bluuebunny/crossref_metadata_2025 huggingface dataset:
Life Prediction of Directionally Solidified Air Cooled HPT Gas Turbine Blade Used in a Supersonic Aircraft Using FEM
Authors: Muthu S. Esakki , Dileep S. , Kumar S. Saji , Girish D. K.
Published: July 2018

Life estimation of Directionally Solidified (DS) MARM-247 HPT gas turbine blade used in a turbofan engine of a supersonic aircraft is presented. These blades were drafted into the engine as a replacement for the polycrystal (NIMONIC) blades since a more efficient, reliable and durable material with high strength and temperature resistance was required to further enhance the life of the turbine blade and the efficiency of the power generation process. The supersonic aircraft is having a repeated mission cycle of a fast acceleration from idle, a 1hr cruise at Mach 1.5 and a fast deceleration to idle. The mission cycle which is a repetition of acceleration, cruise and deceleration cycles can produce wide variety of complex loading conditions which can result in HCF, LCF and creep damage of the turbine blade. Empirical equation of the universal slope developed by Manson was used to estimate the damage component due to LCF. The cumulative stresses and strains due to creep as a function of time was determined using Time hardening rule. Creep data for MARM-247 was correlated using LMP to predict the lives to 1% of creep strain at worst possible combination of temperature and stress value. Damage due to creep per mission cycle was determined using Life fraction Rule proposed by Robinson and Taira. The vibration characteristics of the turbine blade were predicted using Modal analysis. Campbell diagram was plotted to ascertain whether any nozzle passing frequency fall within the working range of the blade. Harmonic analysis was carried out to evaluate the magnitude of the alternating stresses resulting from the blade vibrations at resonance during the acceleration and deceleration cycle. HCF life of the turbine blade was assessed using Goodman diagram. The total damage of the turbine blade per mission cycle due to the above loading was assumed as the combination of the individual damage due to fatigue and creep. Time to failure under combined creep and fatigue damage was estimated using linear damage rule. Non linear features of FEA tool ANSYS12.0 was exploited to calculate the stress distribution, creep, plastic and the total strain encountered by the turbine blade as a function of mission cycle time. The loading spectrum associated with the mission cycle which includes the temperature, gas pressure and the speed profiles were obtained from a sophisticated engine ground test facility which was configured to simulate actual engine operating conditions. The proposed method of cyclic life estimation using FEM was validated by performing various component and engine level tests. A good agreement was observed between the calculated and observed blade lives.
Flutter and Forced Vibration Characteristics of a Turbo Fan Bladed Disk Rotor
Authors: Srinivasan Madhavan , Jeyaraman Sankarkumar , Jain Rajeev , Chandramohan Sujatha , Seshadri Sekhar AnandaRao
Published: July 2018

Aero-elastic excitation can result in excessive blade vibration, which can cause blades to fail in high cycle fatigue (HCF). A severe aero-elastic failure can result in a complete blade separation and loss of thrust and loss of a blade can mean the loss of an aircraft. The primary aeromechanical design concerns are blade flutter and forced vibration that need to be quantified at the early part of engine tests. This paper details the experimental investigation carried out on a transonic shroudless low aspect ratio fan bladed disk that experienced subsonic/transonic stall flutter and forced vibration excitation. Experiments are performed on a full scale engine using tip timing sensors flush mounted on the fan casing to characterize the vibratory responses during flutter and forced vibration conditions during engine operation. Numerical simulations are performed using computational fluid dynamic (CFD) analysis. Blade natural frequencies and mode shapes are obtained from finite element (FE) modal analysis. The experimental data captured from engine tests are used to validate the predicted results.
Studies on Impact of Inlet Viscosity Ratio, Decay Rate and Length Scales in a Cooled Turbine Stage
Authors: Srinivasan Karthik , Newman David
Published: July 2018

Modern aircraft engine designs are driven towards higher operating temperature and lower coolant flow requirements. During the flight mission, the hot gas path components encounter flows at different pressure, temperature and turbulence conditions. During design of such components, there is always an interest towards fundamental understanding of the impact of inlet turbulence on overall performance. The paper presents aerodynamic performance (stage efficiency) impact of stator inlet viscosity ratio, decay rate and length scales in a cooled turbine rig, based on CFD studies only. Through CFD studies, it is observed that an inlet length scale variation by 10 times could impact the aerodynamic efficiency by ∼0.5% to 4% depending on the size of the length scale. Efficiency drops with higher flow length scales and turbulence intensity. The length scale effects are observed to be more predominant with high turbulence intensities than at low turbulence intensities. Similarly a viscosity ratio increase by 1000 times can decrease efficiency by < 0.5% in the lower bounds and can drastically increase to ∼ 3% at higher bounds. The efficiency drop can be as much as 2.5 % for a decay rate change from 0.01 to 1 for viscosity ratio of 10000.
Enhanced Fuel Flexibility and Emissions Compliance for Gas Turbines Through Model Based Controls Technology
Authors: Malapaty Ranjith , M. V. J. J. Suresh
Published: July 2018

The world is facing complex and mounting environmental challenges. Increased fuel costs and increased market capacity in power generation markets is driving a transformation in power plant operations. Power plants are seeking ways to maximize revenue potential during peak conditions and minimize operational costs during off-peak conditions. Although proven natural gas reserves have increased globally by nearly 50% over the last 20 years, much of this growth has been focused in select regions and countries. In parallel to the discovery of new reserves is the increase in power demand across the globe. However, there are many regions of the globe in which power demand is not being matched by increased local supplies of natural gas, or in infrastructure required to supply natural gas to power generation assets. Given these drivers, there is growing global interest in LNG & alternate fuels. This phenomenon is driving a trend to explore the potential of using LNG fuels which can be easily transported across the globe as an alternative for power generation. In a carbon-constrained environment, the technology trend is for combustion systems capable of burning LNG fuel in combination with delivering the required operability. This paper will focus on developments in GE’s heavy duty gas turbines that enable operation on fuels with varying properties, providing fuel flexibility for sustainable power generation and better emissions compliance. GE’s turbine control system employs physics-based models of gas turbine operability boundaries (e.g., emissions, combustion dynamics, etc.), to continuously estimate current boundary levels and make adjustments as required.
Bearing Failure Investigation of Turbomachinery Test Rig
Authors: Chappati Veera Sesha Kumar , Tijare Vijay , Alone Dilipkumar B. , Mudipally Janaki Rami Reddy , Manickam Jayaraman
Published: July 2018

This paper presents the investigation of bearing failure in a compressor test rig which has been satisfactorily in operation. Two pair of single row angular contact ball bearings, each pair in tandem, and the pairs in turn in back to back support the rotor shaft to meet compressor thrust and to provide moderate stiffness for smooth operation. Since being experimental rig, it is reassembled several times involving bearing replacements on each occasion. Recently one bearing on one side pair is found severely damaged and the other bearing of the pair with minor damage. The bearing with minor damage supported the rotor and this evaded the initial diagnostics until the time of severe damage. Initial investigation revealed that the primary cause of failure is washed off by the secondary failure. A thorough, systematic investigation with the help of fishbone approach is carried in order to find out the root cause of the failure and also to decide on new rig. This investigation revealed lack of preload as the major cause and bearing seat clearance as minor problem. New procedure is adopted to ensure proper preload and the rig is back in operation.
Steady State Thermal Analysis of an Afterburner Liner
Authors: Batchu Suresh , Kishore Kumar S.
Published: July 2018

Military aero engines employ afterburner system for increasing the reheat thrust required during combat and takeoff. During reheat the gas temperature in the afterburner is of the order of 2100K.The afterburner liner has to be cooled with the available bypass air to maintain metal temperature within allowable limits. The liner has cooling rings at the rear to cool the liner with tangential film cooling.

This paper discusses the methodology of afterburner liner metal temperature prediction and comparison with measured metal temperature during aero engine testing at reheat condition. All the modes of heat transfer are considered for thermal analysis, radiation due to higher level of gas temperature during reheat, conduction due to presence of low conductivity thermal barrier coating and convection due to higher gas velocities are considered.

At different steady state reheat conditions metal temperature are predicted and compared with measured data during aero engine testing. The predicted skin temperatures and measured temperatures are in good agreement. Empirical correlations are used for estimating the heat loads coming on the liner and adiabatic film temperature near screech holes and cooling rings. Metal temperature and thermal loads coming onto the liner are predicted with 1D code. The estimated thermal loads are applied on 3D FE model to obtain nodal temperature distribution. The thermal Analysis is carried using ANSYS software in which thermal barrier coating is also modeled.

The parameters like gas temperature, thermal barrier coating thickness, coating conductivity, and coolant mass flow distribution are considered for carrying out a sensitivity analysis of liner metal temperature.
Finite Element Analysis for Prediction of Permanent Growth of Rotating Disc of Aero Engine During Over-Speed and Burst-Speed Conditions and Validation of Results Through Experiment
Authors: Rudra Goud M. , Manjunatha C. , Venkateshwarlu M. , Patnaik B. V. A.
Published: July 2018

The service life of critical aerospace components is governed by the modes of degradation and failure such as: yielding, fatigue, fracture, creep, corrosion, wear, etc. A single disc is used for over-speed and burst-speed tests to know the growths (plastic deformation). In this paper, a cyclic symmetry sector of disc model with non linear elastic-plastic material is considered. A non-linear finite element method is utilized to determine the stress and strain state of the disc under over-speed and burst-speed conditions using material stress strain curves.

Permanent growths and strains obtained from the over-speed analysis are incorporated in the burst-speed Finite element Model. The original stress strain curve used in over-speed analysis is modified with plastic strain and used in burst-speed analysis of same disc.

Elastic strains obtained from the over-speed and burst-speed analysis are utilized in stress strain relationship equations to calculate the permanent growths at critical locations of disc.

Growths predicted from Analysis are comparable with the experimental results of disc where a maximum variation of 11% at bore and rim of disc is observed.
Effect of Film Cooling Hole Area Ratio on Adiabatic Film Cooling Effectiveness Over a Flat Plate
Authors: Felix J. , Alen J. Jim , Giridhara Babu Y. , Siva Kumar P. , Vinod Kumar N.
Published: July 2018

In the present study the film cooling performance is analyzed for a flat plate model with different hole area ratios. Here “Area Ratio” is defined as the ratio between the cross sectional area of the hole at inlet to the exit of the hole. The area ratios which are considered for analyzing are 1, 2 and 3. The models are made in a 10 mm thickness flat plate with a row of 7 holes having 5 mm diameter and at an angle of 22° towards the downstream. The first model has an area ratio of 1 with a constant cross sectional area throughout the hole. For the second and third models, the area of hole exit is diverged to the corresponding area ratios of 2 and 3 from the mid of the plate. The divergence of hole is made with the area extended towards the downstream. A stainless steel sheet with a low thermal conductivity substrate is placed at the downstream of test model. To study the film cooling performance, two parameters have been considered namely, convective heat transfer coefficient and adiabatic film cooling effectiveness. Both the film effectiveness and convective heat transfer coefficients can be obtained from the same test plate setup. The heat transfer coefficient is obtained by constant heat flux boundary condition over the stainless steel sheet by heating it through current supply. For the film cooling effectiveness measurement, the mainstream is kept at atmospheric temperature and the coolant is maintained at a temperature to attain a constant density ratio equal to 1.3. Experiments are carried out at various blowing ratios in the range of 0.5 to 2. The temperature measurement over the flat plate is measured through an IR camera. Among the considered three models, the model with the higher area ratio had shown higher adiabatic film cooling effectiveness. On analyzing the heat transfer coefficient distribution, no significant changes were found for all the models.
A Numerical Model for Unsteady Oil Film Motion in Aero-Engine Bearing Chambers and Experimental Verification
Authors: Liu Zhenxia , Zhao Jingyu , Hu Jianping , Lu Yaguo
Published: July 2018

The work presented here focusing on the motion of oil film heat and mass transfer. A complete mathematical model based on theoretical study to solve three-dimensional unsteady oil film motion was established. Numerical simulation for different test rigs (bearing chamber test rig of Karlsruhe Institute of Technology (KIT) and rotating cylinder test rig of Northwestern Polytechnical University (NPU)) and different working conditions was carried out by using CFD commercial software. Particle tracks, oil film thickness change history and film stripping were studied, and the numerical results of oil film thickness were obtained.

The numerical results show that the motion of the oil film will reach the state of basic stability for unsteady oil flow, and a development process from the oil film formation to basic stability in this paper is less than 1.5 seconds. Moreover, comparison between the numerical results and the experimental values shows that the maximum error of oil film thickness is less than 7% at the measurement points under the calculation conditions, which indicates the proposed computational model to solve unsteady oil film motion is a valuable technical means for the study of oil film movement mechanism and oil film heat and mass transfer.
Weld Ductility Evaluation of Aeroengine Materials by Performing Bend Tests
Authors: Petley Vijay , Verma Shweta , Ashique K. M. , Purushothama D. M. , Rajendran R.
Published: July 2018

Welding is an integral part of the fabrication process for realization of the components and sub-components for any structural system. The weld process and the evaluation of the weld zone properties become more significant for the critical application like structural components of an aero engine. Standard tensile testing of the welded specimens provides the ductility for the composite joint i.e. the parent, heat affected zone and the weld zone. Standard bend tests (Three point bend) are specified as the qualitative tests for evaluating the ductility of the welded joints. For these bend tests, the ductility of the parent specimens are utilized for calculating the bend test parameters and the bend angles are specified after performing the tests on the parent specimens. But during the bend tests on the TIG welded specimens of specific materials and the thickness combinations like Ti-64 with thickness of 1.2 and 4.0 mm, it was observed that the specimens used to get fractured during bend tests before the specified bend angle is achieved. Though this suggests that the ductility of the welded joint is lesser than that of the parent specimens, it is not quantified with the premature failure of the test specimen. In the present study, bend tests on these material samples are performed on TIG welded specimens. Load and the displacement were monitored during the bend tests and maximum plunger depth and bend angle was recorded. A term called virtual plunger diameter is introduced in this work. Based on this plunger depth, span length, virtual plunger diameter is estimated at the onset of the fracture. From this plunger diameter the ductility of the weld joint is recalculated and is found to be lesser than the ductility of the welded joint as observed during the tensile test. The proposed bend test result analysis technique provides the quantitative results i.e. weld ductility from the bend test data.
Life Extension of Axial Compressor Disc of a Turbo-Shaft Engine
Authors: Muthu S. Esakki , Selwyn A. , Roy Hardik , Degaonkar Girish K.
Published: July 2018

The cost of aero engine and its maintenance is going higher day by day, the life of the critical parts and its availability play a major role to keep the fleet in operation. Engine components works under extremely high stress levels so the life of the components is limited. Most of the critical components are retired by the operator before they reach their theoretical life. The uncertainty in accurate life prediction induces the risk which is the cause for premature retirement. Metallurgical study of the life expired components and fatigue/fracture methodologies are used to estimate the residual useful life of the components.

This paper describes the life extension methodology used for an axial compressor disc of turbo-shaft engine. The disc has completed its safe life in the aircraft. The studies are carried out to determine the residual life of the disc to extend the life. Two life completed disc are identified. Specimens are cut from the disc for tensile test and LCF tests. Probable mission cycles for the aircraft are collected and fatigue cycle data are prepared. Finite element based stress analysis is carried out using Ansys software with multi axial loads. Based on the stress analysis, disc bore and pin hole are identified as critical area. The computed stress–strain response is used to predict the fatigue crack initiation life using effective strain range parameters on the critical areas. Fatigue damage for different mission cycles are also calculated using critical plane approach. The plane where crack initiate is called critical plane and it is calculated iteratively based on the nodal stress result. Life for different mission cycle is calculated and minimum life of all the cycle is determined. This calculated life gives the amount of residual life available and the scope for life extension. The disc is tested in cyclic spin test rig to confirm the remaining potential life. The test results are compared with the numerical estimation. It is found that the residual life of the life completed component has got potential life of one more overhaul.
Modal Analysis of Multi Layer Viscoelastic Rotors Considering Higher Order Model
Authors: Chandraker S. , Roy H. , Maurya G.
Published: July 2018

This paper involves the development of mathematical model of multilayered viscoelastic rotor using beam finite element and at the same time studying their modal analysis. The operator based constitutive relationship is used to obtain the equations of motion. The FE formulation contents higher order system where the number of order increases with the number of layers exists in the rotor shaft. Under these conditions, the complex modal behaviour of the rotor-shaft is studied to get an insight of the dynamic characteristics of the system, in terms of Modal Damping Factors, Stability Limit of Spin-speed (SLS), the directional Frequency Response Function (dFRF) as well as the direction of whirl of the shaft in different modes. Many researchers adopted this methodology for obtaining the dynamic behaviour of a second order system. This work is started by motivation of the absentia of work for higher order system.
Numerical Studies on the Effect of Design Trim on Aerodynamic Performance of a Micro Propeller for MAV Application
Authors: Ranjanagi Sagar , Nagpurwala Quamber H. , Subbaramu S.
Published: July 2018

Of late, the aerospace industry has taken increasing interest in Micro Air Vehicles (MAV) powered by electric motor driven micro propellers. The endurance of the MAV largely depends upon the propulsive efficiency of its propeller. This has created a need for improved design of propellers through an in-depth understanding of the relevant aerodynamics. Design of micro propellers operating at low Reynolds numbers with sufficiently high propulsive efficiency is a challenging task. This paper deals with the parametric studies on a micro propeller for MAV application through numerical simulations. A propeller of known geometry was selected from the published literature. Geometrical model of the baseline propeller was prepared using CATIA V5 software and CFD analysis was carried out using ANSYS FLUENT 12.0 software. The baseline geometry of the micro propeller was modified by varying the spanwise position of maximum blade chord, maximum chord length, and pitch to diameter ratio to generate new design variants. The performances of these design variants were analysed through CFD simulations and compared in terms of variation of efficiency, torque coefficient and thrust coefficient against advance ratio. No significant change was observed in performance by changing the location of maximum blade chord. However, the required thrust of 1 N was achieved by increasing the chord length by 1.2 times the base line design at an efficiency of 64.2%. The propeller efficiency was further increased to 70.8% at an increased pitch to diameter ratio of 1.2 and at an advance ratio of 1.033.
Numerical Simulations of Liquid Jet Break Up in a Crossflow
Authors: Jain Mohit , Tomar Gaurav , Ravikrishna R. V. , Prakash R. Surya , Raghunandan B. N.
Published: July 2018

Atomization is the process of disintegration of a liquid jet into ligaments and subsequently into smaller droplets. A liquid jet injected from a circular orifice into cross flow of air undergoes atomization primarily due to the interaction of the two phases rather than an intrinsic break up. Direct numerical simulation of this process resolving the finest droplets is computationally very expensive and impractical. In the present study, we resort to multiscale modelling to reduce the computational cost. The primary break up of the liquid jet is simulated using Gerris, an open source code, which employs Volume-of-Fluid (VOF) algorithm. The smallest droplets formed during primary atomization are modeled as Lagrangian particles. This one-way coupling approach is validated with the help of the simple test case of tracking a particle in a Taylor-Green vortex. The temporal evolution of the liquid jet forming the spray is captured and the flattening of the cylindrical liquid column prior to breakup is observed. The size distribution of the resultant droplets is presented at different distances downstream from the location of injection and their spatial evolution is analyzed.
Design and Testing of a Can Combustor for a Small Gas Turbine Application
Authors: Narayana Rao K. V. L. , Kumar N. Ravi , Ramesha G. , Devathathan M.
Published: July 2018

Can type combustors are robust, with ease of design, manufacturing and testing. They are extensively used in industrial gas turbines and aero engines. This paper is mainly based on the work carried out in designing and testing a can type combustion chamber which is operated using JET-A1 fuel. Based on the design requirements, the combustor is designed, fabricated and tested. The experimental results are analysed and compared with the design requirements. The basic dimensions of the combustor, like casing diameter, liner diameter, liner length and liner hole distribution are estimated through a proprietary developed code. An axial flow air swirler with 8 vanes and vane angle of 45 degree is designed to create a re-circulation zone for stabilizing the flame. The Monarch 4.0 GPH fuel nozzle with a cone angle of 80 degree is used. The igniter used is a high energy igniter with ignition energy of 2J and 60 sparks per minute. The combustor is modelled, meshed and analysed using the commercially available ansys-cfx code. The geometry of the combustor is modified iteratively based on the CFD results to meet the design requirements such as pressure loss and pattern factor. The combustor is fabricated using Ni-75 sheet of 1 mm thickness. A small combustor test facility is established. The combustor rig is tested for 50 Hours. The experimental results showed a blow-out phenomenon while the mass flow rate through the combustor is increased beyond a limit. Further through CFD analysis one of the cause for early blow out is identified to be a high mass flow rate through the swirler. The swirler area is partially blocked and many configurations are analysed. The optimum configuration is selected based on the flame position in the primary zone. The change in swirler area is implemented in the test model and further testing is carried out. The experimental results showed that the blow-out limit of the combustor is increased to a good extent. Hence the effect of swirler flow rate on recirculation zone length and flame blow out is also studied and presented. The experimental results showed that the pressure loss and pattern factor are in agreement with the design requirements.
Computational Study on Pressure Side Film Cooling and Flow Structure
Authors: Dhanasegaran Radheesh , Venkatachalapathy Girish , Gnanasekaran Nagarajan
Published: July 2018

A computational investigation is carried out to understand the film cooling performance and flow phenomenon on a pressure side of gas turbine airfoil. A specific geometry with multiple rows of cylindrical holes is considered on the pressure surface and opposite to which a flat surface is kept so as to avoid effect of imposed flow conditions. Meshing of the present model is done by using GAMBIT. Computations are carried out with K-epsilon Realizable model available in the commercial code FLUENT. The film cooling performance is discussed with flow structure followed by the effectiveness distribution on the pressure surface. The blowing ratio is varied from 0.4–2.4 and it is found that, at very low blowing ratio cases in the initial part of the pressure surface higher effectiveness values are observed but at higher blowing ratio these values become very low whereas close to the trailing edge side the effectiveness distribution is just the reverse. It was found that the optimum blowing ratio was close to unity where better flow and temperature distribution were observed.
Correlation Between FEA and Testing for HCF-Safety Assessment of an Aero Engine Turbine Rotor Blade
Authors: Khan Reshma , Kamili Owais Majid , Togere Nagabhushana Suresh , Subbaram Shylaja
Published: July 2018

High Cycle Fatigue (HCF) of turbine blades is one of the major design concerns in an Aero Gas turbine engine developmental program. Resonance induced High Cycle Fatigue (HCF) failure of blades may result in engine catastrophe having expensive consequences leading to program delays and cost overruns in a project. Even though, the resonance regimes in operating envelope can be predicted using FE tools, there are uncertainties involved in theoretical prediction of blade vibratory amplitudes. If these blade amplitudes cross the allowable limits during operation, HCF failures are expected to occur. The purpose of this paper is to assess the safety of the blades from HCF point of view. An integrated approach using test data and analytical model was employed to evaluate the vibratory behavior of a Low Pressure turbine rotor blade of an Aero-Gas Turbine engine. Correlation factors between blade tip amplitudes and dynamic stresses during critical modes of vibration were established using the data from strain gages, Non Intrusive Stress Measurement System (NSMS) and FE Model. Good agreement was found between the predicted stresses using FE/NSMS and measured vibratory stresses from strain gages. Fine tuned FE model was generated for evaluation of vibratory stresses from NSMS data.

Results have shown up to 300% scatter in the dynamic responses across the blades and 2% scatter in natural frequency for a particular resonance. Amplitude–stress relationship shows linearity and is observed to be invariant across the blades. All these statistical variations in responses along-with established correlation factors were considered for the safety assessment of blades from HCF point of view.
Experimental Investigation of a Hollow Cone Spray Using Laser Diagnostics
Authors: Das Mithun , Chatterjee Souvick , Sen Swarnendu , Mukhopadhyay Achintya
Published: July 2018

Atomization of fuel is a key integral part for efficient combustion in gas turbines. This demands a thorough investigation of the spray characteristics using innovative and useful spray diagnostics techniques. In this work, an experimental study is carried out on commercial hollow cone nozzle (Lechler) using laser diagnostics techniques. A hollow cone spray is useful in many applications because of its ability to produce fine droplets. But apart from the droplet diameter, the velocity field in the spray is also an important parameter to monitor and has been addressed in this work. Kerosene is used as the test fuel which is recycled using a plunger pump providing a variation in the injection pressure from 100psi to 300psi. An innovative diagnostic technique used in this study is through illumination of the spray with a continuous laser sheet and capturing the same with a high speed camera. A ray of laser beam is converted to a planer sheet using a lens combination which is used to illuminate a cross section of the hollow cone spray. This provides a continuous planar light source which allows capturing high speed images at 285 fps. The high speed images, thus obtained are processed to understand the non-linearity associated with disintegration of the spray into fine droplets. The images are shown to follow a fractal representation and the fractal dimension is found to increase with rise in injection pressure. Also, using PDPA, the droplet diameter distribution is calculated at different spatial and radial locations at wide range of pressure.
Effect of Inflow Conditions on Wind Turbine Blade Performance
Authors: Kumar Kiran , Piragalathalwar Sudhakar , Bijlani Jitendra , Madsen Jesper
Published: July 2018

One important uncertainty still associated with the design and operation of wind turbines is the response and performance characteristics for the atmospheric inflow conditions. A very important issue in wind turbine design is the validity of the models that are used in the design process, the models used in Computational Fluid Dynamics (CFD) or the aerodynamic simulations. The aerodynamic part of the design basis has been restricted to non-shear turbulent inflow conditions. Therefore, measured detailed flow characteristics on a rotor in natural, turbulent flow environment are needed to be compared with 2D/3D CFD, wind tunnel data and other aerodynamic models. This will improve the prediction of the wind turbine response, but also represent a unique validation basis for 3D CFD computations and aerodynamic engineering models. The overall objective is to validate the CFD prediction with the field measurement.
Coolant Gas Injection on a Blunt-Nosed Re-Entry Vehicle
Authors: Joseph Jeswin , Shine S. R.
Published: July 2018

Very high thermal loads are expected in re-entry vehicles traveling at hypersonic Mach numbers due to severe aerodynamic heating. In the present study, numerical investigations are carried out to analyze the use of film cooling technology for a fully reusable and active thermal protection system of the re-entry vehicle. Simulations are done to examine the fundamental flow phenomenon and the performance of blunt body film cooling in hypersonic flows. Simulations are conducted for a blunt -nosed spacecraft flying at Mach numbers varying from 4 to 8 and 40 deg angle of attack. Film cooling holes are provided on the bottom of the blunt-nosed body. Standard values at an altitude of 30 km are used as in flow boundary conditions. The dependency of blowing ratios, stream-wise injection angle and inlet Mach number on the film cooling effectiveness are investigated. It is observed that the film cooling effectiveness reduces with increase in coolant injection angle. The film cooling performance is found to be decreasing with increase in Mach number. The results could provide useful inputs for optimization of an active thermal protection system of re-entry vehicles.
Enhancing Gas Turbine Operation With Heavy Fuel Oil
Authors: Muralidharan Vikram , Vierling Matthieu
Published: July 2018

Power generation in south Asia has witnessed a steep fall due to the shortage of natural gas supplies for power plants and poor water storage in reservoirs for low hydro power generation. Due to the current economic scenario, there is worldwide pressure to secure and make more gas and oil available to support global power needs. With constrained fuel sources and increasing environmental focus, the quest for higher efficiency would be imminent.

Natural gas combined cycle plants operate at a very high efficiency, increasing the demand for gas. At the same time, countries may continue to look for alternate fuels such as coal and liquid fuels, including crude and residual oil, to increase energy stability and security.

In over the past few decades, the technology for refining crude oil has gone through a significant transformation. With the advanced refining process, there are additional lighter distillates produced from crude that could significantly change the quality of residual oil used for producing heavy fuel.

Using poor quality residual fuel in a gas turbine to generate power could have many challenges with regards to availability and efficiency of a gas turbine. The fuel needs to be treated prior to combustion and needs a frequent turbine cleaning to recover the lost performance due to fouling.

This paper will discuss GE’s recently developed gas turbine features, including automatic water wash, smart cooldown and model based control (MBC) firing temperature control. These features could significantly increase availability and improve the average performance of heavy fuel oil (HFO). The duration of the gas turbine offline water wash sequence and the rate of output degradation due to fouling can be considerably reduced.
Improved Treatment of Anisotropic Scattering for Ultrafast Radiative Transfer Analysis
Authors: Hunter Brian , Guo Zhixiong
Published: July 2018

The necessity of conserving both scattered energy and asymmetry factor for ballistic incidence after either FVM or DOM discretization is convincingly shown by analyzing ultrafast laser radiative transfer in a cubic enclosure housing a participating medium. A phase-function normalization technique introduced previously by the present authors to correct for non-conservation of energy and asymmetry factor in diffuse radiant energy scattering is applied to scattering of ballistic incidence for the first time in 3-D FVM/DOM in order to improve treatment of anisotropic scattering through reduction of angular false scattering errors. Treatment of only the diffuse radiation will not conserve ballistic properties if the direction of ballistic incidence differs from a predetermined discrete direction. Our ultrafast radiative transfer predictions generated using the FVM and DOM are compared to benchmark Monte Carlo predictions in the literature to gauge accuracy and to illustrate the necessity of ballistic phase-function normalization. Additionally, numerical predictions of energy deposition in a tissue-phantom medium are analyzed to further clarify the importance of accurate numerical predictions. It is shown that the addition of proper ballistic phase-function treatment greatly improves predicted heat fluxes and energy deposition for anisotropic scattering and for situations where accurate numerical modeling is crucial.
Numerical Analysis of Ammonia Absorption From a Bubble Expanding at a Submerged Nozzle Into a Binary Nanofluid
Authors: Su Fengmin , Ma Hongbin , Deng Yangbo
Published: July 2018

An absorber is a major component in the absorption refrigeration systems, and its performance remarkably affects the overall system performance. A mathematical model for ammonia absorption from a bubble expanding at a submerged nozzle into a binary nanofluid was developed to analyze the effects of binary nanofluid on ammonia absorption in the forming process of a bubble. The combined effects of nanoparticles on heat transfer, mass transfer, and bubble size all were considered in the model. The concentration of nanoparticles, the radius of the nozzle and the flow rate of ammonia vapor were considered as the key parameters. The numerical results showed that the enhancement of binary nanofluid for bubble absorption has the analogous tendency with the mass transfer enhancement of binary nanofluid. The diameter of the nozzle and the flow rate of ammonia vapor hardly affect the enhancement of the binary nanofluid for the absorption of bubble growing stage. The current investigation can result in a better understanding of the absorption process occurring in thermally-driven absorption refrigeration systems.
Bubble Formation on the Surface of Laser-Irradiated Nano-Sized Particles
Authors: Kwak Ho-Young , Oh Jaekyoon , Yoo Yungpil , Mahmood Shahid
Published: July 2018

It is well known that a phase transition from liquid to vapor occurs in the thermal boundary layer adjacent to a nanoparticle that has a high temperature upon irradiation with a high-power laser. In this study, the mechanism by which the evaporated layer adjacent to a laser-irradiated nanoparticle can grow as a bubble was investigated. The pressure of the evaporated liquid volume due to heat diffusion from the irradiated nanoparticle was estimated using a bubble nucleation model based on molecular interactions. The bubble wall motion was obtained using the Keller-Miksis equation. The density and temperature inside the bubble were obtained by solving the continuity and energy equations for the vapor inside the bubble. The evaporation of water molecules or condensation of water vapor at the vapor-liquid interface and the homogeneous nucleation of vapor were also considered. The calculated bubble radius -time curve for the bubble formed on the surface of a gold particle with a diameter of 9 nm is close to the experimental result. Our study reveals that an appropriate size of the evaporated liquid volume and a large expansion velocity are important parameters for the formation of a transient nano-sized bubble. The calculation result suggests that homogeneous condensation of vapor rather than condensation at the interface occurs.
Flooded Two-Phase Flow Dynamics and Heat Transfer With Engineered Wettability on Microstructured Surfaces
Authors: Zhou Zhou , Chen Chung-Lung
Published: July 2018

Flooding caused by excessive droplet feeding on heat dissipation area periodically occurs for droplet-based thermal management, including spray cooling and electro-wetting. The conventional highly wettable texture of surfaces, which is designed for thin film evaporation, has negligible effect on improving thermal performance during flooding. This work examines a combination of micro-pillar structures and engineered wettability that aims to improve the liquid-vapor phase change intensity and heat dissipation rate during flooding. Numerical simulation has been made to investigate the thermal and dynamic impact of the proposed combination structure on boiling and evaporation, with control variables of pillar height and pillar array density. A transient 3-D volume-of-fluid (VOF) model has been developed to analyze behaviors of bubble growth, coalescence, and departure processes. Parameters including volumetric liquid-vapor mass transfer rate, heat source temperature and heat transfer coefficient are examined. The results indicated the structured surface can reduce bubble sizes and enhance bubble departure rates. The optimized value of pillar height exists. The pillar height has more impact on cooling enhancement than pillar array density when the increased solid-liquid interface area was kept the same.
Flow and Heat Transfer in Branched Wavy Microchannels
Authors: Singh Pawan K. , Tan Hua Feng Samuel , Teo Chiang Juay , Lee Poh Seng
Published: July 2018

The Wavy channels are supposed to enhance performance of microchannel heat sink through chaotic advection. The change in boundary layer thickness (thinning) and the macroscopic mixing due to the formation of Dean’s vortices have been found to be main reasons for enhanced heat transfer in wavy microchannel. Present study carries out a detailed numerical investigation for flow and heat transfer in wavy channel. A 3D geometry for a single loop of wavy channel is modeled in GAMBIT and simulated in CFD software FLUENT. The basic dimensions were 0.15 mm width, 0.3 mm height and 1.5 mm length. The formation of Dean vortices are shown. In parametric study, the effect of Re number on the flow and heat transfer performance is shown. Heat transfer was found to be increased with Re. The effect of Aspect ratio is shown. The channel with the aspect ratio of 0.5 is found to be best among the channels studied including wavy and straight microchannels. A novel concept of secondary branches is introduced to wavy microchannel to take advantage of high pressure zone at crust. The branched wavy microchannel encouraged the secondary flow thus enhanced the macroscopic mixing. Due to disrupt of boundary layer development and its re-initialization, an improved thermal performance was achieved.
Two-Stage Phase Change Phenomenon of Water on Covered Hierarchical Structures
Authors: Chen Hsiu-hung , Zhou Zhou , Chen Chung-lung
Published: July 2018

Surface with hierarchical structures to enhance heat transfer performance has been investigated for decades. Here we present a unique two-stage vaporization phenomenon observed when the heated surface is covered to confine the thickness of liquid film. This multi-stage vaporization will be critical for optimization applications in thermal management. The hierarchical surface is prepared using: a) isotropic etching to form micro-pillars, and b) wet-chemical etching to produce silicon nanowires (SiNWs) on sidewalls of micro-pillars. Oxygen plasma was applied to modify their surface wettability from superhydrophobic to superhydrophilic. A glass slide was placed right on top of the structures, covering about half of the heated surface, and mechanically clamped by a stainless-steel block. Therefore, the liquid film is about the same height as the micro-pillars. The hierarchical surface was wetted with deionized water before being heated. There are two clear and separate stages that were observed under an high-speed camera: i) thinning while liquid is vaporizing, and ii) mixture of vaporizing and condensation until total dry-out happens. The detailed dynamics of this two-stage vaporization were explored and reported in this study.
Experimental Investigation of Heat Transfer Augmentation in Automobile Radiator With CNT/Water Nanofluid
Authors: Chougule Sandesh S. , Sahu S. K.
Published: July 2018

The trend toward higher engine power leads to larger radiators in automobile sector and increased frontal areas, resulting increased fuel consumption. Heat transfer of coolant flow through the automobile radiators is of great importance for the optimization of fuel consumption. Compaq cooling system can be manufactured by introducing nanocoolant with in automobile radiator. In this paper, heat transfer of CNT based nanocoolant has experimentally compared to that of pure water in an automobile radiator. Four different concentrations of nanofluids in the range of 0.15–1 vol. % have been prepared by the addition of CNT nanoparticles into the water. The test liquid flows through the radiator consisted of vertical tubes with rectangle cross section and air makes a cross flow inside the tube bank with constant speed. The CNT nanocoolants are synthesized by functionalization CNT (FCNT) and surface treatment (SCNT) method. The effects of type of nanofluid, variation in pH and nanoparticle concentration on the Nusselt number are deeply investigated. Results demonstrate that both nanocoolant show enormous change Nusselt number in comparison with water. The results of functionalized CNT nanocoolant with 5.5 pH show better performance than 6.8 and 9 pH nanocoolant. The surface treated CNT nanocoolant show results deterioration in heat transfer performance. Furthermore, increasing the nanoparticle concentration and nanofluid velocity enhances the Nusselt number.
Mathematical Modeling of Capillary Pumping Within Micron Sized Channels
Authors: Yang Yuelei , Zhang Dan
Published: July 2018

This paper introduces a mathematical model which can be used to simulate the capillary pumping process of a micro heat engine. The micro heat engine has micron sized channels where the capillary pumping occurs. The classic Volume of Fluids (VOF) method is applied to obtain the velocity profiles of the fluids and to track the motions of the liquid-gas interfaces. The numerical results based this model have been compared with the experimental data and the initial retard of the pumping has been found and this phenomenon can be explained by the initial capillary pressure build-ups across the liquid-gas interfaces.
A Numerical Approach in Predicting Flow Field Induced by Randomly Moving Nano Particles
Authors: Cheng Way Lee , Sadr Reza
Published: July 2018

There have been several reports that suspending nano-particles in a fluid, or nanofluids, can enhance heat transfer properties such as conductivity. However, the extend of the reported enhancement is inconsistent in the literature and the exact mechanisms that govern these observations (or phenomena) are not fully understood. Although the interaction between the fluid and suspended particles is suspected to be the main contributor to this phenomenon, literature shows contradicting conclusions in the underlying mechanism responsible for these effects. This highlights the need for development of computational tools in this area. In this study, a computational approach is developed for simulating the induced flow field by randomly moving particles suspended in a quiescent fluid. Brownian displacement is used to describe the random walk of the particles in the fluid. The steady state movement is described with simplified Navier-Stokes equation to solve for the induced fluid flow around the moving particles with constant velocity at small time steps. The unsteady behavior of the induced flow field is approximated using the velocity profiles obtained from FLUENT. Initial results show that random movements of Brownian particles suspended in the fluid induce a random flow disturbance in the flow field. It is observed that the flow statistics converge asymptotically as time-step reduces. Moreover, inclusion of the transitional movement of the particles significantly affects the results.