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.

Experimental investigations on effects of tip clearance in mixed-flow compressor performance:

Abstract: Experimental investigations were carried out to study the effect of tip clearance (between impeller and stationary shroud) in a mixed-flow compressor stage. Two configurations, namely constant and variable clearance gaps, between impeller and stationary shroud were considered. For the purpose of the present investigations, a mixed-flow compressor stage was designed, fabricated, and experimentally evaluated. The flow investigations were carried out in a closed-circuit compressor rig. Detailed steady and unsteady flow measurements were carried out for three clearance gaps, namely 0.5 mm, 0.75 mm, and 0.9 mm. Through the experimental investigations, it was found that the constant tip-clearance configurations showed better performance in terms of pressure ratio and efficiency as compared to variable clearance configurations. For a given configuration, the pressure ratio and efficiency of the stage decrease with increase in the tip gap without indicating any optimum value. Tip-clearance flow had considerable effect on the flow through the diffuser.

Effect of dual-doping on the thermoelectric transport properties of CaMn1−xNbx/2Tax/2O3

Abstract: The dual-substituted CaMn1−xNbx/2Tax/2O3 is synthesized by solid-state reaction and it's crystal structure-thermoelectric property relationship is established. Rietveld refinement confirms the formation of a single phase orthorhombic structure with a gradual increase of cell parameters and bond lengths with doping level. The electrical resistivity (ρ) shows non-metal like temperature dependence. The ρ-value decreases with increasing doping level indicating an increase in charge-carrier concentration through formation of Mn3+ ions with e1g electron in the Mn4+ matrix of CaMn1−xNbx/2Tax/2O3. The shallow region observed around 500 K in the resistivity curve is interpreted as the formation of local charge-ordering clusters due to the presence of oxygen vacancies in CaMn1−xNbx/2Tax/2O3. The Seebeck coefficient initially decreases with temperature as expected from increasing charge carrier concentration. Above 600 K, the Seebeck coefficient increases with temperature as oxygen vacancies start playing the dominant role. The relatively low thermal conductivity of CaMn1−xNbx/2Tax/2O3 results from the damping of local vibration through substitution of heavier ions of Nb and Ta as well as crystallographic distortion. The dual-substituted CaMn1−xNbx/2Tax/2O3 shows a maximum power factor of 200 μW m−1 K−2 and dimensionless figure-of-merit (ZT) of 0.15 at x = 0.04, arising from low electrical resistivity of 15 mΩ cm, a moderate Seebeck coefficient of −176 μV K−1 and low thermal conductivity of 1.2 W m−1 K−1.

High-Temperature Low-Cycle Fatigue Behavior in HAYNES 282: Influence of Initial Microstructure

Abstract: We present the low-cycle fatigue behavior of a new nickel-based superalloy in the temperature range of 650 °C to 760 °C. Two initial microstructures having different precipitate distribution has been chosen for this. Low-cycle fatigue behavior of these two microstructures has been characterized using mechanical parameters. These parameters include cyclic anisotropy, plastic strain accumulation and back stress evolution. The deformation response has been substantiated by detailed electron microscopy studies. A deformation mechanism map illustrating defect activity at various testing conditions has been constructed based on the microscopy results.

Flow simulation of NAL experimental supersonic airplane/booster separation using overset unstructured grids

Abstract: The overset unstructured grid method developed for multiple-body problems is applied to a flow simulation about an experimental supersonic airplane separation from a rocket booster. An unstructured grid around the rocket booster is overset on the stationary grid around the airplane and moves with time to simulate the separation process. Detailed components of the rocket booster are faithfully reproduced by the unstructured grid. This capability of the unstructured grid reduces the number of required overset grids and significantly simplifies the overset procedure. The computed result of the airplane/booster separation clearly simulates the complex reflection patterns of shock waves between two bodies during the separation process. The computed lift and pitching moment coefficients are compared with the wind tunnel results. The computational accuracy of the aerodynamic coefficients is improved by including the detailed components of the airplane and rocket.

Effect of hygrothermal aging on the mechanical properties of IMA/M21E aircraft-grade CFRP composite:

Abstract: Unidirectional carbon fiber-reinforced plastic (CFRP) IMA/M21E polymer composite was manufactured by standard autoclave curing method. This is a new aircraft-grade CFRP composite presently used in ...