Reentrant Motion in Cloud Cavitation due to Cloud Collapse and Pressure Wave Propagation

It is well known that reentrant jet motion in periodic cloud cavitation means upward flow from the cavity closure area of cloud cavitation. However the mechanism of reentrant motion seems to remain unsolved clearly. In the present study some experiments were conducted about the mechanism of reentrant motion in a fixed type cavity for a convergent-divergent nozzle. High speed video observation and image analysis based on the frame difference method were made about unsteady cloud cavitation with a periodic structure of cavitation cloud shedding. As a result, the main points are experimentally found as follows; 1) a typical pattern of reentrant motions can be caused by the pressure wave propagation from the collapse of cavitation cloud shed downstream and 2) the frame difference method is very useful in an image analysis for high speed video observation of cavitating flow because the trajectory of pressure waves can be clearly visualized by the method.

Download Full-text

1213 Pressure Wave Formation and Its Propagation in Cavitation Clouds : High-Speed-Video Observation and Image Analysis

The Proceedings of Conference of Hokuriku-Shinetsu Branch ◽

10.1299/jsmehs.2010.47.459 ◽

2010 ◽

Vol 2010.47 (0) ◽

pp. 459-460

Author(s):

Keiichi Sato ◽

Yasuhiro Sugimoto

Keyword(s):

Image Analysis ◽

Pressure Wave ◽

High Speed ◽

Wave Formation ◽

Video Observation ◽

High Speed Video

Download Full-text

Unsteady Behavior of Cavitating Waterjet in an Axisymmetric Convergent-Divergent Nozzle: High Speed Observation and Image Analysis Based on Frame Difference Method

Journal of Flow Control Measurement &amp Visualization ◽

10.4236/jfcmv.2014.23011 ◽

2014 ◽

Vol 02 (03) ◽

pp. 94-104 ◽

Cited By ~ 9

Author(s):

Shota Hayashi ◽

Keiichi Sato

Keyword(s):

Image Analysis ◽

Difference Method ◽

High Speed ◽

Frame Difference ◽

Unsteady Behavior

Download Full-text

Effects of Diffuser Length on Cloud Cavitation in an Axisymmetrical Convergent-Divergent Nozzle

Volume 2A: Fora, Part 2 ◽

10.1115/ajkfluids2015-05507 ◽

2015 ◽

Author(s):

Keiichi Sato ◽

Naoya Takahashi ◽

Yasuhiro Sugimoto

Keyword(s):

High Speed ◽

Pressure Effect ◽

Water Jet ◽

Video Observation ◽

Fluid Machinery ◽

Cloud Cavitation ◽

Frame Difference ◽

Upstream Pressure ◽

Cavitating Hydrofoil ◽

Unsteady Behavior

Unsteady behavior of periodic cloud cavitation is typically observed in the field of fluid machinery under a high speed liquid flow such as a cavitating hydrofoil as well as cavitating water jet. The instability of cloud cavitation remains to be completely solved though it has been confirmed that there are two instabilities which is an intrinsic instability of cavitation and a system instability. Sato, et al. have found through previous investigations that the pressure wave at the collapse of shedding clouds can make a trigger to cause a reentrant motion. In the present study, the authors focus on a cavitating water jet to investigate the cavitation aspects in an axisymmetrical convergent-divergent nozzle and examine an unsteady behavior of cloud cavitation through high speed video observation and image analysis based on the frame difference method. Especially, the authors study the effect of nozzle divergent part (diffuser) as well as the upstream pressure effect on cloud cavitation in the nozzle. As a result the authors have found that there are two kinds in the shedding pattern and the reentrant motion pattern for cloud cavitation depending on the nozzle diffuser length.

Download Full-text

Dynamic Behaviors of Re-Entrant Jet and Cavity Shedding During Transitional Cavity Oscillation on NACA0015 Hydrofoil

Journal of Fluids Engineering ◽

10.1115/1.4041716 ◽

2018 ◽

Vol 141 (6) ◽

Cited By ~ 7

Author(s):

Bangxiang Che ◽

Linlin Cao ◽

Ning Chu ◽

Dmitriy Likhachev ◽

Dazhuan Wu

Keyword(s):

Pressure Measurement ◽

High Speed ◽

Large Scale ◽

Dominant Role ◽

Video Observation ◽

Sheet Cavitation ◽

High Speed Video ◽

Cavity Shedding ◽

Cavity Closure ◽

High Instability

Transitional cavity shedding is known as the stage of attached cavitation with high instability and distinct periodicity. In this study, we experimentally investigated the dynamic characteristics of transitional cavity (0.8≤L/c<1) shedding on NACA0015 hydrofoil with high-speed video observation and synchronous pressure measurement. In the partial cavity (0.4<L/c<0.8) oscillation, the sheet cavitation grew along the chord with good spanwise uniformity, and the middle-entrant jet played a dominant role in cavity shedding. Meanwhile, in the transitional cavity oscillation, the previous shedding cavity exhibited a prohibitive effect on the growth of sheet cavitation on the hydrofoil, resulting in concave cavity closure line. Moreover, two symmetrical side-entrant jets originated at the near-wall ends and induced the two-stage shedding phenomenon. The aft and fore parts of the sheet cavitation shed separated as different forms and eventually merged into the large-scale cloud cavity.

Download Full-text

Observation and Scaling of Tip Vortex Cavitation on Elliptical Hydrofoils

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 2, Fora ◽

10.1115/ajk2011-33015 ◽

2011 ◽

Cited By ~ 3

Author(s):

Shigeki Nagaya ◽

Risa Kimoto ◽

Kenji Naganuma ◽

Takayuki Mori

Keyword(s):

Water Quality ◽

Reynolds Number ◽

High Speed ◽

Tip Vortex ◽

Video Observation ◽

Tip Vortex Cavitation ◽

Air Content ◽

Sheet Cavitation ◽

High Speed Video ◽

Systems Research

Experimental study on tip vortex cavitation (TVC) was carried out for elliptical hydrofoils with various chord lengths. The purpose of the experiment was to clarify the influences of Reynolds number and water quality on tip vortex cavitation. Experiments were made in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense Japan. The elliptical hydrofoils tested were NACA 0012 cross section with chord lengths of 500mm, 250mm and 50mm. Reynolds number based on hydrofoil chord length was 2×105 < ReC < 7.4×106. Water quality of the tunnel was characterized by air content and nuclei distribution. Air content of the tunnel was varied between 30% and 80%. Nuclei distribution was measured by a cavitation susceptibility meter (CSM) with center-body venturi. Cavitation inception was determined from high speed video observation. A standard formula, (σL/σS) = (ReL/ReS)n, was applied for the scaling. In the present study, exponent of the scaling law n was found to be 0.2 < n < 0.4. High speed video observation showed that the process of the TVC inception strongly depends on water quality. In the experiments, unsteady behaviors of TVC were also investigated. Strong interactions between sheet cavitation and TVC were observed.

Download Full-text