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.

Power spectrum estimation of complex signals: group delay approach

Abstract: A method for estimating the power spectrum of a complex signal (CS) realised by the group delay (GD) for a CS and the modified GD concept is proposed This extends the performance advantages of the modified GD applicable to a real signal to a complex signal A significant reduction in variance without any compromise in frequency resolution over that of the periodogram is found

Freestream effects on base pressure development of an annular plug nozzle

Abstract: An experimental investigation has been carried out to study the effect of freestream flow and cowl-length variation on (i) upstream flow interference effects and (ii) the base wake-closure nozzle pressure ratio. It is observed that for supersonic freestream Mach numbers the nozzle exhaust seems to only slightly influence the upstream interference effects for M = 1.2 but shows significant influence for M = 1.6. Increasing the cowl-length further reduces the upstream flow interference effects significantly. Further, the reduced momentum thrust from the inner nozzle in the presence of freestream for similar nozzle pressure ratio (relative to static tests) delays the downstream movement of the system of shocks on the plug surface. In the case of the plug truncated at 40% length, this delays the onset of base-wake closure and hence, increases the base-wake closure nozzle pressure ratio with increasing freestream Mach number. Increasing the cowl-length also helps to increase the base pressure thrust contribution at all operating conditions.

Development of robust VAD schemes for Voice Operated Switch application in aircrafts: Comparison of real-time VAD schemes which are based on Linear Energy-based Detector, Fuzzy Logic and Artificial Neural Networks

Abstract: In a fighter aircraft, for the optimal usage of resources during transmission of signals, a Voice Operated Switch (VOS) is used, as it is considered as a better option compared to push to talk (PTT), because it gives hands free environment for the pilot to carry out other crucial tasks. The heart of VOS is a Voice Activity Detection (VAD) algorithm. This paper explores the evolution of a reliable, robust VAD scheme for VOS application in aircraft by comparing real-time robust VAD schemes, which are based on energy-based detectors, fuzzy logic and ANN. MATLAB, is used as the simulation platform and actual fighter aircraft cockpit noise record is used for evaluation of the algorithms.