Swirling flow through a pipe is a highly complex turbulent flow and is still challenging to predict. An experimental investigation is performed to obtain systematic data about the flow and to understand its physics. A free-vortex-type swirling flow is introduced in a long straight circular pipe. The swirling component decays downstream as a result of wall friction. The velocity distributions are continuously changing as they approach fully developed parallel flow. The swirl intensity Ω, defined as a non-dimensional angular momentum flux, decays exponentially. The decay coefficients, however, are not constant as conventionally assumed, but depend on the swirl intensity. The wall shear stresses are measured by a direct method and, except in a short inlet region, are a function only of the swirl intensity and the Reynolds number. The velocity distributions and all Reynolds stress components are measured at various axial positions in the pipe. The structure of the tangential velocity profile is classified into three regions: core, annular and wall regions. The core region is characterized by a forced vortex motion and the flow is dependent upon the upstream conditions. In the annular region, the skewness of the velocity vector is noticeable and highly anisotropic so that the turbulent viscosity model does not work well here. The tangential velocity is expressed as a sum of free and forced vortex motion. In the wall region the skewness of the flow becomes weak, and the wall law modified by the Monin–Oboukhov formula is applicable. Data on the microscale and the spectrum are also presented and show quite different turbulence structures in the core and the outer regions.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112091002124

Experimental study of turbulent swirling flow in a straight pipe.

The rate of decay of swirl in turbulent pipe flow

Heat transfer and friction characteristics in decaying swirl flow generated by different radial guide vane swirl generators

Enhancement of heat transfer by turbulent decaying swirl flow

Heat transfer enhancement in circular tubes using helical swirl generator insert at the entrance

Swirling flows in cylindrical ducts were investigated by many researchers to meet practical requirements, but the detailed nature of the flows has not yet been clarified. This paper describes the experimental results of swirling flow obtained in stationary cylindrical pipes. Except the inlet region of the pipes, velocity distributions of the swirling flow are governed by a single dimensionless parameter Ω defined by (angular momentum flux)/(axial momentum flux), irrespective of the inlet conditions of flows and wall roughness. This swirling flow shows three kinds of flow patterns in its course of decay; (1) forced-free vortex type, (2) transitional type, (3) forced vortex type. The strength of the swirl Ω decreases exponentially along the pipe axis and its decrement varies with change of the flow patterns. Shear stresses for these flow were calculated, and also the total amount of flow energy was discussed in connection with wall pressure measured along the pipe axis.

An Experimental Study of Swirling Flow in Pipes

Swirling flow in a pipe usually has some axi-asymmetricity, detail of which has not been clarified. Here, detailed experimental investigations concerning axi-asymmetric characters of velocity distributions and especially eccentricity of swirl center were performed. Small deviation of velocity distribution from symmetry at inlet section causes non-negligible asymmetricity in downstream section. This increase of asymmetricity in downstream section occurs only in some swirl intensity range. In addition to the velocity distributions, axi-asymmetric character of momentum field and wall pressure were also given.

Axi-asymmetric character of turbulent swirling flow in a straight circular pipe

Near Wall Velocity Distribution of Turbulent Swirling Flow in Circular Pipe

Discharge coefficients of venturi meters and nozzles employed in swirling flows were measured and the change of the coefficients due to swirling components was discussed in relation to the distributions of velocities, pressures and energies measured across sections before and after the constriction meters. Formulae of the discharge coefficients to correct the swirling components were given for the swirling flow range which will be expected to occur in pipe lines in engineering use.

Effects of Swirling Flow Components on Discharge Coefficients of Constriction Meters

Discharge coefficients of pipe orifices in swirling flow were measured and the results were discussed theoretically. Differential pressure across the orifices is affected by the swirling component and its amount is found to be a function of two parameters ; the rate of constriction of orifice opening and the intensity of swirling component. In a small orifice opening the differential pressure is decreased by the swirling component, and in a larger orifice opening it is increased. Relative change of the differential pressure was calculated theoretically by using a potential flow model. Distributions of velocities and pressures were measured and changes of energy and momentum of the flow through the orifices were discussed.

Osami Kito

Papers

An Experimental Study of Swirling Flow in Pipes

Axi-asymmetric character of turbulent swirling flow in a straight circular pipe

Near Wall Velocity Distribution of Turbulent Swirling Flow in Circular Pipe

Effects of Swirling Flow Components on Discharge Coefficients of Constriction Meters

Effects of Swirling Flow Component on Discharge Coefficients of Constriction Meters : In Case of Orifice