Pipe flow

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

Methods and apparatus for a subsea tie back

Abstract: A flow assurance system includes an inner pipe disposed within an outer pipe to assure flow through the outer pipe. During installation and relative axial movement with the outer pipe, the inner pipe is nearly neutrally buoyant or fully neutrally buoyant in the fluids of the outer pipe and may extend partially or completely through the outer pipe. The inner pipe may be anchored at one end within the outer pipe. The inner pipe is preferably composite coiled tubing that is installed using a propulsion system. The system may allow fluids to flow through the inner pipe and commingle with the fluids in the outer pipe or may flow fluids through the inner pipe to the exterior of the outer pipe. Hot fluids may pass through the inner pipe to maintain the temperature of the fluids flowing through the outer pipe and chemicals may flow through the inner pipe to condition the fluids in the outer pipe. Tools may be attached to the end of the inner pipe for conducting flow assurance operations within the outer pipe.

Direct numerical simulation of turbulent channel flows with boundary roughened with virtual sandpaper

Abstract: A method to simulate the effects of a roughened surface on a turbulent boundary layer is introduced. The method is easy to implement, does not increase the numerical overhead of the code, and affects the mean velocity in an a priori predictable way. A single parameter k is sufficient to fully characterize the roughness. The procedure has been tested in turbulent channel flows at Reτ=1000, with roughness heights k+ spanning the transitional regime. The properties of the rough flow agree well with experimental data.

Numerical computation of turbulent flow in a square-sectioned 180 deg bend

Abstract: Fine-grid computations are reported of turbulent flow through a square sectioned U-bend corresponding to that for which Chang et al. (1983a) have provided detailed experimental data. A sequence of modeling refinements is introduced: the replacement of wall functions by a fine mesh across the sublayer; the abandonment of the PSL approximation (in which pressure variations across the near-wall sublayer are neglected); and the introduction of an algebraic second-moment (ASM) closure in place of the usual k-e eddy-viscosity model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation. Direct comparisons with the measured rms turbulent velocity give further support to the view that the ASM scheme achieves a generally satisfactory description of the Reynolds stress field. Even with the most refined model some discrepancies between the experiment and computed development are apparent. It is suggested that their removal may require the use of a turbulent transport model in the semi-viscous sublayer in place of the van Driest (1956) mixing-length treatment used at present.

The separating flow through a severely constricted symmetric tube

Abstract: The axisymmetric flow of an incompressible fluid through a pipe (of radius a) suffering a severe constriction is studied for large Reynolds numbers R, the features of symmetric channel flows being virtually the same. Here ‘severe’ refers to a constriction whose typical dimensions are finite, and the oncoming velocity profile is taken to be of a realistic type, i.e. with no slip at the wall. The study adopts (Kirchhoff) free-streamline theory, which, for the mostly inviscid description, affords a rational basis consistent with viscous separation. The major (triple-deck) separation takes place on the constriction surface and is followed by a downstream eddy of length O(aR). Another, less familiar, separation is predicted to occur at a distance 0.087a In R + O(a) ahead of the finite obstacle. Free-streamline solutions are found in the two main extremes of moderately severe and very severe constriction. In both extremes, and in any slowly varying constriction, the major separation is sited near the maximum constriction point. The upstream separation point is also derived, to O(a) accuracy in each case. The upstream separation can be suppressed, however, if the constriction has no definite starting point and decaysslowly upstream, but then the upstream flow response extends over a much increased distance. Comparisons with Navier-Stokes solutions and with experiments tend to favour the predictions of the free-streamline theory.

Calculation of Numerical Uncertainty Using Richardson Extrapolation: Application to Some Simple Turbulent Flow Calculations

Abstract: Richardson extrapolation has been applied to turbulent pipe flow and turbulent flow past a backward facing step. A commercial CFD code is used for this purpose. It is found that the application of the method is not straightforward and some aspects need careful consideration. Some of the problems are elucidated. The particular code used for the present application employs a hybrid scheme, and it does not give monotonic convergence for all the variables in all regions as the grid is refined. The flow regions and the variables which converge monotonically in these regions should be identified first before the method is applied. When this is done Richardson extrapolation gives good results in calculating the apparent order of the numerical procedure used, as well as obtaining grid independent results with which discretization error bounds can be calculated as measures of numerical uncertainty. Even in cases where it does not work, the method can be used as an error indicator for some obscured user mistakes. This paper also demonstrates several shortcomings of using commercial CFD codes. The present findings should help the users of CFD software in general, to quantify discretization errors in their calculations.