Engineering topics

Taylor, A. M. K. P.

Publications and source records attributed to Taylor, A. M. K. P..

8 records

NASA NTRS1984

Developing flow in S-shaped ducts. 2: Circular cross-section duct

Laser-Doppler velocimetry measured the laminar and turbulent streamwise flow in a S-duct. The wall pressure distribution and one component of cross-stream velocity were also obtained for the turbulent flow case. Boundary layers near the duct inlet were about 25 percent of the hydraulic diameter in the laminar flow and varied around the periphery of the pipe between 10 percent and 20 percent in turbulent flow. Pressure-driven secondary flows develop in the first half of the S-duct and are attenuated and reversed in the second half. For both Reynolds numbers there is a region near the outer wall of the second half of the duct where the sign of the radial vorticity results in an enforcement of the secondary flow which was established in the first half of the S-duct. The core flow migrates, for both Reynolds numbers, to the outside wall of the first half and lies towards the inside wall of the second half of the S-duct at the outlet. The thinner inlet boundary layers in the turbulent flow give rise to weaker secondary motion.

Taylor, A. M. K. P.↗

NASA NTRS1982

Curved ducts with strong secondary motion - Velocity measurements of developing laminar and turbulent flow

Two orthogonal components of velocity and associated Reynolds stresses are determined in a square-sectioned, 90 degree bend of 2.3 radius ratio by utilizing laser-Doppler velocimetry for Reynolds numbers of 790 and 40,000. Results show that boundary layers at the bend inlet of 0.25 and 0.15 of the hydraulic diameter create secondary velocity maxima of 0.6 and 0.4 of the bulk flow velocity, respectively. It is concluded that the boundary layer thickness is important to the flow development, mainly in the first half of the bend, especially when it is reduced to 0.15 of the hydraulic diameter. Smaller secondary velocities are found for turbulent flow in an identical duct with a radius ratio of 7.0 than in the strongly curved bend, although their effect is more important to the streamwise flow development because of the smaller pressure gradients. In addition, the detail and accuracy of the measurements make them suitable for evaluation of numerical techniques and turbulence models.

Taylor, A. M. K. P.↗

NASA NTRS1982

Laser Doppler measurements of laminar and turbulent flow in a pipe bend

The streamwise components of velocity in the flow through a ninety degree bend of circular cross section for which the ratio of radius of curvature to diameter is 2.8 were measured. The development of strong pressure driven secondary flow in the form of a pair of counter rotating vortices in the steamwise direction is shown. Refractive index matching at the fluid wall interface was not employed; the displacement of the measurement volume due to refraction is allowed for in simple geometrical calculations.

Enayet, M. M.↗

NASA NTRS1982

Developing flow in S-shaped ducts. 1: Square cross-section duct

Laser-Doppler velocimetry was used to measure the laminar and turbulent flow in an S-duct formed with two 22.5 deg sectors of a bend with ratio of mean radius of curvature to hydraulic diameter of 7.0. The boundary layers at the inlet to the bend were about 25% and 15% of the hydraulic diameter for the laminar and turbulent flows, respectively. Pressure-driven secondary flows develop in the first half of the S-duct and persist into the second half but are largely reversed by the exit plane as a consequence of the change in the sense of curvature. There is, however, a region near the outer wall of the second bend where the redistribution of the streamwise isotachs results in a reinforcement of the secondary flow which was established in the first half of the S-duct. The net redistribution of the streamwise isotachs is comparable to that occurring in unidirectional bends of stronger curvature. The wall pressure distribution was also measured for the turbulent flow and quantifies the expected large variations in the longitudinal pressure gradient distributions which occur at different radial locations.

Taylor, A. M. K. P.↗

NASA NTRS1982

Developing flow in S-shaped ducts

The velocity characteristics of laminar and turbulent developing flow in an S-duct formed from two 22.5-deg bends of rectangular cross-section have been studied experimentally using laser Doppler velocimetry. It is shown that pressure-driven secondary flows arise in the first bend of the duct and reach maxima of 0.22 and 0.15 of the bulk velocity in the laminar and turbulent flows, respectively. The velocities are greater in the laminar flow, mainly because of the thicker inlet boundary layers. On passing through the second half of the S-duct, a secondary flow is established over most of the section in the direction opposite to that in the first half. Near the outer wall of the second bend, however, the secondary flow generated in the first bend is sustained because of the local sign of radial vorticity. This effect contributes to a redistribution of the streamwise isotachs, by the end of the duct, comparable with that in unidirectional bends.

Anderson, B. H.↗

NASA NTRS1981

Turbulent flow in a square-to-round transition

Measurements of turbulent flow in a duct with a cross sectional transition from square to round are presented. Laser Doppler velocimetry was used to measure the mean velocity components, turbulence levels and shear stresses. The boundary layers at the inlet and exit of the transition were approximately 13 percent and 20 percent of the hydraulic diameter respectively, becoming thicker near the corner fillets. The development of secondary flow, of magnitudes up to 7 percent of the bulk velocity is shown. This flow is directed away from the corner fillets and along the periphery of the duct and is associated with the longitudinal curvature of the wall and the related pressure gradients.

Taylor, A. M. K. P.↗

NASA NTRS1981

Measurements of laminar and turbulent flow in a curved duct with thin inlet boundary layers

Laser Doppler velocimetry was used to measure the laminar and turbulent flow in a 90 deg square bend of strong curvature. The boundary layers at the inlet to the bend were approximately 25 percent and 15 percent of the hydraulic diameter for the laminar and turbulent flows, respectively. The development of the pressure driven secondary motion is more rapid for laminar flow: the maximum cross stream component measured was 60 percent of the bulk velocity in contrast to 40 percent for turbulent flow. The streamwise isotachs show that, for laminar flow, large velocities are found progressively nearer to the outer radius of the bend and along the sidewalls. For turbulent flow, the isotachs move towards the inner radius until about 60 deg around the bend where strong secondary motion results in a similar redistribution. Turbulence level and shear stress measurements are also presented.

Taylor, A. M. K. P.↗

NASA NTRS1981

Measurements in ducted flows by laser-Doppler anemometry

The merits of small-scale, water-flow experiments with measurements by laser-Doppler anemometry are indicated in relation to previously reported results. New measurements are reported in a square-to-round transition duct and show that, for example, the pressure forces overwhelm any small normal-stress driven secondary flows in the inlet plane to given maximum values of around 0.07 of the bulk velocity in the exit plane. The precision of manufacture of the ducts means that the geometric boundary conditions are accurately known and the results are therefore suitable for calculation purposes. Similarly, the instrumentation allows the flow boundary conditions to be accurately determined.

Taylor, A. M. K. P.↗