Understanding the Motivations of Freedom Summer Freedom School Teachers

Significant movements require serious motivations from those involved. During the Civil Rights Movement, those involved in Freedom Summer of 1964 risked their lives and comfort to advance the Movement. Freedom Summer Freedom School teachers had unique motivations; some motivations were shared amongst the teachers, while others were individual. Although it is difficult to fully understand the motivations of Freedom School teachers, this paper identifies three overarching motivations that were shared amongst the teachers: an understanding that African Americans in the South were denied equality in education, the belief that the curriculum of Freedom Schools would address this educational inequality, and the recognition that education has the power to initiate social change. In addition to identifying these overarching motivations, this paper examines three Freedom School teachers, Chude Pam Allen, Gwendolyn Simmon, and Liz Fusco Aaronsohn in order to explain individual motivations for joining the movement. The purpose of this paper is to point out the depth and complexity of overarching and individual motivations and to illustrate the importance of looking at both in order to fully understand the motivations of those who participate in a movement

Characteristics of transitional multicomponent gaseous and drop-laden mixing layers from direct numerical simulation: Composition effects

Transitional states are obtained by exercising a model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer at larger Reynolds numbers, Re, than in a previous study. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete dynamic and thermodynamic coupling between phases is included. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass, is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of their PDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices, resulting into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions, and the effects of the initial mass loading and initial free-stream gas temperature are explored. For reference, simulations are also performed for gaseous multicomponent mixing layers for which the effect of Re is investigated in the direct-numerical-simulation–accessible regime. The results encompass examination of the global layer characteristics, flow visualizations, and homogeneous-plane statistics at transition. Comparisons are performed with previous pretransitional MC-liquid simulations and with transitional single-component (SC) liquid-drop-laden mixing layer studies. Contrasting to pretransitional MC flows, the vorticity and drop organization depend on the initial gas temperature, this being due to drop/turbulence coupling. The vapor-composition mean molar mass and standard deviation distributions strongly correlate with the initial liquid-composition PDF. Unlike in pretransitional situations, regions of large composition standard deviation no longer necessarily coincide with those of large mean molar mass. The rotational and composition characteristics are all liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The classical energy cascade is found to be of similar strength, but the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation for MC flows. The kinetic energy and dissipation are liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The gas composition, of which the first four moments are calculated, is shown to be close to, but distinct from, a SGPDF. Eulerian and Lagrangian statistics of gas-phase quantities show that the different observation framework may affect the perception of the flow

Curvature and confinement effects for flame speed measurements in laminar spherical and cylindrical flames.

This paper discusses methods used to obtain laminar flame speeds in spherical laminar premixed flames. Most recent studies express the laminar flame consumption speed as ρb/ρudR/dt, where R is the flame radius and ρb/ρu is the ratio of the burnt to the fresh gas density (ρb is evaluated at chemical equilibrium and supposed to be constant). This paper investigates the validity of this assumption by reconsidering it in a more general framework. Other formulae are derived and tested on a DNS of cylindrical flames (methane/air and octane/air). Results show that curvature and confinement effects lead to variations of ρb and ρu and to significant errors on the flame speed. Another expression (first proposed by Bradley and Mitcheson in 1976) is derived where no density evaluation is required and only pressure and flame radius evolution are used. It is shown to provide more precise results for the consumption speed than ρb/ρudR/dt because it takes into account curvature and confinement of the flame in the closed bomb

Large-Eddy Simulation of combustion instabilities in a variable-length combustor.

This article presents a simulation of a model rocket combustor with continuously variable acoustic properties thanks to a variable-length injector tube. Fully compressible Large-Eddy Simulations are conducted using the AVBP code. An original flame stabilization mechanism is uncovered where the recirculation of hot gases in the corner recirculation zone creates a triple flame structure. An unstable operating point is then chosen to investigate the mech- anism of the instability. The simulations are compared to experimental results in terms of frequency and mode structure. Two-dimensional axi-symmetric computations are com- pared to full 3D simulations in order to assess the validity of the axi-symmetry assumption for the prediction of mean and unsteady features of this flow. Despite the inaccuracies in- herent to the 2D description of a turbulent flow, for this configuration and the particular operating point investigated, the axi-symmetric simulation qualitatively reproduces some features of the instability

Experimental and numerical study of the accuracy of flame-speed measurements for methane/air combustion in a slot burner

Measuring the velocities of premixed laminar flames with precision remains a controversial issue in the combustion community. This paper studies the accuracy of such measurements in two-dimensional slot burners and shows that while methane/air flame speeds can be measured with reasonable accuracy, the method may lack precision for other mixtures such as hydrogen/air. Curvature at the flame tip, strain on the flame sides and local quenching at the flame base can modify local flame speeds and require correc- tions which are studied using two-dimensional DNS. Numerical simulations also provide stretch, dis- placement and consumption flame speeds along the flame front. For methane/air flames, DNS show that the local stretch remains small so that the local consumption speed is very close to the unstretched premixed flame speed. The only correction needed to correctly predict flame speeds in this case is due to the finite aspect ratio of the slot used to inject the premixed gases which induces a flow acceleration in the measurement region (this correction can be evaluated from velocity measurement in the slot section or from an analytical solution). The method is applied to methane/air flames with and without water addition and results are compared to experimental data found in the literature. The paper then discusses the limitations of the slot-burner method to measure flame speeds for other mixtures and shows that it is not well adapted to mixtures with a Lewis number far from unity, such as hydrogen/air flames

Use of control umbilicals as a deployment mode for free flying telerobotic work systems

Work to date on telerobotic work systems for use in space generally consider two deployment modes, free flying, or fixed within a limited work envelope. Control tethers may be employed to obtain a number of operational advantages and added flexibility in the basing and deployment of telerobotic work systems. Use of a tether allows the work system to be separated into two major modules, the remote work package and the control module. The Remote Work Package (RWP) comprises the free flying portion of the work system while the Control Module (CM) remains at the work system base. The chief advantage of this configuration is that only the components required for completion of the work task must be located at the work site. Reaction mass used in free flight is stored at the Control module and supplied to the RWP through the tether, eliminating the need for the RWP to carry it. The RWP can be made less massive than a self contained free flying work system. As a result, reaction mass required for free flight is lower than for a self contained free flyer

Stabilization of a supercritical hydrogen / oxygen flame behind a splitter plate

The numerical simulation of fluid dynamics and combustion in cryogenic rocket engines is addressed in this paper, with the intent to elucidate flame stabilization mechanisms. A model configuration is devised to allow a fully resolved simulation, both for the dynamics and the flame structure: a two-dimensional splitter plate represents the lip of an injector and the operating point is typical of a real engine. The non-reacting flow field is first scrutinized to evaluate the impact of the large density gradients between the fuel (hydrogen) and oxidizer (oxygen) streams. It is found that the turbulence generated by the splitter is very intense and strongly distorts the high-density-gradient front at both small and large scales. Under reacting conditions, the flame stabilizes right at the lip of the injector, which is a common feature of hydrogen / oxygen flames under these conditions. A particularly complex flame structure is evidenced at the anchoring point, with turbulent transport playing an important role

Effects of hydrogen and steam addition on laminar burning velocity of methane–air premixed flame: Experimental and numerical analysis

Effects of hydrogen enrichment and steam addition on laminar burning velocity of methaneeair premixed flame were studied both experimentally and numerically. Measurements were carried out using the slot burner method at 1 bar for fresh gases temperatures of 27 °C and 57 °C and for variable equivalence ratios going from 0.8 to 1.2. The hydrogen content in the fuel was varied from 0% to 30% in volume and the steam content in the air was varied from 0 to 112 g/kg (0e100% of relative humidity). Numerical calculations were performed using the COSILAB code with the GRI-Mech 3.0 mechanism for one-dimensional premixed flames. The calculations were implemented first at room temperature and pressure and then extended to higher temperatures (up to 917 K) and pressures (up to 50 bar). Measurements of laminar burning velocities of methanee hydrogeneair and methaneeairesteam agree with the GRI-Mech calculations and previous measurements from literature obtained by different methods. Results show that enrich- ment by hydrogen increases of the laminar burning velocity and the adiabatic flame temperature. The addition of steam to a methaneeair mixture noticeably decreases the burning velocity and the adiabatic flame temperature. Modeling shows that isentropic compression of fresh gases leads to the increase of laminar burning velocity