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.

Thermal behavior of carbon fiber precursor polymers with different stereoregularities

Abstract: The effect of stereoregularity, in terms of isotactic triad content on the thermal behavior of carbon fiber precursor polymers synthesized through different polymerization routes such as solid state and radical solution polymerization techniques, was investigated by the thermogravimetric analysis and differential scanning calorimetric measurements. The isotactic contents of I-PAN and A-PAN were estimated with 13C NMR. The thermal cyclization reactions of atactic polyacrylonitrile (A-PAN) with low isotactic content (26.4–29.7 %) occurred at a lower temperature than that of isotactic polyacrylonitrile (I-PAN) with higher content (48.7–51.6 %). The percentage of mass loss observed in I-PAN was less as compared to A-PAN. The molecular mass characteristics of PAN obtained through solid state and radical solution polymerization were [M n (10.2–14.3 × 104), M v (2.44–3.26 × 105)] and [M n (10.2–14.3 × 104), M v (2.29–2.74 × 105)] Daltons (Da).

Viscous Drag Reduction Using Riblets on a Swept Wing

Abstract: Results of viscous drag reduction using 3M riblets on a swept wing with a general aviation wing (GAV)(2) airfoil section at low speeds are presented. The tests, made at a chord Reynolds number of 0.75 x 10 exp 6, covered an incidence range of 0-6 deg. Measurements consisted of surface-pressure distributions and total drag using wake survey over the range of incidence covered; in addition, mean velocity, streamwise turbulence intensity, and Reynolds shear-stress profiles in the boundary layer were measured just ahead of the trailing edge at zero incidence. Surface flow patterns on the wing were obtained using an oil-flow technique employing titanium dioxide as pigment. The results showed viscous drag reduction of about 8 percent at zero incidence, which decreased progressively to about 1 percent at an incidence of 6 deg. The fall in riblet effectiveness appears to be a result of significant riblet yaw angle effects observed at higher incidence. Some reduction in the turbulence intensity and Reynolds shear stress in the boundary layer on the wing's upper surface have been observed in the presence of riblets, as in two-dimensional flows.