This paper investigates the drag exerted by randomly distributed, rigid, emergent circular cylinders of uniform diameter d . Laboratory measurements are presented for solid volume fraction ϕ=0.091 , 0.15, 0.20, 0.27, and 0.35 and cylinder Reynolds number Rep ≡ Up d∕ν=25 to 685, where Up =temporally and cross-sectionally averaged pore velocity and ν =kinematic viscosity. These ranges coincide with conditions in aquatic plant canopies. The temporally and cross-sectionally averaged drag coefficient, CD , decreased with increasing Rep and increased with increasing ϕ under the flow conditions investigated. The dimensionless ratio of the mean drag per unit cylinder length ⟨ fD ¯ ⟩H to the product of the viscosity, μ , and Up exhibits a linear Rep dependence of the form ⟨ fD ¯ ⟩H ∕(μ Up )= α0 + α1 Rep , consistent with Ergun’s formulation for packed columns. In the range of experimental conditions, α1 increases monotonically with ϕ . In contrast, α0 is constant within uncertainty for 0.15⩽ϕ⩽0.35 , which suggests...

Laser-induced fluorescence was used to measure the lateral dispersion of passive solute in random arrays of rigid, emergent cylinders of solid volume fraction φ=0.010–0.35. Such densities correspond to those observed in aquatic plant canopies and complement those in packed beds of spheres, where φ≥0.5. This paper focuses on pore Reynolds numbers greater thanRe_s=250, for which our laboratory experiments demonstrate that the spatially averaged turbulence intensity andK_yy/(U_pd), the lateral dispersion coefficient normalized by the mean velocity in the fluid volume,U_p, and the cylinder diameter,d, are independent ofRe_s. First,K_yy/(U_pd) increases rapidly with φ from φ =0 to φ=0.031. Then,K_yy/(U_pd) decreases from φ=0.031 to φ=0.20. Finally,K_yy/(U_pd) increases again, more gradually, from φ=0.20 to φ=0.35. These observations are accurately described by the linear superposition of the proposed model of turbulent diffusion and existing models of dispersion due to the spatially heterogeneous velocity field that arises from the presence of the cylinders. The contribution from turbulent diffusion scales with the mean turbulence intensity, the characteristic length scale of turbulent mixing and the effective porosity. From a balance between the production of turbulent kinetic energy by the cylinder wakes and its viscous dissipation, the mean turbulence intensity for a given cylinder diameter and cylinder density is predicted to be a function of the form drag coefficient and the integral length scalel_t. We propose and experimentally verify thatl_t=min{d, 〈s_n〉_A}, where 〈s_n〉_Ais the average surface-to-surface distance between a cylinder in the array and its nearest neighbour. We farther propose that only turbulent eddies with mixing length scale greater thandcontribute significantly to net lateral dispersion, and that neighbouring cylinder centres must be farther thanr* from each other for the pore space between them to contain such eddies. If the integral length scale and the length scale for mixing are equal, thenr*=2d. Our laboratory data agree well with predictions based on this definition ofr*.

A lock exchange experiment is used to investigate the propagation of gravity currents through a random array of rigid, emergent cylinders which represents a canopy of aquatic plants. As canopy drag increases, the propagating front varies from the classic profile of an unobstructed gravity current to a triangular profile. Unlike the unobstructed lock exchange, the gravity current in the canopy decelerates with time as the front lengthens. Two drag‐dominated regimes associated with linear and nonlinear drag laws are identified. The theoretical expression for toe velocity is supported by observed values. Empirical criteria are developed to predict the current regime from the cylinder Reynolds number and the array density.

Remaining oil saturation established by waterflooding was measured in Indiana limestone in its original, water‐wet state and under mixed‐wet conditions established by adding organic acid to the oil phase. The porous plate technique was used to establish initial oil saturations ranging from S_nwi = 0.23 to 0.93 under capillary‐dominated conditions. For water‐wet conditions, the residual oil saturation increased linearly with its initial saturation. In contrast, the remaining oil saturation under mixed‐wet conditions, S_nw, displayed three distinct regimes. First, S_nw increased with its initial saturation up to S_nwi = 0.58. Next, S_nw decreased from S_nwi = 0.58 to 0.76. Finally, S_nw increased again as S_nwi approached one. The nonmonotonic dependence of S_nw on S_nwi at S_nwi > 0.5 is well described by a concave‐up quadratic function, and may be a salient feature of mixed‐wet rocks.

We developed a technique for rapid, low-cost assembly of single-use, mineralogically heterogeneous microfluidic rock analogues.