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Development of a retro-reflective screen-based large-field high-speed shadowgraph flow visualization technique and its application to a hydrogen-fueled valveless pulsejet engine
No full textLarge field flow visualization of the unsteady combusting flow inside a hydrogen-fueled valveless pulsejet engine has been successfully demonstrated by using a retro-reflective screen based high-speed shadowgraph technique. A rectangular cross-sectional valveless pulsejet engine with optical access has been designed, fabricated, and successfully used for demonstrating the effective use of a retro-reflective shadowgraph technique for large and spatially wide flow fields of interest. The aspect ratio of the engine considered for the study was 13.5 and the technique helped to understand the acoustically coupled combusting flow structures from the intake to the tailpipe of the pulsejet engine. A Photron FASTCAM SA4 camera was used in this study. High-speed shadowgraph videos were captured with a frame rate of 13500 frames per second with a resolution of 1024 × 272 pixels
Sustainable Machining of Cf/SiC Ceramic Matrix Composite Using Green Cutting Fluids
No full textUnderstanding the machinability of carbon fiber reinforced silicon carbide (Cf/SiC) ceramic matrix composite is important due to its large number of applications in defense, aerospace, and automobile industries. Cf/SiC has unique properties like high hardness, low density, high strength to weight ratio, and high oxidative stability even at a higher temperature. However, machining of Cf/SiC is an arduous task owing to its anisotropic and non-homogeneous structure. In this work, sustainable machining of Cf/SiC composite is carried out using inhouse tailored vegetable-based green cutting fluid (GCF) and compared with “Synergy 735”, a petroleum-based commercial mineral oil (MO) with minimum quantity lubrication (MQL) technique. Surface integrity and surface roughness are measured against varying control variables such as cutting speed, depth of cut, and feed rate. After machining experiments, fiber pullout, fiber breakage, matrix cracking, and interfacial debonding of fiber-matrix are observed on the machined workpiece. Results show that GCF reduces up to 17% of surface roughness of machined workpiece over MO. Also, surface integrity is better for GCF compared to MO machined surfaces
Vibroacoustic performance assessment of aircraft panels in low, mid and high frequency regimes
No full textIn the present work, vibroacoustic (VA) characteristics, namely sound transmission loss (STL), overall sound pressure levels (OASPLs) of aircraft panels made up of aluminum, composites and fiber metal laminates (FML) are studied. The investigation involves modeling of aircraft panels using finite element method (FEM) for low frequency, Boundary Element Method (BEM) for mid-frequency and statistical energy analysis (SEA) in high-frequency bands. To obtain the VA characteristics of the panels, twin chambers, namely source and receiver are numerically modeled, and the panels are placed in between them. The VA performances of the considered panels under low, mid and high-frequency sound environments are numerically simulated using an infinite duct model. The sound source in low, mid and high frequency is modeled in the source chamber as sound pressure, plane wave and diffusive acoustic field, respectively and the receiver chamber is idealized as an anechoic chamber at the ends. This numerical study helps in understanding the VA behavior of aircraft materials and also minimizes the cost and time involved in conducting experiments. The results are presented in the form of STL and OASPL. From this study, it was found that the aluminum and fiber metal laminates have good VA characteristics when compared to composites in all the three frequency regimes and composite panels behaving better in the mid-frequency region of 200 Hz to 300 Hz than aluminum and fiber metal laminates. An optimization approach for aircraft panels is also presented
Ground based variable stability flight simulator
No full textThis paper discusses the development of a ground based variable stability flight simulator. The simulator is designed to meet the pilot training requirements on flying qualities. Such a requirement arose from a premier Flight-Testing School of the Indian Air Force. The simulator also provides a platform for researchers and aerospace students to understand aircraft dynamics, conduct studies on aircraft configuration design, flight mechanics, guidance & control and to evaluate autonomous navigation algorithms. The aircraft model is built using open source data. The simulator is strengthened with optimization techniques to configure variable aircraft stability and control characteristics to fly and evaluate the various aspects of flying qualities. The methodology is evaluated through a series of engineer and pilot-in-the-loop simulations for varying aircraft stability conditions. The tasks chosen are the proven CAT A HUD tracking tasks. The simulator is also reconfigurable to host an augmented fighter aircraft that can be evaluated by the test pilot team for the functional integrity as a fly-through model
Green synthesis of ITO nanoparticles using Carica papaya seed extract: impact of annealing temperature on microstructural and electrical properties of ITO thin films for sensor applications
No full textThis paper reports the synthesis of indium tin oxide (ITO) nanoparticles and the effect of annealing temperature on the microstructural and electrical properties of ITO thin films. The synthesized ITO (90:10) nanoparticles are deposited at 29°C using E beam evaporation to form ITO thin films and annealed at 200, 400 and 500°C. The microstructural properties are investigated using XRD and AFM , and electrical properties such as temperature coefficient of resistance (TCR) and gauge factor are investigated using four-probe and four-point beam bending method, respectively. The investigations results reveal an increase in grain size, carrier concentration and gauge factor with an increase in the annealing temperature. The absolute value of TCR is constant at high temperatures for the film annealed at 500°C. The ITO thin film annealed at 500°C shows improved morphological and electrical properties and can be used for the development of sensors operating at high temperature
Non-destructive method of biomass and nitrogen (N) level estimation in Stevia rebaudiana using various multispectral indices
No full textUnmanned Aerial Vehicle (UAV) based remote sensing is one of the modern techniques for crop management, which has been used in this study for biomass and Nitrogen (N) level estimations for Stevia rebaudiana, a medicinal crop used as an alternative to sugar as a natural sweetener. Different levels of nitrogen treatments were given to S. rebaudiana and the crops were harvested for biomass estimation. Mica sense Altum multispectral sensor on board was used for acquiring the image data of the crop. The linear regression model was used to examine the best vegetation index using K-fold cross validation approach. Excess Green Index (ExG) was identified as best vegetation index for biomass estimation (R2 = 0.7; RMSE = 23.77 g/m2; nRMSE = 29.14%), whereas Enhanced Normalized Difference Vegetation Index (ENDVI) was found as best predictor for Nitrogen (N) level estimation (R2 = 0.9; RMSE = 1.75 g/m2; nRMSE = 14.59%)
Aerodynamic behavior of a transonic axial flow compressor stage with self-recirculating casing treatment.
No full textIn this manuscript, a new discrete type of passive Self-Recirculating Casing Treatment (RCT) is designed for a transonic axial compressor stage, fabricated, and tested for its performance. Parametric evaluation of the casing flush-mounted RCT for injection skew angle is studied experimentally and numerically to achieve considerable stall margin improvements. Detailed flow investigations are carried out for the RCT configurations and baseline solid casing behavior at different flow conditions using steady and unsteady measurements. The unsteadiness in the flow and the rotating stall signatures are captured through Kulite pressure sensors. Results indicate improvements in the stall margin and other overall compressor performance parameters for the investigated speeds. Improvements of stall margin in axial compressor stage with self-recirculating casing treatment are found to be because of the RCT by investing the already worked high-pressure fluid is able to overcome losses associated with the tip leakage flow. There is a delay in the onset of rotating stall instability with casing treatment which plays a role in the enhanced performance improvements
High-Speed Shadowgraph Visualization Studies of the Effectiveness of Ventilating a V-Gutter Flame Holder to Mitigate Screech Combustion Instability in an Aero-Gas Turbine Afterburner
No full textScreech combustion instabilities are high frequency (>1000 Hz) transverse periodic oscillations driven by combustion and which are then manifested as large amplitude oscillations in the afterburner duct pressure, accompanied by the characteristic high-pitched audible tones. These screech instabilities which are detrimental to the engine are conventionally suppressed by embedding Helmholtz resonator arrays in the afterburner liner. This method has been found inadequate when mixed mode combustion instability oscillations occur and also when the frequencies of oscillation were lower. The design of practical Helmholtz resonator arrays is classified and so is not available in the open domain. Hence, it was necessary to evolve a robust design solution to mitigate screech combustion instabilities in an afterburner. In an afterburner, V-gutters are used as flame stabilizers. The high Reynolds number flow past a V-gutter array is dominated by the presence of vortices characterized by the Kelvin–Helmholtz instability, which is a convective flow instability related to the shear layers separating from the V-gutter lips and the Benard–von Karman instability which is related to the asymmetric vortex shedding of the flow in the flame holder wake. The shedding of von Karman vortices at non-reacting and near the blowout conditions, and the transition from a Kelvin–Helmholtz instability to that of a Bernard–von Karman instability during near flame blowout create conditions for the frequency to get locked-on to the duct transverse acoustic mode frequency; screech is triggered. Hence, a smart flame stabilization method which has the intrinsic property of preventing the lock-on between the frequency of the vortex shedding from the V-gutter and the duct transverse acoustic frequency was developed. The test rig with optically accessible critical zones around the V-gutter flame stabilizer had the capability to operate the afterburner model under simulated inlet conditions of pressure and temperatures. A FastCam SA-4 Photron high-speed camera was used in this experimental investigation and high-speed shadowgraph flow visualization studies were carried out to develop a comprehensive method of introducing an aerodynamic splitter plate concept through a ventilated V-gutter; mitigation of screech combustion instability has been demonstrated
Angle only Tracking for Infrared Search and Track (IRST) System Mounted on an Aircraft
No full textThis paper presents an interactive multiple model (IMM) based angle only tracking approach with global nearest neighborhood (GNN) data association algorithm for infrared search and track (IRST) system mounted on an aircraft. Two target motion models are considered in IMM namely, Constant Angular Velocity (CAV) model and Constant Angular Acceleration (CAA) model. Simulation scenarios are generated with targets maneuvering and detected by an IRST in track while scan (TWS) mode of operation. Performance of the proposed algorithm for tracking multiple maneuvering targets with IRST in TWS mode is presented in this paper
Effect of throttling on dual-bell sneak-transition side loads
No full textAn experimental investigation has been conducted on a subscale dual-bell nozzle to study the effect of throttle settings on sneak-transition side loads. The results are from a cold-gas test campaign conducted in a high-altitude simulation chamber for three throttle settings of 1, 2, and 3bar/s. An analysis is carried out by correlating the simultaneously acquired side-load measurements and real-time wall pressure data from transducers mounted in the vicinity of the wall inflection. The study reveals that the longer is the time duration of separation front in the region of wall inflection, the higher is the amplitude of overall sneak-transition side loads. Increasing the throttle settings from 1 to 3bar/s significantly reduces not only the overall sneak-transition duration but also the amplitude of flow unsteadiness in the region of wall inflection during the intermittent flow condition of the sneak transition and, hence, the associated side loads. It is further observed that even though the total transition time decreases with an increase in throttle settings, the actual transition side-load peak amplitude remains more or less similar irrespective of throttle setting