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Pipe flow
About: Pipe flow is a research topic. Over the lifetime, 13826 publications have been published within this topic receiving 351605 citations.
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TL;DR: Nikuradse as mentioned in this paper showed that the concept of critical roughness height, below which roughness does not affect a turbulent wall flow, is erroneous and pointed out that the effect of roughness on the additive constant in the logarithmic law of the wall should vary as the square of the roughness Reynolds number.
Abstract: An unrigorous but plausible analysis suggests that the concept of a critical roughness height, below which roughness does not affect a turbulent wall flow, is erroneous. The Oseen approximation implies that the effect of roughness on the additive constant in the logarithmic law of the wall should vary as the square of the roughness Reynolds number (specifically the roughness height in “wall units”). This is an important point in determining whether surfaces used in experiments at high unit Reynolds number can be regarded as hydraulically smooth. Attention is also called to the qualitative difference between Nikuradse’s measurements of friction factor in pipe flow with uniform-size sand-grain roughness in the “transitional” range of Reynolds number and the data correlation in the Moody chart of 1944; the latter was derived from tests on miscellaneous real-life rough surfaces in the 1930s. Nearly all textbooks on elementary fluid dynamics present, but practically none discuss, this difference. Nikuradse’s m...
95 citations
TL;DR: Choi et al. as mentioned in this paper proposed a feedback control with deformable walls based on the physical arguments of the near-wall coherent structures, where the wall velocity of each actuator is determined to counteract the wall-normal velocity induced by the streamwise vortices.
94 citations
TL;DR: In this paper, the authors examined the numerical simulation of transient non-isothermal flows of a viscoplastic fluid in a pipe and proposed a decoupled transient solution algorithm.
Abstract: This paper examines the numerical simulation of transient non-isothermal flows of a viscoplastic fluid in a pipe. The situation considered refers to the waxy crude oils transportation in a pipeline, where the flowing oil is cooled down due to extreme external temperature conditions. The rheological model used is an extension of the classical Bingham model in which plastic viscosity and yield stress are allowed to be temperature-dependent parameters. To solve the governing equations, we propose a decoupled transient solution algorithm. At each time step, the velocity–pressure problem and the temperature problem are solved sequentially. Particular attention is devoted to the velocity–pressure problem in which the “true” (without regularization procedure) Bingham model is accounted for by using Lagrange multipliers techniques and augmented Lagrangian/Uzawa methods. The mass, momentum, constitutive and energy equations are discretized using a Finite Volume method on a staggered grid with a TVD scheme for the convective term. The resulting numerical method highlights strong and robust convergence properties. Obtained results regarding the steady-state solution underline the influence of the temperature changes on the flow pattern, especially in terms of yielded/unyielded regions. In particular, in a pipe flow, as soon as the temperature field varies in the mean flow direction, the fluid is yielded.
94 citations
TL;DR: In this paper, the authors report the results of a detailed and systematic numerical investigation of developing pipe flow of inelastic non-Newtonian fluids obeying the power-law model and demonstrate that a judicious choice of the Reynolds number allows the development length at high Reynolds number to collapse onto a single curve.
Abstract: In the current study, we report the results of a detailed and systematic numerical investigation of developing pipe flow of inelastic non-Newtonian fluids obeying the power-law model. We are able to demonstrate that a judicious choice of the Reynolds number allows the development length at high Reynolds number to collapse onto a single curve (i.e., independent of the power-law index n). Moreover, at low Reynolds numbers, we show that the development length is, in contrast to existing results in the literature, a function of power-law index. Using a simple modification to the recently proposed correlation for Newtonian fluid flows (Durst, F. et al., 2005, "The Development Lengths of Laminar Pipe and Channel Flows," J. Fluids Eng., 127, pp. 1154-1160) to account for this low Re behavior, we propose a unified correlation for X D /D, which is valid in the range 0.4
94 citations
TL;DR: In this paper, the authors have shown that the turbulent intensities on the centerline of the channel have their maxima near the rear stagnation point of a recirculation region and the contours of coherent vorticity and streamline reproduce clearly the shed vortices from the cylinder observed by the flow visualization.
Abstract: Unsteady turbulent near wake of a rectangular cylinder in channel flow has been studied experimentally with a laser Doppler velocimetry (LDV). The time-averaged and phase-averaged statistics were measured for the cylinders having various width-to-height ratios, b/h. It is shown that the turbulent intensities on the centerline of the channel have their maxima near the rear stagnation point of a recirculation region. The contours of coherent vorticity and streamline reproduce clearly the shed vortices from the cylinder observed by the flow visualization. The characteristics of the flow field, which depends on b/h, are discussed and the significant contribution of the coherent structure to the flow field is clarified. Moreover, the turbulent kinetic energy budget has been examined.
94 citations