Forward Flight Rotor Performance at Martian Atmospheric Densities and Sensitivity to Low Reynolds Numbers

Much effort has been made to enhance exploration on Mars. In addition to a rover and Mars-orbiting satellites, a Mars Helicopter Technology Demonstrator was proposed by the NASA Jet Propulsion Laboratory (JPL) to augment planetary research for the Mars 2020 Mission. Understanding rotor performance is vital for operations at Martian atmospheric conditions. The work presented is a study investigating rotor performance at Martian atmospheric conditions. Forward flight rotor tests were conducted in the Planetary Aeolian Laboratory (PAL) at NASA Ames Research Center, which has the capability to evacuate the air in the chamber to reach Martian atmospheric densities. A 1-meter-diameter rotor, roughly approximating the Mars Helicopter Technology Demonstrator, was tested at multiple atmospheric densities, including that of Mars. Rotor rotational speed, thrust, torque, power, and airspeed measurements were collected during the test. These results were then correlated with simulated cases using a mid-fidelity computational fluid dynamics software, Rotorcraft CFD (RotCFD). C81Generator (C81Gen) was used to generate airfoil aerodynamic coefficient for the spanwise locations along the rotor. To observe the differences between the C81Gen flow type modes at low Reynolds number, the simulations at Martian atmospheric densities were run under the fully turbulent, and the fully laminar flow type. In addition, Reynolds number effects (within 2x104 to 9x104) on experimental thrust coefficient, power coefficient, and figure of merit were analyzed. Within this chord- based Reynolds number range, CT and FM decreased around 26% and 36%, respectively, while CP remained fairly constant, exhibiting variations of no more than 5.5%. Despite the challenges involved in testing at a large difference of atmospheric ensities between Earth and Mars, repeatable data was obtained in all the measurements at Martian atmospheric conditions

Determinants of Maritime Transport Costs

Recent literature has emphasized the importance of transport costs and infrastructure in explaining trade, access to markets, and increases in per capita income. For most Latin American countries, transport costs are a greater barrier to U. S. markets than import tariffs. We investigate the determinants of shipping costs to the U. S. with a large database of more than 300,000 observations per year on shipments of products at the six-digit HS level from different ports around the world. Distance and containerization matter. In addition, we find that efficiency of ports is an important determinant of shipping costs. Improving port efficiency from the 25th to the 75th percentile reduces shipping costs by 12 percent. (Bad ports are equivalent to being 60 percent farther away from markets for the average country. ) Inefficient ports also increase handling costs, which are one of the components of shipping costs. We try to explain variations in port efficiency and find that they are linked to excessive regulation, the prevalence of organized crime, and the general condition of the country’s infrastructure. Finally, we present a number of success stories in Latin America to show that private involvement in port management leads to efficiency and lower costs whenever it is accompanied by labor reform, and when monopoly power is reduced through either regulation or competition.

Effects of a radially varying electrical conductivity on 3D numerical dynamos

The transition from liquid metal to silicate rock in the cores of the terrestrial planets is likely to be accompanied by a gradient in the composition of the outer core liquid. The electrical conductivity of a volatile enriched liquid alloy can be substantially lower than a light-element-depleted fluid found close to the inner core boundary. In this paper, we investigate the effect of radially variable electrical conductivity on planetary dynamo action using an electrical conductivity that decreases exponentially as a function of radius. We find that numerical solutions with continuous, radially outward decreasing electrical conductivity profiles result in strongly modified flow and magnetic field dynamics, compared to solutions with homogeneous electrical conductivity. The force balances at the top of the simulated fluid determine the overall character of the flow. The relationship between Coriolis and Lorentz forces near the outer boundary controls the flow and magnetic field intensity and morphology of the system. Our results imply that a low conductivity layer near the top of Mercury's liquid outer core is consistent with its weak magnetic field.Comment: 30 pages, 11 figures, 2 tables. To be published in Physics of Earth and Planetary Interiors (PEPI)