Pipe flow

About: Pipe flow is a research topic. Over the lifetime, 13826 publications have been published within this topic receiving 351605 citations.

Intraventricular Flow Velocity Vector Visualization Based on the Continuity Equation and Measurements of Vorticity and Wall Shear Stress

Abstract: We have developed a system to estimate velocity vector fields inside the cardiac ventricle by echocardiography and to evaluate several flow dynamical parameters to assess the pathophysiology of cardiovascular diseases. A two-dimensional continuity equation was applied to color Doppler data using speckle tracking data as boundary conditions, and the velocity component perpendicular to the echo beam line was obtained. We determined the optimal smoothing method of the color Doppler data, and the 8-pixel standard deviation of the Gaussian filter provided vorticity without nonphysiological stripe shape noise. We also determined the weight function at the bilateral boundaries given by the speckle tracking data of the ventricle or vascular wall motion, and the weight function linear to the distance from the boundary provided accurate flow velocities not only inside the vortex flow but also around near-wall regions on the basis of the results of the validation of a digital phantom of a pipe flow model.

Two Types of Nonlinear Pressure-Drop Versus Flow-Rate Relation Observed for Saturated Porous Media

Abstract: Previous reports of experiments performed with water (Fand et al., and Kececioglu and Jiang) indicated that beyond the Forchheimer regime the rate of change of the hydrostatic pressure gradient along a porous medium suddenly decreases. This abnormal behavior has been termed transition to turbulence in a porous medium. We investigate the relationship between the hydrostatic pressure gradient of a fluid (air) through a porous medium and the average seepage fluid velocity. Our experimental results, reported here, indicate an increase in the hydrostatic pressure rate beyond a certain transition speed, not a decrease. Physical arguments based on a consideration of internal versus extemal incompressible viscous flow are used to justify this distinct behavior, a consequence of the competition between a form dominated transition and a viscous dominated transition. We establish a criterion for the viscous dominated transition from consideration of the results of three porous media with distinct hydraulic characteristics. A theoretical analysis based on the semivariance model validation principle indicates that the pressure gradient versus fluid speed relation indeed departs from the quadratic Forchheimer-extended Darcy flow model, and can be correlated by a cubic function of fluid speed for the velocity range of our experiments.

Efficient calculation of transient flow in simple pipe networks

Abstract: Extensions to the conventional method of characteristics allow transient conditions in simple pipe networks to be efficiently calculated. In particular, treating both boundary conditions and network topology in a general and comprehensive fashion simplifies the solution of many combinations of hydraulic devices. The algebraic framework presented includes a flexible integration of the friction loss term that reduces to previous linear approximations as special cases. In addition, an explicit algorithm is derived for a general hydraulic element called an external energy dissipator. This boundary condition conveniently represents surge tanks, relief valves, storage reservoirs, valves discharging to the atmosphere, and many other common devices. Significantly, the solution remains explicit even if friction losses and inertia effects are present in both the storage element and a connecting pipe. This comprehensive approach to transient analysis simplifies control logic, encourages accurate reporting of field data, and improves execution times. The procedure is illustrated by analyzing transient conditions in a small network containing a variety of devices.

Flow over periodic hills: an experimental study

Abstract: Two-dimensional flow over periodically arranged hills was investigated experimentally in a water channel. Two-dimensional particle image velocimetry (PIV) and one-dimensional laser Doppler anemometry (LDA) measurements were undertaken at four Reynolds numbers ( $$\text{5,600} \le Re \le \text{37,000}$$ ). Two-dimensional PIV field measurements were thoroughly validated by means of point-by-point 1D LDA measurements at certain positions of the flow. A detailed study of the periodicity and the homogeneity was undertaken, which demonstrates that the flow can be regarded as two-dimensional and periodic for $$Re \ge \text{10,000}$$ . We found a decreasing reattachment length with increasing Reynolds number. This is connected to a higher momentum in the near-wall zone close to flow separation which comes from the velocity speed up above the obstacle. This leads to a velocity overshoot directly above the hill crest which increases with Reynolds number as the inner layer depth decreases. The flow speed up above that layer is independent of the Reynolds number which supports the assumption of inviscid flow disturbance in the outer layer usually made in asymptotic theory for flow over small hills.