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.

Measurement of blade tip clearance using an ultrasonic sensor

Abstract: This paper describes a development and evaluation of a blade tip clearance measurement system using an ultrasonic sensor. Special features of this system are; (i) it is adequate for metal and non-metal blade; (ii) it permits measurement without contact; (iii) it can work in dirty environment; and (iv) it is easy to install. Experimental results using a rotating blade test rig are described. Blade tip speed is restricted to Mach 0.18 due to the limitation of the test rig. It is concluded that the ultrasonic method is a promising candidate for an on-line clearance control of gas turbine engines.

Preparation of pure boehmite, α--Al2O3 and their mixtures by hydrothermal oxidation of aluminium metal

Abstract: A hydrothermal oxidation process for preparing pure boehmite, alpha-Al2O3, and their mixtures by oxidation of pure aluminum metal is described, and the reaction mechanisms involved are identified SEM images are presented which show distinct morphologies of boehmite, alpha-Al2O3, and boehmite + alpha-Al2O3 phases Near sperical shapes of alpha-Al2O3 powder phases are obtained at 550 C with 30 percent volume of fill

Structure and properties of electrodeposited Ni–Co–YZA composite coatings

Abstract: The aim is to develop an economical composite coating with high thermal stability. Ni–Co alloys are found to possess better thermal, physical and mechanical properties compared to Ni. Also, oxide particles as distributed phase can impart better thermal stability. Hence, particulates of composite Yttria stabilised zirconia, a commonly used high temperature material and alumina (YZA) were reinforced in various Ni–Co alloy matrices through electrodeposition. The influence of YZA on the microhardness, tribology and corrosion behaviour of Ni–Co alloys with Co contents of 0 wt.%, 17 wt.%, 38 wt.% and 85 wt.% was evaluated. Optical and Scanning Electron Microscopy (SEM) confirmed the presence of YZA particles and Energy Dispersive X-ray Analysis (EDX) revealed the composition. Tribology testing showed that composite containing 38 wt.% Co displayed better wear resistance. It was found from the immersion corrosion studies that Ni–17Co–YZA coating displayed improved corrosion resistance. Thermal stability studies showed that Ni–85Co–YZA coating retained its microhardness at temperatures of 600 °C. Thus, these coatings can be tailored for various applications by varying the cobalt content.

Gas-Density Effects on Dual-Bell Transition Behavior

Abstract: An experimental investigation was conducted to study the dual-bell transition behavior inside a high-altitude test facility under different back pressure environments. The high-altitude chamber was evacuated using an ejector nozzle and the dual-bell nozzle driving pressure, P 0N, was varied from 30 to 5.3 bar in subsequent test campaigns. As P0N was decreased, the dual-bell transition was observed to get delayed, and the transition nozzle pressure ratio increased by as much as 20% for the lowest driving pressure tested. Similar results were also observed for the dual bell retransition nozzle pressure ratio. For very low values of P0N (of 3.5 bar), transition did not occur at all. The delay in the dual-bell transition process to higher nozzle pressure ratio is primarily attributed to the increase in the width of inflection region with decrease in Reynolds number, which seems to control the dual-bell transition behavior. During these tests, it was also observed that the visible intensity of condensation shock decreased gradually with decreasing P0N and finally, for P0N � 17:4 bar, no condensation shock was observed. The decrease in gas density/reduced mass flow is also accompanied by a significant decrease in the amplitude of wall pressure fluctuations in the region of separation due to decrease in shock strength.