Dimitri Riabouchinsky's works can be classified under eight headings
- Aerodynamics
- Astrophysics
- Ballistics
- Subsonic, Transsonic and Supersonic Dynamics
- Geometry
- Hydrodynamics
- Mathematical Philosophy
- Theoretical Physics
Aerodynamics
The Koutchino aerodynamic wind-tunnel dates back to the heroic epoch when very little was known about the laws of flight.
All had to be imagined and worked out : devices and methods. The field for investigation was wide and it was no easy matter to select the most important problems. Very soon, owing to a serie of researches, Koutchino took the lead.
Ten years after the foundation of the Koutchino Institute, Dimitri Riabouchinsky received from Paris the aeronautical world centre and specialists from all the world proof that his work had been very important in this period.
a) Let us note on this occasion that Dimitri Riabouchinsky's ideas on the autorotational motion and his researches on this subject, in 1905-1906 found practical confirmation only fifteen years after, when aircraft development took place after the first world war (autogyros, spin)
b) The same remark applied to the so-called "hypersustention devices" (slotted wing principle), which are now in common practice.
c) Research on propellers made at that time in Koutchino was an important step towards knowledge of propulsion and static sustention or sustention against a lateral relative wind (helicopters).
Dimitri Riabouchinsky extended his observations to wind-mills and braking-screws, by varying their relative pitch. In water, these results were confirmed in 1922, in a book entitled "Electric ship propulsion" by Commander S. M. Robinson, USA. (Simmon Broadman Publishing Company) and in 1931, by Dr. H. F. Nordström, Statens Skeppsprovningsanstalt, Götenberg, Sweden.
d) Dimitri Riabouchinsky devoted several works to the comparative study of aerodynamic wind- tunnel various systems and, in 1922, he enlightened the question of influence of wind-tunnel type and dimensions, flow turbulence and soustainment of the model on observation results. For instance, whether a thin square plate is held in the flow by its center or by its edge, a discontinuity in pressure variation is obtained or not; artificial increasing of flow turbulence has the same effect as holding the plate by its edge.
In 1913, in the article "Flüssigkeitsbewegung" published in the first edition of the Handwörterbuch der Naturwissenschaften and in the extract of this article entitled "Lehre von der Flüssigkeits und Gasbewegung", L. Prandlt, referring to the sharp maximum and the discontinuity in the resistance rate of a plate, wrote: "In a turbulent flow the phenomenon no longer exists (Riabouchinsky)."
e) We are indebted to Dimitri Riabouchinsky for an interesting method aerodynamic spectra, pertaining to visualization of air flows around on obstacle placed upon an horizontal metallic plate besprinkled with lycopod powder. Stream line appearance is determined in the lycopod powder by striking the border of the surface. Dimitri Riabouchinsky named this phenomenon "boundary layer striation". According to a theory, he developed, vortex lines are orthogonal with flow lines within close vicinity from the surface; but, if the kinematic viscosity is insufficient, vortex lines and stream lines tend to coincide within a certain distance from the surface. This striation is found again when using wet paint, instead of lycopod powder, in water (Barillon, Hinderks, Winter), in a subsonic high speed wind tunnel (Higgins, Jacobs, Weick) and in a supersonic wind tunnel (Riabouchinsky, Wolkowisky, Katlama).
Dimitri Riabouchinsky demonstrated, in 1930 that stream lines could be obtained by Hele Shaw's method in cyclic movements when a suitable "barrier" is introduced between the glass walls.
Mrs V. Popovitch-Schneider applied this theory to calculate the shape of theses "barriers" in the case of certain movements with circulation, and experimentally confirmed it.
f) As early as 1908, Dimitri Riabouchinsky undertook the study of air friction, using the momentum projection theorem, and constructed an apparatus based on this principle. He completed this research by studying discs rotating in their plane, in air and in water. He was the first, to apply integral equations to the study of laminar and turbulent frictional resistance.
g) In January 1910 he studied the movements of plain and articulated pendulums, the initial oscillations of witch are determined by Bénard's alternative eddies.
He also foresaw and took photographic records of opening, accompanying and landing vortices of a parachute, using the analogy he pointed out between cavitations in liquids and sudden local variations of density in gases.
h) As early as 1909, Dimitri Riabouchinsky systematically used in aerodynamics the method now named "dimensional analysis" for representing graphically experimental data.
In 1911, he developed the theory of his method by introducing the notion of dimensional determinant and then gave a new generalisation thereof.
Astrophysics
Here is found a striking example of the variety of Dimitri Riabounchinsky's thoughts. In a study published in 1914 and developed later, he gave a theory of sunspots periodicity and built a demonstrative apparatus to illustrate this theory.
In his work "On the theory of rotating stars" (Astrophysica Norvegea), S. Rosseland mentions that the notion of sunspot formation due to some kind of dynamical instability is now generally acknowledged and that he had considered it himself in a paper published in 1929, but that this notion is however older and dates back at least to Riabouchinsky's experiment previous to the first world war. S. Rosseland mentions that the notion of sunspot formation due to some kind of dynamical instability is now generally acknowledged and that he had considered it himself in a paper published in 1929, but that this notion is however older and dates back at least to Riabouchinsky's experiment previous to the first world war. S. Rosseland mentions that the notion of sunspot formation due to some kind of dynamical instability is now generally acknowledged and that he had considered it himself in a paper published in 1929, but that this notion is however older and dates back at least to Riabouchinsky's experiment previous to the first world war.
Ballistics
From the beginning of the first world war the Koutchino Institute was militarized and entrusted with the study and the realisation of inventions useful to national defence and chosen by Artillery Technical Committee.
Among these inventions was General Pomortzeff's pneumatic rocket. D. Riabouchinsky developed the theory of this rocket. He dealt also from a new point of view with the problem of air resistance at ballistic speeds and his memoir was presented and commented at the Academy of Sciences by Paul Appell.
In 1916, D. Riabouchinsky proposed to the Artillery Technical Committee his recoilless gun (reaction gun, rocket gun). Firing tests of this gun were made in Petrograd before the Commission of Experiments on the 24th of October 1916.
Everyone knows now the "recoilless gun", modern anti-tank weapon extensively used during the last world war (for firing hollow charge projectiles).
But no one seems to know that this weapon was invented by Dimitri Riabouchinsky, and constructed by him in Koutchino, in 1916.
In several works published between the two wars, Dimiti Riabouchinsky brought new ideas on this interesting question. But was there anyone able to guess, in those days, the practical importance of recoilless arms ? Dimitri Riabouchinsky remained alone in spite of all his attempts.
Dimitri Riabouchinsky also continued to show interest for external ballistics. These works were very closely related to his studies on supersonic dynamics.
Projectile instability, when no stabilizing axial rotation or tail-fins are used, is an autorotational phenomenon as Dimitri Riabouchinsky made it clear with a projectile light model suspended by a thread in the flow of a wind-tunnel.
In March 1914, in view of the tenth anniversary of the Aerodynamic Institute of Koutchino, Riabouchinsky published a booklet in which he gave a survey of the Institute activity since its foundation and concluded as follows :
"The problem of aerodynamical flying is solved"; but after the conquest of air spaces, another conquest, more difficult and of higher import is offered to the imagination of man, the conquest of interplanetary spaces.
"The brillant progress of science gives hope that in a more or less distant future, this problem will be solved in its turn, through the patient and coordinated efforts of searchers impassioned by the greatness of this idea".
When Riabouchinsky wrote these lines his intention was as his subsequent works proved to undertake systematic researches concerned with gas jet reaction, air resistance at ballistic speeds, various type rockets, direct jets propellers.
The Koutchino Institute may thus be considered as the first scientific laboratory to have included the astronautical problem in its program and begun to realise it.
Subsonic, Transsonic and Supersonic Dynamics
Jet propulsion drew the attention of Dimitri Riabouchinsky a long time ago and was dealt with in fascicle VI of the Kouchino Bulletin published in Paris in 1920. At t`e Paris Institute of Fluid Mechanics he constructed a set of apparatuses which were displayed in 1936 at the official exhibition of the Paris Salon Aeronautique. In 1939, he published his important memoir on jet propulsion.
Dimitri Riabouchinsky was the first to establish the analogy between the two-dimensional flow of a compressible fluid and the flow of a thin layer of water with free surface. Many interesting theoretical and experimental researches were devoted by him to this important question. These researches brought valuable information on supersonic movements.
During the first official presentation of European Laboratories films in New-York, on the 4th December 1936, Colonel Norbert Champsaur, Air Attached of the French Embassy in the United States, exhibited (Journal of the Aeronautiacal Sciences, December 1936, p.78) a film on which Dimitri Riabouchinsky had registred, at the Laboratory of Fuid Mechanics of the Paris University, numerous experiments illustrating the hydraulic analogy of bidimensional movements of a compressible fluid.
This method is named "Riabouchinsky's analogy" in publications of the late Professor Pietro Teofilato.
Dimitri Riabouchinsky developped a mathematical method for studying plane and tridimensional, nearly rectilinear, movements of compressible fluids, without discontinuities or in the presence of weak shock waves.
Geometry
In a brief note "Prerivistaja Geometria" (Discontinuous Geometry, Mathematicheski Sbornik, T. XV, Moscow, 1891), N. V. Bougaïeff had considered the possibility for establishing between function theory and discontinuous geometry a connection similar to that existing between analysis and geometry.
As an illustration of this idea, Bougaïeff gave equations of areas, of straight and isolated points systems where he used the discontinuous function E (x) defined as the lesser value of two entire numbers between which the value of x is placed.
In his publication "On the use of absolute values in analytical geometry", A. Söderblom (Göteborg, 1906) showed with a great number of examples the diversity of geometrical figures which can be obtained with the symbol | x |.
Söderblom had not noticed the essential distinction between convex and concave polygon equations. This lacuna was filled by H. Grauers (Nyt Tidsskift for Matematik, 20 Aargang. N°. 4, Kopenhagen, 1909, p. 109)
In studying analytically polygonal and discontinuous figures, Dimitri Riabouchinsky came to the interesting ideas of deriving from the direct operation y = | x | its inverse operation x = ± éy, and of the use of the new imaginary quantity
j = - - - é-1, | j | = -1.
, | j | = -1.
Introducing the operation of the "return to the relative value" Dimitri Riabouchinsky was able to develop a thouroughly general theory for solving equations containing absolute and relative values of the unknown number, without the help of inequalities. These equation roots can be real, imaginary, indeterminate or coincident. It is a problem of fluid mechanics which led Dimitri Riabouchinsky to develop this calculus.
He gave numerous examples of its application among which I will mention an interesting case in the kinematics of fluid discontinuous movements, developped by J. Hadamard in his most valuable Work On wave propagation (Paris 1903).
The new imaginary quantity, | j | = -1, led Dimitri Riabouchinsky to establish the theory of complex variable function
j + e y = f ( x + e y ) where e² can be not only negative, but also nought or positive.
Dimitri Riabouchinsky demontrated that these three cases have important applications respectively, in subsonic, sonic and supersonic flows of compressible fluids.
Hydrodynamics
Mathematical Philosophy
The definition of numbers by their numerical value and by their origin is the basic concept of Dimitri Riabouchinsky' mathematical philosophy.
He named origin of a number the operative forms applied to it and which distinguish it from other numbers with the same numerical value.
The problem of fluid mechanics mentioned in chapter "Geometry" suggested to him this concept.
Dimitri Riabouchinsky deduced from it multiple and remarkable consequences.
Without anticipating the future, surely Dimitri Riabouchinsky's ideas deserve the greatest attention.
Theoretical Physics
Dimitri Riabouchinsky looks upon Fluid Mechanics as a guide-science, which can contribute to the development of others sciences treating subjects less capable of affecting our senses directly.
He admits, for instance, that the notion of a stream line in a space of n dimensions, defined by a velocity-potential an n-1 stream functions, and the various singularities which the motion of a fluid may lead us to consider, could be as instructive and fruitful in suggestions as the notion of the curvature of a space of n dimensions.
He also studied systematically the points of contact and divergency between the differential equations governing the motion of a perfect gas and those of Maxwell. He specifies the limits within which these equations, as well as those which determine the transfer of energy, present themselves in an identical form.
In the general case, however, this analogy ceases to be perfect and the author makes it evident why this is so, and he has demonstrated that an univocal and reciprocal connection between the constitutive elements of both fields continues to exist.
These researches obliged him to go all the way back to the axioms and fundamental definitions of Newton' Mechanics and to state precisely what modifications they must undergo in order that Maxwell's equations may be deducted from them. The junction of these two mechanics comes forward in the plane of energy.
Appling this theory to Fluid Mechanics, Riabouchinsky proves that free "aether" appears as a perfect incompressible fluid, but the eddies are no longer indestructible: they can be created or destroyed, for instance when a wave is passing.
Let us mention likewise the remark of Riabouchinsky which Garret Birkhoff (Hydrodynamics, Princeton University Press, 1950, p. 89) has designated as "the remarkable paradox of Riabouchinsky".
Riabouchinsky drew attention (Nature, London, XIV, 1915, p.591) to the circumstance that a problem solved by Lord Rayleigh (I. c. p. 66), considering temperature as a fourth fundamental unity, admits a different solution if temperature is defined as the mean kinetic energy of molecules. In his answer Lord Rayleigh (I. c. p. 644), mentioned that this question "would be well worthy of further discussion".
He took part in this dicussion himself, as well as J. L. (Sir Joseph Larmor), E. Buckingham, P. W. Bridgman, Mrs P. Ehrenfest- Afanassieva, Norman Campbell, A. W. Porter, Robert Esnault-Pelterie.
Extract from the Scientific Jubilee of Mr. Dimitri P. RIABUSHINSKY
REPORT ON THE MECHANIC OF THE FLUIDS
offered by HIS FRIENDS, HIS COLLEAGUES AND HIS OLD BOYS
8 MAY 1954
Extract : TRAINING OF A SCIENTIST
by Wladimir RIABOUCHINSKY, President of Association "the ICONE "
Extract : GREAT STAGES OF A SCIENTIFIC CAREER
per Pierre KOVALEVSKY, DOCTOR OF THE UNIVERSITY OF PARIS
Extract : The ROLE OF A WOMAN
per Julie KARMALINE, born from ZYBINE