Prediction of plane‐wise turbulent events to the Reynolds stress in a flow over scour‐bed

Abstract

In this paper, we intend to quantify the contribution of turbulent events to the total Reynolds shear stresses trueu′v′‾, trueu′w′‾, and truev′w′‾ from the four different quadrants of three different planes (xy, xz, yz); and to make a comparative study among the planes in the scour geometry developed by short circular cylinder of fixed length with a fixed diameter placed over the sand bed transverse to the flow. We also intend to predict the magnitude of covariance terms u′v′, u′w′, and v′w′ and their contributions in the four quadrants by making use of the conditional probability distribution of the Reynolds shear stresses −u′v′, −u′w′, and −v′w′, which can be derived by applying the cumulant‐discard method to the Gram‐Charlier probability distribution of the two variables. This consideration motivates the work on the flow over the obstacle marks generated on sand bed using different short cylinders. The contributions of burst‐sweep cycles to the Reynolds shear stresses from the planes over and within the scour around the obstacle are computed using the quadrant analysis to identify the leading shear stress plane, which are responsible to form the scour geometry. It is discovered that the yz and xy‐ planes are much more important in the scouring regions, whereas xz‐ plane is important for the smooth surface. Using cumulant‐discard method (taking into account the cumulants of less than fourth order), it is shown that the qualitative behaviours of turbulent events agree well with experimental data. Thus, it is confirmed that even the third‐order probability distribution of the Reynolds stresses can describe the experimental results very well.

Bursting phenomenon created by bridge piers group in open channel flow

“…As H is the hole size, those events that occur within the hole are excluded from the quadrant analysis. In large values of the hole size, only strong events are considered [7,9,31].…”

Bursting phenomenon created by bridge piers group in open channel flow

“…In large values of the hole size, only strong events are considered (Cellino andLemmin, 2004, Maity andMazumder, 2017). Based on a threshold level of the hyperbolic hole region, the contribution of each quadrant to the RSS was determined by Dey et al (2011) and Balachandar and Bhuiyan (2007), and the fractional contributions, Si,H, to RSS for each event can be estimated as follows (Roussinova et al 2008, Debnath et al 2012, Izadinia et al 2013: (5)…”

Calibration and Verification of Operation Parameters for an Array of Vectrino Profilers Configured for Turbulent Flow Field Measurement around Bridge Piers—Part I

“…ADV Vectrinos have been available since the 1990s as one of the most popular instruments for laboratory experiments, with several upgrades having been made, such as Vectrino II or the Vectrino profiler (ADVP) [20]. ADVs are versatile instruments for measuring turbulent and mean flows in hydraulic laboratories that can be used for various applications in fluid flow environments: velocity profiling in challenging situations, such as bores and positive surges [21] or turbidity currents [22], near-wall turbulence [23], turbulence in fish passes [24,25], flow-vegetation interaction [26], turbulence in scour holes [27,28], suspended ashes concentration [29,30], salinity estimation [31], etc. The Vectrino Profiler was released in 2011, offering velocity sampling in volumes ranging up to 30 mm over a 45-75 mm distance from the probe and sampling rates of up to 200 Hz.…”