National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Flight validation of an embedded structural health monitoring system for an unmanned aerial vehicle

Abstract: This paper presents the design and flight validation of an embedded fiber Bragg gratings (FBG) based structural health monitoring (SHM) system for the Indian unmanned aerial vehicle (UAV), Nishant. The embedding of the sensors was integrated with the manufacturing process, taking into account the trimming of parts and assembly considerations. Reliable flight data were recorded on board the vehicle and analyzed so that deviations from normal structural behaviors could be identified, evaluated and tracked. Based on the data obtained, it was possible to track both the loads and vibration signatures by direct sensors’ cross correlation using principal component analysis (PCA) and artificial neural networks (ANNs). Sensor placement combined with proper ground calibration, enabled the distinction between strain and temperature readings. The start of a minor local structural temporary instability was identified during landing, proving the value of such continuous structural airworthy assessment for UAV structures.

A simple performance prediction model of clustered linear aerospike nozzles

Abstract: Causes of thrust performance loss on a clustered linear aerospike nozzle were investigated by conducting cold flow tests with a 3-cell-clustered nozzle. Loss due to clustering was found to be caused by lower pressure acting on a gap surface between cells and by the loss due to the total pressure loss caused by shock waves generated behind the gap. Based on the results, a model to predict the thrust coefficients of linear aerospike nozzles was developed. Thrust coefficients obtained by ground level combustion tests for a 14 kN clustered linear aerospike nozzle were compared with that estimated by the model. The model value was about 2% higher than the measured values. NOMENCLATURE Ag: Gap area At: Throat area of cell nozzles AE: Exit area of truncated-spike nozzles and full-spike nozzles AEceli: Exit area of cell nozzles Ab: Base area CFtotal: Thrust coefficient of aerospike nozzles CFcluster: Thrust coefficient of clustered nozzle CFMcell: Theoretical thrust coefficient of cell nozzle for momentum force CFs=5: Theoretical thrust coefficient at 8= 5 Fciuster: Thrust of clustered nozzle NPR: Nozzle pressure ratio, Pce»/Pa Pcell: Plenum pressure of cell combustor Pceli,E: Calculated pressure which is attained if the cell exhaust expands to the gap space PE: Calculated pressures at the end of the full-spike nozzle PEceil: Exit pressure of cell nozzles Pa: Ambient pressure Pw: Pressure on the spike surface Pb: Pressure at truncated nozzle base surface Pg: Pressure at the base surface of the gap between the cell nozzles PT: Calculated pressures at the point of truncation Gcell: Tilt angle of cell nozzle to the spike axis 6cell: Expansion area ratio of cell nozzle * Researcher, Kakuda Space Propulsion Laboratory, NAL, Member AIAA jSenior Researcher, Kakuda Space Propulsion Laboratory, NAL JSenior Researcher, Kakuda Space Propulsion Laboratory, NAL, Member AIAA §Group Leader, Kakuda Space Propulsion Laboratory, NAL, Senior Member AIAA. Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 8E: Expansion area ratio of spike nozzle T|CF: Thrust coefficient efficiency T|CFceii: Thrust efficiency of a cell nozzle msVs: Momentum thrust of secondary flow NDP: (PW Pa)/Pcell W: Width of the spike INTRODUCTION For future fully reusable SSTOs, reusable rocket engines characterized by lightweight and high performance from low altitude to high altitude are essential. Engines with an altitude compensation nozzle are drawing attention as promising candidates that satisfy the requirement of high performance. Advantages of aerospike engines are that they are characterized by light weight and the best theoretical altitude compensation among all of the engine concepts. Theoretical altitude compensation is not achieved by real aerospike engines because of various factors, for example, the loss due to spike truncation, the loss due to cell-to-cell interaction of the exhaust jets, and the gain due to base bleed. However, there is no aerodynamical design method for aerospike nozzles which take these factors into account. The National Aerospace Laboratory has studied aerospike nozzles for the past several years to establish an optimum design method for spike nozzles [1-9], and cold flow tests, CFD analysis and combustion tests have been conducted. The thrust of full-spike nozzles, the impact of spike truncation, the impact of sidewall on thrust, and the impact of base bleed on thrust have been clarified by cold flow tests [5-6]. Based on the test results, a simple method to predict the thrust coefficients of aerospike nozzles has been proposed[9]. By combustion tests, measured thrust of a aerospike nozzle has been shown, as has heat-load distribution on a spike[8]. The purpose of the present study was to investigate the thrust loss of clustered linear aerospike 1 American Ins t i tu te of Aeronaut ics and As t ronau t ics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. nozzles. To acquire detailed information on losses due to clustering of cell nozzles, cold flow tests with a 3-cell-clustered model were conducted. Based on the results, the losses due to the clustering were modeled and the model was combined with a simple method to predict the thrust coefficients of aerospike nozzles. To evaluate the method, measured thrust coefficients of a 14 kN clustered linear aerospike nozzle composed of six rectangular cell nozzles and a two-dimensional truncated spike nozzle were compared with the estimated thrust coefficients obtained by the model. A SIMPLE MODEL TO PREDICT THRUST COEFFICIENTS OF AEROSPIKE NOZZLES Thrust performance of linear full-spike nozzles The theoretical thrust coefficients of linear full-pike nozzles can be obtained by an equation 1 . x cos ° cell = FMcell x °S Oc *£•* —— (0 Pcell The first term on the right-hand side represents the contribution of the momentum of the exhaust jets from the cell nozzles, the second term is that of the pressure at the exit planes of the cell nozzles, the third term indicates that of the pressure on the spike nozzle surface, and the fourth term represents that of atmospheric pressure. The pressure on the spike nozzle surface, Pw, in the third term can be evaluated by the method of characteristics. The thrust coefficients can be obtained when the expansion ratio of the cell nozzles and that of the full-spike nozzle are known. Figure 1 shows a photograph and a schematic of a cold flow test model. The test model is composed of two-dimensional ideal contoured cell nozzles and an ideal contoured full-spike nozzle. Figure 2 shows a variation with NPR of theoretical thrust efficiencies obtained by equation 1 and measured thrust efficiencies. Thrust efficiency was defined as the measured or the theoretical thrust coefficient divided by an optimum thrust coefficient at each NPR. Corrected thrust efficiencies are also shown in Fig. 1. These corrected thrust efficiencies were obtained by a specific heat ratio correction due to the real gas effect and an effective throat area correction based on a throat discharge coefficient. The measured thrust efficiencies show a 2.6 percent loss compared with the theoretical thrust efficiencies at NPR = 100, and a 5 percent loss at NPR = 10. The corrected thrust efficiencies show no loss at NPR = 100 and about 5 percent loss at NPR = 10. Based on the results, it can be concluded that the 2.6% loss of the measured thrust observed at NPR = 100 is caused by the real gas effect and the change of the effective throat area. The other test models in this section ,mentioned below, have the same configuration in the upstream throat and were tested under very Xaxij Figure 1 Photograph and schematic of a cold flow test model. i.oo

Effects of Material and Test Parameters on the Wear Behavior of Particulate Filled Composites Part 1: SiC-Epoxy and Gr-Epoxy Composites

Abstract: Studies were carried out on a (RT) cure epoxy (LY556xFE;HY951) composite system13; comprising of silicon carbide (SiC) and graphite (Gr) particulates. Results showed that13; the wear resistance and coefficient of friction of both the composites increased with sliding13; distance and contact load (contact pressure) for the range of filler contents (5x2013;40% wt) considered.13; The Gr-composite exhibited its distinct (superior) tribological feature compared to the13; SiC-composite. A wear endurance index has been identified from the experimental data, to serve13; as a parameter to assess the long term wear life (residual wear life) of these composites.

Reference-Free Real-Time Power Line Monitoring Using Distributed Anti-Stokes Raman Thermometry for Smart Power Grids

Abstract: We report the experimental demonstration of a reference-free Distributed Anti-Stokes Raman Thermometry (DART) scheme for real-time power line monitoring in overhead power transmission (OPGW/OPC) cables. Our work is based on the loop configuration in which only the anti-Stokes intensity is captured and processed to determine the temperature, thereby providing a self-calibrated solution that is tailor-made for a rugged field measurement. Temperature experienced by the optical fiber embedded in the power cable is estimated through a simple heat transfer model and is experimentally validated using a homebuilt DART system with a root mean square (RMS) temperature error of 0.33 °C.