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

A three-dimensional Euler aerodynamic method based on a finite-volume, multistage time-stepping algorithm is used to simulate free vortices generated by flow separation along the edges of swept, slender wings at moderate to high angles of attack. Computed results for a cropped-delta wing, an arrow wing, and a strake-wing-body configuration are correlated with experimental data and, for cropped-delta wing, with predictions of other numerical methods also. The flow is impulsively started and the vortices are automatically captured. The following two issues are specifically addressed: 1) sensitivity of the solutions to artificial viscosity and 2) effect of grid density on the results. Relatively small changes in the subsonic solutions are noticed with variations in the magnitude of artificial viscosity parameters and grid density. The correlations presented here provide an added measure of confidence in computational simulations using the Euler equations. The present investigation also raises some new issues related to vortex instabilities.

Free-vortex flow simulation using a three-dimensional Euler aerodynamic method

A procedure has been developed to optimize the mean camber surface of a cranked slender wing having leading-edge vortex flow at transonic maneuver conditions using the suction analogy. This type of flow was assumed because it was anticipated that the slenderness of the wing would preclude attached flow at the required lift coefficient. A constraint was imposed in that the camber deflections were to be compatible with a realistic structural-box requirement. The resulting application yielded mean camber shapes which produced effective suction levels equivalent to 11% of the full-planar leading-edge value at the design lift coefficient. A a

Development of a vortex-lift-design method and application to a slender maneuver-wing configuration

OMPUTATIONAL aerodynamics has been defined as the engineering discipline which deals with the simulation of flowfields about aircraft through the numerical solution of the equations of fluid motion using digital computers This simulation process is referred to as numerical flow simulation; another way of simulating flow about airplanes is the wind tunnel Wind tunnel technology is almost as old as aeronautics; wind tunnel testing became the principal tool of aerodynamic design and development very early in the history of airplane engineering Of course in addition to the ex perimental approach analytical methods based on aerodynamic theory always have been used to obtain valuable design information; but in order to reduce the computational effort to a humanly tolerable level, many simplifying assumptions had to be introduced These simplifications not only had to do with the mathematical modeling of the physical problem e g inviscid incompressible flow but they also involved the geometry of the configuration and flow condition e g the lifting line concept to represent a wing These simplications did not make possible the calculation of many aerodynamic characteristics and posed a high degree of uncertainty about the accuracy and validity of the numerical results Therefore these results could be used only as design guidelines and large emphasis had to be placed on wind tunnel testing The advent of the digital computer and the impressive growth of its capabilities and cost effectiveness—as illustrated in Fig 1—now have made it possible to eliminate many of the simplifications that had been introduced in analytical methods This has increased the amount of in formation that can be extracted from a calculation and at the same time provides more accuracy and a greater range of validity for the results of numerical flow simulation This has turned computational aerodynamics into a major tool for airplane design This paper surveys the use of computational aerodynamics as a design tool Much development work in computational aerodynamics is of a fundamentally scientific nature con cerned with what type of numerical flow simulation is feasible within the boundaries of our knowledge of flow physics and numerical algorithms This paper deals with the engineering aspects of numerical flow simulation i e. what elements are practical in an environment where schedule and budget constraints predominate and where multidisciplinary in teraction is the way of life and particularly with the factors that affect its effectiveness in such an environment Even though computer system characteristics do fundamentally affect the effectiveness of computational aerodynamics they are not the subject of this paper The survey presented here is of necessity, selective and consequently incomplete The main intent of this paper is to highlight those elements of computational aerodynamics that are important for airplane application what form they have taken and to indicate what future developments are considered necessary to increase the general utility of computational aerodynamics Three dimensionality geometrical complexity and computational efficiency are stressed as overdriving considerations for design application First some general characteristics and needs of airplane design projects are discussed; within this context particular attention is given to the meaning of effectiveness and the identification of the computer code characteristics that affect it Next the code elements that are part of a typical numerical flow simulation are identified; the nature of these elements how they impact code effectiveness and how they are affected by considerations of effectiveness are addressed subsequently The author has drawn freely from developments at the Lockheed California Company to illustrate some points; for this he is indebted to many of his colleagues at Lockheed

Application of computational aerodynamics to airplane design

A computational method for lateral-directional aerdynamics of fighter configurations is developed. The leading-edge vortices are represented by free vortex filaments which are adjusted iteratively to satisfy the forcefree condition. The forebody vortex separation, both symmetrical and asymmetrical, is calculated with a slender body theory. Effect of boundary layer separation on lifting surfaces is accounted for by using the effective sectional angles of attack. The latter are obtained iteratively by matching the nonlinear sectional lift with the computed results based on a lifting-surface theory. Results for several fighter configurations are employed for comparison with available data. It is shown that the present method produces reasonable results in predicting sideslip derivatives, while roll- and yaw-rate derivatives do not compare very well with forced-oscillation test data at high angles of attack.

Calculation of high angle-of-attack aerodynamics of fighter configurations

A numerical method is developed to predict distributed and total aerodynamic characteristics for low aspect-ratio wings with partial leading-edge separation. The flow is assumed to be steady and inviscid. The wing boundary condition is formulated by the quasi-vortex-lattice method. The leading-edge separated vortices are represented by discrete free vortex elements which are aligned with the local velocity vector at mid-points to satisfy the force free condition. The wake behind the trailing-edge is also force free. The flow tangency boundary condition is satisfied on the wing, including the leading- and trailing-edges. Comparison of the predicted results with complete leading-edge separation has shown reasonably good agreement. For cases with partial leading-edge separation, the lift is found to be highly nonlinear with angle of attack.

C. E. Lan

Papers

A theoretical investigation of the aerodynamics of low-aspect-ratio wings with partial leading-edge separation