3 results
Partially filled pipes: experiments in laminar and turbulent flow
- Henry C.-H. Ng, Hope L. F. Cregan, Jonathan M. Dodds, Robert J. Poole, David J. C. Dennis
-
- Journal:
- Journal of Fluid Mechanics / Volume 848 / 10 August 2018
- Published online by Cambridge University Press:
- 05 June 2018, pp. 467-507
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
Pressure-driven laminar and turbulent flow in a horizontal partially filled pipe was investigated using stereoscopic particle imaging velocimetry (S-PIV) in the cross-stream plane. Laminar flow velocity measurements are in excellent agreement with a recent theoretical solution in the literature. For turbulent flow, the flow depth was varied independently of a nominally constant Reynolds number (based on hydraulic diameter, $D_{H}$; bulk velocity, $U_{b}$ and kinematic viscosity $\unicode[STIX]{x1D708}$) of $Re_{H}=U_{b}D_{H}/\unicode[STIX]{x1D708}\approx 30\,000\pm 5\,\%$. When running partially full, the inferred friction factor is no longer a simple function of Reynolds number, but also depends on the Froude number $Fr=U_{b}/\sqrt{gD_{m}}$ where $g$ is gravitational acceleration and $D_{m}$ is hydraulic mean depth. S-PIV measurements in turbulent flow reveal the presence of secondary currents which causes the maximum streamwise velocity to occur below the free surface consistent with results reported in the literature for rectangular cross-section open channel flows. Unlike square duct and rectangular open channel flow the mean secondary motion observed here manifests only as a single pair of vortices mirrored about the vertical bisector and these rollers, which fill the half-width of the pipe, remain at a constant distance from the free surface even with decreasing flow depth for the range of depths tested. Spatial distributions of streamwise Reynolds normal stress and turbulent kinetic energy exhibit preferential arrangement rather than having the same profile around the azimuth of the pipe as in a full pipe flow. Instantaneous fields reveal the signatures of elements of canonical wall-bounded turbulent flows near the pipe wall such as large-scale and very-large-scale motions and associated hairpin packets whilst near the free surface, the signatures of free surface turbulence in the absence of imposed mean shear such as ‘upwellings’, ‘downdrafts’ and ‘whirlpools’ are present. Two-point spatio-temporal correlations of streamwise velocity fluctuation suggest that the large-scale coherent motions present in full pipe flow persist in partially filled pipes but are compressed and distorted by the presence of the free surface and mean secondary motion.
Glyphosate Tolerance in Enhanced Glyphosate-Resistant Cotton (Gossypium hirsutum)
- Jonathan A. Huff, Daniel B. Reynolds, Darrin M. Dodds, J. Trenton Irby
-
- Journal:
- Weed Technology / Volume 24 / Issue 3 / September 2010
- Published online by Cambridge University Press:
- 20 January 2017, pp. 289-294
-
- Article
- Export citation
-
Glyphosate applied to glyphosate-resistant (RR) cotton varieties after the four-leaf stage can decrease boll retention resulting in severe yield reductions. Enhanced glyphosate-resistant cotton (RR Flex), released for commercial use in 2006, offers a wider window of glyphosate applications without the risk of yield loss. However, no data exist regarding the effect of glyphosate application, especially late season applications, on fruit partitioning in RR Flex cotton. The objective of this research was to determine the effect of glyphosate rate and application timing on RR Flex cotton yield and fruit partitioning compared with current RR cotton. Studies were conducted during a 3-yr period (2004 to 2006), throughout the cotton growing regions of Mississippi. Roundup Ready (ST 4892 Bollgard/Roundup Ready [BR]) and Roundup Ready Flex (Mon 171 Enhanced Roundup Ready and ST 4554 Bollgard II/Roundup Ready Flex [B2RF]) cotton was planted, and glyphosate was applied at various rates and cotton growth stages. Data were collected using box mapping, a technique designed to depict yield partitioning on a cotton plant. RR Flex cotton yields were unaffected by glyphosate application timing or rate. Yields for ST 4892 BR were affected by application timings after the sixth leaf. ST 4892 BR had increased yield partitioning to position-three bolls and upper nodes with later application timings of glyphosate. Increases in seed cotton partitioned to higher nodes and outer fruiting positions were unable to compensate for fruit shed from innermost, lower fruiting sites. These data indicate that RR Flex cotton has excellent tolerance to late-season glyphosate applications.
Effect of Pendimethalin Formulation and Application Rate on Cotton Fruit Partitioning
- Darrin M. Dodds, Daniel B. Reynolds, Jonathan A. Huff, J. Trenton Irby
-
- Journal:
- Weed Technology / Volume 24 / Issue 2 / June 2010
- Published online by Cambridge University Press:
- 20 January 2017, pp. 77-84
-
- Article
- Export citation
-
Because of the development of glyphosate-resistant weed species, the lack of new herbicide chemistry, and the late-season emergence of annual grass species, efforts are underway to expand the use of currently available herbicides for use in cotton. Field studies were conducted in 2005 and 2006 to evaluate the effect of POST-applied pendimethalin formulation and application rate on cotton fruit partitioning. Oil- and water-based pendimethalin formulations as well as S-metolachlor were applied to cotton that had four true leaves. All pendimethalin and S-metolachlor applications included glyphosate for broad-spectrum weed control. Pendimethalin formulation and application rate had no effect on seed-cotton partitioning to horizontal fruiting zones, on second- or third-position horizontal fruiting sites, or on monopodial branches. However, increased seed-cotton partitioned to plants that had lost apical dominance was observed when the water-based pendimethalin formulation was applied at rates of 1.7 kg ai/ha and higher as well as when the oil-based pendimethalin formulation was applied at 3.3 kg ai/ha. Application of water-based pendimethalin at rates of 1.7 and 3.4 kg ai/ha and oil-based pendimethalin at rates of 0.8, 1.7, and 3.3 kg ai/ha resulted in reduced seed-cotton located at position 1 fruiting sites compared with the untreated check. POST application of S-metolachlor had no effect on fruit partitioning to horizontal fruiting positions or vertical fruiting zones. Minor differences in seed-cotton partitioning to cohorts and individual fruiting nodes were observed from application of glyphosate, pendimethalin, and S-metolachlor. However, no differences in seed-cotton yield were observed from application of glyphosate, S-metolachlor, or pendimethalin, regardless of formulation or application rate. POST pendimethalin application at rates less than 1.7 kg ai/ha is relatively safe and should provide cotton producers with an additional tool for herbicide-resistant weeds and late-season annual grasses.