Characterization of the jet emanating from a self-exciting flexible membrane nozzle
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University of Cincinnati / OhioLINK
2012
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ndltd-OhioLink-oai-etd.ohiolink.edu-ucin13378873222021-08-03T06:15:34Z Characterization of the jet emanating from a self-exciting flexible membrane nozzle Lakhamraju, Raghava Raju Aerospace Materials flow control flexible nozzle self-excitation pulsatile jet noncircular jet starting and entrainment vortices The present research investigates the development and characterization ofa novel self-exciting flexible membrane nozzle. Upon excitation (oscillations that areproduced by exerting tension at the nozzle exit and passing air through it), theflexible nozzle is capable of producing time-dependent flow that is fairlyconsistent at a flow condition (a particular tension and volume flow rate ofair). The fluidic device is a passive means of enhancing mixing as there is noexternal excitation mechanism. The resultant flow is self-excited over a rangeof conditions and produces pulsatile flow that is excited by the motion of theflexible membrane. The baseline configuration of the flexible membrane nozzleinvolves symmetrical placement of the edges at the nozzle exit. The exit of thenozzle offers variable area geometry, with the shape approximately resembling avariable aspect ratio ellipse. Particle Image Velocimetry (PIV) is employed toillustrate and characterize the large-scale flow structures of the jet motion and the eduction of coherent structures was performed using ProperOrthogonal Decomposition (POD). For a particular nozzle diameter, the flow conditions are controlled by the tension applied to the flexible nozzle and volume flowrate of air throughit. PIV measurements have been conducted mainly along the mid-minor axis plane since the crucial flow structure interactions occur in this plane due to the nozzle operation. Based on a set of experiments conducted within the physical limitations of the nozzle, the near field of the nozzle exit was found to be governed by the interactions of two sets of large-scale vortical structures - starting vortices and entrainment vortices (features of pulsatile flows) and the exact nature of their evolution is dependent on the operating conditions. As in elliptic jets, the near field of the nozzle is found to be extremely sensitive to the initial conditions (nozzle configuration). A cross-spectral analysis is also performed in the near field of the jet using two hot-wire anemometers to characterize the evolution of large-scale flow structures for the various flow conditions. For a baseline nozzle in fully closed configuration, for a given tension at the nozzle exit, increase in volume flow tends to produce higher jet spread (more prominent at lower tensions) and increased range of turbulence production. For a particular flow rate, increase in tension results in a more symmetric jet along the centerline and high turbulence production in the near field. Under certain flow conditions, the dynamic flapping of the jet generated half-width spreading rates that exceeded that of slot nozzles. The flow characteristics are compared to that of existing nozzles that generate high mixing rates at the exit. The application of POD on the PIV information shows that the reconstructed images from few modes provide decent illustrations of the flow structures with filtered effect on the turbulent flow field. In essence, this analysis separates the oscillation of the jet from the velocity fluctuations due to the turbulent flow behavior. In the current study, with certain operating conditions, increased half-width spreading rates and enhanced centerline velocity decay can be generated. A predominant flapping jet or highly turbulent jet at the nozzle exit can be achieved by modifying the flow conditions. 2012-10-05 English text University of Cincinnati / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337887322 http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337887322 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Aerospace Materials flow control flexible nozzle self-excitation pulsatile jet noncircular jet starting and entrainment vortices |
| spellingShingle |
Aerospace Materials flow control flexible nozzle self-excitation pulsatile jet noncircular jet starting and entrainment vortices Lakhamraju, Raghava Raju Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| author |
Lakhamraju, Raghava Raju |
| author_facet |
Lakhamraju, Raghava Raju |
| author_sort |
Lakhamraju, Raghava Raju |
| title |
Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| title_short |
Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| title_full |
Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| title_fullStr |
Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| title_full_unstemmed |
Characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| title_sort |
characterization of the jet emanating from a self-exciting flexible membrane nozzle |
| publisher |
University of Cincinnati / OhioLINK |
| publishDate |
2012 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337887322 |
| work_keys_str_mv |
AT lakhamrajuraghavaraju characterizationofthejetemanatingfromaselfexcitingflexiblemembranenozzle |
| _version_ |
1719433620183056384 |