A general numerical model for wave rotor analysis

Wave rotors represent one of the promising technologies for achieving very high core temperatures and pressures in future gas turbine engines. Their operation depends upon unsteady gas dynamics and as such, their analysis is quite difficult. This report describes a numerical model which has been developed to perform such an analysis. Following a brief introduction, a summary of the wave rotor concept is given. The governing equations are then presented, along with a summary of the assumptions used to obtain them. Next, the numerical integration technique is described. This is an explicit finite volume technique based on the method of Roe. The discussion then focuses on the implementation of appropriate boundary conditions. Following this, some results are presented which first compare the numerical approximation to the governing differential equations and then compare the overall model to an actual wave rotor experiment. Finally, some concluding remarks are presented concerning the limitations of the simplifying assumptions and areas where the model may be improved

Preliminary Computational Assessment of Disk Rotating Detonation Engine Configurations

A rotating detonation engine (RDE) configuration whereby the working fluid enters and exits in a predominantly radial manner is examined using a quasi-two-dimensional computational fluid dynamic simulation. The simulation, based on a Cartesian coordinate system, was originally developed to examine the physics and performance of the more typical annular RDE. Modifications required to accommodate the radial and circumferential flowfield are discussed. The centripetal forces that arise in this disk RDE (DRDE) configuration create a different wave structure than that seen in the annular RDE. They also give rise to markedly different fluid behavior depending on whether the flow is radially inward or radially outward. Using an entropy-based measure of pressure gain, it is found that for the preliminary idealized calculations performed in this paper, the inward flowing DRDE outperforms the outward flowing variant. The inward flowing DRDE is further shown to outperform the equivalent annular RDE. The effects on performance of several parameters are examined, including inner-to-outer diameter ratio, inner-to-outer cross-sectional area ratio, and inlet throat-to-channel area ratio

Determining the Pressure Gain of Pressure Gain Combustion

Over the past few decades, there has been significant research into propulsion concepts attempting to employ pressure gain combustion. Pressure gain combustion concepts to date have resulted in dynamic, non-uniform gas flows which are difficult to characterize and compare with more conventional forms of propulsion. This paper proposes a technique to derive for the pressure gain combustion device an equivalent, steady, uniform gas pressure that is available to do work or provide thrust, thereby providing a direct comparison with conventional propulsive devices

A model for the space shuttle main engine high pressure oxidizer turbopump shaft seal system

A simple static model is presented which solves for the flow properties of pressure, temperature, and mass flow in the Space Shuttle Main Engine pressure Oxidizer Turbopump Shaft Seal Systems. This system includes the primary and secondary turbine seals, the primary and secondary turbine drains, the helium purge seals and feed line, the primary oxygen drain, and the slinger/labyrinth oxygen seal pair. The model predicts the changes in flow variables that occur during and after failures of the various seals. Such information would be particularly useful in a post flight situation where processing of sensor information using this model could identify a particular seal that had experienced excessive wear. Most of the seals in the system are modeled using simple one dimensional equations which can be applied to almost any seal provided that the fluid is gaseous. A failure is modeled as an increase in the clearance between the shaft and the seal. Thus, the model does not attempt to predict how the failure process actually occurs (e.g., wear, seal crack initiation). The results presented were obtained using a FORTRAN implementation of the model running on a VAX computer. Solution for the seal system properties is obtained iteratively; however, a further simplified implementation (which does not include the slinger/labyrinth combination) was also developed which provides fast and reasonable results for most engine operating conditions. Results from the model compare favorably with the limited redline data available

Inter-industry labor mobility in Taiwan, China

Do flexible labor markets lubricate growth? Using data from Taiwan, China, to analyze the effects of labor market flexibility, the authors find that: 1) Workers are more likely to move to industries that tend to be similar to their industry of origin (including intrasectoral moves that would be considered intersectoraal if there were more sectoral disaggregation). The degree of similarity between two industries is measured in several ways, all of them based on the input-output flows across industries. Workers are more likely to move from industry"i"to industry"j"if"i"supplies a large share of"j's"inputs, receives a large share of its inputs from"j,"or uses many of the same inputs. 2) Moves to more similar industries produce larger wage gains. This is especially true when the industries'similarity is based on their using many of the same inputs. Thid may be partly because the close proximity of industries, occupations, and individuals provides an environment in which ideas flow quickly from person to person. 3) Gains are more likely to accrue to industries as a result of labor mobility.Labor Policies,Water and Industry,Health Monitoring&Evaluation,Public Health Promotion,Environmental Economics&Policies,Water and Industry,Health Monitoring&Evaluation,Environmental Economics&Policies,Industrial Management,Banks&Banking Reform

Is African manufacturing skill-constrained?

Total factor productivity has been low in most Sub-Saharan Africa. It is often said that the binding constraint on African industrial development is the inadequate supply of technologically capable workers. And many cross-country studies imply that the low level of human capital in Africa is an important source of low growth in per capita income. The results of the authors'study do not necessarily conflict with this view. They indicate that in non-competitive industrial sectors, with little inflow of new technology, the contribution of technological abilities, however it is measured, is limited. If liberalization of the economy generated greater competition, or if export growth were accelerated --permitting the import of inputs embodying new technology - local skills could contribute significantly more in raising output. The experience of other countries also suggests that as the economy opens to flows of international knowledge - whether through technology transfers or through informal transfers from purchasers of export - the technological capacity of local industry becomes important. The policy implications of this analysis are clear: Without the prospect of a more competitive environment, continued efforts to develop high-level industrial skills may be wasteful. But the absence of such skills may limit the benefits to the industrial sector from future liberalization, as a result of which the supply response toimproved incentives may be weak.Environmental Economics&Policies,Economic Theory&Research,Curriculum&Instruction,ICT Policy and Strategies,Small and Medium Size Enterprises,Economic Theory&Research,Environmental Economics&Policies,ICT Policy and Strategies,Curriculum&Instruction,Health Monitoring&Evaluation

Do school facilities matter? : the case of the Peruvian Social Fund (FONCODES)

Since its creation in 1991, the Peruvian Social Fund (FONCODES) has spent about US$570 million funding micro-projects throughout Peru. Many of these projects have involved building and renovating school facilities. The authors analyze the targeting and impact of FONCODES investments in the education sector, using data from FONCODES, Peru's population census, Peru's 1994 and 1995 Living Standards Measurement Surveys, and a 1996 household survey conducted by the Peruvian Statistical Institute. They present their results based on various descriptive and econometric techniques, including non-parametric regressions, differences-in-differences, and instrumental variablesestimators. They show that FONCODES projects in the education sector have reached poor districts and, to the extent they live in those districts, poor households. FONCODES has had a positive effect on school attendance rates for young children, but not on the likelihood that children will be at an appropriate school level for their age. Among other recommendations, they suggest that FONCODES consider random assignment of some education projects for a sub-sample of the population, to test the robustness of the study's assumptions and results. Lack of disaggregated data on such measures as the time children spend in school, pupil-teacher ratios, and scholastic achievement precluded analysis of the impact of FONCODES education projects on school quality. Collecting such data, and understanding how improvements in school infrastructure interact with other school-level changes to produce more learning, should be a research priority.Environmental Economics&Policies,Poverty Monitoring&Analysis,Public Health Promotion,Health Economics&Finance,Decentralization,Poverty Monitoring&Analysis,Health Monitoring&Evaluation,Health Economics&Finance,Environmental Economics&Policies,Housing&Human Habitats

Mothers and Others: Who Invests in Children's Health?

We estimate the impact of family structure on investments made in children's health, using data from the 1988 National Health Interview Survey Child Health Supplement. Controlling for household size, income and characteristics, we find that children living with step mothers are significantly less likely to have routine doctor and dentist visits, or to have a place for usual medical care, or for sick care. If children living with step mothers have regular contact with their birth mothers, however, their health care does not suffer relative to that reported for children who reside with their birth mothers. In addition to health investments, we find a significant effect of step mothers on health-related behaviors: children living with step mothers are significantly less likely to wear seatbelts, and are significantly more likely to be living with a cigarette smoker. We cannot reject that investments for children living with birth fathers and step mothers are the same as those made by birth fathers living alone with their children. Who invests in children's health? It appears these investments are made, largely, by a child's mother, and that step mothers are not substitutes for birth mothers in this domain.

Mortality, Income, and Income Inequality Over Time in Britain and the United States

We investigate age-specific mortality in Britain and the United States since 1950. Neither trends in income nor in income inequality provide plausible explanations. Britain and the US had different patterns of income growth but similar patterns of mortality decline. Patterns of income inequality were similar in both countries, but adult and elderly mortality rates declined most rapidly during the period when inequality increased. Changes in the rate of mortality decline in the US led changes in Britain by about four years, most notably for infant and older adult mortality where there have been significant technical improvements in treatment. British mortality is lower, but the schedules cross at around age 65. This pattern was established before Medicare, and most likely comes from rationing by age in Britain. Merged income, income inequality, and mortality data on an age/year (or cohort/year) basis show no evidence that income has any effect on mortality in Britain. Education is protective, but less so than in the US. Understanding the effect of income on mortality presents many puzzles, between countries, and between analyses at different levels of aggregation. Our results suggest an important role for medical technology in determining the rate of mortality decline since 1950.

Child health and the 1988-92 economic crisis in Peru

The effect of economic crises on child health is a topic of great policy importance. The authors use data from the Demographic and Health Surveys (DHS) to analyze the impact of the profound 1988-92 economic crisis in Peru on infant mortality and anthropometrics. They show that there was an increase in the infant mortality rate of about 2.5 percentage points for children born in late 1989 and 1990, implying that about 17,000 more children died than would have in the absence of the crisis. The authors also present suggestive evidence that the crisis affected children's nutritional status. In 1992 children under the age of 6 who had been exposed to the crisis were shorter than same-aged children in 1996 and 2000. The authors do not have data on child height prior to the crisis, but the age profile of changes in nutritional status and the fact that the 1996 and 2000 height-for-age schedules are very similar to each other both suggest that the 1992 values represent declines from previous levels. Accounting for the precise source of the increase in infant mortality and in malnutrition is difficult, but it appears that both the decrease in household incomes and the collapse in expenditures on public health played an important role.Early Child and Children's Health,Public Health Promotion,Early Childhood Development,Health Monitoring&Evaluation,Health Systems Development&Reform,Health Monitoring&Evaluation,Early Child and Children's Health,Early Childhood Development,Adolescent Health,Health Economics&Finance