A numerical simulation of three-dimensional flow in an adaptive wall wind tunnel

Numerical simulations of three dimensional flows in a prototype adaptive wall wind tunnel are conducted at the Mach number of 0.6 to investigate: (1) wind tunnel wall interference, (2) active streamline control by varying air removal or injection along the walls, and (3) to develop a method for establishing wall boundary conditions for interference free flows. Wind tunnel wall interference could be controlled by using only the vertical velocity components. For the configuration tested, interference free flow with solid sidewalls can be approximated by using only floor and ceiling blowing/suction

The Quality of Philippine Coconut Statistics

Being the most important Philippine crop, this study concentrates on the evaluation study of the coconut industry. The results are hoped to provide insights to the quality of statistics on the agricultural commodities classified as “other crops” and to offer wider assessment of the quality of the country's statistics on other agricultural products as well.coconut industry, agriculture sector, data and statistics, corn and corn products

The Quality of Philippine Coconut Statistics

Being the most important Philippine crop, this study concentrates on the evaluation study of the coconut industry. The results are hoped to provide insights to the quality of statistics on the agricultural commodities classified as “other crops” and to offer wider assessment of the quality of the country's statistics on other agricultural products as well.coconut industry, agriculture sector, data and statistics, corn and corn products

Fiscal Policy and Macroeconomic Uncertainty in Emerging Markets: The Tale of the Tormented Insurer

Governments in emerging markets often behave like a "tormented insurer", trying to use non-state-contingent debt instruments to avoid sharp adjustments in their payments to private agents despite sharp fluctuations in public revenues. In the data, their ability to sustain debt is inversely related to the variability of their revenues, and their primary balances and current expenditures follow a procyclical pattern that contrasts sharply with the evidence from industrial countries. This paper proposes an equilibrium model of a small open economy with incomplete markets and aggregate uncertainty that can rationalize this behavior. In the model, a fiscal authority that chooses optimal expenditure and debt plans given stochastic revenues interacts with private agents that also make optimal consumption and asset accumulation plans. The competitive equilibrium of this economy is solved numerically as a Markov perfect equilibrium using parameter values calibrated to Mexican data. If perfect domestic risk pooling were possible, the ratio of public-to-private expenditures would be constant. With incomplete markets, however, this ratio fluctuates widely and results in welfare losses that dwarf previous estimates of the benefits of risk sharing and consumption smoothing. The model also yields a negative relationship between average public debt and revenue variability similar to the one observed in the data, and a correlation between output and government purchases that matches Mexican dataoptimal debt, fiscal solvency, procyclical fiscal policy, incomplete markets

Adaptive-wall wind-tunnel research at NASA-Ames Research Center

Adaptive wall wind tunnel research is summarized. Small scale two and three dimensional wind tunnel experiments and numerical experiments with a three dimensional adaptive wall simulator are included. A NACA 0012 airfoil was tested in a 25 by 13 cm slotted wall test section. Airflow through the test section walls was controlled by adjusting the pressures in segmented plenums. Interference free conditions were successfully attained in subsonic and transonic flows. For the three dimensional experiment, the 25 by 13 cm wind tunnel was modified to permit cross stream wall adjustments. The test model was a semispan wing mounted to one sidewall. Wall interference was substantially reduced at several angles of attack at Mach 0.60. A wing on wall configuration was also modeled in the numerical experiments. These flow simulations showed that free air conditions can be approximated by adjusting boundary conditions at only the floor and ceiling of the test section. No sidewall control was necessary. Typical results from these experiments are discussed

Public Debt, Fiscal Solvency, and Macroeconomic Uncertainty in Latin America: The Cases of Brazil, Colombia, Costa Rica, and Mexico

The ratios of public debt as a share of GDP of Brazil, Colombia, and Mexico were 12 percentage points higher on average during the period 1996-2005 than in the period 1990-1995. Costa Rica's debt ratio remained stable but at a high level near 50 percent. Is there reason to be concerned for the solvency of the public sector in these economies? We provide an answer to this question based on the quantitative predictions of a variant of the framework proposed by Mendoza and Oviedo (2006). This methodology yields forward-looking estimates of debt ratios that are consistent with fiscal solvency for a government that faces revenue uncertainty and can issue only non-state-contingent debt. In this environment, aversion to a collapse in outlays leads the government to respect a ``natural debt limit" equal to the annuity value of the primary balance in a ``fiscal crisis." A fiscal crisis occurs after a long sequence of adverse revenue shocks and public outlays adjust to their tolerable minimum. The debt limit also represents a credible commitment to remain able to repay even in a fiscal crisis. The debt limit is not, in general, the same as the sustainable debt, which is driven by the probabilistic dynamics of the primary balance. The results of a baseline scenario question the sustainability of current debt ratios in Brazil and Colombia, while those in Costa Rica and Mexico are inside the limits consistent with fiscal solvency. In contrast, current debt ratios are found to be unsustainable in all four countries for plausible changes to lower average growth rates or higher real interest rates. Moreover, sustainable debt ratios fall sharply when default risk is taken into account.

An evaluation of the method for determining the Whitham F-function using distributions of downwash and sidewash angles

The method of computing the Whitham F function using distributions of downwash and sidewash angles was evaluated with two different models. F functions which were calculated for a half angle cone cylinder at M infinites = 2.01, using theoretically and experimentally derived flow angles, show that the method is sensitive to small inaccuracies in the measured flow angles. An oblique wing transport model was tested at 0 deg angle of attack at M infinitely = 2.01. In this test, two different probes were used at two different distances from the model. The pressure signature derived from the F function was extrapolated and compared to the pressure signature measured at the distance of 0.87 body lengths with the static pressure probe. The agreement between the two pressure signatures was poor due to the many inaccuracies involved in using a probe designed to measure flow angularity