MODERN AERODYNAMICS AS PSEUDO-SCIENCE

CLAES JOHNSON

PSEUDO-SCIENCE

• SUBSTANTIAL EFFECT FROM

• UNKNOWN CAUSE OR• CAUSE TOO SMALL FOR

• EXPERIMENTAL VERIFICATION

EXAMPLES OF PSEUDO-SCIENCE

• ASTROLOGY• CROP CIRCLES• LYSENKOISM• PARAPSYCHOLOGY• UFOLOGY• PSYCHOKINESIS• LEVITATION

PSEUDO-SCIENCE

• PSYCHO-ANALYSIS: UNCONSCIOUS SELF• MARXISM: SOCIALISM INEVITABLE + GOOD

BECAUSE CAPITALISM IS UNSTABLE

• BASIC ASSUMPTIONS CANNOT BE TESTED• PREDICTIONS CANNOT BE TESTED • EXPERIMENTALLY OR THEORETICALLY

PSEUDO-SCIENCE??

• STRING THEORY: TOO SMALL SCALES• STATISTICAL MECHANICS: MOLECULAR CHAOS

• BASIC ASSUMPTIONS CANNOT BE TESTED• PREDICTIONS CAN/CANNOT BE TESTED

KUTTA + ZHUKOVSKY + PRANDTL 1904FATHERS OF MODERN AERODYNAMICS

PROVED THAT FLYING IS POSSIBLE AFTER WRIGHT SHOWED IT IN 1903

MODERN AERODYNAMICS: LIFT + DRAG

• KUTTA-ZHUKOVSKY:• LIFT FROM CIRCULATION FROM• SHARP TRAILING EDGE SINGULARITY

• PRANDTL:• DRAG FROM • VANISHINGLY THIN BOUNDARY LAYER

UNKNOWN OR SMALL CAUSE: TESTING IMPOSSIBLE

• LIFT:• SHARP TRAILING EDGE SINGULARITY

• DRAG: • VANISHINGLY THIN BOUNDARY LAYER

EFFECT OF KUTTA-ZHUKOVSKY

• UIUC AIRFOIL DATABASE: 1500 AIRFOILS• ALL WITH SHARP TRAILING EDGE

• REAL WING: ROUNDED OR BLUNT • 1% - 10% CHORD LENGTH

ROUNDED TRAILING EDGE: REAL TURBIN BLADE

EFFECT OF PRANDTL

• AERODYNAMICS UNCOMPUTABLE

• AERODYNAMICS MYSTERY

LUDWIG PRANDTL: BIG EFFECT FROM SMALL FRICTION

PRANDTL BOUNDARY LAYER 1904

A very satisfactory explanation of the physical process in the boundary layer [Grenz-schicht] between a fluid and a solid body could be obtained by the hypothesis of an adhesion of the fluid to the walls, that is, by the hypothesis of a zero relative velocity between fluid and wall.

SMALL FRICTION – BIG EFFECT

If the viscosity was very small and the fluid path along the wall not too long, the fluid velocity ought to resume its normal value at a very short distance from the wall. In the thin transition layer, however, the sharp changes of velocity, even with small coefficient of friction, produce marked results.

EFFECT FROM EVER-SO-SMALL VISC.

In the steady motion around a sphere, there is a transition from the motion with viscosity to the limit of non-viscosity, then something quite different from the Dirichlet motion is produced. The latter is then only an initial condition, which is soon disturbed by the effect of an ever-so-small viscosity.

SUCCESS CLAIMED

This plan has proved to be very fruitful, in that, on the one hand, it produces mathematical formulas, which enable a solution of the problems and, on the other hand, the agreement with observations promises to be very satisfactory.

KUTTA-ZHUKOVSKY: BIG EFFECT FROM UNKNOWN CAUSE

• IF THERE IS CIRCULATION THEN THERE IS LIFT

INCORRECT LOGIC:• LIFT IS OBSERVED• HENCE THERE MUST BE CIRCULATION• BUT FROM WHERE?

NO ANSWER. HENCE IT MUST BE: • TRAILING EDGE SINGULARITY + VISCOSITY

KUETHE-SCHETZER: TEXT BOOK: FOUNDATIONS OF AERODYNAMICS:

• A body with a sharp trailing edge which is moving through a fluid will create about itself a circulation of sufficient strength to hold the rear stagnation point at the trailing edge.

SCHLICHTING: STUDENT OF PRANDTL:

• The technically most important wing profiles have, in general, a more or less sharp trailing edge.

• Then the magnitude of circulation can be derived from experience, namely, that there is no flow around the trailing edge, but that the fluid flows off the trailing edge smoothly.

DANGER OF SUCCESS AND FATHERHOOD

• KZP PARALYZED MODERN AERODYNAMICS INTO PSEUDO-SCIENCE