Experiments in Fluids

, Volume 21, Issue 6, pp 401–409

An experimental study of supersonic microjets

  • S. D. Scroggs
  • G. S. Settles
Originals

Abstract

Miniature axisymmetric supersonic nozzles were produced with exit Mach numbers ranging from 1.0 to 2.8 by forming Pyrex® capillary tubing of 0.6 and 1.2 mm inside diameter into converging-diverging channels. The nozzle contours were measured and were found to compare favorably to ideal solutions given by the axisymmetric method of characteristics. In addition, the surfaces of these nozzles were quite smooth, providing featureless flows at perfect expansion. Schlieren visualization and pitot pressure measurements of the resulting microjets were compared to the literature available for jets produced by larger-scale nozzles. A postponed transition to turbulence is noted in these microjets due to their low Reynolds number. The pitot pressure on centerline is nearly uniform at perfect expansion over core lengths up to 12 nozzle exit diameters. Supersonic microjet nozzles thus provide a more effective small-scale high-pressure gas delivery device than do sonic nozzles of comparable scale at equivalent mass flow rates. Supersonic microjets may therefore have several industrial applications.

List of symbols

δ*

boundary layer displacement thickness, mm

d

diameter of nozzle exit, mm

L

length of nozzle diverging section, mm

Lc

inviscid core length, mm

Ls

supersonic region length, mm

Mc

convective Mach number

Me

exit Mach number

Pb

backpressure at nozzle exit, (equal to ambient pressure in this experiment)

Pe

exit pressure of the supersonic jet

Pbe

exit pressure ratio (Pb/Pe)

Pp

impingement pressure (pitot pressure)

P0

stagnation pressure supplied to nozzle

Pn

overall pressure ratio (P0/Pb,)

r

radial dimension (cylindrical coordinate system), mm

r0

radius of throat, mm

Red

Reynolds number, based on nozzle exit diameter

Ve

exit velocity, m/s

x

axial dimension (cylindrical coordinate system), mm

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Adamson T; Nicholls J (1959) On the structure of jets from highly underexpanded nozzles into still air J. Aero/space Sci. Jan 16–24Google Scholar
  2. Carroll BF; Dutton JC; Addy AL (1986) NOZCS2: A computer program for the design of continuous slope supersonic Nozzles. University of Illinois at Urbana-Champaign, Report No. UILU ENG 86-4007Google Scholar
  3. Donaldson C; Gray KE (1966) Theoretical and experimental investigation of the compressible free mixing of two dissimilar gases. AIAA J 4: 2019–2028Google Scholar
  4. Donaldson C; Snedeker R (1971) A study of free jet impingement. J Fluid Mech 45: 281–319Google Scholar
  5. Fourgette DC; Mungal MG; Dibble RW (1991) Time evolution of the shear layer of a supersonic axisymmetric jet AIAA J 29: 1123–1130Google Scholar
  6. Hu T; McLaughin D (1990) Flow and acoustic properties of low Reynolds number underexpanded supersonic jets. J of Sound and Vibration 141: 485–505Google Scholar
  7. Jindra KJ (1970) Geometric effects on the performance characteristics of very small nozzles. Masters Thesis, Air Force Inst. of Tech., Wright-Patterson AFB, Ohio School of Engineering, Dec.Google Scholar
  8. John JEA (1984) Gas dynamics. 2 ed., New York: Prentice HallGoogle Scholar
  9. Merzkirch W (1987) Flow visualization, 2 ed. Orlando: Academic PressGoogle Scholar
  10. Morrison GL; McLaughlin DK (1980) Instability process in low Reynolds number supersonic jets. AIAA J 18: 793–800Google Scholar
  11. Novopashin SA; Perepelkin AL (1988) Axial symmetry loss of a preturbulent jet. Phys Lett 135: 290–293Google Scholar
  12. Novopashin SA; Perepelkin AL (1992) Transition to turbulence in a supersonic jet. Russian J Eng Thermophys 2: 51–61Google Scholar
  13. Nagamatsu HT; Sheer RE (1969) Supersonic jet noise theory and experiments. NASA SP-207Google Scholar
  14. Prandtl L (1952) The essentials of fluid dynamics. Glasgow: Blackie & SonGoogle Scholar
  15. Sherman PM; Glass DR; Duleep KG (1976) Jet flowfield during screech. Appl. Scient. Res. 32: 283–303Google Scholar
  16. Zapryagaev VI; Solotchin AV (1991) Three-dimensional structure of flow in a supersonic underexpanded Jet. J Appl Mech Tech Phys 32: 503–507Google Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • S. D. Scroggs
    • 1
  • G. S. Settles
    • 1
  1. 1.Gas Dynamics Lab Mechanical Engineering DepartmentThe Pennsylvania State UniversityUniversity ParkUSA

Personalised recommendations