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.

Rotating Cavitation in Three and Four-Bladed Inducers

Abstract: Recently, rotating cavitation occurred in the inducers of propellant feed pumps during the development of large advanced rocket engines, such as the LE-7, Ariane 5, and the Space Shuttle Main Engine. With regard to suction and overall performance, some comparisons have been made as to the numbers of blades. For example, it was reported that good suction performance was obtained with a small number of blades and that a three-bladed inducer is preferable if design considerations permit. Furthermore, it is well known that alternate blade cavitation occurs in the four-bladed inducer. However, it was recently clarified that attached cavitation or steady asymmetric cavitation occurs in the three-bladed inducer. Attached cavitation causes radial thrust due to an asymmetric pressure distribution around the periphery of the inducer inlet, while alternate blade cavitation does not cause radial thrust due to symmetric pressure distribution. We performed further experiments to investigate the difference of rotating and attached (or alternate blade) cavitation between three- and four-bladed inducers which had almost the same dimensions.

Nonlinear unsteady aerodynmiac modeling by Volterra variational approach

Abstract: The aerodynamics at high-angle-of-attack is an unsteady and nonlinear phenomena in time. In this paper, we present a phenomenological and mathematically rigorous approach to nonlinear modeling of the unsteady aerodynamics based on Volterra variational equations. The model consists of dierential equations of internal states corresponding to dierent kernels of the Volterra series. The model structure is generic as the number of states can be chosen contingent on available wind tunnel test data and delity of the model desired. Model parameters are estimated using forced oscillation wind tunnel test data. We present modeling of the normal force coecient of a delta-wing aircraft. We nd that two-states are sucient for accurate modeling of the normal force coecient in small and large amplitude oscillations in pitch at dierent frequencies. We show that the model is consistent with various experimental observations reported in literature. In the end we compare it with other models proposed in literature.

Lamb wave detection in prepreg composite materials with fibre Bragg grating sensors

Abstract: This paper demonstrates that existing Structural Health Monitoring (SHM) techniques have potential during the production phase in addition to their application for maintenance and for in-flight monitoring. Flaws occur during composite fabrication in industry, due to an imperfect process control and human errors. This decreases production efficiency and increases costs. In this paper, the monitoring of Lamb waves in unidirectional carbon fibre (UD-CFRP) prepreg material is demonstrated using both Fibre Bragg Gratings (FBG)s and piezolectric acoustic sensors, and that these SHM sensors may be used for flaw detection and production monitoring. The detection of Lamb waves in a one ply thick sheet of prepreg UD-CFRP material is demonstrated for an FBG sensor aligned with the carbon fibre orientation and bonded to the surface of the prepreg, Furthermore, the velocity of Lamb waves in prepreg UD-CFRP in different orientations is investigated. Finally the successful detection of a material crack in a prepreg UD-CFRP sheet using the Lamb wave detection method is demonstrated.

Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverter

Abstract: The recent increase in the use of speed control of ac induction motor for variable speed drive using pulse width modulation (PWM) inverter is due to the advent of modern power electronic devices and introduction of microprocessors. There are many advantages of using ac induction motor for speed control applications in process and aerospace industries, but due to fast switching of the modern power electronic devices, the parasitic coupling produces undesirable effects. The undesirable effects include radiated and conducted electromagnetic interference (EMI) which adversely affect nearby computers, electronic/electrical instruments and give rise to the flow of bearing current in the induction motor. Due to the flow of bearing current in the induction motor, electrical discharge machining takes place in the inner race of the bearing which reduces the life of the bearing. In high power converters and inverters, the conducted and radiated emissions become a major concern. In this paper, identification of bearing current due to conducted emission, the measurement of bearing current in a modified induction motor and to minimize the bearing current are discussed. The standard current probe, the standard line impedance stabilization network (LISN)), the electronics interface circuits are used to measure high frequency common mode current, bearing current and to minimize the conducted noise from the system. The LISN will prevent the EMI noise entering the system from the supply source by conductive methods, at the same time prevents the EMI generated if any due to PWM, fast switching in the system, will not be allowed to enter the supply line. For comparing the results with Federal Communications Commission (FCC) and Special Committee on Radio Interference (CISPR) standards, the graphs are plotted with frequency Vs, line voltage in dBµ V, common mode voltage in dBµ V and the bearing current in dBµ A with out and with minimizing circuits.