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.

Synthesis and Densification of Monolithic Zirconium Carbide by Reactive Hot Pressing

Abstract: Synthesis and densification of monolithic zirconium carbide (ZrC) has been carried out by reactive hot pressing of zirconium (Zr) and graphite (C) powders in the molar ratios 1:1, 1.25:1, 1.5:1, and 2:1 at 40 MPa, 1200 degrees-1600 degrees C. Monolithic ZrC could be synthesized with a C/Zr ratio similar to 0.5-1.0 and the post heat-treated samples have the lattice parameter in the range 4.665 to 4.698 A. Densification improves with an increasing deviation from the stoichiometry. Fine-grained (similar to 1 mu m) and nearly fully dense material (99% RD) could be obtained at a temperature as low as 1200 degrees C with C/Zr similar to 0.67. Microstructural and XRD observations suggest that densification occurred at low temperatures with nonstoichiometric Zr-C powder mixtures.

Electromagnetic Design and Performance Analysis of Airborne Radomes: Trends and Perspectives [Antenna Applications Corner]

Abstract: The spectacular advancements in antenna technologies for control, guidance, surveillance, and communication applications for airborne platforms have resulted in the realization of novel conformal antenna arrays, embedded antenna systems on the body of the fuselage, and structurally integrated radiating systems. Such antenna systems/ radiating structures facilitate superior functional capabilities with reduced payloads, desirable for airborne applications. They demand novel airborne radome structures with superior electromagnetic (EM) performance characteristics. Furthermore, rapid progress in the fields of frequency-selective surfaces (FSS) and metamaterials has had significant impact on the development of radome technology. Since conventional EM design techniques, based on transmission-line models, may not be sufficient for such applications, new techniques, based on numerical methods, have been developed. In order to circumvent the limitations of conventional low-frequency/high-frequency methods in analyzing antenna-radome interaction phenomena, hybrid methods, in conjunction with novel algorithms, are currently used. Considering the significant growth in EM technologies for airborne radome applications, the objective of this paper is to provide a glimpse of the techniques/methods for the EM design and analysis of airborne radomes. Some of the challenging EM issues/problems pertaining to airborne radome development are also discussed, which may be of interest to the radome community in the aerospace sectors.

Density Measurements in an Axisymmetric Underexpanded Jet by Background-Oriented Schlieren Technique

Abstract: The background-oriented schlieren (BOS) technique has been applied to obtain the mean density field of a complex underexpanded jet flow. The measurements were made on an axisymmetric sonic jet operating at ideally expanded and highly underexpanded values of nozzle pressure ratios. The methodology involved two steps: validation of the filtered backprojection tomography used here, by making measurements of a four-jet configuration followed by density measurements on axisymmetric sonic jets. Pitot measurements made on an ideally expanded sonic jet were utilized for validation of BOS. The presented density fields show that meaningful quantitative data can be extracted by using minimal hardware with this technology.