Effects of Sweep Angle on the Boundary-Layer Stability Characteristics of an Untapered Wing at Low Speeds

An investigation was conducted in the Ames 12-Foot Low-Turbulence Pressure Tunnel to determine the effects of sweep on the boundary-layer stability characteristics of an untapered variable-sweep wing having an NACA 64(2)A015 section normal to the leading edge. Pressure distribution and transition were measured on the wing at low speeds at sweep angles of 0, 10, 20, 30, 40, and 50 deg. and at angles of attack from -3 to 3 deg. The investigation also included flow-visualization studies on the surface at sweep angles from 0 to 50 deg. and total pressure surveys in the boundary layer at a sweep angle of 30 deg. for angles of attack from -12 to 0 deg. It was found that sweep caused premature transition on the wing under certain conditions. This effect resulted from the formation of vortices in the boundary layer when a critical combination of sweep angle, pressure gradient, and stream Reynolds number was attained. A useful parameter in indicating the combined effect of these flow variables on vortex formation and on beginning transition is the crossflow Reynolds number. The critical values of crossflow Reynolds number for vortex formation found in this investigation range from about 135 to 190 and are in good agreement with those reported in previous investigations. The values of crossflow Reynolds number for beginning transitions were found to be between 190 and 260. For each condition (i.e., development of vortices and initiation of transition at a given location) the lower values in the specified ranges were obtained with a light coating of flow-visualization material on the surface. A method is presented for the rapid computation of crossflow Reynolds number on any swept surface for which the pressure distribution is known. From calculations based on this method, it was found that the maximum values of crossflow Reynolds number are attained under conditions of a strong pressure gradient and at a sweep angle of about 50 deg. Due to the primary dependence on pressure gradient, effects of sweep in causing premature transition are generally first encountered on the lower surfaces of wings operating at positive angles of attack

Structuring national and sub-national economic incentives to reduce emissions from deforestation in Indonesia

We estimate the impacts that alternative national and sub-national economic incentive structures for reducing emissions from deforestation (REDD+) in Indonesia would have had on greenhouse gas emissions and national and local revenue if they had been in place from 2000-2005. The impact of carbon payments on deforestation is calibrated econometrically from the pattern of observed deforestation and spatial variation in the benefits and costs of converting land to agriculture over that time period. We estimate that at an international carbon price of $10/tCO2e, a “basic voluntary incentive structure” modeled after a traditional payment-for-ecosystem-services (PES) program would have reduced emissions nationally by 62 MtCO2e/yr, or 8% below the without-REDD+ reference scenario (95% CI: 45-76 MtCO2e/yr; 6-9%), while generating a programmatic budget shortfall. By making four policy improvements—paying for net emission reductions at the scale of an entire district rather than site-by-site, paying for reductions relative to estimated business-as-usual levels rather than historical levels, sharing a portion of district-level revenues with the national government, and sharing a portion of the national government’s responsibility for costs with districts—an “improved voluntary incentive structure” would have reduced emissions by 175 MtCO2e/yr, or 22% below the reference scenario (95% CI: 136-207 MtCO2e/yr; 17-26%), while generating a programmatic budget surplus. A “regulatory incentive structure” such as a cap-and-trade or symmetric tax-and-subsidy program would have reduced emissions by 211/yr, or 26% below the reference scenario (95% CI: 163-247 MtCO2e/yr; 20-31%), and would not have required accurate predictions of business-as-usual emissions to guarantee a programmatic budget surplus.Climate change, land-use change, REDD+, reference levels, economic incentives

Valuing water for sustainable development

Achieving universal, safely managed water and sanitation services by 2030, as envisioned by the United Nations (UN) Sustainable Development Goal (SDG) 6, is projected to require capital expenditures of USD 114 billion per year (1). Investment on that scale, along with accompanying policy reforms, can be motivated by a growing appreciation of the value of water. Yet our ability to value water, and incorporate these values into water governance, is inadequate. Newly recognized cascading negative impacts of water scarcity, pollution, and flooding underscore the need to change the way we value water (2). With the UN/World Bank High Level Panel on Water having launched the Valuing Water Initiative in 2017 to chart principles and pathways for valuing water, we see a global opportunity to rethink the value of water. We outline four steps toward better valuation and management (see the box), examine recent advances in each of these areas, and argue that these four steps must be integrated to overcome the barriers that have stymied past efforts