Shuh-Jing Ying

The fire whirl

A fire whirl from a liquid-fuel pool (acetone) is formed at the center of a rotating screen which imparts a controlled angular momentum to the ambient air. Measurements show that outside of the core the fluid motion is that of a free vortex. A hot-wire method of measurement of the radial temperature distribution is developed. The temperature distribution shows that the fire whirl consists of a rotating cylinder, fuel rich inside, lean outside. The turbulent plume theory is extended to include combustion and angular momentum. This theory checks the experimental results and provides: o 1. The turbulent mixing coefficient decreases with increasing angular momentum, as is to be expected. 2. The turbulent mixing coefficient increases with elevation above the ground. This effect was not expected. Its cause remains unknown, although it may be in some way related to the vertex-jump (vortex breakdown) phenomena which may be required if the whirl is to satisfy both ground-level and “high”-altitude boundary conditions.

Exploratory Model Study of Tornado-Like Vortex Dynamics

Abstract A laboratory model of the tornado-like vortex near the ground is developed and studied. The circulation is produced by a rotating cylindrical screen and the updraft is produced by an exhaust fan at the opening of the top hood. By means of kerosene smoke, the vortex core and a reverse flow zone were observed in the experiment. The profiles of velocity and pressure were measured at three different circulation strengths. The maximum inward radial velocity in the boundary layer is approximately proportional to the circulation strength. Outside the vortex core, the top hood and ground boundary layers, the flow is a potential vortex flow with a very small inward radial velocity. The vertical velocity distribution generally has a Gaussian profile except that it is slightly downward in the annular reverse flow region. The diameter of the reverse flow region is controlled by the opening size of the outlet on the top hood. The reverse flow region extends to the top of the ground boundary layer only when th...

Thermally Driven Nonlinear Oscillations in a Pipe with Traveling Shock Waves

Nonlinear vibrations in a pipe closed at both ends with a plane heater in its midsection and containing a perfect gas are studied. When the frequency of a sinusoidal heat release is equal to twice the fundamental resonance frequency of the pipe, the level of fluctuation increases with time; shock waves are formed and ultimately the fluctuation attains a limiting value. It is shown that if the rate of heat release is small compared to the total enthalpy in the volume traversed by an acoustic front in a unit time, the fluctuation in the pipe, after many oscillations, builds up to (σ0/p0a0)½, where σ0 is the amplitude of the rate of heat release per unit area of the heater, and p0, a0 are respectively the initial pressure and sound speed. The nature of vibration in the pipe is found to be similar to that excited in a cylinder by a piston driven sinusoidally near a resonance frequency. The pressure and velocity at a fixed point in the pipe are shown to vary sinusoidally with time between the successive arriva...

An extension of MacCormack's method for flows with higher-order equations and in different configurations

The numerical scheme for the computation of a shock discontinuity developed by MacCormack has been extended to solve a number of differential equations, including cases explicitly containing higher-order derivatives: (1) Korteweg-de Vries equation with a term of third-order derivative, (2) a system of nonlinear equations governing nonsteady one-dimensional plasma flow in cylindrical coordinate, (3) equations of solar wind. Comparisons with previous results are made, if available, to illustrate the advantages of the present method. The question of convergence of the numerical calculation is discussed.

Flame propagation of burning solid material with moisture

The author has developed an analytical model in an effort to determine the effect of moisture on flame propagation. To some degree, the study clarifies the fire controlling mechanism of liquids.

Reduced chemical kinetics for propane combustion

It is pointed out that a detailed chemical kinetics mechanism for the combustion of propane consists of 40 chemical species and 118 elementary chemical reactions. An attempt is made to reduce the number of chemical species and elementary chemical reactions so that the computer run times and storage requirements may be greatly reduced in three-dimensional gas turbine combustion flow calculations, while maintaining accurate predictions of the propane combustion and exhaust emissions. By way of a sensitivity analysis, the species of interest and chemical reactions are classified in descending order of importance. Nineteen species are chosen, and their pressure, temperature, and concentration profiles are presented for the reduced mechanisms, which are then compared with those from the full 118 reactions. It is found that 45 reactions involving 27 species have to be kept for comparable agreement. A comparison of the results obtained from the 45 reactions to that of the full 118 shows that the pressure and temperature profiles and concentrations of C3H8, O2, N2, H2O, CO, and CO2 are within 10 percent of maximum change.

Modeling the plasma near-wakes

An ambient unmagnetized plasma is considered in which a flat-based projectile of radius R and zero surface potential moves along its axis of symmetry at a constant mesothermal speed. The plasma cavity-filling process is likened to the transient flow associated with a radially imploding cylindrical shock seen immediately after the rupture of a cylindrical diaphragm of radius R. A modeling scheme is presented assuming that electron temperature remains constant and is much higher than the ion temperature in plasma and that ions move in a self-consistent electric field with which the electrons are already in Boltzmann equilibrium. A figure illustrates the ion density distributions at consecutive times after the start of implosion and the existence of an ion wavefront as a result of charge separation is clearly seen.

The promising chemical kinetics for the simulation of propane-air combustion with KIVA-II code

The development of chemical kinetics for the simulation of propane-air combustion with the use of computer code KIVA-II since 1989 is summarized here. In order to let readers understand the general feature well, a brief description of the KIVA-II code, specially related with the chemical reactions is also given. Then the results of recent work with 20 reaction mechanism is presented. It is also compared with the 5 reaction mechanism. It may be expected that the numerical stability of the 20 reaction mechanism is better as compared to that of 5 reaction mechanism, but the CPU time of the CRAY computer is much longer. Details are presented in the paper.

On the initial expansion of meteor trails

The asymptotic solution of the equation governing the number density n(r,t) of evaporated meteoric atons behind a steadily moving meteor is obtained which is suitable to depict the initial expansion of a meteor trail. Some unusual results of meteor observations are elucidated.

Numerical simulation of Jet-A combustion approximated by improved propane chemical kinetics

Through the effort devoted to the chemical kinetics for propane air combustion, three mechanisms are developed. The full mechanism consists of 131 reactions. This mechanism is used as a guide for the evaluation of other mechanisms, but because of the long expected cpu time, it is not to be incorporated into the computer code KIVA-II for actual simulation. Through the sensitivity analysis, a reduced mechanism of 45 reactions is produced. But the calculated results from the 45 reaction mechanism are always low in temperature. Some efforts are devoted to correct this situation and details are included in this report. A simplified mechanism of reactions is successfully improved and computed results are compared with experimental data. Contour plots of physical parameters and species concentrations and results for emission indices of CO and NOx are presented.