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.

Effect of micron-sized roughness on transition in swept-wing flows

Abstract: Boundary-layer transition-to-turbulence studies are conducted in the Arizona State University Unsteady Wind Tunnel on a 45-degree swept airfoil. The pressure gradient is designed so that the initial stability characteristics are purely crossflow-dominated. Flow visualization and hot-wire measurements show that the development of the crossflow vortices is influenced by roughness near the attachment-line. Comparisons of transition location are made between a painted surface, a machine-polished surface, and a hand-polished surface. Then, isolated 6 micron roughness elements are placed near the attachment line on the airfoil surface under conditions of the final polish (0.25 micron rms). These elements amplify a centered stationary crossflow vortex and its neighbors, resulting in localized early transition. The diameter, height, and location of these roughness elements are varied in a systematic manner. Spanwise hot-wire measurements are taken behind the roughness element to document the enhanced vortices. These scans are made at several different chord locations to examine vortex growth.

Solar energy absorption mediated by surface plasma polaritons in spectrally selective dielectric-metal-dielectric coatings: A critical review

Abstract: The effective use of solar energy has become significantly important due to unnatural weather changes and fossil fuel exhaustion Concentrating Solar Power (CSP) technology is a promising approach to harvest solar energy in the form of heat using solar selective absorber coating These coatings are expected to absorb maximum incoming solar radiation (α ≥ 095) and prevent loss of the absorbed energy as infrared radiation (e ≤ 005) Efficiency of the absorber coating can be evaluated by a metric called “Solar selectivity (α/e)” In recent years, a number of attempts have been made to achieve remarkable selective property and high temperature stability of the absorber coating using the concept of Surface Plasma Polaritons (SPPs) The SPPs have the capability to capture solar energy by confining electromagnetic field at the metal-dielectric interface Solar absorption, can be maximized by tailoring the optical constants of the metal and dielectric In this review, we have described different types of solar absorber coatings with particular emphasis on dielectric-metal-dielectric (DMD) -based absorber coatings We have presented a brief theoretical overview to comprehend physics of DMD coatings This review additionally highlights some of the case studies based on the DMD -based absorber coatings with the high temperature stability and their importance in the context of CSP technologies

Electrospinning of alumina nanofibers using different precursors

Abstract: Electrospinning technique is becoming increasingly13; popular for the preparation of nanofibers [1x2013;5]. The13; process involves the application of a strong electrostatic13; field to a capillary connected with a reservoir13; containing a polymer solution or melt. Under the13; influence of the electrostatic field, a pendant droplet of13; the polymer solution at the capillary tip is deformed13; into a conical shape (Taylor cone). If the voltage surpasses13; a threshold value, electrostatic forces overcome13; the surface tension, and a fine charged jet is ejected.13; The jet moves towards a ground plate, which acts as a13; counter electrode. The solvent begins to evaporate13; immediately after the jet is formed. The result is the13; deposition of nanofibers on a substrate located above13; the counter electrode. Initially, this technique was used13; for the preparation of polymer nanofibers [6x2013;9]. In13; recent years; this technique has been used for the13; preparation of metal oxide/ceramic nanofibers such as13; silica, zirconia, titania, nickel oxide, barium titanate,13; lead zirconate titanate and other oxide materials [10x2013;13; 30]. The nanofibers formed could be aligned (parallel13; and cross patterns) when an insulated cylinder attached13; to the axel of a DC motor is used as the substrate [31].13; Xia et al. [32] prepared polymeric and ceramic nanofibers13; as axially aligned arrays by the use of a collector13; consisting of two pieces of electrically conductive13; substrate separated by a gap. Katta et al. used copper13; wires spaced evenly in the form of a circular drum as a13; collector of the electro spun nanofibers