Обучение чтению литературы на английском языке по специальности «Аэродинамика». В 2 ч. Ч. 1 (96
.pdfText IIIC. Flow Characteristics
Although the Mach number is used to define the occurrence of some flow features, the basic parameters defining the speed characteristics are three: Reynolds number; Mach number; Knudsen number.
Reynolds Number Effects: Viscosity
The Reynolds number (first introduced by L. Prandtl) dominates the viscous effects by defining the size of the boundary layers.
Almost all aerodynamic flows occur at high Reynolds number, which implies viscous phenomena are limited to narrow boundary layers. The notion high is somewhat arbitrary, although the value of 0.5 · 106 is often the switching boundary.
Flows at Reynolds numbers in the range 0.1 · 106 < Re < 0.5 · 106 are called Low&Reynolds Number Aerodynamics .
Flows at very small Reynolds numbers are dominated by viscosity and are better described with the use of Stanton number. These flows (sometimes called creeping motions or Stokes flows) are not considered proper domain of aerodynamics.
Mach Number Effects: Compressibility
The Mach number (introduced by J. Ackeret, 1992 ) defines the appearance of compressibility effects and the charges associated with the shock waves. In the subsonic speed range of the compressibility of the flow is negligible.
At transonic speeds there are pockets of flow below and above the speed sound. The main feature of this speed range is the presence of compression and expansion shock waves.
А supersonic flow is exclusively above the speed of sound. Supersonic aerodynamics differs from aerodynamics at lower speeds because the flow is highly compressible.
The Reynolds and Mach numbers are independent and are both needed to define the characteristics of speeds in the transonic regime. At subsonic speeds the flow is generally treated as a constant&density flow and the Mach number influence is neglected.
Knudsen Number Effects: Molecular Flow
Flows at higher Mach numbers are object of hypersonics (a term due to Tsien, 1946). Other definitions sometimes used for this speed regime is
31
gasdynamics, rarefied gasdynamics and magnetigasdynamics for yet
higher speeds . |
|
Two more |
dimensionless parameters are useful to describe |
the physics: the |
Knudsen number and the Damkolner ratio (e. g. |
the ratio between a characteristic time and the molecular relaxation time). The Knudsen number is not quite independent, since it can also be written as ratio between Mach and Reynolds numbers.
Flows at Knudsen numbers Kn 1 are basically collisionless flows (artificial satellites in orbital motion above the Earth); flows at Kn < 1 are in regime of slight rarefaction and are called slip flows; flows at inter& mediate Knudsen numbers are called transitional flows. These flows re& quire some modeling of the molecular gas, and are beyond the domain of validity of the Navier&Stokes equations.
At speeds above M = 5 there are changes in the physics of the flow, because of changes in the medium and of the aero&thermodynamic heating . At M > 7 the medium becomes chemically reactive; at M > 12 it is also ionized . The energy produced by the propulsion system is used to overcome the resistance of the flight vehicle (drag), and is converted into compression work on the surrounding medium.
12. Read and explain the formulae given in texts IIIA , IIIB and IIIC:
Kn 1
0.1 106 < Re < 0.5 106 Re = V · r · l / µ
V = C2 · T
pv = nRT / m.
13. Give a summary of text IIIC.
СПИСОК ЛИТЕРАТУРЫ И САЙТОВ
Англо&русский политехнический словарь: В 2 т. / Авт.&сост. М.В. Адамчик. – Минск: Харвест, 2004.
Большой англо&русский словарь: В 2 т. / Под ред. И.Р. Гальпери& на. –М.: Русский язык, 1987.
Климзо Б.Н. Ремесло технического переводчика: Об английском языке, переводе и переводчиках научно&технической литературы: 2&е изд., перераб. и доп. – М.: Р. Валент, 2006.
Рубцова М.Г. Чтение и перевод английской научно&технической литературы: Лексико&граммат. справочник. – М.: АСТ, 2003.
Hornby F.S. Oxford Advanced Learner’s Dictionary, 7th ed. – Oxford: Oxford Univ. Press, 2006.
Longman Dictionary of Scientific Usage: The Reprint Edition. – Moscow: Longman, 1988.
Macmillan English Dictionary for Advanced Learners: International Student Edition. – L.: Macmillan Education, 2006.
www.en.wikipedia.org/wiki/Aerodynamics
www.grc.nasa.gov
Contents |
|
Предисловие .................................................................................................. |
3 |
Unit I ................................................................................................................. |
3 |
New Words and Word Combinations ........................................................ |
3 |
Text IA: Gas Properties Definitions ...................................................... |
5 |
Text IB: Gas Pressure ............................................................................... |
10 |
Text 1C: Gas Temperature ...................................................................... |
12 |
Unit II .............................................................................................................. |
15 |
New Words and Word Combinations ................................................... |
15 |
Text IIA: Aerodynamic Forces ................................................................ |
16 |
Text IIB: What Is Drag? .......................................................................... |
20 |
Text IIC: What Is Lift? ............................................................................ |
22 |
Text IID: What Is Weight? ..................................................................... |
23 |
Unit III ............................................................................................................. |
24 |
New Words and Word Combinations ................................................... |
24 |
Text IIIA: Boundary Layer ...................................................................... |
25 |
Text IIIB: Equation of State .................................................................. |
29 |
Text IIIC: Flow Characteristics ............................................................. |
31 |
Список литературы и сайтов .................................................................... |
33 |
Учебное издание
Алявдина Наталья Георгиевна Шашмурина Анна Владимировна
Обучение чтению литературы на английском языке по специальности
«Аэродинамика»
Редактор Н.М. Маслова Корректор Э.Я. Ахадова
Компьютерная верстка И.А. Марковой
Подписано в печать 12.12. 2007. Формат 60× 84/16. Бумага офсетная.
Усл. печ. л. 2,09. Уч.&изд. л. 1,95. Тираж 100 экз. Изд. ¹ 63. Заказ
Издательство МГТУ им. Н.Э. Баумана Типография МГТУ им. Н.Э. Баумана 105005, Москва, 2&я Бауманская ул., 5
Для заметок