It is estimated that the net efficiency of IGCC integrated with 1700 °C-class GT has a total improvement of about 6 percentage points relative to that of IGCC integrated with a GE PG9351FA GT.
The Optimization of an Integrated Strut OGV Configuration
Authors: Xie Yadong , Yang Xiaohe , Ding Jianguo , Liu Xiaofeng , Feng Jinzhang
Published: September 2014

In a core-mounted high-bypass ratio aero engine the bypass strut is designed to support the intermediate casing and to go the RDF (radial drive shaft) of a large diameter. Therefore the maximum thickness of the strut and maximum thickness distribution along the chord are restricted by the maximum diameter of the RDF.

In order to enhance the total pressure recovery coefficient as well as reducing the backpressure circumferential variation, in this paper we describe the optimization of a datum configuration of the circumferential integrated strut OGV (Outlet Guide Vane).

The datum configuration was designed based on an original configuration in which OGV and struts are separated axially. In the datum configuration, OGV is moved down-stream to be combined with the struts. The combined strut not only supports the casing as discussed above but also plays the role of turning the flow from the upstream fan to the axial direction. At the same time, the maximum thickness of the strut is about 8 times thicker than that of the OGV. The datum configuration will reduce noise because of larger axial distance between fan and OGVs as well as reducing weight because of fewer struts used in datum configuration.

A re-staggering of OGV with sweep and dihedral both at the tip and hub will be used to optimize this datum configuration. Both datum configuration and optimized configuration will be compared with respected to the pressure loss included in the OGV and struts and the backpressure circumferential distribution variation.
Wind Turbulence Behavior and Study of Tower Distortion and Scatter Factors
Authors: Rehman Shafiqur , Al-Hadhrami Luai M.
Published: September 2014

The performance of wind speed sensors installed at different heights on a 40-meter mast was evaluated during 3 months between July 01, 2006 and April 01, 2009. This evaluation involved estimating the tower distortion factor (TDF) and the scatter factor, and studying the correlation between the co-located wind speed sensors. A total of 23,730 hourly mean wind speed records were used to evaluate each sensor. The overall values of the tower distortion of the wind speed measured by sensors installed at 40 and 30m were found to be 0.025 and 0.021 without tower shading, and 0.047 and 0.035 with tower shading. As indicated by the slightly decreasing TDF values the wind speed measured by the sensors is not distorted with time. Tower shading effect for the wind speed sensor WS5 at 40 meters is pronounced (>1) when wind direction range from 169° to 195°, while that for the wind speed sensors at 30 meters and WS6 at 40 meters, it is less than one when the wind direction is in the 240° to 270° range. The wind speed sensors at 30meters displayed similar behavior and the scatter factor for wind speed sensors at 40meters is higher than that for those at 30meters.
Improved Film Cooling Effectiveness With a Round Film Cooling Hole Embedded in a Contoured Crater
Authors: Kalghatgi Prasad , Acharya Sumanta
Published: September 2014

Studies of film cooling holes embedded in craters and trenches have shown significant improvements in the film cooling performance. In this paper a new design of a round film cooling hole embedded in a contoured crater is proposed for improved film cooling effectiveness over existing crater designs. The proposed design of the contour aims to generate a pair of vortices that counter and diminish the near-field development of the main kidney-pair vortex generated by the flm cooling jet. With a weakened kidney-pair vortex, the coolant jet is expected to stay closer to the wall, reduce mixing, and therefore increase cooling effectiveness. In the present study, the performance of the proposed contoured crater design is evaluated for depth between 0.2D and 0.75D. A round film cooling hole with a 35° inclined short delivery tube (l/D = 1.75), free stream Reynolds number ReD = 16000 and density ratio of coolant to free stream fluid ρj/ρ∞ = 2.0 is used as the baseline case. Hydrodynamic and thermal fields for all cases are investigated numerically using large eddy simulation technique. The baseline case results are validated with published experimental data. The performance of the new crater design for various crater depths and blowing ratios are compared with the baseline case. Results are also compared with other reported crater designs with similar flow conditions and crater depth. Performance improvement in cooling effectiveness of over 100% of the corresponding baseline case is observed for the contoured crater.
Effect of Entrance Geometry and Rotation on Heat Transfer in a Narrow (AR = 1:4) Rectangular Internal Cooling Channel
Authors: Saha Krishnendu , Acharya Sumanta
Published: September 2014

This paper studies the effect of entrance geometries on the heat transfer and fluid flow in a narrow aspect ratio (AR = 1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade, under rotating condition. Numerical simulations are performed to understand the role of the rotation generated forces on the flow for different entrance geometries representative of those encountered in practice. Three different entrance geometries are tested: a S-shape entrance, a 90 degree bend entrance and a twisted entrance that changes its aspect ratio along its length. Numerical simulations are run at a constant Reynolds number (Re = 15000), for a range of rotation numbers (Ro = 0–0.2) and density ratios (DR = 0–0.4). Detailed heat transfer coefficient data at the leading and trailing walls are presented along with streamline profiles at different cross sectional planes that provide an insight into the flow field. It is seen that the entrance profile upstream of the actual test section is significantly different for the different entrance geometries, and has a significant impact on the rotation generated secondary flows. Non-uniformity in flow distribution at the exit of entrance geometry is small for the S-shape entrance while the non-uniformity is prominent at the exit of the changing AR entrance geometry. The entrance effect dies down as the flow progresses further downstream inside the cooling channel and the rotation effect becomes dominant.
Resolving Large- and Small-Scale Structures in the Swirl Flow of a Typical Land-Based Gas Turbine Combustor Single Nozzle Rig
Authors: Katreddy R. K. R. , Chakravarthy S. R.
Published: September 2014

The present study focuses on identifying and resolving large-scale energy containing structures and turbulent eddies in a typical gas turbine combustor single nozzle rig, using particle image velocimetry in cold flow. A generic fuel-air nozzle through a swirler is integrated with a sudden expansion square duct with optical access to perform laser diagnostics. Experiments are conducted to analyze the swirl flow field under starting and operating flow conditions. Three-component velocities are obtained in cross-sectional planes of Z/D = 0, 1.25, and 2.5 (normalized by the nozzle diameter), and two-component velocities are obtained in the mid-plane along the longitudinal (Z-) axis from Z/D = 0 to 2.5D. Velocity splitting is performed using spatial Gaussian smoothing with a kernel with filter width equal to integral scale is performed over the velocity fields to resolve the field of large-scale energy containing eddies. Proper orthogonal decomposition is performed over the large-scale velocity field, and the modes obtained indicate the existence of the precessing vortex core (PVC), formation of small scales Kelvin-Helmholtz (K-H) vortices for Z/D < 1.25D, and large-scale growing K-H structures in 1.25D < Z/D < 2.5D. Turbulent kinetic energy (TKE) is obtained from the turbulent velocity fluctuations below the integral length scale and is observed to be higher at the interface of the corner recirculation zone (CRZ) and central toroidal recirculation zone (CTRZ). Resolving the swirl velocity field obtained in the above manner into large-scale structures formed by the PVC, CTRZ, K-H vortices, CRZ, and small-scale turbulence field, indicates the clear distinction in rapid mixing zones and unsteady convective zones. The length-scales and zones of these structures within the swirl combustor are identified.
Robust Compressor Blades for Desensitizing Operational Tip Clearance Variations
Authors: Seshadri Pranay , Shahpar Shahrokh , Parks Geoffrey T.
Published: September 2014

Robust design is a multi-objective optimization framework for obtaining designs that perform favorably under uncertainty. In this paper robust design is used to redesign a highly loaded, transonic rotor blade with a desensitized tip clearance. The tip gap is initially assumed to be uncertain from 0.5 to 0.85% span, and characterized by a beta distribution. This uncertainty is then fed to a multi-objective optimizer and iterated upon. For each iteration of the optimizer, 3D-RANS computations for two different tip gaps are carried out. Once the simulations are complete, stochastic collocation is used to generate mean and variance in efficiency values, which form the two optimization objectives.

Two such robust design studies are carried out: one using 3D blade engineering design parameters (axial sweep, tangential lean, re-cambering and skew) and the other utilizing suction and pressure side surface perturbations (with bumps). A design is selected from each Pareto front. These designs are robust: they exhibit a greater mean efficiency and lower variance in efficiency compared to the datum blade. Both robust designs were also observed to have significantly higher aft and reduced fore tip loading. This resulted in a weaker clearance vortex, wall jet and double leakage flow, all of which lead to reduced mixed-out losses. Interestingly, the robust designs did not show an increase in total pressure at the tip. It is believed that this is due to a trade-off between fore-loading the tip and obtaining a favorable total pressure rise and higher mixed-out losses, or aft-loading the tip, obtaining a lower pressure rise and lower mixed-out losses.
Part Load Behavior of a Micro Gas Turbine Fed With Different Fuels
Authors: Calabria Raffaela , Chiariello Fabio , Massoli Patrizio , Reale Fabrizio
Published: September 2014

The performance of a micro gas turbine in terms of global efficiency and exhaust emissions at different loads and methane-hydrogen blends has been experimentally studied. The load was varied from full load down to half load. A critical comparison between experimental data and results of the 3D CFD analysis of the combustor is discussed in order to study the effects of part load operation. Additional objective of the present study is to extend the numerical analysis of the combustor in order to describe the influence of a wider range of hydrogen concentrations in the fuel gas mixture. Numerical simulations were performed through the commercial code ANSYS CFX 14.5. Turbulence model adopted was the RSM RANS model, which ensures a good evaluation of effects of swirled turbulent flows in the combustion chamber. The oxidation of methane is simulated by using multistep kinetics models. They assure a better reproduction of CO emissions with load. Boundary and initial conditions were defined by using experimental data, when available, and results of numerical matching analysis, which assumes importance in case of absence of specific measurements at combustor inlet. Discussion of results is mainly focused on the variation in terms of exhaust gaseous emissions and temperature distributions in the combustor by varying load and fuel. A numerical evaluation of the MGT combustor behavior in critical conditions is also presented.
The Effects of Cowling Geometry, Area Ratio and Dump Gap on a Combustor Diffusion System
Authors: Shen Shanping , He Pei , Shang Mingtao , Mao Ronghai
Published: September 2014

This paper presents numerical simulation of a combustor diffusion system, mainly focusing on the effects of the cowling geometry, the area ratio of the pre-diffuser and the axial length of the dump gap. The diffusion system of a full-scale single annular combustor is analyzed, using commercial software Fluent. Six different geometries are designed and numerically analyzed. Case 1 is a baseline, for which low emission technology burning in a lean mode is adopted. Cases 2, 3, and 4 are simulated to study the influence of the cowling geometry, especially the area of cowl capture plane. The study of cowling geometry shows that the best layout is case 4, owing to its least spillage of the air from the dome region into the inner and outer annuli of combustor. The normalized total pressure loss over the combustor is 3.49%. The total pressure distribution at the inlet of the main stage is more uniform than the baseline case 1. Cases 4 and 5 are also analyzed to investigate the influences of area ratio of the pre-diffuser, which varies from 1.4 in case 4 to 1.5 in case 5. The normalized combustor total pressure loss decreased to 3.30%, whose total pressure loss of pre-diffuser decreased while the static pressure recovery coefficient of the pre-diffuser increased from 0.43 to 0.52. Cases 4 and 6 are examined for the axial length of the diffuser dump gap, which is increased by 20% from case 4 to case 6. The combustor total pressure loss increases slightly, with little impact on the pressure loss of the pre-diffuser and dump gap region.
Experimental Study on the Efficiency of Multiple Nozzle Oil Jet Pump for Lubrication System of Steam Turbine
Authors: Zhang Jun , Wang Shunsen , Mao Jingru , Yu Xin , Zhang Cong , Zhang Junjie , Xu Yatao , Sun Peng
Published: September 2014

The efficiency of the multiple nozzle oil jet pump was systematically investigated using the Mobile DTE Light Oil based on the similarity theory in experiment. The experimental condition is the same as that for the multiple nozzle oil jet pump in lubrication system of steam turbine in the power plant. Thus, the influence of the area ratio and the pressure ratio on the efficiency and the pressure ratio interval of variable conditions with stable efficiency was studied in the area ratio range of 4∼9. Results show that there is a fixed relationship between the area ratio and the pressure ratio, which leads to the high efficiency of multiple nozzle oil jet pump. However, the high efficiency value and the pressure ratio interval of variable conditions with stable efficiency show different tendencies with the changing area ratio of multiple nozzle oil jet pump. In the area ratio range of 4∼9, the pressure ratio with the high efficiency value increases by 0.03 with the decrement of 1 for the area ratio. When the area ratio is larger than 6.3, the high efficiency value increases by 1% absolutely with the area ratio decreasing by 1, but remains almost unchanged for the area ratio less than 6.3. Furthermore, the increasing area ratio widens the pressure ratio interval of variable conditions with stable efficiency. The increase of the area ratio by 1 leads to the increment of 9.7% relatively for the pressure ratio interval of variable conditions with stable efficiency. This study provides the quantitative criteria for the determination of the area ratio and the pressure ratio of multiple nozzle oil jet pump, which keeps the high and stable efficiency simultaneously. Apparently, this study has significant engineering contribution.
Numerical Studies on Application of Blended Blade and Endwall Technique on Transonic Centrifugal Compressor
Authors: Yi Weilin , Chen Zhi-min , Ji Lucheng
Published: September 2014

With the continuous improvement of pressure ratio and efficiency in centrifugal compressors, the aerodynamic load is increased significantly. Some unnoticed tiny structures are found having notable influence on centrifugal compressor performance, for example, corners profile between the end walls and the blades. Aiming at this problem, the present paper mainly focuses on the applicability of Blended Blade and EndWall (BBEW) design on the transonic centrifugal compressor.

Firstly the Krain transonic impeller is chosen and the predicted flow field is compared with detailed measurement data using commercial CFD code Numeca. The results show that the overall performances are consistent and the details of flow fields are captured accurately. Then a series of uniform value fillets along streamwise are implemented to the hub of transonic centrifugal impeller. The numerical tests show that the aerodynamic performance is deteriorated with the augment of fillets radius, but it seems that adding fillet to the hub of splitter blade can brought positive and negative returns at the same time. Next, as a preliminary original work, a kind of simple Blended Blade and EndWall (BBEW) design which adapt variable radius distribution fillets along streamwise are implemented to the hub of the impeller. Through designing different configurations, the authors find that the performances of some impellers designed by BBEW can be not only higher than impellers with uniform value fillets, but higher than original impeller slightly. In addition, some results are presented on the comparison of flow field structures in different impellers.
Numerical Investigation of Steam Turbine Exhaust Diffuser Flows and Their Three Dimensional Interaction Effects on Last Stage Efficiencies
Authors: Tanuma Tadashi , Sasao Yasuhiro , Yamamoto Satoru , Niizeki Yoshiki , Shibukawa Naoki , Saeki Hiroshi
Published: September 2014

The purpose of this paper is to present the methodology for high accurate aerodynamic numerical analysis and its design application of steam turbine down-flow type exhaust diffusers including their three dimensional flow interaction effects on last stage efficiencies.

Down-flow type exhaust diffusers are used in large scale steam turbines from 200MW to 1400MW class units for power generation plants mainly. The axial length of typical 1000MW class large scale steam turbines is about 30–40m and its four low pressure (LP) down-flow type exhaust diffusers occupy a large amount of space. The axial lengths and diameters of these exhaust diffusers contribute significantly to the size, weight, cost, and efficiency of the turbine system. The aerodynamic loss of exhaust hoods is nearly the same as that of stator and rotor blading in LP steam turbines, and there remains scope for further enhancement of steam turbine efficiency by improving the design of LP exhaust hoods.

In the design process of last stages, the average static pressure in the last stage exit is introduced accurately using numerical analysis and experimental data of model steam turbines and model diffusers. However the radial and circumferential unsteady aerodynamic interaction effects between last stages and their exhaust diffusers are still need to be investigated to increase the accuracy of the interaction effect on the last stage efficiencies.

This paper presents numerical investigation of three dimensional wet steam flows including three dimensional flow interaction effects on last stage efficiencies in a down-flow type exhaust diffuser with non-uniform inlet flow from a typical last stage with long transonic blades designed with recent aerodynamic and mechanical design technology.
Ignition Probability in a Stratified Turbulent Flow With a Sunken Fire Igniter
Authors: Sforzo Brandon , Kim Jaecheol , Jagoda Jeff , Seitzman Jerry
Published: September 2014

The evolution of a spark kernel ejected by a sunken fire igniter into a turbulent, fuel-air stratified cross-flow was studied both experimentally and using a model in a configuration that is similar to the conditions found in turbine engine combustors. This study allows for variations in the transit time of the kernel across a uniform non-flammable region, before entering a second stream containing a flammable fuel-air mixture. High speed schlieren and emission imaging systems are used to visualize the evolution of the kernel and determine the probability of ignition based on measurements over many spark events. Experiments are performed for a range of mean velocities, transit times, inlet (preheat) temperatures, flammable zone equivalence ratios, and non-flammable zone equivalence ratios. In addition to the typical dependence of ignition on the equivalence ratio of the flammable mixture, the results indicate the strong influence of the kernel transit time and the inlet flow temperature on the probability of ignition. The entrainment between the kernel and the surrounding flow appears to be primarily controlled by the kernel ejection-induced flowfield. Reduced-order modeling suggests that the lowering of the kernel temperature associated with entrainment of the non-flammable mixture significantly reduces the ignition probability, and leads to the conclusion that the presence of fuel close to the igniter is necessary to ensure reliable ignition under adverse conditions.