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R. Venkatraman ¹, S. Sankaran ¹, S. V. Subba Rao ¹, P. Krishnaiah ², T. Sundararajan ³

Affiliations
1 Satish Dhawan Space Centre, Sriharikota-524124, IN
2 Sri Venkateswara Univeristy, Tirupathi, IN
3 Department of Mechanical Engineering, IIT Madras, IN

Abstract

Several transient events occur during the startup of the Solid Rocket Motor (SRM) during the launch vehicle lift-off. Each event produces a complex transient signal and requires systematic assessment. The event discussed in this paper is Ignition Over Pressure (IOP). This Ignition Over Pressure is resulting from fluid dynamic compression of the accelerating plume gas, subsequent rarefaction and propagation during the pressure rise rate period in the rocket combustion chamber. These high-amplitude unsteady fluid-dynamic perturbations can adversely affect the vehicle and its surrounding structure. This wave behaves as a blast or shock wave characterized by a positive triangular shaped first pulse and negative half sine wave second pulse. The pulse travels upwards towards the propulsion system and has the potential to overload the individual elements or exciting overall vehicle dynamics. The later effect results from the phase difference of the wave from one side of the vehicle to the other due to the skew in the ignition of the strap-on boosters. In the case of the launchers, the mechanical stress due to the ignition over pressure wave comes, in addition to the acoustic constraint due to the jet noise. The over pressure phasing or ΔP environment, because of its spectral content as well as amplitudes becomes a crucial input for the design of sub-assemblies viz., thermal shields, and pay loads etc. In this paper, an attempt is made to numerically visualize the propagation of the blast wave causing the unsteady pressure oscillations during the transient pressure rise in the combustion chamber. To understand further, pressure measurements have been made at different heights along the umbilical tower during the solid rocket motor lift-off with the presence of jet deflectors, in order to capture the shock propagation phenomena. From the results, it appears that a sudden shock front that is generated during flow development within the rocket nozzle leaves a clear signature in the form of a well defined peak at typical time intervals. This overpressure amplitude seems to be related to the slope of the combustion chamber pressure rise rate during the transient period. It is also observed that the shock front initially propagates at supersonic speed but decays with time later. Similarly, the magnitude of the IOP peaks are also seen to decay with distance.

Keywords

Ignition Over Pressure, Shock Wave Propagation, Ignition Transient, Solid Rocket Motor, Numerical Flow Visualization

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R. Venkatraman ¹, S. Sankaran ¹, G. Krishnaiah ², P. Malleswara Rao ¹, P. K. Vivekanand ³, T. Sundararajan ³

Affiliations
1 Satish Dhawan Space Centre, Sriharikota-524124, IN
2 Sri Venkateswara Univeristy, Tirupathi, IN
3 Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai-600 036, IN

Abstract

The Ignition Over Pressure (IOP) is an unsteady pressure wave generated by the ignition of solid rocket motor during launch vehicle lift-off. This wave behaves as a blast or a shock wave followed by a low frequency excitation characterized up to 40 Hz, would cause severe damage to the launch vehicle, its structures and surroundings. However, in case of huge propulsion system, having two solid rocket motors as its boosters, due to the skew in their ignition, during lift-off, the phase difference of the wave from one side of the vehicle to the other could cause a severe moment, which is detrimental to the vehicle. The present paper deals with the occurrence of such blast waves during the testing of various scaled down solid rocket motors. Also, an attempt has been made experimentally to characterize and understand the propagation of the IOP wave causing unsteady pressure oscillations and transient pressure rise in the vicinity of a solid rocket motor. The spectral and directional characteristics of the IOP wave are also highlighted. Typical scaled-down solid rocket motors with and without nozzle shutters have been tested in horizontal firing configuration and the results are compared to study their effect. The resulting shock wave propagation has axial downstream as well as angular directivities. The pressure rise rate in the chamber is found to be directly correlated to the over pressure measured at various locations at the downstream of the nozzle.

Keywords

Directionality, Ignition Over Pressure, Ignition Transient, Shock Wave Propagation, Solid Rocket Motor.

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K. Venkat Raman ¹, P. Dayakar ¹, S. Sankaran ²

Affiliations
1 Department of Civil Engineering, Bharath University, Chennai - 600073, Tamilnadu, IN
2 Department of Civil Engineering, S. K. P. Engineering College, Tiruvannamalai - 606611, Tamilnadu, IN

Abstract

The role of Geotechnical engineering application in land reclamation, construction of highway, railway and canal embankments require a very large quantity of soil of desirable properties. It is often difficult to obtain good quality soil for the above applications from the nearby quarries. In such a situation, the locally available problematic soils (having low shear strength high compressibility and swelling nature) after stabilizing the same with the addition of admixtures such asuse of sand, lime, cement etc. for the improvement of problematic soils is costly because of their high demand in other civil engineering applications. To overcome the difficulties experienced with problematic soils in geotechnical applications on one side and safe disposal of solid wastes on the other side, an attempt is made in this study to explore the possibilities of utilizing to improve the engineering behaviour of problematic soils. In this study an attempt is made to know the index properties, compaction and unconfined compressive strength, may be used to improve the strength properties in four different types of problematic soil which have high swelling and high compressible nature. It can be concluded the as the L/D ratio decreases the unconfined compressive strength increases.

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S. Gowrisankaran , S. Sankaran ¹

Affiliations
1 Bharat Heavy Electricals Ltd., Tiruchy, IN

Abstract

Welding technology over the years has made tremendous strides and has established itself as a major fabrication technique. Special welding processes have come into being to join materials that were hitherto considered unweldable. Electron beam welding is one such process that was developed to meet the requirements of aerospace and nuclear industry. Today the process has spread into a number of engineering applications. An effort has been made through this paper to review the process of electron beam welding and its applications. The probable defects that may occur during the electron beam process and special techniques of inspection to detect these defects have been discussed at length. The economics of the process has also been studied.

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S. Sankaran ¹

Affiliations
1 D/S, Boiler MTCF/ TSIl. Neyveli Lignite Corporation, Neyveli, IN

Abstract

Maintenance Methods always cannot be the same as Erection / Manufacturing processes. In Erection / Manufacturing the processes methodical steps are preplanned and work is organised in a conducive atmosphere with well-laid out procedures, whereas in maintenance works time available to do the work will be limited and there may be constraints in space availability etc. coupled with unfriendly surroundings. Hence improved methods may have to be adopted to gain easy accessibility and to carry out the work quickly with minimum down time of the equipment. A typical example of the above viz. the window type welding technique adopted in wel^ling of certain inaccessible areas is narrated in the paper.

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