IU Indianapolis ScholarWorks :: Browsing by Author "Nalim, M. Razi"

Browsing by Author "Nalim, M. Razi"

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Air-Standard Aerothermodynamic Analysis of Gas Turbine Engines With Wave Rotor Combustion
(2009-09) Nalim, M. Razi; Li, H; Akbari, Pezhman
The wave rotor combustor can significantly improve gas turbine engine performance by implementing constant-volume combustion. The periodically open and closed combustor complicates thermodynamic analysis. Key cycle parameters depend on complex gas dynamics. In this study, a consistent air-standard aerothermodynamic model with variable specific heat is established. An algebraic model of the dominant gas dynamics estimates fill fraction and internal wave compression for typical port designs, using a relevant flow Mach number to represent wave amplitudes. Nonlinear equations for thermodynamic state variables are solved numerically by Newton–Raphson iteration. Performance measures and key operating conditions are predicted, and a quasi-one-dimensional computational model is used to evaluate the usefulness of the algebraic model.
Analytic Design Methods for Wave Rotor Cycles
(1994-09) Resler, Edwin L.; Moscari, Jeffrey C.; Nalim, M. Razi
A procedure to design a preliminary wave rotor cycle for any application is presented. To complete a cycle with heat addition there are two separate-but related-design steps that must be performed. Selection of a wave configuration determines the allowable amount of heat added in any case, and the ensuing wave pattern requires associated pressure discharge conditions to allow the process to be made cyclic. This procedure, when applied, gives a first estimate of the cycle performance and the necessary information for proceeding to the next step in the design process, namely, the application of a characteristic-based or other appropriate detailed one-dimensional wave calculation that locates more precisely the proper porting around the periphery of the wave rotor. Examples of the design procedure are given to demonstrate its utility and generality. These examples also illustrate the large gains In performance that might be realized with the use of wave rotor enhanced propulsion cycles.
Assessment of Combustion Modes for Internal Combustion Wave Rotors
(1999-04) Nalim, M. Razi
Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.
Coupled Dynamic Analysis of Flow in the Inlet Section of a Wave Rotor Constant Volume Combustor
(2011-12) Smith, Keith Cameron; Nalim, M. Razi; Zhu, Likun; Xie, Jian
A wave rotor constant volume combustor (WRCVC) was designed and built as a collaborative work of Rolls Royce LibertyWorks, Indiana University-Purdue University at Indianapolis (IUPUI), and Purdue University, and ran experimental tests at Purdue's Zucrow Laboratories in 2009. Instrumentation of the WRCVC rig inlet flow included temperature and pressure transducers upstream of the venturi and at the fuel delivery plane. Other instrumentation included exhaust pressures and temperatures. In addition, ion sensors, dynamic pressure sensors, and accelerometers were used to instrument the rotating hardware. The rig hardware included inlet guide vanes directly in front of the rotating hardware, which together with concern for damage potential, prevented use of any pressure transducers at the entrance to the rotor. For this reason, a complete understanding of the conditions at the WRCVC inlet is unavailable, requiring simulations of the WRCVC to estimate the inlet pressure at a specific operating condition based on airflow. The operation of a WRCVC rig test is a sequence of events over a short time span. These events include introduction of the main air flow followed by time-sequenced delivery of fuel, lighting of the ignition source, and the combustion sequence. The fast changing conditions in the rig inlet hardware make necessary a time-dependent computation of the rig inlet section in order to simulate the overall rig operation. The chosen method for computing inlet section temperature and pressure was a time-dependent lumped volume model of the inlet section hardware, using a finite difference modified Euler predictor-corrector method for computing the continuity and energy equations. This is coupled with perfect gas prediction of venturi air and fuel flow rates, pressure drag losses at the fuel nozzles, pressure losses by mass addition of the fuel or nitrogen purge, friction losses at the inlet guide vanes, and a correlation of the non-dimensional flow characteristics of the WRCVC. The flow characteristics of the WRCVC are computed by varying the non-dimensional inlet stagnation pressure and the WRCVC's operational conditions, assuming constant rotational speed and inlet stagnation temperature. This thesis documents the creation of a computer simulation of the entire WRCVC rig, to understand the pressure losses in the inlet system and the dynamic coupling of the inlet section and the WRCVC, so that an accurate prediction of the WRCVC rotor inlet conditions can be computed. This includes the computational development of the WRCVC upstream rig dynamic model, the background behind supporting computations, and results for one test sequence. The computations provide a clear explanation of why the pressures at the rotor inlet differ so much from the upstream measured values. The pressure losses correlate very well with the computer predictions and the dynamic response tracks well with the estimation of measured airflow. A simple Fortran language computer program listing is included, which students can use to simulate charging or discharging of a container.
Coupled thermal-fluid analysis with flowpath-cavity interaction in a gas turbine engine
(2013-12) Fitzpatrick, John Nathan; Wasfy, Tamer; Nalim, M. Razi; Yu, Huidan (Whitney); Anwar, Sohel
This study seeks to improve the understanding of inlet conditions of a large rotor-stator cavity in a turbofan engine, often referred to as the drive cone cavity (DCC). The inlet flow is better understood through a higher fidelity computational fluid dynamics (CFD) modeling of the inlet to the cavity, and a coupled finite element (FE) thermal to CFD fluid analysis of the cavity in order to accurately predict engine component temperatures. Accurately predicting temperature distribution in the cavity is important because temperatures directly affect the material properties including Young's modulus, yield strength, fatigue strength, creep properties. All of these properties directly affect the life of critical engine components. In addition, temperatures cause thermal expansion which changes clearances and in turn affects engine efficiency. The DCC is fed from the last stage of the high pressure compressor. One of its primary functions is to purge the air over the rotor wall to prevent it from overheating. Aero-thermal conditions within the DCC cavity are particularly challenging to predict due to the complex air flow and high heat transfer in the rotating component. Thus, in order to accurately predict metal temperatures a two-way coupled CFD-FE analysis is needed. Historically, when the cavity airflow is modeled for engine design purposes, the inlet condition has been over-simplified for the CFD analysis which impacts the results, particularly in the region around the compressor disc rim. The inlet is typically simplified by circumferentially averaging the velocity field at the inlet to the cavity which removes the effect of pressure wakes from the upstream rotor blades. The way in which these non-axisymmetric flow characteristics affect metal temperatures is not well understood. In addition, a constant air temperature scaled from a previous analysis is used as the simplified cavity inlet air temperature. Therefore, the objectives of this study are: (a) model the DCC cavity with a more physically representative inlet condition while coupling the solid thermal analysis and compressible air flow analysis that includes the fluid velocity, pressure, and temperature fields; (b) run a coupled analysis whose boundary conditions come from computational models, rather than thermocouple data; (c) validate the model using available experimental data; and (d) based on the validation, determine if the model can be used to predict air inlet and metal temperatures for new engine geometries. Verification with experimental results showed that the coupled analysis with the 3D no-bolt CFD model with predictive boundary conditions, over-predicted the HP6 offtake temperature by 16k. The maximum error was an over-prediction of 50k while the average error was 17k. The predictive model with 3D bolts also predicted cavity temperatures with an average error of 17k. For the two CFD models with predicted boundary conditions, the case without bolts performed better than the case with bolts. This is due to the flow errors caused by placing stationary bolts in a rotating reference frame. Therefore it is recommended that this type of analysis only be attempted for drive cone cavities with no bolts or shielded bolts.
Design Optimization of Injection Molds with Conformal Cooling for Additive Manufacturing
(Office of the Vice Chancellor for Research, 2015-04-17) Wu, Tong; Jahan, Suchana A.; Kumaar, Praveen; Tovar, Andres; El-Mounayri, Hazim; Zhang, Yi; Zhang, Jing; Acheson, Doug; Nalim, M. Razi
Abstract This is a framework for optimizing additive manufacturing of plastic injection molds. The proposed system consists of three modules, namely process and material modeling, multi-scale topology optimization, and experimental testing, calibration and validation. Advanced numerical simulation is implemented for a typical die with conformal cooling channels to predict cycle time, part quality and tooling life. A thermo-mechanical topology optimization algorithm is being developed to minimize the die weight and enhance its thermal performance. The technique is implemented for simple shapes for validation before it is applied to dies with conformal cooling in future work. A method for designing a die with porous material which can be produced in additive manufacturing is developed. Also a comprehensive set of systemic design rules are developed and to be integrated with CAD modeling to automate the process of obtaining viable plastic injection dies with conformal cooling channels. Finally, material modeling using simulation as well as design of experiments is underway for obtaining the material properties and their variations.
Design Requirements of Human-Driven, Hybrid, and Autonomous Trucks for Collision-Avoidance in Platooning
(2024-05) Shanker, Shreyas; Nalim, M. Razi; Anwar, Sohel; Tovar, Andres
The trucking industry faces many challenges, the most pressing of them being the rising costs to run the fleets. This is mainly caused by driver shortage, low driver retention and high wages for the drivers as well as rising fuel costs. Autonomous trucks promise to solve these issues by eliminating this bottleneck in the industry and bringing some relief to logistics companies and fleet owners. A prelude to fully autonomous trucks is expected to be seen as part of a hybrid platoon where a human driver would lead one or more autonomous trucks close behind them thus enabling higher tonnage to be transported by one driver. This enables early autonomous software to be tested and phased onto highways in a more controlled manner since present software can maintain set distances behind vehicles and respect lane markers already. Platooning also enables significant fuel savings from reduced aerodynamic drag on all vehicles at close distances. Since vehicle functionality is largely built around the driver, the removal of this piece affords the opportunity to rethink parts of the design to suit the needs of the future more favorably. Based on the prevalent literature as well as simulation of platooning scenarios under various vehicle and environmental conditions, the thesis will analyze the development of autonomous vehicles with a focus on the opportunities to rethink conventional design constraints of a truck and to design one that is better suited to the functions it will be carrying out autonomously and in the context of technologies that are in development and would be available in the future with a special emphasis on platooning scenarios. In this thesis, a MATLAB model was used to simulate a 2-vehicle platoon where the lead truck is a conventional class 8 vehicle while the key parameters of the following truck was tested in various road conditions to minimize Inter Vehicular Distance (IVD) and maximize fuel savings while ensuring safety. The study was able to conclude that an alternative design to autonomous trucks would result in maximum benefits from synergistic technologies like platooning and battery powered trucks. The results showed the most benefits from a reduction in perception-reaction time and communication technology followed by strategic configuration of vehicles in a platoon by Gross vehicle weight (GVW). Also, the need to account for coefficient of friction due to non-ideal environmental conditions with an adjustment in IVD is observed.
Empirical study of acoustic instability in premixed flames: measurements of flame transfer function
(2012-08) Hojatpanah, Roozbeh; Nalim, M. Razi; Anwar, Sohel; Zhu, Likun
In order to conform to pollutant-control regulations and minimize NOx emissions, modern household boilers and central heating systems are moving toward premixed combustors. These combustors have been successful with regards to emissions along with efficiency. However, their implementation has been associated with acoustical instability problems that could be solved through precise optimization in design rather than trial and error experimentation. This thesis introduces an experimental apparatus, which is designed to investigate the acoustic instability problem at the flame level. The goal is an experimental determination of the flame transfer function and comparison of the experimental data with a theoretical model of the flame. An experimental procedure is designed to diagnose the origins of the combustion instabilities by measurement of the flame transfer function. This research is carried out in three steps. The first step is to understand the acoustic instability problem through study of the theoretical models of the flame transfer function and selection of a model, which is most functional in industrial applications. A xiii measurement technique for the flame transfer function is developed according to the required accuracy in measurements, repeatability, and configurability for a wide range of operating conditions. Subsequently, an experimental apparatus is designed to accommodate the flame transfer function measurement technique. The components of the acoustic system are carefully sized to achieve precise measurement of the system parameters such as flows, pressures, and acoustic responses, and the apparatus is built. The apparatus is operated to measure the flame transfer function at several operating conditions. The experimentally measured flame transfer function is compared with a theoretical model for further verification. The experimental apparatus provides an improved assessment of the acoustic instability problem for industrial applications.
Experimental and Numerical investigation of hot-jet ignition with shock effects in a constant-volume combustor
(Office of the Vice Chancellor for Research, 2015-04-17) Paik, Kyong-Yup; Khan, Nazmuzzaman; Tarraf Kojok, Ali; Nalim, M. Razi
A wave rotor, an array of channels arranged around the axis of a cylindrical drum, can be used as a combustor in gas turbine engines in order to reduce the consumption of the fuel by increasing the fuel efficiency. Since the wave rotor combustor consumes fuel in constant volume channels, the engine system derives benefit from not only high temperature of the combusted gas, but also high pressure by containing the hot gas in the channels. Combustion of gas mixture in one of channels ignited by hot jet penetration under the necessity of rapid ignition accompanies complex non-steady phenomena, such as shock wave propagation, shock-flame interaction, and vortex generation in the channel. Especially, when a shock wave passes through the flame surface, the heat release rate and fuel consumption rate can be suddenly increased by a deformation of the flame surface, which are closely related with the combustion time of the fuel mixture. This research aims to investigate the ignition process, and the shock-flame interaction in a constant volume combustor experimentally and numerically to extract useful information for future wave rotor combustor design. Varıous mixtures of CH4 and H2 with equivalence ratio 1.0 were set as fuel for the main chamber, providing variation in chemical kinetic timescale. The hot gas jet consists of combusted gas mixture of a fuel composed of 50% CH4+ 50% H2 (by volume), burned in the pre-chamber with air at equivalence ratio 1.1. For experimental research, three dynamic pressure transducers were installed on the main chamber to measure the pressure changes caused by shock waves and flame propagation in the main chamber. Time-dependent flame and shock wave images up to 20,000 fps were obtained by a high speed camera, and a Z-type schlieren system. The schlieren technique, an optimum system to capture shock waves in the channel, utilizes light deviation due to flow density gradient, visualizing flows which are invisible to the human eye. In numerical research, adaptive mesh refinement for velocity and temperature, and multi-zone reaction modeling to speed up the kinetics were used to analyze turbulent combustion with minimum computational cost. Advanced post-processing techniques were used to calculate flame surface area, heat release rate, and vorticity deposited on flame surface to understand the flame wrinkling and surface increase. Finally, pressure data in main chamber, flame propagation speed, and the large scale of vortices under different initial conditions obtained from the experimental study were compared to the numerical results under the same conditions in order to suggest reference data for designing future wave rotors.
Experimental Investigation into Combustion Torch Jet Ignition of Methane-Air, Ethylene-Air, and Propane-Air Mixtures
(2010-12) Perera, Ukwatte Lokuliyanage Indika Upendra; Nalim, M. Razi; Xie, Jian; Zhu, Likun
Ignitability and the ignition delay time of a combustible mixture in a long combustion chamber, ignited by a hot combustion torch jet generated in a pre-chamber was investigated experimentally in relation to application as a viable igniter method for wave rotor combustors. Methane-air, ethylene-air, and propane-air in varying equivalence ratios were investigated as the combustible mixture in the combustion chamber. The effects of variation in the torch jet fuel, initial equivalence ratio in the pre-chamber, and nozzle geometry on the ignitability and the ignition delay time of combustible mixtures were observed and analyzed. The single-channel wave-rotor combustion rig at Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University, Indianapolis was used for this study. High-speed video imaging techniques to observe the ignition and flame propagation in the combustion chamber and fast-response pressure transducers to measure the dynamic pressure fluctuations in the combustion chambers were used in the current study. The present work explains how the experimental procedure and preliminary testing was carried out in order to conduct the necessary testing to find the ignitability and ignition delay time of a combustible mixture. Ignitability of methane, ethylene, and propane were much broader in range compared to conventional spark ignitable lean and rich limit equivalence ratios. The methane and propane ignition lean limits were similar to radical activated ignition lean limits found in previous studies of the same fuels. Ethylene exhibited the widest range in equivalence ratios from 0.4 to 2.4, while methane had the narrowest ranging from equivalence ratio 0.4 to 1.4. The ignition delay studies indicated both chemical kinetics and mixing between the combustion torch jet and the combustible mixture were critical. The mixing phenomena dominated chemical kinetics; unlike in ignition delay studies conducted using shock heated ignition techniques. Ethylene-air mixtures had the shortest ignition delay times ~1 ms for lean but near-stoichiometric mixtures. Methane and propane indicated similar ignition delay time characteristics with lean near-stoichiometric mixtures. The fuel-air equivalence ratio which was used to generate the combustion torch jet and the torch jet nozzle geometry had a direct influence over the ignition delay time in the main chamber combustible mixture. The slightly rich fuel-air ratios used to generate the combustion torch jet had the lowest delay times in igniting the main chamber fuel-air mixtures.

Browsing by Author "Nalim, M. Razi"

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