The STURM tanks use a resuspension paddle that produces uniform bottom shear stress across the sediment surface while gently mixing a 1 m deep overlying water column. 4 weeks), over muddy sediments with or without infaunal organisms. The 1 m3 tanks can be programmed to produce tidal or episodic sediment resuspension over extended time periods (e.g. Shear TUrbulence Resuspension Mesocosm (STURM) tanks, with high instantaneous bottom shear stress and realistic water column mixing in a single system, allow more realistic benthic-pelagic coupling studies that include sediment resuspension. STURM: Resuspension mesocosms with realistic bottom shear stress and water column turbulence for benthic-pelagic coupling studies: Design and Applications Entrainment of high streamwise momentum on the outer sides of this vortex pair generates streamwise shear stress maxima, 70 δν downstream, which are displaced laterally by 35 δν from the local minimum. Due to increasing velocity with elevation, this element bends downstream, forming a pair of inclined streamwise vortices, aligned at 45^0 to freestream, with ejection-like flow between them. This structure develops as an initially spanwise vortex element rises away from the surface, due to local disturbance, causing a local stress minimum. Conditional sampling based on maxima and minima of wall shear stresses, as well as examination of instantaneous flow structures, lead to development of a conceptual model for a characteristic flow phenomenon that seems to generating extreme stress events. Results, based on 700 instantaneous realizations, provide detailed statistics on the spatial distribution of both wall stress components along with characteristic flow structures. Resolution of Ëœ1μm over a sample volume of 1.5x2x1.5mm (x^+=50, y^+=60, z^+=50) is sufficient for resolving buffer layer and lower log layer structures, and for measuring instantaneous wall shear stress distributions from velocity gradients in the viscous sublayer. Statistics on Near Wall Structures and Shear Stress Distribution from 3D Holographic Measurement.ĭigital Holographic Microscopy performs 3D velocity measurement in the near-wall region of a turbulent boundary layer in a square channel over a smooth wall at ReÏ„=1,400. The study brings with it important consequences, especially in the context of the current debate regarding the appropriate scaling as well as the validation of new predictive models of near-wall turbulence. The present paper shows that the electrochemical technique is a powerful experimental method for hydrodynamic studies involving highly unsteady flows. Higher-order statistics of the wall shear stress, spectra, and the turbulence kinetic energy budget at the wall are also investigated. The corrected relative wall shear stress fluctuations fit well with the best DNS data available and meet the need for clarification of the small discrepancy observed in the literature between the experimental and numerical results of such quantities. The Reynolds number dependency of the statistical wall quantities is carefully investigated. For the latter, frequency response and nonuniform correction methods are used to provide an accurate, well-resolved wall statistics database. A one-dimensional LDA system is used to measure the streamwise velocity fluctuations, and an electrochemical technique is utilized to measure the instantaneous wall shear stress. Abstract: Instantaneous velocity and wall shear stress measurements are conducted in a turbulent channel flow in the Kármán number range of Re Ï„ = 74–400. â–º Reynolds number dependency of the statistical wall quantities is investigated. â–º Frequency response and non-uniform correction methods were used to provide an accurate, well-resolved wall-statistics database. â–º Electrochemical probe is used to measure wall shear stress. â–º LDA is used to measure near-wall streamwise velocity. Highlights: â–º Accurate measurements of instantaneous wall shear stress are conducted. International Nuclear Information System (INIS) Statistical properties of wall shear stress fluctuations in turbulent channel flows The original shear-modulus based version shows a slight correlation to the Poisson ratio, which is eliminated by the energy-landscape formulation of the model in which the bulk modulus plays. Data for a large selection of metallic glasses are compared to three different versions of the shoving model. We point out that the instantaneous shear modulus G∞ of the shoving model for the non-Arrhenius temperature dependence of viscous liquids’ relaxation time is the experimentally accessible highfrequency plateau modulus, not the idealized instantaneous affine shear modulus that cannot be measured. The instantaneous shear modulus in the shoving model
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