Dwarshala Siva Krishna Reddy

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

The present work aims at the prediction of shock wave position on the heat shield region of a three body launch vehicle in transonic region. The launch vehicle consists of a cylindrical core body and two boosters. The core body is made of a spherical nose, followed by a cone and heat shield region which is a flat surface. The heat shield is followed by a boat tail. Simulations are performed with commercial CFD package, ANSYS –FLUENT. Reynolds stresses are computed using the k-ω SST turbulence model. Explicit time integration is used to obtain steady-state solutions. A structured grid over the vehicle is generated using ICEMCFD software. In the near-wall region of the launch vehicle fine mesh is employed to capture the boundary layer. Simulations are performed for angle of attacks (AOA) 0° and 4° for Mach number 0.95. The computed nose stagnation pressure compared with the isentropic relations and deviation found to be .067%. A standing normal shock wave is observed for AOA 0 whereas an oblique shock wave is observed for angle of attack 4°. The predicted flow structure in terms of density distribution is compared with experimental schlieren images. The predictions captured essential flow features such as expansion around the conical part, boundary layer over the heat shield, shock wave on the heat shield, and flow separation in the boat tail region. The predicted flow structure and shock wave position for AOA O matched well with the experiments. However, for AOA 4°, the deviation between flow structure and shock position is noticed. Possible reasons for the deviation are explained.

In the present work, three dimensional numerical simulations over a launch vehicle at 70 m/s are performed for 3 scale models. The vehicle has a cylindrical core body and two strap on boosters. The scaled models chosen so that they represent a wind tunnel blockage ratio of 3%, 4% and 5% respectively. Simulations are performed using commercial CFD software Ansys Fluent. Three dimensional structured mesh is generated using ICEMCFD software. The solver depends on finite volume technique, and SIMPLE calculation is utilized to address the couple continuity and energy conditions. K-w SST model is utilized for disturbance demonstration. The computed flow field is analyzed in terms of velocity, pressure and turbulent kinetic energy contours. Surface pressure acquired from the three simulation (relating to every blockage ratio) arrangements in balance plane is compared to understand the impact of blockage ratio on the stream field and drag coefficients. As the blockage is increased, it was observed that maximum velocity is increasing. Lowest blockage found to give highest drag coefficient.

The dissipation of heat in tiny engineering systems can be achieved with fluid flow through micro pipes. They have the advantage of less volume to large surface ratio convective heat transfer. There are deep-rooted analytical relations for convective heat transfer available for fluid flow through macro size pipes. But differences exist between the convective heat transfer for fluid flow through macro and micro pipes. Therefore, there is a good scope of work in micro convection heat transfer to study the mechanism of fundamental flow physics. There have been studies with either constant heat flux wall boundary conditions or constant wall temperature boundary conditions with constant and variable property flows. In this article, first, the numerical simulations are validated with the experimental data for 2D axisymmetric conventional pipe with pipe diameter of 8 mm is taken with laminar, steady, and single-phase water flows with constant wall heat flux boundary condition of 1 W/cm2. The computed Nusselt number is compared to the experimental results at different Reynolds numbers of 1350, 1600 and 1700. In the next study, three-dimensional micropipe laminar flow is studied numerically using water with an inlet velocity of 3 m/s and pipe diameter of 100 µm. The mixed wall boundary conditions with upper half pipe surface subjecting to constant wall temperature of 313 K and lower half surface subjecting to 100 W/cm2 are used in the simulations. The focus of research would be to consider the effect of temperature-dependent properties like thermal conductivity, viscosity, specific heat, and density (a combined effect we call it as variable properties) on micro-pipe flow characteristics like Nusselt number at mixed wall boundary conditions and compare it with the constant property flows. The conventional pipe showed no significant difference with variable and constant property flows with different Reynolds numbers. On contrary the flow through 3D micropipe shows that the Nusselt number with variable property flows is less as compared to the constant property flows.

This numerical study reports the aerodynamic properties of a hybrid airship. The hybrid airships were designed by combining two semi-ellipsoids with a semi-discoid as the base model. From the base model, three different geometrics were identified to study their aerodynamic characteristics. A circular slot was provided between the pressure side and the suction side of the airship. The objective of this study was to realize the flow behavior, aerodynamic characteristics, and stability properties of such slotted hybrid flying vehicles. Interestingly, the results imply that the lift coefficient increases with an increase in the angle of attack for the slotted configurations; this is because the flow separation is delayed due to the slot opening, which in turn is due to the flow of energies from the high-pressure region to the bottom through the slots. The delayed stall angle was 50 degrees, which was 10% more than that of the base model. Aerodynamic characteristics are discussed based on surface pressure, coefficient of lift, and coefficient of drag for various slotted hybrid airships.