question: PHYSICS] [FLUID DYNAMICS] Why does the vapor cone suddenly vanish after passing the speed of sound? See video inside:
comment: The shuttle is going nearly 800 mph straight up, they might just have passed into another air mass with a lower humidity level. The border doesn't need to be super sharp for it to seem to happen quickly when moving at such a speed.
passages: In 1883, Osborne Reynolds showed that noise interfered with laminar flow, precipitating turbulence at much lower flow rates. As Mach 1 nears, the Doppler effect increasingly concentrates aircraft sound intensity, with an associated extreme increase in ultrasonic noise frequency. The intense high-frequency noise of air in the anterior sound cone prevents laminar flow, with much higher resistance to penetration by the leading edges (the “sound barrier” effect), leading to compression bands (“shock wave” effect).
   During acceleration toward Mach 1, the aerodynamic and mechanical aircraft sound is confined to a sound cone. At Mach 1, the angle of the cone margins is 45 degrees to the line of flight; the cone’s apex is the aircraft nose. 
   If the speed of sound is reached in a stage, the group of stages can be analyzed till that stage, which is the last in the group, the remaining stages forming another group of analysis. This division is imposed by the stage working in "limited" (choked) mode. The cone is shifted in the formula_24 axis direction, appearing a triangular surface, depending on the critical pressure ratio formula_25, where formula_26 is the outlet critical pressure of the stage group.
  
  The analytical expression of the flow ratio is:
  
  For condensing turbine the ratio formula_28 is very low, previous relation reduces to:
   In addition to making the shock waves themselves visible, water condensation can also occur in the trough between two crests of the shock waves produced by the passing of the object. However, this effect does not necessarily coincide with the acceleration of an aircraft through the speed of sound or Mach 1.
  
  Section::::Examples.
   In the case of aircraft, the cloud is caused by expansion fans decreasing the air pressure, density and temperature below the dew point. Then pressure, density and temperature suddenly increase across the stern shock wave associated with a return to subsonic flow behind the aircraft. Since the local Mach number is not uniform over the aircraft, parts of the aircraft may be supersonic while others remain subsonic — a flight regime called transonic flight.
   When the deflagration begins, a zone of significantly elevated pressure travels outward through both air masses as a compression wave. This wave moves at the speed of sound through both the intake and tailpipe air masses. (Because these air masses are significantly elevated in temperature as a result of earlier cycles, the speed of sound in them is much higher than it would be in normal outdoor air.) When a compression wave reaches the open end of either tube, a low pressure rarefaction wave starts back in the opposite direction, as if "reflected" by the open end. This low pressure region returning to the combustion zone is, in fact, the internal mechanism of the Kadenacy effect. There will be no "breathing" of fresh air into the combustion zone until the arrival of the rarefaction wave.
   Section::::Characteristics.
   It is useful to keep in mind that although the waves traverse the entire expansion chamber over each cycle, the actual gases leaving the cylinder during a particular cycle do not. The gas flows and stops intermittently and the wave continues on to the end of the pipe. The hot gases leaving the port form a "slug" which fills the header pipe and remains there for the duration of that cycle. This causes a high temperature zone in the head pipe which is always filled with the most recent and hottest gas. Because this area is hotter, the speed of sound and thus the speed of the waves that travel through it are increased. During the next cycle that slug of gas will be pushed down the pipe by the next slug to occupy the next zone and so on. The volume this "slug" occupies constantly varies according to throttle position and engine speed. It is only the wave energy itself that traverses the whole pipe during a single cycle. The actual gas leaving the pipe during a particular cycle was created two or three cycles earlier. (This is why exhaust gas sampling on two stroke engines is done with a special valve right in the exhaust port. The gas exiting the stinger has had too much resident time and mixing with gas from other cycles causing errors in analysis.)
   The idea behind the aerospike design is that at low altitude the ambient pressure compresses the exhaust against the spike. Exhaust recirculation in the base zone of the spike can raise the pressure in that zone to nearly ambient. Since the pressure in front of the vehicle is ambient, this means that the exhaust at the base of the spike nearly balances out with the drag experienced by the vehicle. It gives no overall thrust, but this part of the nozzle also doesn't "lose" thrust by forming a partial vacuum. The thrust at the base part of the nozzle can be ignored at low altitude.
   When the back pressure, p, is lowered enough, the flow speed is Mach 1 at the throat, as in figure 1b. The flow pattern is exactly the same as in subsonic flow, except that the flow speed at the throat has just reached Mach 1. Flow through the nozzle is now choked since further reductions in the back pressure can't move the point of M=1 away from the throat. However, the flow pattern in the diverging section does change as you lower the back pressure further.
   When the descending piston first exposes the exhaust port on the cylinder wall, the exhaust flows out powerfully due to its pressure (without assistance from the expansion chamber) so the diameter/area over the length of the first portion of the pipe is constant or near constant with a divergence of 0 to 2 degrees which preserves wave energy. This section of the system is called the "header pipe" (the exhaust port length is considered part of the header pipe for measurement purposes). By keeping the header pipe diameter near constant, the energy in the wave is preserved because there is no expansion needed until later in the cycle. The flow leaving the cylinder during most of the blowdown process is sonic or supersonic, and therefore no wave could travel back into the cylinder against that flow.
   During this phase, too, there is a difference in action between the very different masses in the intake and tailpipe. The intake air mass is again fairly low, but it now almost totally consists of outside air; therefore, fresh air is available almost immediately to begin re-filling the combustion zone from the front. The tailpipe air mass is also pulled, eventually reversing direction as well. The tailpipe will never be completely purged of hot combustion gases, but at reversal it will be easily able to pull in fresh air from all sides around the tailpipe opening, so its contained mass will be gradually increasing until the next deflagration event. As air flows rapidly into the combustion zone, the rarefaction wave is reflected rearward by the front of the engine body, and as it moves rearward the air density in the combustion zone naturally rises until the pressure of the air/fuel mixture reaches a value where deflagration can again commence.
   As an example calculation using the above equation, assume that the propellant combustion gases are: at an absolute pressure entering the nozzle "p" = 7.0 MPa and exit the rocket exhaust at an absolute pressure "p" = 0.1 MPa; at an absolute temperature of "T" = 3500 K; with an isentropic expansion factor "γ" = 1.22 and a molar mass "M" = 22 kg/kmol. Using those values in the above equation yields an exhaust velocity "v" = 2802 m/s, or 2.80 km/s, which is consistent with above typical values.
   Viscous liquids, such as glycerol, flow very slowly. Glycerol has high dynamic viscosity, and if a researcher aspirates a sample of glycerol too quickly with an air displacement pipette, It will draw up air bubble. When a researcher attempts to dispense the liquid, some of it will stick to the pipette tip wall, dispense very slowly and remain in the tip. Surfactants also produce this effect, but the remaining liquid film is thinner.
   The United States Naval Research Laboratory (NRL) and the United States Department of Defense Space Test Program (STP) conducted the Charged Aerosol Release Experiment (CARE) on September 19, 2009, using exhaust particles from a Black Brant XII suborbital sounding rocket launched from NASA's Wallops Flight Facility to create an artificial noctilucent cloud. The cloud was to be observed over a period of weeks or months by ground instruments and the Spatial Heterodyne IMager for MEsospheric Radicals (SHIMMER) instrument on the NRL/STP STPSat-1 spacecraft. The rocket's exhaust plume was observed and reported to news organizations in the United States from New Jersey to Massachusetts.
   It appears much like a standard bell nozzle, but at the throat is a 'centrebody' or 'pintle' which deflects the flow towards the walls. The exhaust gas flows past this in a more outward direction than in standard bell nozzles while expanding before being turned towards the exit. This allows for shorter nozzles than the standard design whilst maintaining nozzle expansion ratios. Because of the atmospheric boundary, the atmospheric pressure affects the exit area ratio so that atmospheric compensation can be obtained up to the geometric maximum allowed by the specific nozzle.
   Section::::Critical interpretations.
   In the Earth's atmosphere, the chief factor affecting the speed of sound is the temperature. For a given ideal gas with constant heat capacity and composition, the speed of sound is dependent "solely" upon temperature; see Details below. In such an ideal case, the effects of decreased density and decreased pressure of altitude cancel each other out, save for the residual effect of temperature.
   A further lowering of the back pressure changes and weakens the wave pattern in the jet. Eventually the back pressure will be low enough so that it is now equal to the pressure at the nozzle exit. In this case, the waves in the jet disappear altogether (figure 1f), and the jet will be uniformly supersonic. This situation, since it is often desirable, is referred to as the 'design condition'.
   Several versions of the design exist, differentiated by their shapes. In the toroidal aerospike the spike is bowl-shaped with the exhaust exiting in a ring around the outer rim. In theory this requires an infinitely long spike for best efficiency, but by blowing a small amount of gas out of the center of a shorter truncated spike (like base bleed in an artillery shell), something similar can be achieved.
   BULLET::::- Dynaflow was referred to in an episode of "The Honeymooners" called "" (which first aired on December 10, 1955). In it, Ed Norton (Art Carney) tries to explain the troubles with the vacuum cleaner purchased as a wedding anniversary gift by Ralph Kramden (Jackie Gleason) thus: "The armature sprocket is causing interference; which, in turn, causes the combustion line to interfere with the flow and the dynaflow." This was a subtle sponsor plug/inside joke, as Buick was the sponsor of the show in the 1955–56 season.
   For aerodynamic reasons the flow goes sonic ("chokes") at the narrowest part of the nozzle, the 'throat'. Since the speed of sound in gases increases with the square root of temperature, the use of hot exhaust gas greatly improves performance. By comparison, at room temperature the speed of sound in air is about 340 m/s while the speed of sound in the hot gas of a rocket engine can be over 1700 m/s; much of this performance is due to the higher temperature, but additionally rocket propellants are chosen to be of low molecular mass, and this also gives a higher velocity compared to air.
   The Venturi effect may be observed or used in the following:
  
  BULLET::::- Cargo eductors on oil product and chemical ship tankers
  
  BULLET::::- Inspirators that mix air and flammable gas in grills, gas stoves, Bunsen burners and airbrushes
  
  BULLET::::- Water aspirators that produce a partial vacuum using the kinetic energy from the faucet water pressure
  
  BULLET::::- Steam siphons using the kinetic energy from the steam pressure to create a partial vacuum
  
  BULLET::::- Atomizers that disperse perfume or spray paint (i.e. from a spray gun).
  
  BULLET::::- Carburetors that use the effect to suck gasoline into an engine's intake air stream
   Figure 1a shows the flow through the nozzle when it is completely subsonic (i.e. the nozzle is not choked). The flow in the chamber accelerates as it converges toward the throat, where it reaches its maximum (subsonic) speed at the throat. The flow then decelerates through the diverging section and exhausts into the ambient as a subsonic jet. Lowering the back pressure, in this state, will increase the flow speed everywhere in the nozzle.
   The limiting case of the Venturi effect is when a fluid reaches the state of choked flow, where the fluid velocity approaches the local speed of sound. When a fluid system is in a state of choked flow, a further decrease in the downstream pressure environment will not lead to an increase in the mass flow rate. However, mass flow rate for a compressible fluid will increase with increased upstream pressure, which will increase the density of the fluid through the constriction (though the velocity will remain constant). This is the principle of operation of a de Laval nozzle. Increasing source temperature will also increase the local sonic velocity, thus allowing for increased mass flow rate but only if the nozzle area is also increased to compensate for the resulting decrease in density.
  
raw_presuppositions: vapor cone suddenly vanishes after passing the speed of sound.
raw_corrections: Just passed into another air mass with lower humidity. 