Compressible Dynamic Stall Control Using Dynamic Shape Adaptation

(AIAA Paper 99-0655), AIAA Journal, Vol. 39, No. 10, pp. 2021-2024, Oct. 2001.U.S. Army Research Office, Research Grant MIPR8BNP-SARO0

Design and Development of a Dynamically Deforming Leading Edge Airfoil for Unsteady Flow Control

ICIASF '97 RECORD, IEEE Publication No. 97CH36121, pp. 132-140.A novel approach to unsteady flow separation and dynamic stall control using a dynamically deforming leading edge airfoil is described. The design details of a carbon-fiber composite skin airfoil having a thickness of 0.002 in. at the leading edge and capable of deforming at 20 Hz in unsteady flow at freestream Mach numbers of up to 0.45, are discussed. Implementation of the scheme at model scales places extraordinary demands on the design, material and fabrication of such an airfoil. Rate scaling further requires very-rapid-response instrumental ion, measurement techniques and data acquisition schemes. The special instrumentation control system developed for these experiments as well as the fluid dynamic results of successful flow control that was achieved using this method, are also discussed.U.S. Army Research Office ARO MIPR 133-94, ARO 32480.11-EGU.S. Army Research Office ARO MIPR 133-94, ARO 32480.11-E

Innovative and New Approaches to Laboratory Diagnosis of Zika and Dengue: A Meeting Report

Epidemics of dengue, Zika, and other arboviral diseases are increasing in frequency and severity. Current efforts to rapidly identify and manage these epidemics are limited by the short diagnostic window in acute infection, the extensive serologic cross-reactivity among flaviviruses, and the lack of point-of-care diagnostic tools to detect these viral species in primary care settings. The Partnership for Dengue Control organized a workshop to review the current landscape of Flavivirus diagnostic tools, identified current gaps, and developed strategies to accelerate the adoption of promising novel technologies into national programs. The rate-limiting step to bringing new diagnostic tools to the market is access to reference materials and well-characterized clinical samples to facilitate performance evaluation. We suggest the creation of an international laboratory-response consortium for flaviviruses with a decentralized biobank of well-characterized samples to facilitate assay validation. Access to proficiency panels are needed to ensure quality control, in additional to in-country capacity building

Zika virus infection in pregnancy: a protocol for the joint analysis of the prospective cohort studies of the ZIKAlliance, ZikaPLAN and ZIKAction consortia

INTRODUCTION: Zika virus (ZIKV) infection in pregnancy has been associated with microcephaly and severe neurological damage to the fetus. Our aim is to document the risks of adverse pregnancy and birth outcomes and the prevalence of laboratory markers of congenital infection in deliveries to women experiencing ZIKV infection during pregnancy, using data from European Commission-funded prospective cohort studies in 20 centres in 11 countries across Latin America and the Caribbean. METHODS AND ANALYSIS: We will carry out a centre-by-centre analysis of the risks of adverse pregnancy and birth outcomes, comparing women with confirmed and suspected ZIKV infection in pregnancy to those with no evidence of infection in pregnancy. We will document the proportion of deliveries in which laboratory markers of congenital infection were present. Finally, we will investigate the associations of trimester of maternal infection in pregnancy, presence or absence of maternal symptoms of acute ZIKV infection and previous flavivirus infections with adverse outcomes and with markers of congenital infection. Centre-specific estimates will be pooled using a two-stage approach. ETHICS AND DISSEMINATION: Ethical approval was obtained at each centre. Findings will be presented at international conferences and published in peer-reviewed open access journals and discussed with local public health officials and representatives of the national Ministries of Health, Pan American Health Organization and WHO involved with ZIKV prevention and control activities

Heat Flux Gage Studies of Compressible Dynamic Stall

The article of record as published may be found at http://dx.doi.org/10.2514/6.2002-291Compressible dynamic stall was studied using 148 closely spaced heat flux gages distributed over the surface of an oscillating, 6-inch chord NACA 0012 airfoil. The study has revealed the various surface flow features of compressible dynamic stall and their changes under different flow conditions. It has also provided a description of the events that are precursors to dynamic stall onset. The imprint of a leading edge shock has been recorded for the first time in the surface flow signature. The data indicate that extremely large gradients develop prior to onset of dynamic stall, pointing to a singular event that drives the flow into the stalled state.Army Research Office under grant no. MIPROKNPGAS052Army Research Office under grant no. MIPROKNPGAS05

Heat Flux Gage Studies of Compressible Dynamic Stall

(AIAA Paper 2002-0291) AIAA Journal, Vol.41, No. 5, pp. 757-762, May 2003.The article of record as published may be found at http://dx.doi.org/10.2514/2.2019Compressible dynamic stall was studied using 148 closely spaced heat-flux gauges distributed over the surface of an oscillating, 15.24-cm chord NACA 0012 airfoil. The study has revealed the various surface flow features of compressible dynamic stall. These include the rapid movement of the transition onset point over the airfoil upper surface on the upstroke with increasing angle of attack, the signature of the convecting dynamic-stall vortex, and the relaminarization of the reattaching shear layer on the downstroke. The imprint of a leading-edge shock has been captured for the first time in the surface flow signature. Even though compressible dynamic stall can originate from several causes depending upon flow conditions, the study led to the conclusion that a deterministic precursor of dynamic-stall onset is a sharp rise in the surface shear stress in the leading-edge adverse pressure gradient region, which is a common and singular flow feature at all conditions tested.Army Research Office under Grant MIPROKNPGAS052Army Research Office under Grant MIPROKNPGAS05

Boundary Layer Tripping Studies of Compressible Dynamic Stall Flow

(AIAA Paper 94-2340), AIAA Journal, Vol. 34, No. 1, Jan. 1996, pp. 96-103.The challenging task of properly tripping the boundary layer of a leading-edge-stalling airfoil experiencing compressible dynamic stall at Reynolds numbers between 3.6 X 10⁵ and 8.1 X 10⁵ has been addressed. Real-time interferometry data of the flow over an oscillating airfoil have been obtained at freestream Mach numbers of 0.3 and 0.45. The airfoil was tripped by separately placing five different trips of varying lengths near the leading edge. The trip heights ranged from 40 to 175 µm. The resulting flow and airfoil performance were evaluated using the criteria of elimination of the laminar separation bubble that otherwise forms, delay of dynamic stall onset to higher angles of attack, and production of consistently higher suction peaks. Quantitative analysis of the interferograms showed that the laminar separation bubble was still present with the smallest trip and premature dynamic stall occurred with the largest trip. The right trip was determined to be a distributed roughness element extending from 0.5 to 3% chord. Its height was found to compare reasonably with the airfoil boundary-layer thickness at the dynamic stall vortex formation angle of attack, at a location slightly upstream of the vortex origin in the adverse pressure gradient region.ARO-MIPR-125-93AFOSR-MIPR-93-0003U.S. Naval Postgraduate SchoolARO-MIPR-125-93AFOSR-MIPR-93-0003U.S. Naval Postgraduate Schoo

Transition Effects on Compressible Dynamic Stall of Transiently Pitching Airfoils

AIAA Paper 93-2978 Orlando, FL, Jul. 6-9, 1993.Experimental results and analysis of the effects of boundary layer tripping on dynamic stall of a transiently pitching airfoil are presented. At low Mach numbers, the tripped airfoil exhibits qualitative similarity with the behavior of the untripped airfoil. However, the local supersonic flow at Mach numbers greater than 0.3 is significantly modified by the trip leading to vastly different shock/boundary layer interactions, dynamic stall onset and vortex formation angles. The formation of the laminar separation bubble is found to have a favorable influence in delaying dynamic stall on the untripped airfoil flow. In both Mach number regimes, the tripped flow actually stalls at slightly lower angles of attack. Further experimentation with three trips on an oscillating airfoil showed that the dynamic stall process is very sensitive to the state of the turbulence in the boundary layer. This sensitivity points to a need for finer turbulence modeling techniques for use in dynamic stall computations.AFOSR grant MIPR-93-0003ARO-MIPR-125-9

Unsteady Stall Control Using Dynamically Deforming Airfoils

The article of record as published may be found at http://dx.doi.org/10.2514/2.294An experiment documenting the compressible flow over a dynamically deforming airfoil is presented. This airfoil, which has a leading-edge radius that can be dynamically changed, was tested at various deformation rates for fixed airfoil angle of attack. Selected leading-edge shapes were also tested during airfoil oscillation. These tests show that for a range of Mach numbers observed on the retreating blades of helicopter rotors the dynamic stall vortex can be avoided by a judicious variation of leading-edge curvature.ARO-MIPR-96-7Air Force Office of Scientific ResearchS.S. Davis, Fluid Mechanics Laboratory, NASA Ames Research CenterARO-MIPR-96-7Air Force Office of Scientific ResearchS.S. Davis, Fluid Mechanics Laboratory, NASA Ames Research Cente