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In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics and hydrodynamics. Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.
In aerodynamics, a hypersonic speed is one that exceeds five times the speed of sound, often stated as starting at speeds of Mach 5 and above.
In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium.
Compressible flow is the branch of fluid mechanics that deals with flows having significant changes in fluid density. While all flows are compressible, flows are usually treated as being incompressible when the Mach number is smaller than 0.3. The study of compressible flow is relevant to high-speed aircraft, jet engines, rocket motors, high-speed entry into a planetary atmosphere, gas pipelines, commercial applications such as abrasive blasting, and many other fields.
A swept wing is a wing angled either backward or occasionally forward from its root rather than perpendicular to the fuselage.
Transonic flow is air flowing around an object at a speed that generates regions of both subsonic and supersonic airflow around that object. The exact range of speeds depends on the object's critical Mach number, but transonic flow is seen at flight speeds close to the speed of sound, typically between Mach 0.8 and 1.2.
In fluid dynamics, a Mach wave, also known as a weak discontinuity, is a pressure wave traveling with the speed of sound caused by a slight change of pressure added to a compressible flow. These weak waves can combine in supersonic flow to become a shock wave if sufficient Mach waves are present at any location. Such a shock wave is called a Mach stem or Mach front. Thus, it is possible to have shockless compression or expansion in a supersonic flow by having the production of Mach waves sufficiently spaced. A Mach wave is the weak limit of an oblique shock wave where time averages of flow quantities don't change. If the size of the object moving at the speed of sound is near 0, then this domain of influence of the wave is called a Mach cone.
Specular reflection, or regular reflection, is the mirror-like reflection of waves, such as light, from a surface.
Inlet cones are a component of some supersonic aircraft and missiles. They are primarily used on ramjets, such as the D-21 Tagboard and Lockheed X-7. Some turbojet aircraft including the Su-7, MiG-21, English Electric Lightning, and SR-71 also use an inlet cone.
Mach tuck is an aerodynamic effect whereby the nose of an aircraft tends to pitch downward as the airflow around the wing reaches supersonic speeds. This diving tendency is also known as tuck under. The aircraft will first experience this effect at significantly below Mach 1.
The Busemann biplane is a theoretical aircraft configuration invented by Adolf Busemann, which avoids the formation of N-type shock waves and thus does not create a sonic boom or the associated wave drag. However in its original form it does not generate lift either. A Busemann biplane concept, which provides adequate lift, and which can reduce the wave intensity and drag but not eliminate them, has been studied for a "boomless" supersonic transport.
An oblique shock wave is a shock wave that, unlike a normal shock, is inclined with respect to the direction of incoming air. It occurs when a supersonic flow encounters a corner that effectively turns the flow into itself and compresses. The upstream streamlines are uniformly deflected after the shock wave. The most common way to produce an oblique shock wave is to place a wedge into supersonic, compressible flow. Similar to a normal shock wave, the oblique shock wave consists of a very thin region across which nearly discontinuous changes in the thermodynamic properties of a gas occur. While the upstream and downstream flow directions are unchanged across a normal shock, they are different for flow across an oblique shock wave.
Shock diamonds are a formation of standing wave patterns that appear in the supersonic exhaust plume of an aerospace propulsion system, such as a supersonic jet engine, rocket, ramjet, or scramjet, when it is operated in an atmosphere. The "diamonds" are actually a complex flow field made visible by abrupt changes in local density and pressure as the exhaust passes through a series of standing shock waves and expansion fans. The physicist Ernst Mach was the first to describe a strong shock normal to the direction of fluid flow, the presence of which causes the diamond pattern.
A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached.
A supersonic expansion fan, technically known as Prandtl–Meyer expansion fan, a two-dimensional simple wave, is a centered expansion process that occurs when a supersonic flow turns around a convex corner. The fan consists of an infinite number of Mach waves, diverging from a sharp corner. When a flow turns around a smooth and circular corner, these waves can be extended backwards to meet at a point.
An intake ramp is a rectangular, plate-like device within the air intake of a jet engine, designed to generate a number of shock waves to aid the inlet compression process at supersonic speeds. The ramp sits at an acute angle to deflect the intake air from the longitudinal direction. At supersonic flight speeds, the deflection of the air stream creates a number of oblique shock waves at each change of gradient along at the ramp. Air crossing each shock wave suddenly slows to a lower Mach number, thus increasing pressure.
This article briefly describes the components and systems found in jet engines.
In fluid dynamics, the process of a laminar flow becoming turbulent is known as laminar–turbulent transition. The main parameter characterizing transition is the Reynolds number.
A supersonic airfoil is a cross-section geometry designed to generate lift efficiently at supersonic speeds. The need for such a design arises when an aircraft is required to operate consistently in the supersonic flight regime.
Taylor–Maccoll flow refers to the steady flow behind a conical shock wave that is attached to a solid cone. The flow is named after G. I. Taylor and J. W. Maccoll, whom described the flow in 1933, guided by an earlier work of Theodore von Kármán.
References
- Chapman, C.J. (2000). High Speed Flow. CUP. ISBN 978-0-521-66169-0.
- Anderson, John D. Jr. (January 2001) [1984]. Fundamentals of Aerodynamics (3rd ed.). McGraw-Hill Science/Engineering/Math. ISBN 978-0-07-237335-6.
- 1 2 "Transition between Regular Reflection and Mach Reflection in the Dual-Solution Domain" (PDF). 2007. Retrieved 2010-08-13.
- 1 2 Ben-Dor, Gabi (2007). Shock Wave Reflection Phenomena (2nd ed.). Springer. ISBN 978-3-540-71381-4.
- ↑ Gavrenkov, S. A.; Gvozdeva, L. G. (2012). "Numerical investigation of the onset of instability of triple shock configurations in steady supersonic gas flows". Technical Physics Letters. 38 (6): 587–589. Bibcode:2012TePhL..38..587G. doi:10.1134/S1063785012060223.
- ↑ Gvozdeva, L. G.; Gavrenkov, S. A. (2013). "Influence of the adiabatic index on switching between different types of shock wave reflection in a steady supersonic gas flow". Technical Physics. 58 (8): 1238–1241. Bibcode:2013JTePh..58.1238G. doi:10.1134/S1063784213080148.
- ↑ Gvozdeva, L. G.; Gavrenkov, S. A. (2012). "Formation of triple shock configurations with negative reflection angle in steady flows". Technical Physics Letters. 38 (4): 372–374. Bibcode:2012TePhL..38..372G. doi:10.1134/S1063785012040232.