Small Cylinder Research Articles

Fluid-structure interactions (FSI) behaviour of two unequal-diameter flexible cylinders in tandem configuration

Fluid-structure interactions (FSI) of multiple cylindrical structures frequently occur in crossflows. Due to the different wake interference regions of flexible cylinders with different diameters, the interaction between multiple cylinders is complicated and sensitive to the centre-to-centre spacing ratio and diameter ratio. Limited information has been presented on the flow-induced vibration (FIV) of two unequal-diameter flexible cylinders in a tandem arrangement. In this paper, an experimental investigation was carried out in a towing tank to study the FIV of two tandem flexible cylinders with different diameters that can vibrate in both the cross-flow (CF) and in-line (IL) directions. There were two IL spacing ratios (T/d = 12.0 and 6.0, where T is the centre-to-centre distance between two cylinders, and d is the diameter of the small cylinder), and the diameter ratio (d/D, where D is the diameter of the large cylinder) was nearly 0.5. The aspect ratios/mass ratios of the small cylinder and the large cylinder were 350/1.90 and 181/1.47, respectively. The towing velocity varied from 0.05 to 1.00 m/s with an interval of 0.05 m/s. The Reynolds numbers for the small and large cylinder were 800–16000 and 1600–32000, respectively. The CF vibration of the upstream large cylinder with T/d = 6.0 was suppressed at Vrs = 16.28–18.79, whereas the CF vibration of the large cylinder with T/d = 12.0 was not influenced. The downstream cylinder exhibited more complicated behaviour due to the significant wake effect from the upstream cylinder, which is consistent with the two equal-diameter cylinders. The FIV response of the downstream small cylinder was more sensitive to the IL spacing ratio. Because of the wake shielding effect of the large cylinder, the downstream small cylinder vibrated at low IL dominant frequencies, and the IL to CF frequency ratio (fIL/fCF) was approximately 1.0. Moreover,wake-induced flutter was observed on the downstream small cylinder.

Reinforcement learning for bluff body active flow control in experiments and simulations.

We have demonstrated the effectiveness of reinforcement learning (RL) in bluff body flow control problems both in experiments and simulations by automatically discovering active control strategies for drag reduction in turbulent flow. Specifically, we aimed to maximize the power gain efficiency by properly selecting the rotational speed of two small cylinders, located parallel to and downstream of the main cylinder. By properly defining rewards and designing noise reduction techniques, and after an automatic sequence of tens of towing experiments, the RL agent was shown to discover a control strategy that is comparable to the optimal strategy found through lengthy systematically planned control experiments. Subsequently, these results were verified by simulations that enabled us to gain insight into the physical mechanisms of the drag reduction process. While RL has been used effectively previously in idealized computer flow simulation studies, this study demonstrates its effectiveness in experimental fluid mechanics and verifies it by simulations, potentially paving the way for efficient exploration of additional active flow control strategies in other complex fluid mechanics applications.

Wear of uncoated and PVD coated cemented carbide tools for processing of copper based materials part I: Lab test verification in dry and lubricated sliding

In the manufacturing of metal zippers, including several complicated forming and shearing process steps, the tool wear is a limiting factor, since it deteriorates the quality of the zipper elements. Hence, an increased understanding of the tool wear mechanisms occurring in the zipper production is important to prolong the tool life.To gain deeper insights into the tool wear mechanisms active in the process of shearing Cu alloy wire into separate zipper elements, the present study utilizes a simplified sliding test rig. The rig comprises a small tool material cylinder sliding against a large rotating work material cylinder, in a crossed cylinders configuration. One uncoated and two PVD-coated cemented carbide cylinders were tested under contact conditions similar to those of the actual shearing. The tool material cylinder was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) at selected intervals during the test. The surface appearance was investigated and compared with observations on tools used in actual zipper production. The degradation was found to include gradual wear against the Cu alloy, transfer of the Cu alloy and characteristic modifications of the topography, indicative of wear mechanisms operating at a very small scale, confirming that the wear of the shearing tools can be mimicked by the test.

The Effect of Barodiffusion on the Distribution of Biological Fluid Velocity and Concentration During Filtration Through a Cylindrical Layer

A model of filtration of a biological fluid for a cylindrical layer in a stationary regime is presented. The model takes into consideration finite compressibility and concentration expansion associated with barodiffusion. Dimensionless complexes relating characteristic physical scales of different phenomena are singled out. The influence of the revealed effects on the flow characteristics are studied numerically. The flow can be either convective or diffusive, depending on the relation between the dimensionless complexes. New qualitative relationships are distinguished in the component concentration and flow velocity distributions. A significant influence of the thickness of the porous cylinder wall is shown. It is found out that barodiffusion has a significant effect on the flow in the convective mode and a small cylinder wall thickness.

Correlation-induced steady states and limit cycles in driven dissipative quantum systems

We study a driven-dissipative model of spins one-half (qubits) on a lattice with nearest-neighbor interactions. Focusing on the role of spatially extended spin-spin correlations in determining the phases of the system, we characterize the spatial structure of the correlations in the steady state, as well as their temporal dynamics. In dimension one we use essentially exact matrix-product-operator simulations on large systems, and pushing these calculations to dimension two, we obtain accurate results on small cylinders. We also employ an approximation scheme based on solving the dynamics of the mean field dressed by the feedback of quantum fluctuations at leading order. This approach allows us to study the effect of correlations in large lattices with over one hundred thousand spins, as the spatial dimension is increased up to five. In dimension two and higher we find two new states that are stabilized by quantum correlations and do not exist in the mean-field limit of the model. One of these is a steady state with mean magnetization values that lie between the two bistable mean-field values, and whose correlation functions have properties reminiscent of both. The correlation length of the new phase diverges at a critical point, beyond which we find emerging a new limit cycle state with the magnetization and correlators oscillating periodically in time.

Response of Two Unequal-Diameter Flexible Cylinders in A Side-by-Side Arrangement: Characteristics of FIV

Till now, little information is available on the flow-induced vibration (FIV) of multiple flexible cylinders with unequal diameters. Some FIV characteristics of unequal-diameter cylinders can be predicted based on the knowledge of equal-diameter cylinders, while there are still other features remaining unrevealed. In this paper, the FIV characteristics of two flexible cylinders with unequal diameters arranged side-by-side are experimentally investigated. The diameter ratio of the small cylinder (Small Cyl.) to the large cylinder (Large Cyl.) is nearly 0.5. The aspect ratios and mass ratios of the two flexible cylinders are 350/181 and 1.90/1.47, respectively. The centre-to-centre spacing ratio in the cross-flow (CF) direction is kept constant as 6.0 and the two cylinders can oscillate freely in both the CF and in-line (IL) directions. The towing velocity varies from 0.05 m/s to 1.00 m/s. The dominant modes and frequencies, CF and IL displacement amplitudes and response trajectories are discussed. Compared with the case of two identical cylinders in our previous study, the FIV responses demonstrate some similarities and differences. The similarities are as follows. Both cylinders exhibit multi-mode vibration features and they interact with each other. Meanwhile, the IL FIV shows a more complex behaviour than that in the CF direction. The difference is that as the diameter of one cylinder is increased, the effect on the smaller cylinder becomes more significant. For Large Cyl., the FIV response is similar to its isolated counterpart, which indicates that Small Cyl. has a negligible effect on the FIV of the larger one. Whereas Large Cyl. perplexes the FIV of Small Cyl. during the vibration process. The spacing would change when both cylinders are oscillating. Proximity interference between the two cylinders and wake shielding effect of the Large Cyl. may occur. The dominant frequencies of Small Cyl. are reduced and the wake-induced flutter of Small Cyl. is observed from the response trajectories at different measuring points.

Subject Preferences and Psychological Implications of Portable Oxygen Concentrator Versus Compressed Oxygen Cylinder in Chronic Lung Disease.

Oxygen therapy represents the elective therapy to improve the quality of life for patients with chronic respiratory diseases like COPD and interstitial lung disease. Lightweight portable oxygen concentrators (POCs) are a valid alternative to traditional systems such as portable compressed oxygen cylinders. However, patient preference and the possible psychological implications related to the use of both devices have been poorly assessed. We sought to evaluate patient preference between the ambulatory oxygen systems (ie, a POC or a small cylinder) for patients with COPD and interstitial lung disease experiencing exertional desaturation in a rehabilitation setting. Furthermore, the use of one device in comparison with the other was related to specific mechanical characteristics and related to perceived quality of life, anxiety, and depressive symptoms. 30 subjects with COPD and interstitial lung disease, who demonstrated exertional desaturation on room air during 6-min walk test (6MWT), were recruited. Each subject performed 2 6MWTs, in random order: one breathing oxygen via a POC and one with a portable compressed oxygen cylinder. Both devices were set up to ensure oxyhemoglobin saturation between 92% and 95% during the 6MWTs. All subjects completed a questionnaire assessing anxiety, depression, and quality of life. Each device was randomly assigned to each subject for 1 week, and then replaced with the other in the following week. At the end of the trial period, all subjects completed a questionnaire evaluating several aspects of the oxygen therapy devices. There were no significant differences in oxygen saturation or the mean distances achieved during the 6MWTs between the 2 portable oxygen devices. The subjects expressed greater preference for the POC (73.3%), basing their choice mainly on ease of transport and lower weight. Subjects' age also correlated with preferences: younger subjects were more negatively focused on the weight of the portable compressed oxygen cylinder, whereas older subjects considered the POC easier to manage. No significant differences in preferences were present between COPD and interstitial lung disease. The POC and the portable compressed oxygen cylinder performed in a comparable manner during 6MWT for subjects with COPD and interstitial lung disease and exertional desaturation. Subjects preferred the POC because it was associated with better mobility.

Absence of Superconductivity in the Pure Two-Dimensional Hubbard Model

We study the superconducting pairing correlations in the ground state of the doped Hubbard model -- in its original form without hopping beyond nearest neighbor or other perturbing parameters -- in two dimensions at intermediate to strong coupling and near optimal doping. The nature of such correlations has been a central question ever since the discovery of cuprate high-temperature superconductors. Despite unprecedented effort and tremendous progress in understanding the properties of this fundamental model, a definitive answer to whether the ground state is superconducting in the parameter regime most relevant to cuprates has proved exceedingly difficult to establish. In this work, we employ two complementary, state-of-the-art many-body computational methods, constrained path (CP) auxiliary-field quantum Monte Carlo (AFQMC) and density matrix renormalization group (DMRG) methods, deploying the most recent algorithmic advances in each. Systematic and detailed comparisons between the two methods are performed. The DMRG is extremely reliable on small width cylinders, where we use it to validate the AFQMC. The AFQMC is then used to study wide systems as well as fully periodic systems, to establish that we have reached the thermodynamic limit. The ground state is found to be non-superconducting in the moderate to strong coupling regime in the vicinity of optimal hole doping.

Impact of various iodine concentrations of iohexol and iodixanol contrast media on image reconstruction techniques in a vascular-specific contrast media phantom: quantitative and qualitative image quality assessment.

The aim of our study is to investigate the impact of iodine quantification on image reconstruction when employing a vascular-specific contrast media phantom with varying iodine concentrations. A 30-cm phantom simulating arterial and venous blood vessel diameters was manufactured. Small (9mm) and medium (12mm) cylinders contained iodine concentrations from 10 to 100% while large (21mm) cylinders were in quartiles from 25 to 100% diluted in blood equivalent medium. Each phantom was filled with either iohexol 350 mgI/mL (Group A) or iodixanol 320 mgI/mL (Group B) and then scanned separately. For each group, tube potential (80-140 kVp) and current (50-400mAs) were changed and all image series were reconstructed with filtered back projection (FBP), hybrid-based iterative reconstruction (HBIR) and model-based iterative reconstruction (MBIR). Mean opacification was measured in all groups. All data were compared employing an independent t test and Pearson's correlation. Visual grading characteristic (VGC) and Cohens' kappa analyses were performed. At 80 kVp, mean opacification using HBIR was significantly higher in Group B (2165 ± 1108 HU) than in Group A (2040 ± 1036 HU) (p < 0.009). At 140 kVp, MBIR and HBIR were greater in Group A (1704 ± 1033 HU and 1685 ± 1023 HU) versus Group B (1567 ± 1036 HU and 1567 ± 1034 HU) (p < 0.022). CNR using FBP, HBIR and MBIR was higher in Group B (46 ± 42 HU, 70 ± 163 HU and 83 ± 74 HU, respectively) than in Group A (43 ± 39 HU, 174 ± 130 HU and 80 ± 65 HU, respectively) (p < 0.0001-0.035). Qualitative image analysis demonstrated no difference in Cohen's kappa analysis. VGC was higher in Group A at all image reconstruction groups. Iohexol outperforms iodixanol in observer performance when assessing image reconstruction techniques and iodine concentrations in a vascular-specific contrast media phantom.

Experimental investigation of a variable geometry vertical axis wind turbine

An experimental study is presented on the performance of a vertical axis wind turbine with variable blade geometry of the design developed by Austin Farrah. This is experimentally compared with the performance of a correspondingly sized Bach-type Savonius turbine using the same electrical generator and measurement instrumentation in a wind tunnel. Experiments were performed for Reynolds numbers, based on blade chord, in the range 5 × 103to 1 × 105, and for blade settings between −40° and +40o. The study shows that for the tip speed ratios that have been investigated, the Farrah vertical axis wind turbine design can only marginally outperform a corresponding two-bladed Bach-type Savonius turbine and then only when its blades are set to 40° pitch angle. The presence of a small inner cylinder, which rotates with the turbine, does not enhance its performance due to the fact that it is immersed in an extensive column of relatively static air.

Measurement Uncertainty Analysis of a Stitching Linear-Scan Method for the Evaluation of Roundness of Small Cylinders

Influences of angular misalignments of a small cylinder on its roundness measurement by the method referred to as the stitching linear scan method are theoretically investigated. To compensate for the influences, a technique for measuring angular misalignments of a small cylinder by utilizing the linear-scan surface form stylus profilometer, which is employed for roundness measurement, is newly proposed. In addition, for roundness measurement, a holder unit capable of compensating for the angular misalignments of a small cylinder is developed, and the feasibility of the proposed technique is verified in experiments. Furthermore, a measurement uncertainty analysis of the stitching linear-scan method is carried out through numerical calculations based on a Monte Carlo method.

Research on balanced self-weight of horizontal link heavy duty servo cylinder

In this article, the horizontal hinged heavy duty servo cylinder is taken as the research object. In the actual working process, while the servo hydraulic cylinder outputs the curve force, the cylinder body will also rotate with the hinge point to a certain extent. Because the position of the center of gravity is constantly changing, and the weight of the cylinder body is too large, the friction causes damage to the sealing structure and seriously affects the working efficiency of the equipment. In order to improve the sealing performance of the servo hydraulic cylinder, a corresponding study is carried out. Firstly, the working angle interval of servo cylinder is optimized to ensure that the friction is the least in this range. Based on this, a new supporting structure is proposed, in which a small hydraulic cylinder is installed at the bottom of the servo hydraulic cylinder body. By controlling the output force of the small hydraulic cylinder, the cylinder body and piston rod are aligned all the time. The servo cylinder body is flexibly processed to more realistically see the adverse effect of the friction, and the co-simulation method using MSC.ADAMS and MATLAB/Simulink verifies the new support structure to improve the sealing performance. According to the simulation results and experiment results, and combined with the deformation curve of the hydraulic cylinder, when the maximum displacement is 336 mm, the maximum rotation angle is 15.6°, the friction is the smallest, about 5801.9 N. It is known from the experiment results that after adding the new support structure, the frictional force is reduced to 1365.9 N, which reduces the friction of nearly 76.5%.

Sampled-data model validation: An algorithm and experimental setup of dual fuel IC engine

This research work investigates the usage of hybrid based Artificial Neural Network-Harris Hawks and whale optimization algorithm (ANN-HHOWOA) for forecast of emission properties and performance of small utility single cylinder direct injection (DI) diesel engine inlet with rice bran biodiesel blends under dual fuel mode along with biogas. This Artificial Neural Network based hybrid Harris Hawks and whale optimization algorithm was developed and optimized to forecast the values of brake thermal efficiency (BTE), hydrocarbon (HC), carbon monoxide (CO) and carbon dioxide (CO2) based on the gathered input data from the experimental setup of dual fuel engine by varying engine operating load, blends of rice bran biodiesel, air fuel ratio and injection timings. To experimentally validate the results by using hybrid based Artificial Neural Network-Harris Hawks and whale optimization algorithm (ANN-HHOWOA), 500 trial runs were performed on objective functions of gathered data to find optimal solution. 70% of data were used for training, 15% for testing and other 15% were used for validation. It has been concluded that hybrid based Artificial Neural Network-Harris Hawks and whale optimization algorithm (ANN-HHOWOA) gave remarkable results with classification rate 98.6667% which is much better than other meta-heuristic algorithms. It is found that Artificial Neural Network based hybrid Harris Hawks and whale optimization algorithm is a very useful tool for prediction and optimization of combustion performance and emissions properties of dual fuel engine fuelled with biogas-biodiesel blends.

Biogeomorphology in the marine landscape: Modelling the feedbacks between patches of the polychaete worm Lanice conchilega and tidal sand waves

AbstractTidal sand waves are dynamic bedforms found in coastal shelf seas. Moreover, these areas are inhabited by numerous benthic species, of which the spatial distribution is linked to the morphological structure of sand waves. In particular, the tube‐building worm Lanice conchilegais of interest as this organism forms small mounds on the seabed, which provide shelter to other organisms. We investigate how the interactions between small‐scale mounds (height ∼dm) and large‐scale sand waves (height ∼m) shape the bed of the marine environment. To this end, we present a two‐way coupled process‐based model of sand waves and tube‐building worm patches in Delft3D. The population density evolves according to a general law of logistic growth, with the bed shear stress controlling the carrying capacity. Worm patches are randomly seeded and the tubes are mimicked by small cylinders that influence flow and turbulence, thereby altering sediment dynamics. Model results relate the patches with the highest worm densities to the sand wave troughs, which qualitatively agrees with field observations. Furthermore, the L. conchilegatubes trigger the formation of sandy mounds on the seabed. Because of the population density distribution, the mounds in the troughs can be several centimetres higher than on the crests. Regarding sand wave morphology, the combination of patches and mounds are found to shorten the time‐to‐equilibrium. Also, if the initial bed comprised small sinusoidal sand waves, the equilibrium wave height decreased with a few decimetres compared to the situation without worm patches. As the timescale of mound formation (years) is shorter than that of sand wave evolution (decades), the mounds induce (and accelerate) sand wave growth on a similar spatial scale to the mounds. Initially, this leads to shorter sand waves than they would be in an abiotic environment. However, near equilibrium the wavelengths tend towards their abiotic counterparts again. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd

Flow-induced vibration of two staggered flexible cylinders with unequal diameters

The flow-induced vibration (FIV) of multiple flexible cylinders typically involves multi-mode and complex flow-structure interactions. The FIV characteristics of two staggered flexible cylinders with unequal diameters are experimentally studied in this paper. The two flexible cylinders have aspect ratios of 350 and 181 and mass ratios of 1.90 and 1.47 and are free to oscillate in both the cross-flow (CF) and in-line (IL) directions. According to the relative positions of the two cylinders, 10 different staggered arrangements are studied (P/d = 6, where P is the centre-to-centre spacing and d is the small cylinder diameter; α = 15°, 30°, 45°, 60°, and 75°, where α is the position angle of the downstream cylinder). The multi-mode FIV behaviours of the two staggered flexible cylinders with unequal diameters were investigated with respect to various aspects, e.g., strain and displacement responses, dominant frequencies and dominant modes. Due to the presence of the small cylinder, the CF vibration of the large cylinder was suppressed at α = 15° and 30° when the large cylinder was upstream or downstream. Furthermore, the CF and IL response amplitudes of the small cylinder were significantly enhanced by flow interactions at various position angles. When the small cylinder was located downstream, the FIV behaviours were most greatly affected at small and large position angles (α = 15° or 75°). In addition, the wake-induced flutter phenomenon was observed in the IL FIV response when the small cylinder was downstream. However, this phenomenon was not observed when the large cylinder was located downstream.

Jet impingement using an adjustable spreading-angle sweeping jet

This experimental study proposes a master-slave fluidic oscillator that can produce sweeping impinging jets with adjustable spreading angles. The flow fields of the jet impingement on convex cylinders are measured using time-resolved particle image velocimetry (TR-PIV) in a water tank. By increasing the proportion of the flow rate that passes through the master layer from 0 to 1 (master flow rate, MFR), the range of the jet spreading angle can be smoothly increased from 0° to about 100°. This new design is then applied in impingement upon two convex cylinders with different diameters. The large cylinder has a diameter of D/Dh = 12.5, where Dh is the hydraulic diameter of the jet exit. When the jet spreading angle is maximized by setting MFR = 1, the jet can cover half of the large cylinder. On the other hand, for the small cylinder with a diameter of D/Dh = 2.5, the jet can enclose the whole convex surface when the jet spreading angle is minimized at MFR = 0. In addition, proper orthogonal decomposition (POD) analysis reveals different unsteady flow patterns induced by the jet interaction with the cylinders. This study demonstrates, very first time, flexibility of the novel sweeping jet oscillator and guides towards some potential applications.

Influence of the packing structure on the flow through packed beds with small cylinder diameter to particle diameter ratios

The influence of different packing structures of packed bed particles on the fluid flow through packed beds was investigated. The flow through cylindrical packed beds consisting of mono-sized spherical particles was simulated using an explicit approach. These beds had cylinder to particle diameter ratios between 1.6 and 6.33. The results for the friction factor over a wide range of Reynolds numbers were compared with results from literature. It was found that the Eisfeld and Schnitzlein friction factor correlation was confirmed by the CFD results. The lower cylinder diameter to sphere diameter limit of the KTA friction factor correlation was also evaluated and adjusted. This adjustment was incorporated into a new formulation for the limiting line of the KTA equation, which is presented in this paper. It was further found that in the creeping flow regime the bed friction has an overwhelming effect on the pressure drop, whereas in the turbulent regime the inertial forces and the porous structure has the overwhelming influence.

Effectiveness of BFRP confinement on the compressive behaviour of clay brick masonry cylinders

This paper presents the results of an experimental and analytical study on the compressive behaviour of small clay brick masonry cylinders reinforced with a basalt fibre reinforced polymer (BFRP) composite. Fourteen cylinders, manufactured using two assembling schemes and confined using either one or two layers of BFRP grids, were tested under monotonic compression loading. Traditional strain measuring systems were integrated with digital image correlation (DIC) technique. The BFRP confined masonry cylinders showed a ductile behaviour characterised by a softening branch of the stress–strain curve. The experimental strains, strength, and full stress–strain curves were modelled using analytical models available in the literature. A modified version of the CNR model proposed in this study provided the best strength prediction.

Effect of Ethanol and Gasoline Blending on the Performance of a Stationary Small Single Cylinder Engine

To reduce dependency on fossil fuel, alternative fuel may be considered either to replace fossil fuel or to improve the characteristics of fossil fuel. Ethanol is one of the alternative fuels that has been used as an additive to gasoline fossil fuel in many countries, particularly for spark ignition engine system. This research aims to investigate the effect of ethanol and gasoline blending on the performance of a non-road small single cylinder engine. Ethanol–gasoline blends of different concentrations are considered in this paper, to experimentally compare their performances, under varying engine speed but constant engine load. The experimental results showed that the addition of ethanol to gasoline has improved the overall engine performance. High ethanol–gasoline fuel blend (E40) is suitable for low engine speed, while low ethanol–gasoline fuel blend (E10) can replace the neat gasoline without modification as their performance is very identical.

Effects of geometry on resistance in elliptical pipe flows

This paper considers the significant role of cross-sectional geometry on resistance in co-axial pipe flows. We consider an axially flowing viscous fluid in between two long and thin elliptical coaxial cylinders, one inside the other. The outer cylinder is stationary, while the inner cylinder (rod) is free to move. The rod poses a resistance to the axial flow, while the viscous fluid poses a resistance to any motion of the rod. We show that the equations for flow in the axial direction – driven by a prescribed flux – and for flow within the cross-section of the domain – driven by the motion of the rod – decouple in the asymptotic limit of small cylinder aspect ratio into axial Poiseuille flow and transverse Stokes flow, respectively. The objective of this paper is to calculate numerically the axial and cross-sectional resistances and to determine their dependence on cross-sectional geometry – i.e. rod position and the ellipticities of the rod and bounding cylinder. We characterise axial resistance, first for three reduced parameter spaces that have not been fully analysed in the literature: (i) a circle in an ellipse, (ii) an ellipse in a circle and (iii) an ellipse in an ellipse of equal eccentricity and orientation, before extending our geometric parameter space to determine the overall optimal geometry to minimise axial flow resistance for fixed cross-sectional area. Cross-sectional resistance is characterised via coefficients in a Stokes resistance matrix and we highlight the interdependent effects of cross-sectional ellipticity and boundary interactions.