This paper studies the influence of rigid vegetation on the vertical distribution of the Suspended Sediment Concentration (SSC) through a series of flume experiments. Acoustic Doppler Velocimetry (ADV) and a carefully designed water sampling device were used to measure the turbulent velocities and the SSC in non-vegetated, submerged vegetated, and emergent vegetated flows. The results reveal the differences in vertical distributions of the SSC in these three vegetation situations. The vertical distribution of the SSC in non-vegetated and submerged vegetated flows exhibits a reverse "S" shape, while, in emergent vegetated flows, it shows a hyperbolic concave shape. The non-uniformity of the vertical distributions differs greatly under the three hydraulic conditions, with the greatest in non-vegetated flow, followed by emergent vegetated flow and the smallest in submerged vegetated flow. By analyzing the turbulence characteristics, the concept of Turbulent Diffusion Potential (TDP) is proposed, which refers to the movement tendency of sediment particles because of the turbulent diffusion. The value of TDP is defined as the skewness coefficient of the turbulent velocity fluctuation. In turbulent flows, the non-uniformity of the vertical distribution of the SSC is closely related to the vertical distribution of TDP.

The shear and elongational rheology of linear and pom-pom shaped polystyrene (PS) blends was investigated experimentally and modeled using constitutive models such as the Doi–Edwards and the molecular stress function (MSF) model. The pom-pom molecule is the simplest topology to combine shear thinning with strain hardening in elongational flow. A PS pom-pom with a self-entangled backbone (Mw,bb = 280 kg mol−1) and 22 entangled sidearms (Mw,a = 22 kg mol−1) at each star was blended with two linear PS with weight average molecular weights of Mw = 43 and 90 kg mol−1 and low polydispersities (Ð < 1.05). A semilogarithmic relationship between the weight content of the pom-pom, ϕpom-pom, and the zero-shear viscosity was found. Whereas the pure pom-pom has in uniaxial elongational flow at T = 160 °C strain hardening factors (SHFs) of SHF ≈100, similar values can be found in blends with up to ϕpom-pom = 50 wt. % in linear PS43k and PS90k. By blending only 2 wt. % pom-pom with linear PS43k, SHF = 10 can still be observed. Furthermore, above ϕpom-pom = 5–10 wt. %, the uniaxial extensional behavior can be well-described with the MSF model with a single parameter set for each linear PS matrix. The results show that the relationship between shear and elongational melt behavior, i.e., zero-shear viscosity and SHF, can be uncoupled and customized tuned by blending linear and pom-pom shaped polymers and very straightforwardly predicted theoretically. This underlines also the possible application of well-designed branched polymers as additives in recycling.

Oil and gas well primary cementing operations involve pumping a sequence of fluids into the well, for example, cement along a circular pipe (casing) to remove (displace) in situ drilling mud. Cementing is vital to the implementation of zonal isolation and well integrity in the completion of oil and gas wells. The success of a cementing operation is largely determined by the displacement efficiency. There are several factors, such as rheological properties of fluids, geometrical specifications of the annulus, flow rate, and pipe movement, which can considerably affect the displacement efficiency. A casing rotation is generally believed to improve the displacement process, but without solid laboratory experiments to prove that such rotation is indeed effective. In this work, the influence of a pipe rotation on a displacement flow which consists of a yield stress displaced fluid is analyzed via experimental methods. A heavy Newtonian fluid (salt water) displaces a light viscoplastic fluid (Carbopol gel) in a long, inclined pipe. Our results show that the pipe rotation helps break up the Carbopol gel remained on the surface of the flow geometry, and eventually leads to an efficient removal of the displaced fluid above a critical rotation speed. The analysis includes measuring the propagation velocity of the leading front (V̂f) for different parameters, such as the pipe inclination angle, the imposed flow velocity (V̂0) and the rotation speed. The leading front velocity decreases as the rotation speed increases and it is found V̂f ≈ 1.6V̂0. Three flow regimes are observed: slumping type, ripped type and effective-removal type.

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