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.

Base Drag Reduction Caused by Riblets on a GAW(2) Airfoil

Abstract: AMONG various methods explored for turbulent drag reduction on aerodynamic surfaces, riblets have beer the most promising.' As much as 4-8% of viscous drag reduction has been reported for simple two-dimensional configurations Plastic sheets with symmetric v-grooves (manufactured by the 3M Co.) have been employed widely in research- Assessment of viscous drag reduction on two-dimensional airfoils. both at low and transonic speeds, has been reported as well.- Excellent reviews on the subject covering aspects of drag reduction and flow structure are contained in Refs. 1 and 7. 13; There have been very few attempts exploring the fuse of giblets in separated flows, either from the point of view of drag reduction or separation control-r'xB0; Recently. Krishnan et al.' showed that riblets actually increase the base drag (about 8.7 on a long axisymmetric body with a blunt base at low speeds: the base diameter was about four times the boundary -layer thickness ahead of the base corner-They used 3M riblet sheers and systematically studied the effect of h+` on base pressure. They also speculated that, while riblets caused an increase in the base drag for a large-scale separated flow (like on the axisymmetric blunt base'), the effect could be favorable on an airfoil with a blunt trading edge, which is a case of a small-scale separated flow. 13; The present investigation was undertaken specifically to assess the effect of 3M riblets on the base pressure of an airfoil with a blunt trailing edge. Experiments were made at low speeds on a 13.6% thick GAW(2) airfoil model, which has a trailing-edge thickness ratio of 0.5%. The results show very clearly that the base drag reduction of an engineering value can be achieved for the optimized riblet geometry.

Solution Combustion Synthesis as a Novel Route to Preparation of Catalysts

Abstract: Solution combustion synthesis (SCS) is a solution approach to the self-propagating high-temperature synthesis (SHS) of nanomaterials. Since its invention in 1988, several simple oxides, mixed oxides, complex oxides, metals, alloys, and sulfides have been prepared by this method. Uniqueness of this technique is in its simplicity, lost cost, energy saving, and short reaction time and it can be scaled up to any kind of application. In the last 20 years, different types of catalysts, especially oxide ones, have been prepared and employed in several kinds of heterogeneous catalytic reactions related to environment, energy, and fine chemical processing. This review addresses the SCS method and catalytic properties of noble metal ionic catalysts, spinels, perovskites, delafossites, and other catalysts prepared in this route. Reactions associated with environmental catalysis, hydrogen energy related catalysis, conversion of CO2, and CH4 to useful chemicals and fuels, H2-O2 recombination, organic compounds related reactions and electrocatalysis are discussed. Special emphasis has been made on the origin of SCS-synthesized noble metal ionic catalysts and their excellent catalytic properties.

Dielectric, ferroelectric and piezoelectric properties of (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], 0 ≤ x ≤ 1

Abstract: The dielectric, ferroelectric, and piezoelectric properties of ceramic materials of compositions (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], x = (0, 0.2, 0.4, 0.6, 0.8, and 1.0) were studied. The above compositions were prepared by mixing the individual Pb0.91La0.09(Zr0.60Ti0.40)O3 (PLZT) and Pb(Mg1/3Nb2/3)O3 (PMN) powders in order to design materials with different combination of piezo and dielectric properties. The powders were calcined at 850 °C for 4 h. The presence of various phases in the calcined powders was characterized by X-ray diffraction (XRD) technique. The compacts were prepared by uniaxial pressing and were sintered at 1250 °C for 2 h. The sintered compacts were electroded, poled at 2 kV/mm dc voltage and their dielectric, ferroelectric, and piezoelectric properties were measured. In general, it was observed that the dielectric constant, loss factor and the slimness of the ferroelectric curves increase with the PMN content while the remnant polarization, saturation polarization, and the coercive fields were decreased. It is now possible to design materials with a wide combination of d 33, K, and loss factor by varying PLZT and PMN ratio.