Kevin R. Anderson

Classification of Absolute and Convective Instabilities in Premixed Bluff Body Stabilized Flames

A local, small perturbation, linear, inviscid stability analysis is applied to co-flowing reacting shear layers downstream of a bluff body flame holder. Velocity and density profiles are taken from premixed flame experiments. Linear stability theory is employed to determine the regions of transition from absolute to convective instabilities in the wakes of transverse circular cylinder and rectangular bar stabilized flames at two fuel lean conditions, one close to blow off and the other further from blow off. Instabilities in the near wake region of the flame holders are found to be absolute in nature while further downstream in the recirculation zone, the stabilities are of the convective type. Frequencies corresponding to regions of absolute instabilities are determined and compared to previously measured experimental values known to result in vortex shedding.

CFD analysis for assessing the effect of wind on the thermal control of the Mars Science Laboratory Curiosity Rover

The challenging range of landing sites for which the Mars Science Laboratory Rover was designed, requires a rover thermal management system that is capable of keeping temperatures controlled across a wide variety of environmental conditions. On the Martian surface where temperatures can be as cold as -123C and as warm as 38C, the rover relies upon a Mechanically Pumped Fluid Loop (MPFL) Rover Heat Rejection System (RHRS) and external radiators to maintain the temperature of sensitive electronics and science instruments within a -40C to 50C range. The RHRS harnesses some of the waste heat generated from the rover power source, known as the Multi Mission Radioisotope Thermoelectric Generator (MMRTG), for use as survival heat for the rover during cold conditions. The MMRTG produces 110 W of electrical power while generating waste heat equivalent to approximately 2000 W. Heat exchanger plates (hot plates) positioned close to the MMRTG pick up this survival heat from it by radiative heat transfer. Winds on Mars can be as fast as 15 m/s for extended periods. They can lead to significant heat loss from the MMRTG and the hot plates due to convective heat pick up from these surfaces. Estimation of this convective heat loss cannot be accurately and adequately achieved by simple textbook based calculations because of the very complicated flow fields around these surfaces, which are a function of wind direction and speed. Accurate calculations necessitated the employment of sophisticated Computational Fluid Dynamics (CFD) computer codes. This paper describes the methodology and results of these CFD calculations. Additionally, these results are compared to simple textbook based calculations that served as benchmarks and sanity checks for them. And finally, the overall RHRS system performance predictions will be shared to show how these results affected the overall rover thermal performance.

Numerical simulation of conduction heat transfer in a system of slowly rotating concentric shells separated by small annular gap distances

Conduction dominated heat transfer in a system of concentric shells with a very small annulus distance and surface eccentricities is studied numerically using IDEAS TMGTM in conjunction with a user-programmed subroutine to model the heat transfer across the gas layer as a function of eccentricity and rotation rate. Sphere diameters range from 30 cm to 40 cm, annular gap sizes range from 0.5 mm to 1 mm, and eccentricities range from 0.05 mm to 0.25 mm. External thermal gradients are found to be attenuated significantly. The inner surface temperature deltas increase by a factor of 4.5, for a doubling in the eccentricity. A correlation for the effective heat transfer across the inner spheres also is presented.

Numerical Study of Vortex/Flame Interaction in Actively Forced Confined Non-Premixed Jets

Numerical simulations of coplanar reacting jets subjected to near wall confinement have been performed. The primary conclusion is that for a fixed level of heat release, the mechanism of baroclinic vorticity production increases with more severe wall confinement.

A two-dimensional planar computational investigation of flame broadening in confined non-premixed jets

The near-exit region of confined, unsteady, momentum dominated, non-premixed, chemically reacting jets is investigated computationally using one-step chemistry. Non-premixed flame/wall interaction is manifested in the form of reaction zone broadening. Depending on the value of the stoichiometric mixture fraction, the flame zone moves into or out of the region of strong shear. For flames with large stoichiometric mixture fraction, the flame region is located in closer proximity to the isothermal wall. With increased stoichiometric mixture fraction, reaction thicknesses predicted by asymptotic theory differ from flame zone thicknesses obtained from the simulation databases.

CO2 Insulation for Thermal Control of the Mars Science Laboratory

The National Aeronautics and Space Administration (NASA) is sending a large (>850 kg) rover as part of the Mars Science Laboratory (MSL) mission to Mars in 2011. The rovers primary power source is a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) that generates roughly 2000 W of heat, which is converted to approximately 110 W of electrical power for use by the rover electronics, science instruments, and mechanism-actuators. The large rover size and extreme thermal environments (cold and hot) for which the rover is designed for led to a sophisticated thermal control system to keep it within allowable temperature limits. The pre-existing Martian atmosphere of low thermal conductivity CO2 gas (8 Torr) is used to thermally protect the rover and its components from the extremely cold Martian environment (temperatures as low as -130 deg C). Conventional vacuum based insulation like Multi Layer Insulation (MLI) is not effective in a gaseous atmosphere, so engineered gaps between the warm rover internal components and the cold rover external structure were employed to implement this thermal isolation. Large gaps would lead to more thermal isolation, but would also require more of the precious volume available within the rover. Therefore, a balance of the degree of thermal isolation achieved vs. the volume of rover utilized is required to reach an acceptable design. The temperature differences between the controlled components and the rover structure vary from location to location so each gap has to be evaluated on a case-by-case basis to arrive at an optimal thickness. For every configuration and temperature difference, there is a critical thickness below which the heat transfer mechanism is dominated by simple gaseous thermal conduction. For larger gaps, the mechanism is dominated by natural convection. In general, convection leads to a poorer level of thermal isolation as compared to conduction. All these considerations play important roles in the optimization process. A three-step process was utilized to design this insulation. The first step is to come up with a simple, textbook based, closed-form equation assessment of gap thickness vs. resultant thermal isolation achieved. The second step is a more sophisticated numerical assessment using Computational Fluid Dynamics (CFD) software to investigate the effect of complicated geometries and temperature contours along them to arrive at the effective thermal isolation in a CO2 atmosphere. The third step is to test samples of representative geometries in a CO2 filled chamber to measure the thermal isolation achieved. The results of these assessments along with the consistency checks across these methods leads to the formulation of design-guidelines for gap implementation within the rover geometry. Finally, based on the geometric and functional constraints within the real rover system, a detailed design that accommodates all these factors is arrived at. This paper will describe in detail this entire process, the results of these assessments and the final design that was implemented.

Analysis and Design of a Lightweight High Specific Power Two-Stroke Polygon Engine

Current trends in engine design have pushed the state of the art regarding high power-to-weight ratio gasoline engines. Newly developed engine systems have a power-to-weight ratio near 1 hp per pound. The engine configuration presented herein makes it possible to package a large number of power producing pistons in a small volume, resulting in a power-to-weight ratio near 2 hp per pound, which has never before been realized in a production engine. The analysis and design of a lightweight two-stroke 6-sided in-plane polygon engine having a geometric compression ratio of 15.0, an actual compression ratio of 8.8, and a piston speed of 3500 ft/min are presented in this investigation. Typical results show that for a hexagonal engine with 2 in. diameter pistons and 1.25 in. stroke, a single piston displacement is 7.85 cubic in., while the total engine displacement is 47. 1 cubic in. Full power at 12,960 rpm at an air flow rate of 353 cubic feet per minute affords 0.444 cubic ft/min/hp for specific power. For an efficiency of 21%, the blower power is 168 hp. Our air-flow analysis shows that the power of the engine does not depend on the number of pistons, but rather on the volume of the gas-air mixture which passes through the engine. System level engineering of power output, kinematic modeling, air-flow modeling, efficiency, scavenging predictions, crankshaft sizing, and weight estimates are presented.

Analysis of a Solar Updraft Tower Utilizing Compost Waste Heat

This paper presents the results for a feasibility study of a solar chimney which uses low-grade waste heat from compost in conjunction with solar energy transmitted via a transparent roof top. The feasibility study shows that the solar chimney’s turbine power increases with pressure ratio, the height of the chimney as well as the differential temperature in the chamber. This paper also outlines the thermodynamic modeling related to using waste heat from composting to increase the air temperature in the inlet chamber of a solar chimney. It is found that from this analysis that the average temperature in the chamber increases as a function of the chimney inlet chamber axial length. For a chimney 1150 ft (350 m) high and 24 ft (7.3 m) in diameter processing 8000 tons of composting material it is found that a power output of 38 kW can be harnessed at the turbine.Copyright

A Review on Nanofluid Heat Pipe

This paper reviews the improvement in the heat pipe’s performance using nanofluid as the working fluid. The use of nanofluid enhances heat transfer in the heat pipe due to its improved thermo-physical properties, such as a higher thermal conductivity. Nanofluids proved to be the innovative approach to a variety of applications, such as electronics, medical instruments, and heat exchangers. The influence of different nanoparticles on heat pipe’s performance has been studied. Utilizing nanofluid as the working fluid leads to a significant reduction in heat pipe thermal resistance, an increase in maximum heat transfer, and an improvement of heat pipe thermal performance.© 2014 ASME

Survey of Active Aeroelastic Control for Flutter Suppression

Aeroelastic flutter is the potentially destructive aerodynamic vibration of an elastic body in an air-stream. The interactions of aerodynamic, inertial and structural forces cause coupled torsional and bending modes on the aircraft, which can exceed its structural strength. An aircraft’s wing, tail and control surfaces are at the greatest risk of experiencing flutter. The goal of a flutter suppression system is to clear the flight envelope from flutter. This paper provides an overview regarding the current state-of-the-art hardware, techniques and analytical methods used in implementing Active Aeroelastic Control (AAC) in the design of a flutter suppression system.Copyright