This paper seeks to clarify what is meant by the ‘social construction of nature’, which has become a crude but common term used to describe very different understandings of nature, knowledge and the world. I distinguish two broad varieties of construction talk in the social sciences: construction-as-refutation and construction-as-philosophical-critique. The first uses the construction metaphor to refute false beliefs about the world and is consistent with orthodox philosophical stances, such as positivism and realism. By contrast, I identify four other, more radical sorts of construction-as-philosophical-critique that use the construction metaphor to question the culture/nature, subject/object and representation/reality dualisms that provide the conventional philosophical foundation for distinguishing true conceptions of nature from false ones. Another source of confusion has been the question of precisely what is meant by the term ‘nature’. Making distinctions among different senses of that term can prov...

What is the ‘social construction of nature’? A typology and sympathetic critique

Lift-generated vortex wakes of subsonic transport aircraft

The effect of the porous leading edge of an airfoil on the blade-vortex interaction noise, which dominates the far-field acoustic spectrum of the helicopter, is investigated The thin-layer Navier-Stokes equations are solved with a high-order upwind-biased scheme and a multizonal grid system The Baldwin-Lomax turbulence model is modified for considering transpiration on the surface The amplitudes of the propagating acoustic wave in the near field are calculated directly from the computation The porosity effect on the surface is modeled in two ways: (1) imposition of prescribed transpiration velocity distribution and (2) calculation of transpiration velocity distribution by Darcy's law Results show leading-edge transpiration can suppress pressure fluctuations at the leading edge during blade-vortex interaction and consequently reduce the amplitude of propagating noise by 30% at a maximum in the near field

Reduction of blade-vortex interaction noise through porous leading edge

Longitudinal vortices have tremendous practical utility for flow control (control by vortices) and in some cases have exhibited tremendous potential for causing harm if uncontrolled (i.e. control of vortices is required). Vortex control has thus far been carried out via multitudinous approaches in an empirical fashion, aided by the essentially inviscid nature of much of longitudinal vortex behaviour. Further refinement and several applications of vortex flow control require knowledge regarding the detailed flow physics of longitudinal vortices such as transition, transitional flow regimes, turbulence structure and modelling, and interaction with shock waves, other vortices and surfaces. This paper summarises vortex control applications and extant techniques for the control of longitudinal vortices produced by bodies, leading edges, tips, and intersections.

Longitudinal vortex control: techniques and applications

Exploratory concepts are described which were investigated to achieve a reduction in the vortex induced rolling upsets produced by heavy aircraft trailing vortexes. The initial tests included the use of mass injection, oscillating devices, wingtip shape design, interacting multiple vortexes, and end plates. Although later refinements of some of these concepts were successful, initial test results did not indicate a capability of these concepts to significantly alter the vortex induced rolling upset on a following aircraft.

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Unsuccessful Concepts for Aircraft Wake Vortex Minimization

: A research program was conducted to study in detail the importance of various aerodynamic and geometric parameters on the dissipation of a concentrated trailed vortex in which the dissipation is greatly enhanced by the continuous injection of a mass of air into its core. The basic results of the research program demonstrated that the efficiency of vortex dissipation would be maximized by designing the injection system so that the vortex was injected at its center and parallel to the axis of the trailed vortex core with a linearly- directed mass of air at sonic speeds. The efficiency of the optimum system was shown to be almost an order of magnitude better than had been demonstrated previously.

An Investigation of the Mixing of Linear and Swirling Flows

: An experimental program was conducted to investigate the modifications of a tip vortex which could be obtained by injecting the core of a tip vortex with a stream of air. Wind tunnel tests of an airfoil model were conducted. The results obtained from flow-visualization studies, balance data, and vortex-meter measurements show how the strength of the tip vortex can be reduced significantly by the injection of a linear mass flow of air into the core of the tip vortex. The reduction in drag obtained with injection is important since it allows the recovery of power required to inject the tip vortex core with mass flow.

An Experimental Study of Tip Vortex Modification by Mass Flow Injection

: An experimental research program was conducted to investigate the general characteristics of a line vortex trailed from a three-dimensional lifting surface, and to determine how its general velocity distribution, turbulence level, turbulent frequency content, and dissipation rates are affected by the injection of a jet of turbulent air and by a fixed turbulence generator. Three component hot-wire surveys indicated that injection of the vortex core reduced the peak tangential velocity, established a strong axial flow component, increased the core diameter, altered the turbulence spectrum, and enhanced the turbulence level in the viscous core. (Modified author abstract)

Investigation of viscous line vortices with and without the injection of core turbulence

: The report describes an experimental research program in which the outer section of a UH-1D helicopter blade was modified to incorporate a system for injecting the tip vortex produced by the blade with a mass of linearly directed air. The effects of nozzle geometry, the velocity of injection, the turbulence wavelength, and the angle of injection on the resulting strength of the trailed tip vortex were investigated, and the results are presented in terms of quantitative measurements of the circulation strength as a function of the injected mass of air.

Investigation of the Dissipation of the Tip Vortex of a Rotor Blade by Mass Injection

: An experimental research program was conducted to investigate methods of improving the performance characteristics of low-aspect ratio, swept-wing surfaces in the post-stall region. Wind tunnel tests were conducted with an unmodified wing panel and with snags, strakes and combinations thereof affixed to the panel. The prediction of changes in the performance characteristics by simplified theoretical analyses is discussed with regard to the observed complexity of the flow field produced by the vortex generators.

Richard P. White

Papers

An Investigation of the Mixing of Linear and Swirling Flows

An Experimental Study of Tip Vortex Modification by Mass Flow Injection

Investigation of viscous line vortices with and without the injection of core turbulence

Investigation of the Dissipation of the Tip Vortex of a Rotor Blade by Mass Injection

An Experimental Investigation of Vortex Flow Control for High Lift Generation.