Gas dynamics

The property of compressibility consists of the ability of substance to change its initial volume under the action of a pressure differential or with a change in the temperature. Therefore compressibility becomes essential only with the high speeds of the motion of medium, commensurate with the speed of propagation of sound in this medium and exceeding it, when in the medium appear large drops in the pressure (see Bernoulli equation) and the high gradients of temperature. Contemporary g. d. studies also the flows of gases with the the high rate -.pax, that are accompanied by chemical (dissociation, combustion and other chem. reaction) and physical (ionization, emission) processes. The study of the motion of gases with such conditions, when it is not possible to consider gas continuous medium, and it is necessary to examine interaction of the components of its molecules between themselves and with solid bodies, it relates to the region of aerodynamics of the rarefied gases, based on the molecular- kinet. theory of gases. The dynamics of the compressible gas with the low speeds of motion large air of masses in the atmosphere composes the basis of dynamic meteorology. G. d. historically arose as further development and the generalization of aerodynamics; therefore frequently they speak about the united science - gas aerodynamics.

The application of osn of the laws of mechanics and thermodynamics to the moving volume of the compressible gas composes theoretical basis g. d.. Navier Stokes the equations, which describe the motion of the viscous compressible gas, were obtained into the 1st floor. 19 v. Ger. scientific B. Riemann (1860), Eng. - U. Rankine (1870), French- A. By Hugoniot (1887) was investigated propagation in the gas of the shock waves, which appear only in the compressible media and tyuey dvizhutsya at a velocity, which exceeds the velocity of propagation in them of acoustic waves. Riemann created also principles of the theory of the unsteady motions of gas, i.e. such motions, when the parameters of gas flow at each of his points change in the course of time.

Fundamental role in the formation g. d. as independent science it played published. in 1902 works s. A. Chaplygin "about the gas jets". The methods of solving gazodinamich. of tasks developed in it obtained subsequently wide acceptance and generalization. The fruitful method of solution of problems g. d. proposed into 1908 Ger. scientists L. Prandtl and T. Mayer, that investigated a special case of flowing the gas with a continuous increase in the speed. In 1922 in the work "experience of the hydromechanics of compressible liquid" Sov. scientist A. A. Friedman placed the bases of dynamic meteorology. In 1929 by Ger. scientists By l. Prandtl and A. Busemann developed effective chislenno-grafich. method of solving the broad class of gazodinamich. of tasks, extended into 1934 by Sov. scientific F. i. Frankl to the more complex cases of flowing the gas. These methods widely adapt during the solution of problems g. d. with the aid of THE COMPUTER(S). It was created in 1921 V OF THE USSR, while into 1927 was designed as scientific establishment the gas-dynamic laboratory, whose the activity together with the group of the study of reactive motion (1932) placed the bases of Sov. rocket engineering.

As tyuey samostoyat, the division of fluid mechanics g. d. exists from 1930, when an increase in the velocities in the aviation required a serious study of compressibility effect during the study of the movement of air. In 1935 in Rome took place the 1st internat. congress for g. d. intensive development g. d. it began during and especially after the end of 2-1 world war 1939-45 in connection with the wide use g. d. in the technology: the application of jet aviation, of rocket weapon, rocket and jet engines; the supersonic flights of aircraft and projectiles; the creation of the A-bombs, whose the explosion entails the propagation of strong explosive and shock waves. During this period g. d. the salient role played studies of Sov. scientists s. A. khristianovich, A. A. Dorodnitsyn, L. i. Sedov, G. i. Petrov, G. g. chernogo and other, Ger. scientists of Prandtl, Busemann, Eng, scientists of J. Taylor, J. Lighthill, Amer. scientists Of t. Karman, A. ferri, U. Hayes, Chin. scientist Of tsyan' Of syue-senya, and also scientific other countries.

Tasks g. d. with the design of diverse apparatuses, engines and gas machines consist of the determination of force of pressures and friction, temperature and heat flux at any point of the body surface or channel, washed by gas, at any moment of time. With a study of the propagation of gas jets, explosive and shock waves, combustion and detonation by methods g. d. are determined the pressure, the rate -.pa and other parameters of gas in the entire region of propagation. The study of complex problems stated by technology converted contemporary. G. d. into the science about the motion of the arbitrary mixtures of gases, which can contain also solid and liquid particles (for example, exhaust gases of rocket engines on the liquid or solid propellant), the parameters, which characterize the state of these gases (pressure, rate -.pa, density, electrical conductivity, etc.), can change over wide limits.

For the development of contemporary. G. d. the characteristically indissoluble combination of theoretical methods, use BY COMPUTER(S) and setting of complex aerodinamich. and fizich. experiments. The theoretical ideas, which are partially rested on the experimental data, make it possible to describe the gas mixture of complex composition, in Vol. h. polyphase mixtures with the presence of physico- chem. transformations with the aid of the equation of motions. By the methods of applied mathematics are developed the effective methods of solving these equations on THE COMPUTER(S). Finally, from the experimental data are determined the necessary values of fizich. and the chem. characteristics, characteristic of the studied medium and to the processes (coeff. of viscosity and thermal conductivity, the rate of chem. reactions, the relaxation times , etc.) in question.

Mn. of tasks, set by contemporary technology before g. d., until they can be solved by calculated- theoretical methods, in these cases widely they use gazodinamich. by the experiments, set on the basis of the similarity of theory and laws of hydro-dynamic. and aerodinamich. simulation. Gazodinamich. experiments into aerogazodi-namich. laboratories are conducted in the supersonic and hypersonic wind tunnels, to ballistich. installations, in the impact and impulse tubes and to other gazodinamich. the installations of the special designation (see also aerodynamic measurements).

Laws g. d. they widely use in the external and vnutr. to ballistics, during the study of such phenomena as explosion, combustion, detonation, condensation in the moving flow. Applied g. d., in which commonly are used those simplified of theoretical idea about the parameters of gas flow averaged over the cross section and basic laws governing the motion, found experimentally, is used with the calculation of compressors and turbines, nozzles and diffusers, rocket engines, aerodinamich. of pipes, ejectors, gas pipes and many others of technical devices.

Gazodinamich. of a study are conducted in the same scientific establishments as studies on aerodynamics, and their results are published in the same scientific journals and collections.

Lit.: Bases of gas dynamics, edited by G. Emmons, translated from English, M., 1963; Pocket T., Supersonic Aerodynamics. Principles and application, translated from English, M., 1948; Abramovich g. n., applied gas dynamics, 3 publ., M., 1969; Black g. g., the flows of gas with the high supersonic speed, M., 1959; Stanyukovich k. p., the unsteady motions of continuous medium, M., 1955; Zeldovich 4. B., Rayzer Yu. p., physics of shock waves and high-temperature hydrodynamic phenomena, M., 1963.

S. L. vishnevetskiy.