Anil K. Kulkarni

Bifurcation of Low Reynolds Number Flows in Symmetric Channels

The flowfields in two-dimensional channels with discontinuous expansions are studied numerically to understand how the channel expansion ratio influences the symmetric and nonsymmetric solutions that are known to occur. For improved confidence and understanding, two distinct numerical techniques are used. The general flowfield characteristics in both symmetric and asymmetric regimes are ascertained by a time-marching finite difference procedure. The flowfields and the bifurcation structure of the steady solutions of the Navier-Stokes equations are determined independently using the finite element technique. The two procedures are then compared both as to their predicted critical Reynolds numbers and the resulting flowfield characteristics. Following this, both numerical procedures are compared with experiments.

A comprehensive model for AP-based composite propellant ignition

A comprehensive model and numerical solutions for ignition of AP-based composite solid propellants are presented. The analysis simulates the ignition process of a propellant sample, located in a stagnation region, under rapid pressure loading conditions. Specific features considered in the model include: 1) detailed chemical kinetics information for the ignition of AP-based composite propellants, 2) two-dimensional (axisymmetric) geometry for the composite propellant, and 3) rapid pressurization of the gas phase. An implicit finite difference scheme is used to solve the set of transient, second-order, coupled, inhomogeneous, nonlinear, governing partial differential equations. Numerical solutions reveal a number of important events occurring during the ignition sequence, including: igniter gas penetration to the region near the sample surface, combustion of unburned species upon arrival of compression waves, heat transfer to the propellant, pyrolysis of the oxidizer and fuel, and gas-phase reactions leading to ignition. The model correctly predicts the experimental observation that the ignition delay time decreases as the pressurization rate is increased. The various ignition criteria considered show the same trend as that measured experimentally.

SIMULATIONS OF PLANAR FLAPPING JETS IN CONFINED CHANNELS

Computational analyses are used to provide a more complete understanding of the mechanisms that contribute to the development of oscillating planar jets. The geometry considered is a two-dimensional jet exhausting into a blind channel, whose open end is opposite to the initial direction such that the jet must turn through 180 deg to exit. The resulting flowfields exhibit three distinct characters that depend on the channel expansion ratio and the Reynolds number. At low Reynolds numbers the flow is steady and symmetric. A symmetry-breaking bifurcation at intermediate Reynolds numbers produces steady asymmetric flows. A Hopf bifurcation at higher Reynolds numbers yields unsteady flows. Predicted critical Reynolds numbers and oscillation frequencies are presented for different expansion ratios. Solutions are obtained from the time-dependent Navier-Stokes equations by means of an incompressible formulation based on dual-time stepping via artificial compressibility