Pipe flow

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

Bounds for turbulent shear flow

Abstract: Bounds on the transport of momentum in turbulent shear flow are derived by variational methods. In particular, variational problems for the turbulent regimes of plane Couette flow, channel flow, and pipe flow are considered. The Euler equations resemble the basic Navier–Stokes equations of motion in many respects and may serve as model equations for turbulence. Moreover, the comparison of the upper bound with the experimental values of turbulent momentum transport shows a rather close similarity. The same fact holds with respect to other properties when the observed turbulent flow is compared with the structure of the extremalizing solution of the variational problem. It is suggested that the instability of the sublayer adjacent to the walls is responsible for the tendency of the physically realized turbulent flow to approach the properties of the extremalizing vector field.

Closure to “Efficient Code for Steady-State Flows in Networks”

Abstract: A complete algorithm for the computer solution of steady-state fluid flows in networks is given. Particular stress is placed on fast solution, minimal storage requirements and simplicity of the input data. Although the Hardy Cross method is the classical method of solution of this type of problem, convergence is slow for large networks. To overcome this problem, the whole network is considered simultaneous, and this produces a large system of non-linear equations. Newton's method is applied, which results in an iterative solution of a system of linear equations. In order to reduce computer storage requirements and to simplify the data input, a number of algorithms from graph theory are involved. The resulting matrix of coefficients associated with the system of linear equations is banded and symmetric for which efficient (in time and memory requirements) methods of solution exist.

Large-eddy simulation of low frequency oscillations of the Dean vortices in turbulent pipe bend flows

Abstract: Large-eddy simulations are performed to investigate turbulent flows through 90° pipe bends that feature unsteady flow separation, unstable shear layers, and an oscillation of the Dean vortices Single bends with curvature radii of one- and three-pipe diameters are considered at the Reynolds number range 5000–27 000 The numerically computed distributions of the time-averaged velocities, Reynolds stress components, and power spectra of the velocities are validated by comparison with particle image velocimetry measurements The power spectra of the overall forces onto the pipe walls are determined The spectra exhibit a distinct peak in the high frequency range that is ascribed to vortex shedding at the inner side of the bends and shear layer instability At the largest Reynolds number the spectra also exhibit an oscillation at a frequency much lower than that commonly observed at vortex shedding from separation It turns out that the associated flow pattern is similar to the swirl switching phenomenon earl

Three dimensional numerical simulations of viscoelastic flows through planar contractions

Abstract: We present in this paper a fully three dimensional (3D) convergent numerical study of planar viscoelastic contraction flows. A 3D finite volume method (FVM) with the primary variable elastic viscous split stress (EVSS) formulation is employed, and a very efficient 3D block solver coupled with block correction is developed to speed up the convergence rate. Full 3D simulations of viscoelastic flows in 4:1 planar abrupt contractions are carried out using experimental conditions. Upstream vortex patterns comparable with the existing flow visualisation observations are captured using the upper convected Maxwell model for a Boger fluid and the Phan-Thien–Tanner model for a shear thinning fluid. Comprehensive comparisons between numerical simulation results and data measured in the dynamic fields in a 4:1 planar abrupt contraction are made, and the results indicate that the experimental measurements can be quantitatively reproduced if the fluid is well characterised by an appropriate viscoelastic model. It is confirmed numerically that the shear thinning of the fluid reduces the intensity of the singularity of viscoelastic flow near the re-entrant corner. With the Oldroyd-B model, by extensive computations on successively refined meshes with the minimum dimensionless size being 0.16–0.014 on the contraction plane in 2D configuration, it is revealed that, although the asymptotic flow behavior near the re-entrant corner and the build-up of the overall pressure and extensional stresses as well as the kinematic behavior along the centreline are insensitive to mesh refinement, completely different vortex activities may be predicted if the mesh is not sufficiently fine. It is verified numerically that, depending on the flow inertia and rheological properties of fluids, both the lip vortex mechanism and the corner vortex mechanism may be responsible for the vortex activities of viscoelastic fluids in 4:1 planar contraction flow, and the elasticity number E and Mach number M of the flow can be used to determine the vortex mechanism approximately. It is clear that the development process of the vortex activities could be underestimated with 2D simplification, and overpredicted with the creeping flow assumption, particularly when Re>0.5. Therefore, in planar contraction flow analyses, numerical artifacts may be produced with a coarse mesh, and 2D flow simulation is only a good approximation to the fully 3D flow if the upstream aspect ratio W/H in the experiment is at least 10.