Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Mach number & Turbulence. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Behaviour of turbulent Prandtl/Schmidt number in compressible mixing layer

Abstract: The behaviour of turbulent Prandtl/Schmidt number is explored through the model-free simulation results. It has been observed that compressibility affects the Reynolds scalar flux vectors. Reduced peak values are also observed for compressible convective Mach number mixing layer as compared with the incompressible convective Mach number counterpart, indicating a reduction in the mixing of enthalpy and species. Pr-t and Sc-t variations also indicate a reduction in mixing. It is observed that unlike the incompressible case, it is difficult to assign a constant value to these numbers due to their continuous variation in space. Modelling of Pr-t and Sc-t would be necessary to cater for this continuous spatial variation. However, the turbulent Lewis number is evaluated to be near unity for the compressible case, making it necessary to model only one of the Pr-t and Sc-t..

Performance analysis of nominal scheme and decoupling loop scheme for rf seeker

Abstract: Airborne seeker has to perform the role of target tracking with low pointing error as well as good disturbance rejection particularly with respect to flight vehicle motion. Although seeker with high stabilization loop gain (Ksl) performs the role of good disturbance rejection, it inherently increases the cost, weight and power requirements of the seeker. Good disturbance rejection is essential as disturbances in the form of high magnitude body rates has to be attenuated sufficiently so that its effect is as low as possible in the guidance signals to be tapped from the seeker. A special configuration known as decoupling loop scheme is sometimes employed to annul the effect of body rate disturbances in the synthesized LOS rate signal which is generally tapped from the seeker for guidance. Decoupling loop approach works well with IR / IIR seeker based homing guidance, but its effectiveness is not yet explored when a parasitic path exists in seeker in the form of radome aberration error as is the case in all RF seekers. The present paper deals with performance analysis of decoupling loop scheme and nominal scheme from the point of view of inner guidance loop (fig.1 and fig.2) stability and body rate decoupling from synthesized sight line rate in the presence of radome slope error. Generic formula of body rate decoupling from guidance signal; i.e synthesized sight line rate is derived in case of RF seeker for both nominal and decoupling loop scheme in the presence of radome slope error. The basic difference of both the schemes affecting seeker and guidance performance is brought out in a generic manner for different types of flight vehicles with varying response characteristics and different engagement situations. The stability of inner guidance loop of the two schemes, characterized by different realistic stabilization loop gains for different types of (fast or slow) flight vehicles, different engagement situations and guidance loop response time achievable in both the schemes are compared. The reported studies show that decoupling

Numerical Study of Pulse Detonation Engine with One-step Overall Reaction Model

Abstract: This paper presents an insight for the study of transient, compressible, intermittent pulsed detonation engine with one-step overall reaction model to reduce the computational complexity in detonation simulations. Investigations are done on flow field conditions developing inside the tube with the usage of irreversible one-step chemical reactions for detonations. In the present simulations 1-D and 2-D axisymmetric tubes are considered for the investigation. The flow conditions inside the detonation tube are estimated as a function of time and distance. Studies are also performed with different grid sizes which influence the prediction of Von-Neumann spike, CJ Pressure and detonation velocity. The simulation result from the single-cycle reaction model agrees well with the previous published literature of multi-step reaction models. The present studies shows that one-step overall reaction model is sufficient to predict the flow properties with reasonable accuracy. Finally, the results from the present study were compared and validated using NASA CEA. Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 265-271, DOI: http://dx.doi.org/10.14429/dsj.65.8730

Investigation of High-Temperature Stability and Thermal Endurance of Silicone Potting Compound by Thermo-Gravimetric Analysis

Abstract: The high-temperature stability and thermal life of silicone resin-based potting compound (SC-3), used in the aerospace application for electrical insulation, is investigated Thermo-Gravimetry Analysis (TGA) in an inert environment. Nonisothermal TGA is performed in the temperature range of 30 °C to 900 °C at 10, 20, and 30 °C / min heating rates. The kinetic parameters such as activation energy and pre-exponential factor are obtained by the model-free method proposed by Kissinger-Akahira-Sunose (KAS) and Flynn Wall Ozawa (FWO) at various degree of conversion. The thermal degradation of the SC-3 compound is observed in the temperature range of 350 °C to 580 °C, and thermal endurance or time of failure of potting compound SC-3 is estimated as per ASTM E1877 standard. The results reveal that the potting compound SC-3 can be safely used continuously at 100 °C and for ~3.6 min at 350 °C. Experimental results are also useful to understand the degradation mechanism of the SC-3 compound.