The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads

Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant source of impulsive loading and noise, particularly in descending flight. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the accuracy with which the high-frequency airloads associated with blade-vortex interactions can be predicted. The Vorticity Transport Model yields a very accurate representation of the structure of the wake, and allows significant flexibility in the way that the blade loading, and hence the source of vorticity into the wake, can be represented. Two models for the local blade aerodynamics are compared. The first is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Indeed, the lifting-line model increasingly overpredicts the amplitude of the lift response to blade-vortex interactions as the computational grid is refined, exposing clearly the fundamental deficiencies in this commonly-used approach particularly when modelling the aerodynamic response of the blade to interactions with vortices that are much smaller than its chord. In comparison, the airloads that are predicted using the lifting-chord model are relatively insensitive to the resolution of the computation, and there are fundamental reasons to believe that properly converged numerical solutions may be attainable using this approach

Digitalization and the American Workforce

This Fact Sheet examines the rate of digitalization within the Metropolitan Statistical Areas (MSAs) of the Mountain West division using the findings and data from Digitalization and the American Workforce, a report from the Brookings Institution

Signs of Digital Distress: The Mountain West

This Fact Sheet examines the broadband services available and their subscription rates across major metro areas in the Mountain West, using the data and analysis found in “Signs of Digital Distress,” a report by the Brookings Institution

How Startups Help Cities Measure Their Economic Development Frontier

This Fact Sheet provides data on the ability of Metropolitan Statistical Areas (MSAs) in the Mountain West to foster innovative and technology-driven industries, utilizing information presented by the Brookings Institution report, “How startups help cities measure their economic development frontier

Migration of Millennials and Seniors in the Mountain West

This Fact Sheet examines trends in intraregional migration of millennials and seniors since the Great Recession, with a focus on the Mountain West. The data presented were originally published in a report by the Brookings Institution, titled “How migration of millennials and seniors has shifted since the Great Recession.

Foot Traffic & Walkable Urbanism

This fact sheet highlights the performance and expansion of WalkUPs (regionally significant, walkable areas) with a focus on Denver, Los Angeles, Orlando, Phoenix, and Las Vegas as detailed in Foot Traffic Ahead: Ranking Walkable Urbanism in America’s Largest Metros, a report by George Washington University

Alien Registration- Kane, Mary E. (Portland, Cumberland County)

https://digitalmaine.com/alien_docs/23887/thumbnail.jp