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.

Design of low observable antenna using active hybrid-element FSS structure for stealth applications

Abstract: A novel EM (electromagnetic) design of low observable antenna using active hybrid-element frequency selective surface (FSS) as ground plane is presented in this paper for stealth applications. The EM characteristics of active hybrid-element FSS structure are reconfigured from reflecting mode to transmitting mode and vice versa by switching ON and OFF the PIN diode at 10 GHz. In ON state of diode (reflection mode), the FSS structure shows extremely less transmission ( 2 ) as compared to conventional MPA. Finally, a prototype active FSS-based antenna is fabricated and measured for proof-of-the concept.

Separation control by tangential blowing inside the bubble

Abstract: Experiments have been carried out investigating the effectiveness of steady tangential blowing (inside the separation bubble) to control an axisymmetric separated flow at low speeds. Turbulent boundary separation was induced on a contoured afterbody and the separated shear layer reattached on a narrow cylindrical sting. Measurements made consisted of model surface pressures, mean velocity, turbulent shear stress and kinetic energy profiles using a 2-component LDV system. The results explicitly demonstrate that blowing downstream of the separation location, but within the bubble, can be an effective means of separation control, considering both wall and wake flow reversals.

Influence of multiwall carbon nanotube alignment on vibration damping of nanocomposites

Abstract: In the present work, the damping behavior of multiwall carbon nanotubes/polymer nanocomposites has been studied by aligning the carbon nanotubes (CNTs) in the matrix using DC electric field during the curing of composite. Nanocomposite specimens have been fabricated for three different CNT loadings (0.1, 0.2, and 0.3 wt%) to prepare two types, namely randomly oriented and aligned. The alignment of nanocomposites has developed a strong anisotropy in the composite. Microstructural analysis and electrical conductivity tests are carried out to examine the CNTs alignment. It is evident from the obtained results that a significant improvement is achieved in electrical conductivity of aligned nanocomposites over randomly oriented one. Dynamic mechanical analysis and flexural vibration experiments have been performed to study the frequency dependent damping behavior of nanocomposites. In case of aligned nanocomposites, significant enhancement is noticed in the material damping for the tested frequency band width ...

Properties of Cf/SiC-ZrB2-TaxCy composite produced by reactive hot pressing and polymer impregnation pyrolysis (RHP/PIP)

Abstract: Cf/SiC-ZrB2-TaxCy composite was synthesized by reactive hot pressing (RHP) of Cf cloth, polycarbosilane (PCS), ZrB2, and Ta powders at 4 MPa and 1200 °C. PIP cycle influenced sintering process by increasing density of the composite from 2.34 to 2.82 g/cc. Residual carbon produced during the PIP cycles at 1200 °C was utilized to yield TaxCy by the addition of Ta. SEM images illustrate that by increasing the number of PIP cycles, SiC derived from the PCS cover the Cf fibre, micropores, and cracks. PIP cycles and TaxCy phase improved flexural strength of the composite from 20 to 114 MPa. Mass and linear ablation resistance studies at 1600–2000 °C exhibited that oxide formation at the outer surface caused a barrier; further, no oxidation underneath the composite was observed. SEM images display that at 2000 °C, SiO2 and TaxOy were molten and sealed the pores. Hence, ablation resistance was enhanced by blocking the penetration in high-temperature flame.