Showing papers on "Pipe flow published in 1985"

Features of a reattaching turbulent shear layer in divergent channel flow

Abstract: Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step in a diverging channel flow. Mean velocities, Reynolds stresses, and triple products that were measured by a laser Doppler velocimeter are presented for two cases of tunnel wall divergence. Eddy viscosities, production, convection, turbulent diffusion, and dissipation (balance of kinetic energy equation) terms are extracted from the data. These data are compared with various eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model; however, like the others, it dramatically overpredicts the experimentally determined dissipation rate.

Compressible fluid flow

Abstract: 1. Fundamental Concepts and Definitions. 2. Equation of Flow. 3. Isentropic Flow. 4. Normal Shock Waves. 5. Adiabatic Frictional Flow in a Constant-Area Duct. 6. Flow with Heat Interaction and Generalized Flow. 7. Two-Dimensional Waves. 8. Linearized Flow. 9. Method of Characteristics. 10. Computational Fluid Dynamics. 11. Methods of Experimental Measurements. Appendix: Tables and Figures. General References. Index.

The structure of the vorticity field in turbulent channel flow. I - Analysis of instantaneous fields and statistical correlations

Abstract: An investigation into the existence of hairpin vortices in turbulent channel flow is conducted using a database generated by the large-eddy simulation technique. It is shown that away from the wall the distribution of the inclination angle of vorticity vector gains its maximum at about 45° to the wall. Two-point correlations of velocity and vorticity fluctuations strongly support a flow model consisting of vortical structures inclined at 45° to the wall. The instantaneous vorticity vectors plotted in planes inclined at 45° show that the flow contains an appreciable number of hairpins. Vortex lines are used to display the three-dimensional structure of hairpins, which are shown to be generated from deformation (or roll-up) of sheets of transverse vorticity.

Recirculation in swirling flow - A manifestation of vortex breakdown

Abstract: The addition of a sufficiently high degree of swirl to flow going into a circular pipe produces a limited region of reversed flow. Such a vortex breakdown, as it is termed, represents a zone of transition from a supercritical to a subcritical flow state. If the flow remains subcritical, an unavoidable consequence is that the geometry and conditions downstream directly affect the upstream flow up to, and including, the breakdown region. Laser Dopper anemometer measurements of the swirl and axial velocity components, as well as the corresponding streamline patterns, are presented for water flow in a model based upon the geometry of a swirl combustor. It is shown that a strong exit contraction (55 percent of the diameter) has practically no influence on a flow which reverts to supercritical, whereas even a weak contraction (15 percent of the diameter) has a significant influence on a flow which remains subcritical. It is argued that a cold flow is likely to be totally unrepresentative of a reacting flow through the same geometry, and, also, that great care has to be taken over the boundary conditions to be imposed for the numerical computation of subcritical flows. 20 references.

Apparent Slip Flow of Polymer Solutions

Abstract: The flow behavior of aqueous and organic polymer solutions in laminar flow was studied experimentally in small‐diameter tubes. The tube diameters ranged from 0.0190 to 0.1097 cm and the L/D (length/diameter) ratios were 20–2700. The experimental flow rates were abnormally higher than the predictions based on viscometric cone‐and‐plate data. This abnormal flow enhancement is termed here apparent slip and it was quantified by an effective slip velocity. The effective slip velocity was found to increase with the wall shear stress. The contribution of slip, however, to the total flow rate for a given tube diameter decreased with increasing wall stress due to shear thinning. Additionally, for a given wall stress, the contribution of slip increased with decreasing tube diameter. Qualitatively, the apparent slip phenomenon is expected to occur for the flow of elastic high‐molecular‐weight, nondilute polymer solutions in inhomogeneous stress fields.

On the structure of jets in a crossflow

Abstract: Spectral analysis and flow visualization are presented for various velocity ratios and Reynolds numbers of a jet issuing perpendicularly from a developing pipe flow into a crossflow. The results are complete with conditional averages of various turbulent quantities for one jet-to-cross-flow velocity ratio R of 0.5. A unique conditional-sampling technique separated the contributions from the turbulent jet flow, the irrotational jet flow, the turbulent crossflow and the irrotational crossflow by using two conditioning functions simultaneously. The intermittency factor profiles indicate that irrotational cross-flow intrudes into the pipe but does not contribute to the average turbulent quantities, while the jet-pipe irrotational flow contributes significantly to them in the region above the exit where the interaction between the boundary-layer eddies and those of the pipe starts to take place. Further downstream, the contributions of the oncoming boundary-layer eddies to the statistical averages reduce significantly. The downstream development depends mainly on the average relative eddy sizes of the interacting turbulent fields.

Flow along a channel with a time-dependent indentation in one wall: the generation of vorticity waves

Abstract: We describe flow-visualization experiments and theory on the two-dimensional unsteady flow of an incompressible fluid in a channel with a time-dependent indentation in one wall. There is steady Poiseuille flow far upstream, and the indentation moves in and out sinusoidally, its retracted position being flush with the wall. The governing parameters are Reynolds number Re, Strouhal number (frequency parameter) St and amplitude parameter e (the maximum fraction of the channel width occupied by the indentation); most of the experiments were performed with e ≈ 0.4. For St ≤ 0.005 the flow is quasi-steady throughout the observed range of Re (360 0.005 a propagating train of waves appears, during every cycle, in the core flow downstream of the indentation, and closed eddies form in the separated flow regions on the walls beneath their crests and above their troughs. Later in the cycle, a second, corotating eddy develops upstream of the first in the same separated-flow region (‘eddy doubling’), and, later still, three-dimensional disturbances appear, before being swept away downstream to leave undisturbed parallel flow at the end of the cycle. The longitudinal positions of the wave crests and troughs and of the vortex cores are measured as functions of time for many values of the parameters; they vary with St but not with Re. Our inviscid, long-wavelength, small-amplitude theory predicts the formation of a wavetrain during each cycle, in which the displacement of a core-flow streamline satisfies the linearized Kortewegde Vries equation downstream of the indentation. The waves owe their existence to the non-zero vorticity gradient in the oncoming flow. Eddy formation and doubling are not described by the theory. The predicted positions of the wave crests and troughs agree well with experiment for the larger values of St used (up to 0.077), but less well for small values. Analysis of the viscous boundary layers indicates that the inviscid theory is self-consistent for sufficiently small time, the time of validity increasing as St increases (for fixed e).

A new analysis of the turbulent flow of non‐newtonian fluids

Abstract: A new analysis has been developed for the turbulent flow of non-Newtonian fluids. Based on enhanced viscosity effects at the small time and length scales of the dissipative micro-eddies, the analysis predicts a thickening of the viscous sub-layer tending to increase throughput velocity and thus promoting drag reduction. The required flow parameters can be determined directly from rheograms, without employing correlations based on pipe-flow data. The results give good descriptions of flows of fluids with both power-law and Bingham behaviour and explain a number of peculiarities of such flows.

Large Eddy Simulation of Turbulent Channel Flow by One-Equation Modeling

Abstract: Turbulent plane channel flow is numerically studied using Large Eddy Simulation(LES). Cyclic boundary conditions are imposed on velocity and pressure in the downstream and spanwise directions. The noslip boundary condition is imposed on the walls. Both Smagorinsky model and 1-equation model are applied, and the comparison is made. The importance of the diffusion term in subgrid scale (SGS) turbulent energy balance is pointed out.

Hyperbolicity and change of type in the flow of viscoelastic fluids through channels

Abstract: We consider the steady flow of an upper convected Maxwell fluid through a pipe with wavy walls The analysis is an extension to round pipes of the methods introduced by Yoo and Joseph [1] to study the same problem in plane channels As in the channel problem, the vorticity in a small cylinder at the center of the pipe becomes hyperbolic when the centerline velocity is larger than the speed of shear waves into rest The region of hyperbolicity is smaller, but the decay of vorticity is less, when the elasticity parameter is larger

Water distribution system optimization

Abstract: : This report describes the development of a computer program WADISO (Water Distribution Systems Optimization) which can be used to optimally size pipes in water distribution systems and select optimal pipes for cleaning and lining. The program can also be used as a steady-state simulation program to calculate flows and pressures in pipe networks. The simulation portion of the program uses the node method with sparse matrix techniques to reduce computations. The optimization portion uses a bounded enumeration technique, based on minimizing the sum of pipe installation, pipe cleaning and lining, and present worth of pumping energy costs. Only discrete commercially available pipe sizes are considered. The program can handle any typical water distribution system and includes pumps, pressure reducing valves, multiple pressure zones, and check valves. To use the optimization, the user must also specify costs as a function of pipe diameter (or use default costs in the program), minimum pressures, up to five water use loadings, a list of which pipes are to be sized, and a range of sizes to be considered. The program user's guide is included as an appendix to the report. Other appendices address how to access the program, how to obtain detailed documentation, the nature of pipe sizing, existing literature on pipe optimization, and a discussion of the relationship of pipe sizing and water distribution performance criteria. Keywords: Optimization, Pipe flow, Pipe networks, Pipe sizing, Water conveyance, Water distribution.

Structure of the wall pressure fluctuations in a shock-induced separated turbulent flow

Abstract: This paper presents the results of an experimental study of the unsteady nature of a shock wave/turbulent boundary layer interaction. The interaction was generated using an unswept compression ramp. The incoming freestream Mach number was 2.9 and the flow was separated at the corner. An array of flush mounted miniature high frequency pressure transducers was used to make multi-channel measurements of the fluctuating wall pressure within the interaction. From the present results, an overall picture of the instantaneous structure of the unsteady shock system (as inferred from the wall pressure signals) can be constructed. The flow ahead of the corner can be considered as composed of two regions, namely the 'intermittent' region where there is essentially a single leading shock which exhibits significant streamwise 'flapping' and spanwise 'rippling', and the separated region where the flow experiences continuous compression.

Bifurcation in steady laminar mixed convection flow in horizontal ducts

Abstract: The fully developed laminar mixed-convection flow in horizontal ducts of rectangular, circular and semicircular cross-sections has been studied using a numerical model of the governing equations of motion, subject to the Boussinesq approximation and an axially uniform heat-flux condition. Dual solutions with a two- and a four-vortex flow pattern have been observed in all cases. The rectangular geometry, with its aspect ratio and Grashof number as parameters, is posed as a two-parameter problem. In this parameter-space, the critical points where the transition between the two- and the four-vortex pattern occur, follow a tilted cusp. This is akin to the phenomenon in the Taylor problem which has been thoroughly investigated by Benjamin and co-workers in a general study of bifurcation phenomena for viscous flow problems. The bifurcation phenomenon in circular ducts, which is essentially a one-parameter problem, has features similar to that observed for the Dean problem, by Nandakumar and Masliyah.

Laminar flow through a slowly rotating straight pipe

Abstract: We consider fully developed steady laminar flow through a pipe that is rotating slowly about a line perpendicular to its own axis. The solution is expanded for low Reynolds numbers in powers of a single combined similarity parameter and the series extended to 34 terms by computer. Analysis shows that convergence is limited by a square-root singularity on the negative real axis of the similarity parameter. An Euler transformation and extraction of the leading, secondary and tertiary singularities at infinity render the series accurate for all values of the similarity parameter. The major conclusion of this investigation is that the friction ratio in a slowly rotating pipe grows asymptotically as the ⅛ power of the similarity parameter and not as the ¼ power as previously deduced from boundary-layer analysis. This discrepancy between the present computer-extended method and boundary-layer analysis has also occurred in the similar problem of flow through a loosely coiled pipe (Van Dyke 1978).

Flow Control In A Diffusing S-Duct

Abstract: Accurate measurements have been made of secondary flow in a 1.51 area ratio diffusing 30 deg - 30 deg S-Duct with circulair cross section. Turbulent flow was entering the duct at Mach number of 0.6, the boundary layer thickness at the duct entrance was ten percent of the duct inlet diameter. Through measurements made, local flow velocity vector as well as static and total pressures mapping of the flow at several stations were obtained. Strong secondary flow was measured in the first bend which continued into the second bend with new vorticity produced in there in the opposite direction. Surface oil flow visualization and wall pressures indicated a region of separated flow starting at theta approximately equal to 22 deg on the inside of the first bend up to theta approximately equal to 44 deg on the outside of the second bend. The flow separated in 'cyclone' form and never reattached in the duct. As a result of the secondary flow and the flow separation, significant total pressure distortion was observed at the exit of the duct. Using flow control devices the separation was eliminated while the exit distortion was improved.

Self-sustained radial oscillating flows between parallel disks

Abstract: The flow-visualization methods of dye injection, hydrogen-bubble generation and paraffin mist are employed to investigate radial flow between parallel circular disks with a steady influx. Three distinct flow patterns are observed in the range of Re between 1.5 and 50. (1) Steady flow without boundary-layer separation and re-attachment, for Re < Rec. (2) A self-controlled flow oscillation which decays further downstream, in the range of Rec [les ] Re < Ret. (3) A self-sustained flow fluctuation which develops into a laminar-turbulent transition with a reverse transition further downstream, when Re [ges ] Ret. Rec and Ret are the critical and transition Reynolds number, respectively.The oscillating flows are caused by a vortex street consisting of vortices (i.e. separating annular bubbles) that separate periodically and alternately from both disks. Finite-difference solutions of the unsteady vorticity transport equation broadly agree with certain experimental observations. The study concludes that the separation and reattachment of shear layers in the radial flow through parallel disks are unsteady phenomena and the sequence of nucleation, growth, migration and decay of the vortices is self-sustained.