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: Turbulence & Mach number. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Numerical Simulation of a Dual Pulse Solid Rocket Motor Flow Field

Abstract: Numerical simulations are carried out for the internal flow field of a dual pulse solid rocket motor port to understand the flow behaviour. Three dimensional Reynolds Averaged Navier Stokes equations are solved alongwith shear stress transport turbulence model using commercial code. The combustion gas is assumed as a mixture of alumina and gases and single phase flow calculations are done with the thermo chemical properties provided for the mixture. The simulation captures all the essential features of the flow field. The flow accelerates through the pulse separation device (PSD) port and high temperature and high velocity gas is seen to impinge the motor wall near the PSD port. The overall total pressure drop through motor port and through PSD is found to be moderate. Defence Science Journal, 2012, 62(6), pp.369-374 , DOI:http://dx.doi.org/10.14429/dsj.62.1418

Flow forming of thin-walled precision shells

Abstract: Flow forming is an innovative form of cold and chipless metal forming process, used for the production of high precision, thin-walled, net-shaped cylindrical components. During this process, the length of a thick walled tube, commonly known as a preform, is increased with a simultaneous decrease in the thickness of the preform without any change in the internal diameter. Forming of the preform is carried out with the help of one or more rollers over a rotating mandrel. By a pre-determined amount of thickness reduction in one or more number of forming passes, the work material is plastically deformed in the radial direction by compression and made to flow in an axial direction. The desired geometry of the workpiece is achieved when the outer diameter and the wall of the preform are decreased, and the available material volume is forced to flow longitudinally over the mandrel. Over the last three and a half decades the flow forming technology has undergone several remarkable advancements. The versatility of the process makes it possible to produce a wide variety of axi-symmetric, nearer to the net-shape tubular parts with a complex profile using minimum tooling changes. In this review article, process details of flow forming have been elaborated. The current state-of-the-art process has been described, and future developments regarding research and industrial applications are also reviewed.

Thermo-mechanical characterization of laser textured LaMgAl11O19/YSZ functionally graded thermal barrier coating

Abstract: The ablation resistance and adhesion strength of laser textured and as-sprayed functionally graded LaMgAl 11 O 19 /YSZ based thermal barrier coating (FG-TBC) was studied and compared with a duplex coating of LaMgAl 11 O 19 and YSZ (DC-TBC). The thermal barrier coatings were sprayed over Hastelloy C263 using atmospheric plasma spray process (APS). The laser texturing was performed using a picosecond pulsed laser. The width-to-depth ratio and groove spacing were varied to analyse and correlate the significance of groove parameters in providing strain tolerance under extreme thermal loading conditions. The ablation behaviour of the coatings was investigated using a scramjet test rig. The shear force induced through the ablation load spalled the as-sprayed DC-TBC. The thermal stress mismatch instigated through the difference in coefficient of thermal expansion (CTE) between discrete YSZ and LaMgAl 11 O 19 layers led to the failure of the as-sprayed DC-TBC. The as-sprayed FG-TBC exhibited an improved ablation resistance. The varying thermo-mechanical properties along the ceramic layer thickness in as-sprayed FG-TBC minimise the concentration of thermal stress across the coating and imparts better thermal stability. The improved mechanical interlocking of molten splats during re-solidification of five discrete layers of ceramic composites inhibits the concentration of stress around the weak links. Compared to the textured DC-TBCs, the textured FG-TBCs exhibited minimal level of distortion and better resistance to ablation. The textured surfaces restrict the propagation of crack across the top surface and also provide improved strain tolerance. The graded structure minimises the stress built up and improves the coating resistance compared to textured DC-TBCs. The adhesion strength of all test surfaces was analysed following the standard test procedure. The textured surfaces having higher surface roughness (in terms of surface area) exhibited improved adhesion strength. The groove parameters were observed to have significant influence in improving the ablation resistance and adhesion strength of the coatings.

Ranking based uncertainty quantification for a multifidelity design approach

Abstract: Computer simulation based design processes are being extensively used in complex systems like scramjet powered hypersonic vehicles. The computational demands associated with the high-fidelity analysis tools for predicting the system performance restrict the number of simulations that are possible within the design cycle time. Hence, analysis tools of lower fidelity are generally used for design studies. To enable the designer to make better design decisions in such situations, the lower fidelity analysis tool is complemented with an uncertainty model. An approach based on ranks is proposed in this study to aggregate high-fidelity information in a cost effective manner. Based on this information, a cumulative distribution function for the difference between high-fidelity response and low-fidelity response is constructed. The approach is explained initially for uncertainty quantification in a synthetic example. Subsequently an uncertainty model for estimating the mass flow capture of air, a typical disciplinary performance metric in hypersonic vehicle design, is presented.