Numerical simulation of turbulent reacting flow plays an important role in the design of high performance propulsion system as the experimental investigation is both very expensive and time consuming. Numerical simulations help to understand the important flow feature and to reduce the developmental time in the design cycle. Core competence in numerical simulation of turbulent reacting flows pertaining to the propulsion system of various ongoing and future missile projects has been established in Computational Combustion Dynamics (CCD) Division of the DRDO. This involves geometric modelling, formulation, solving the flow equations for non-reacting and the reacting flow conditions, and post processing of data to obtain the variation of parameters in time and space. Indigenous and commercial softwares have been used to study the complex flow field inside the propulsion systems and extensive validation exercises for reacting and non-reacting flows have been carried out to find the range of the application of software and the error band of the computations.

         Very important contribution in design and analysis of scramjet combustor of Hypersonic Air-breathing Technology Demonstrator has been made through numerous simulation results and important design changes have been suggested to achieve better efficiency in terms of thrust and other propulsive parameters. Aerodynamic characterisation of jet vane geometry is yet another important area where numerical simulation of the flow field has played a significant role. At the initial phase of a missile launch, when the speed of the missile is not very high, the control and stability requirement of the vehicle is satisfied by jet vane thrust vector control system. Numerical simulations have been carried out for jet vane geometry in the cold-flow condition in the wind tunnel as well as in the presence of hot rocket exhaust. Very good agreement has been obtained for the jet vane characteristics with the wind tunnel measured values. Attempts are also being made to couple the erosion pattern with the flow solver to predict the performance of the jet vane in the extreme thermal and mechanical load conditions. Other notable areas for which numerical simulations are being used include Air Intake Flow Field, Tip-to-Tail Aero-Propulsive Simulation of Hypersonic Air-breathing missile, Liquid Fuel Ramjet (LFRJ) Combustor Flow Field, Conjugate Heat Transfer Studies, etc.

Reacting flow of DRDO scramjet combustor

         Major initiatives have been taken by DRDO to develop an indigenous turbulent reacting flow simulator ‘RETURNS’ to achieve self-reliance in this important area. The software is being developed in a modular way using object-oriented concept. It uses AUSM+ for inviscid fluxes and central differencing for viscous fluxes. Turbulence is modelled with K-e turbulence model with low Reynolds number correction. The laminar version of the software has been developed and validated against various test cases. Validation and development for the turbulent and reacting flows are in progress. Various advanced topics like Modelling of Ignition, Atomisation Modelling, Reduced Chemistry, Turbulence Chemistry Interactions and Large Eddy Simulations (LES) are also being pursued.

          Advanced tools for numerical flow simulation to predict the flow characteristics in high performance propulsion system makes the design feasible and gives confidence in conducting the experiments.