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Nozzle external geometry as a boundary condition for the azimuthal mode selection in an impinging underexpanded jet
- Source :
- Journal of Fluid Mechanics. 862:421-448
- Publication Year :
- 2019
- Publisher :
- Cambridge University Press (CUP), 2019.
-
Abstract
- The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of $3.4$ and plate spacing of $5.0D$, where $D$ is the nozzle exit diameter, are investigated using high resolution particle image velocimetry (PIV) and acoustic measurements. Proper orthogonal decomposition is applied to the PIV fields and a difference in dominant instability mode is found. To investigate possible explanations for the change in instability mode, additional nozzle external boundary conditions are investigated, including the addition of acoustic dampening foam. A difference in acoustic feedback path is suggested to be the cause for the change in dominant azimuthal modes between the flows. This is due to the thin-lip case containing a feedback path that is concluded to be closed exclusively by a reflection from the nozzle base surface, rather than directly to the nozzle lip. The ability of the flow to form a feedback path that maximises the impingement tone gain is discussed with consideration of the numerous acoustic feedback paths possible for the given nozzle external boundary conditions.
- Subjects :
- Physics
Jet (fluid)
Mechanical Engineering
Nozzle
Mechanics
Condensed Matter Physics
01 natural sciences
Instability
Jet noise
010305 fluids & plasmas
Particle image velocimetry
Mechanics of Materials
0103 physical sciences
Reflection (physics)
Supersonic speed
Boundary value problem
010306 general physics
Subjects
Details
- ISSN :
- 14697645 and 00221120
- Volume :
- 862
- Database :
- OpenAIRE
- Journal :
- Journal of Fluid Mechanics
- Accession number :
- edsair.doi...........5527f24b727e60f1f1ce9fc89b704dcf