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 plasma nitriding on structure and biocompatibility of self-organised TiO2 nanotubes on Ti–6Al–7Nb

Abstract: TiO2 nanotubes formed by anodic oxidation of Ti–6Al–7Nb were nitrided in a nitrogen plasma. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nano hardness testing (NHT) and field emission scanning electron microscopy (FESEM). The corrosion behaviour of the substrate, plasma nitrided substrate, substrate with self-organised TiO2 nanotubes (TNT) and with plasma nitrided TiO2 nano tubes (TNT + PN) was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks' solution). The investigations show that the native oxide on the sample is replaced by a self assembled nano array by an anodisation process. XPS spectra of the TNT plasma nitrided sample show the presence of oxy nitride and nitride on the surface. The nano hardness of the samples was increased after nitriding. FESEM images of samples immersed in Hanks' solution show that growth of calcium phosphate phases is more and the size of the deposits are larger on TNT and nitrided TNT samples, as compared to the untreated substrate. XPS spectra of TNT and nitrided TNT samples immersed in Hanks' solution show a higher amount of calcium, phosphorous and oxygen than on the substrate. Electrochemical studies show that nitriding decreases the corrosion resistance.

Evaluation of recursive methods for aircraft parameter estimation

Abstract: Recursive parameter estimation consists of extracting aerodynamic stability and control derivatives using the flight measured input/output data in a real-time mode. It is useful in applications such as on-board verification of recorded data, iterative experiment design, verification of flight control laws, and reconfiguration of control system following damages. Three recursive algorithms, namely the Recursive Least Squares (RLS), Extended Kalman Filter (EKF) and Discrete Fourier Transform (DFT) are formulated and a comparative study has been carried out in the off-line environment using simulated and flight data for longitudinal and lateral-directional modes of aircraft motion. The results from the standard iterative Output Error Method (OEM) form the basis for evaluating the performance of these recursive methods. All the recursive methods discussed in this document gave results matching with those from OEM. The overall performance of DFT method was found to be better than that of the RLS and EKF methods. Also, DFT is computationally simpler and unlike the other two methods, there is no requirement of any tuning parameter. From this aspect, the DFT technique seems to be preferable for online identification purposes.

Drag Reduction of Afterbodies by Controlled Separated Flows

Abstract: The zero-lift drag characteristics of a class of multistep afterbodies that utilize the concept of controlled separated flows are documented at transonic and supersonic speeds. The important geometrical and flow parameters affecting the drag of such afterbodies are identified, and their effects are examined through a parametric study. The results show that multistep afterbodies can be designed that provide significant total drag reduction (as high as 50%) compared to (unmodified) blunt bases; however, compared to axisymmetric boattailed afterbodies of a given base area, the multistep afterbodies have relatively higher drag. Finally, the certain flow features involving separation and reattachment on multistep afterbodies are discussed based on flow visualization studies