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.

A comparison of repetitive corrugation and straightening and high-pressure torsion using an Al-Mg-Sc alloy

Abstract: A comparative study was conducted to evaluate the influence of two different severe plastic deformation (SPD) processes: repetitive corrugation and straightening (RCS) and high-pressure torsion (HPT). Samples of an Al-3Mg-0.25Sc alloy with an initial grain size of ∼150 μm were processed by RCS through 8 passes at room temperature either without any rotation during processing or with a rotation of 90° around the longitudinal axis between each pass. Thin discs of the alloy were also processed for up to 5 turns by HPT at room temperature. The results show that both procedures introduce significant grain refinement with average grain sizes of ∼0.6–0.7 μm after RCS and ∼95 nm after HPT. Measurements of the Vickers microhardness gave values of ∼128 after RCS and ∼156 after HPT. The results demonstrate that processing by HPT is the optimum processing technique in achieving both high strength and microstructural homogeneity.

A novel pyrene-based binary pressure sensitive paint with low temperature coefficient and improved stability

Abstract: Pyrene-based pressure sensitive paints (PSP) have certain advantages due to their high pressure sensitivity and low temperature coefficient but their major drawback is the paint degradation under wind tunnel conditions. This is due to the loss of pyrene as a result of diffusion and sublimation from the coating. We have developed a novel stable binary PSP formulation in which pyrene is covalently bonded to the polymer binder so that paint degradation is prevented. The coating thus obtained is a siloxane-based hybrid organic-inorganic material. The pressure sensitive paint also contains an additional reference luminophore, which is insensitive to pressure but sensitive to intensity variations on the model surface. The second luminophore is incorporated in the paint to correct for the excitation intensity variations during the wind tunnel experiment. The temperature coefficient of second luminophore exactly cancels the temperature coefficient of the pressure sensitive luminophore, thereby resulting in a binary paint with negligible temperature sensitivity.

Testing of a scramjet engine with a strut in M8 flight conditions

Abstract: To attain intensive combustion in M8 flight conditions at which a basic strutless engine failed to initiate intensive combustion, a strut for the inlet contraction ratio of 5 with fuel injectors was installed and the engine was tested in M8 flight conditions, with a total temperature of 2550 K, a total pressure of 10 MPa and an airflow Mach number of 6.7. In the small fuel flow rate regime, pressure increments in the diverging combustor were observed due to the boundary layer combustion. This pressure rise was enhanced with the auxaliry injection from the strut which enhanced the mixing of the main fuel. The intensive combustion within the constant area combustor was attained at higher fuel flow rates, which resulted in transitions to an engine unstart condition. A prediction method was adopted to estimate the limiting fuel flow rate for attainment of the intensive combustion within the constant area combustor and for the transition to the unstart. Introduction Supersonic combustion ramjet (scramjet) is expected to be the most effective propulsion system for Single Stage To Orbit (SSTO) transportation system and the hypersonic transportation system of next generation. Many studies on components of the scramjet engines such as inlet, combustor and nozzle have been carried out. On the other hand, intensive interactions between these components are expected in real engines [1]. Thus, it is necessary to conduct testing of complete engine model to investigate the interactions and the engine performances. However, only limited data on these complete engine models and their performances have been published [2]. Using a blow-down type wind tunnel facility (denoted as RamJet engine Test Facility; RJTF) at NALKRC, we have conducted tests of a scramjet engine at various flight conditions from M4 to M8 [3-8]. This engine had a sidewall compression type inlet section with a contraction ratio of 2.9. The ratio was limited to assure starting capability in the M4 flight conditions. However, this low contraction ratio resulted in low pressure levels at the combustor entrance in the M6 and M8 flight conditions, and no intensive combustion within the engine was observed at both flight conditions [3, 6]. To attain intensive combustion in M6 flight conditions, it was necessary to place a strut within the engine for further compression and low velocity region enlargement [4]. To attain intensive combustion also in M8 flight conditions, a strut for the inlet contraction ratio of 5 with fuel injectors was fabricated and installed. Present paper reports the results of the engine tests in the M8 flight conditions, with a total temperature of 2550 K, a total pressure of 10 MPa and an airflow Mach number of 6.7. Copyright © 1998 by American Institute of Aeronautics and Astronautics, Inc. All right reserved. * Researcher, Ramjet Combustion Section, Ramjet Propulsion Dvision. Member AIAA. t Head, Ramjet System Section. Member AIAA. $ Senior Researcher, Ramjet Aerodynamics Section. § Head, Ramjet Combustion Section. Member AIAA. 1 Head, Ramjet Guidance Section. Member AIAA # Head, Research Coordinate Office. Experimental apparatus Wind tunnel facility and test conditions The RJTF was designed to simulate flight conditions of M4, M6, and M8. The facility is equipped with two heating systems to obtain high enthalpy flow. A storage air heater (denoted as SAH) is used to obtain pure hot air for the M4, M6, and M8 flight condition tests. Two types of vitiation air heaters (VAH) fueled by H2 are used to obtain vitiated hot air for the M6 and M8 flight condition tests, respectively. The M6 flight conditions are achieved with the SAH alone or the VAH alone (denoted as M6S and M6V conditions, respectively), whereas the M8 conditions are achieved with a combination of the SAH and the VAH. Table 1 shows the operational conditions of the RJTF at the simulated Mach 8 flight conditions. The high enthalpy flow obtained at the heaters was accelerated through a rectangular nozzle. The exit cross section of the nozzle was 510 mm x 510 mm. The engine model was set in a low pressure chamber which was connected to a steam ejector system to reduce the pressure within the chamber for simulation of high altitude atmosphere. The engine model was located in such a way that it breathed in the boundary layer on the facility nozzle wall. The displacement thickness of the boundary layer was about 33 mm. Table 1 Flow condition in M8 conditions Stagnant Engine inlet

Characterization and corrosion behavior of Co and Co–P coatings electrodeposited from chloride bath

Abstract: Co–P coatings with low and high phosphorous contents are electrodeposited using direct current (DC) and pulse current (PC) methods from cobalt chloride baths. The low phosphorous content coatings obtained from DC and PC methods are crystalline with predominantly fcc structure, while the high P content coatings are amorphous. Electrochemical corrosion studies reveal an increase in corrosion resistance with increasing phosphorous content in both DC and PC plated coatings. The PC coatings show a higher polarization resistance (Rp) and a lower corrosion current density (icorr), indicating better corrosion resistance. Compositional analysis shows a slight or no increase in P content after corrosion in PC coatings with a high P content, indicating better corrosion resistance. Comparisons of the surface morphologies before and after corrosion illustrate that the PC plated coatings are less affected than their DC counterparts. X-ray photoelectron spectroscopy (XPS) reveals a larger amount of oxidized cobalt in the PC electrodeposited coatings, whereas mainly metallic Co species are found in the DC plated coatings. This study demonstrates that the overall corrosion resistance for the PC deposited coatings is better than that of the DC deposited coatings because of the high P content, amorphous structure, smooth morphology, and higher metal oxide content in the deposits.

Cold-gas experiments to study the flow separation characteristics of a dual-bell nozzle during its transition modes

Abstract: An experimental investigation has been carried out to study the effect of test environment on transition characteristics and the flow unsteadiness associated with the transition modes of a dual-bell nozzle. Cold-gas tests using gaseous nitrogen were carried out in (i) a horizontal test-rig with nozzle exhausting into atmospheric conditions and, (ii) a high altitude simulation chamber with nozzle operation under self-evacuation mode. Transient tests indicate that increasing δP0/δt (the rate of stagnation chamber pressure change) reduces the amplitude of pressure fluctuations of the separation shock at the wall inflection point. This is preferable from the viewpoint of lowering the possible risk of any structural failure during the transition mode. Sea-level tests show 15–17% decrease in the transition nozzle pressure ratio (NPR) during subsequent tests in a single run primarily due to frost formation in the nozzle extension up to the wall inflection location. Frost reduces the wall inflection angle and hence, the transition NPR. However, tests inside the altitude chamber show nearly constant NPR value during subsequent runs primarily due to decrease in back temperature with decrease in back pressure that prevents any frost formation.