Flow Visualization and Frequency Characteristics of Velocity Fluctuations of Complex Turbulent Flow in a Short Elbow Piping Under High Reynolds Number Condition

Abstract

Flow visualization was performed on a single short elbow piping by means of two-dimensional particle image velocimetry. The piping was designed as a 1/7-scale model of a section of the cold-leg piping of a Japan sodium-cooled fast reactor. This study characterized the periodic motions and flow structures that appeared in and downstream of the elbow and potentially affected flow-induced vibrations. The flow field that related flow separation and frequency characteristics of the flow velocity fluctuation were explored for Reynolds number from 0.3 × 106 to 1.0 × 106, which belonged to the post-critical regime. Experimental results show that flow structures are not strongly dependent on Reynolds number in this range. Frequency analysis for the velocity fluctuation in terms of Strouhal number (St) reveals that there exist not only two kinds of vortices with different shedding periods, but also one periodic flow in the circumferential direction. In the flow separation region, vortices are periodically emitted with St ≈ 0.5, while those with about 1.0 are shed in a shear flow region located between the separation region and the pipe center. Moreover, a periodic motion with St ≈ 0.5 appeared in the circumferential direction in the vicinity near the separation region. These values of St were not strongly dependent on Reynolds number in this study.

Direct numerical simulation of a turbulent 90° bend pipe flow

“…Time signals of velocity fluctuations at different locations downstream of the pipe bend were also used in several studies (Brücker, 1998;Takamura et al, 2012;Kalpakli and Orlü, 2013) to extract the characteristic frequency of the unsteady flow motions. Typically, azimuthal velocity near the axis of symmetry was measured close to the inner side (Brücker, 1998;Kalpakli andÖrlü, 2013).…”

“…This phenomenon is associated with the unsteady motions of the Dean vortices (Dean, 1927(Dean, , 1928 downstream of 90 • bends. It has been the focus of many studies in the past two decades (Rütten et al, 2001(Rütten et al, , 2005Ebara et al, 2010;Ono et al, 2011;Takamura et al, 2012;Sakakibara and Machida, 2012;Kalpakli et al, 2012;Kalpakli andÖrlü, 2013;Hellström et al, 2013;Kalpakli Vester et al, 2015;Carlsson et al, 2015;Tunstall et al, 2016;Noorani and Schlatter, 2016;, and this phenomenon is directly associated with the thermal and mechanical fatigue in pipeline systems.…”

“…Brücker (1998) used filtered streamwise vorticity from his PIV experiments, and the filtering was applied to reduce the noise from the PIV data. Velocity fluctuations on the symmetry plane were used by Takamura et al (2012); Sakakibara and Machida (2012), while pressure fluctuations were used by Ebara et al (2010); they all reported a frequency of St = 0.5. The variation of the outer stagnation point of the Dean vortices was used by Rütten et al (2001Rütten et al ( , 2005.…”

A Review of Embedded Large Eddy Simulation for Internal Flows

“…The capturing of these secondary flow features has been studied extensively by Takamura et al [98], Yuki et al [127], Tanaka and Ohshima [99] amongst others for the Japan Sodium cooled Fast Reactor (JSFR).…”

Numerical Prediction of Flow Patterns after Various Pipe Fittings

“…Furthermore, these methods allow the capturing of large-scale as well as small-scale flow structures. Takamura [2] investigated the complex turbulent flow in a short elbow pipe under high Reynolds number conditions. In addition, Tanaka [3] carried out some URANS simulations of unsteady eddy motion in pipe flows at high Reynolds numbers conditions.…”