Potential Flow Velocity Research Articles

Time-Resolved Dynamic Optical Coherence Tomography for Retinal Blood Flow Analysis.

Optical coherence tomography (OCT) representations in clinical practice are static and do not allow for a dynamic visualization and quantification of blood flow. This study aims to present a method to analyze retinal blood flow dynamics using time-resolved structural OCT. We developed novel imaging protocols to acquire video-rate time-resolved OCT B-scans (1024 × 496 pixels, 10 degrees field of view) at four different sensor integration times (integration time of 44.8 µs at a nominal A-scan rate of 20 kHz, 22.4 µs at 40 kHz, 11.2 µs at 85 kHz, and 7.24 µs at 125 kHz). The vessel centers were manually annotated for each B-scan and surrounding subvolumes were extracted. We used a velocity model based on signal-to-noise ratio (SNR) drops due to fringe washout to calculate blood flow velocity profiles in vessels within five optic disc diameters of the optic disc rim. Time-resolved dynamic structural OCT revealed pulsatile SNR changes in the analyzed vessels and allowed the calculation of potential blood flow velocities at all integration times. Fringe washout was stronger in acquisitions with longer integration times; however, the ratio of the average SNR to the peak SNR inside the vessel was similar across all integration times. We demonstrated the feasibility of estimating blood flow profiles based on fringe washout analysis, showing pulsatile dynamics in vessels close to the optic nerve head using structural OCT. Time-resolved dynamic OCT has the potential to uncover valuable blood flow information in clinical settings.

Electro-separation of chitooligosaccharides with specific degrees of polymerization using electrodialysis ultrafiltration

Biological activities of chitooligosaccharides (COSs) are related to their purity and intrinsic structure. However, a wide range of size distribution and degree of polymerization (DP) of COS make it challenging for their meticulous biological research and applications. This research investigated the protonation behavior and the separation mechanism of individual COSs molecules at semi-pilot scale using an electrodialysis-ultrafiltration membrane. Results indicated that COSs were protonated to varying degrees in the pH ranges of 3.28 to 7.95 with a pKa value stand nearly at 6.44. A semi pilot scale investigation of operational parameters successfully separated a fraction with degree of polymerization (DP) ≤ 4 (>93% of total COS migrated) at flow velocity 6.79 cm/s and electric potential of 9 V/cm with highest DP 3 (>36% of the fraction) in 60 min. Additionally, few other fractions (DP ≤ 3 and DP ≤ 5) were efficiently separated from the industrial sample at different processing times. Moreover, the selective conditions also prevent the fouling of ultrafiltration membrane. Conclusively, the inadequate or too high applied electric potential and solution flow velocities have significant influence on migration of target molecules.

On the Possibility of Cross-Flow Vortex Cancellation by Plasma Actuators

Cancellation of the cross-flow vortices in a swept-wing boundary layer is attempted by plasma actuator array in numerical simulation. The response of the boundary layer to the stationary excitation by a single actuator section is measured experimentally and compared to the response obtained from the solution to the parabolized stability equations. A linear approach is shown to be held within the peak-to-peak magnitude of the stationary cross-flow vortices below 10% of the local potential flow velocity. Within the linear model, an optimal control strategy and a faster suboptimal one are developed to calculate voltage amplitude distribution across the electrodes, taking into account the forcing constraints. Simulation of the cancellation process is performed, showing up to a 20 dB reduction in the initial spanwise velocity modulation in the boundary layer. The minimal actuator resolution required for the successive implementation of the control is shown to be in the order of a quarter of the most amplified wavelength, or 3–4 displacement thickness of the boundary layer. Linear estimates predict up to a 150 mm (22% of flow acceleration region length) transition delay for an actuator momentum coefficient of 0.005%.

Nonsimilar stagnation flow of Williamson fluid over an isothermal linearly stretched sheet

The objective of this work is to analyze the boundary layer flow in the vicinity of a stagnation point on a linearly stretched isothermal flat surface. The ambient fluid temperature is considered different than that of the sheet. The streaming fluid rheological behavior is approximated via the Williamson fluid model. The normalized partial differential equations based on the balances of mass, momentum, and energy are simulated numerically via the symbolic and numeric computing software Maple for two entirely different scenarios. In the first scenario, the outer potential flow velocity dominates the sheet velocity whilst it is the other way round for the second scenario. The plots showing the behaviors of velocity and temperature are presented at various streamwise locations. The skin friction and Nusselt number are also visualized graphically and listed in tabular forms. The analysis reveals that all quantities including velocity and temperature show a strong dependence on the streamwise co-ordinate. In general, velocity distribution and temperature rise with a gradual march along the streamwise direction. The heat transfer coefficient also elevates upon an increase in the streamwise co-ordinate. This contradicts several previously published results on the boundary layer flow of Williamson fluid where no such dependence is seen.

Implementation of a velocity decomposition method coupled with volume-of-fluid method for simulating free-surface flows

An efficient velocity decomposition method (VDM) is proposed for simulating free surface flows based on OpenFOAM platform, which is primarily intended for marine hydrodynamics applications. In this method, it is assumed that the free surface can be treated as a source region, which introduces rotating velocity related to the wave elevation. In the implemented solver called cpVDFoam, the decomposed potential flow velocity is computed by solving the Laplace equation without considering the effect of free surface, and the remaining non-potential velocity is determined with a complimentary Navier–Stokes (N-S) equation. Further, the free surface is modeled using volume-of-fluid (VOF) method in the viscous domain for obtaining the non-potential velocity. Flow field analysis shows that non-potential velocity magnitude contributed by freesurface is positive correlation with wave elevation, and which value shall decrease to zero in the zero wave elevation region. The efficacy of the proposed VDM is validated by comparing the simulation results with the results obtained using standard OpenFOAM solver interFoam and earlier reported experiment. All results indicate that the present method exhibited similar accuracy as the conventional CFD method but less sensitive to the domain size.

Drivers of Spatiotemporal Eukaryote Plankton Distribution in a Trans-Basin Water Transfer Canal in China

Planktonic eukaryotes are important components of aquatic ecosystems, and analyses of the whole eukaryotic planktonic community composition and function have far-reaching significance for water resource management. We aimed to understand the spatiotemporal variation and drivers of eukaryotic plankton distribution in the Middle Route Project of the South-to-North Water Diversion in Henan Province, China. Specifically, we examined planktonic assemblages and water quality at five stations along the canal and another one located before the dam in March, June, September, and December 2019. High-throughput sequencing revealed that the eukaryotic plankton community was primarily composed of 53 phyla, 200 genera, and 277 species, with Cryptophyta, Ciliophora, and norank_k_Cryptophyta being the dominant phyla. Redundancy analysis of the eukaryotic community and environmental factors showed that five vital factors affecting eukaryotic plankton distribution were oxidation-reduction potential, nitrate nitrogen, pH, total phosphorus, and water flow velocity. Furthermore, the geographical distribution of eukaryotic communities was consistent with the distance decay model. Importantly, environmental selection dominantly shaped the geographical distribution of the eukaryotic community. In summary, our study elucidates the ecological response of planktonic eukaryotes by identifying the diversity and ecological distribution of planktonic eukaryotes in trans-basin diversion channels.

Unsteady electromagnetohydrodynamic flow of couple stress fluid through a microchannel: A theoretical analysis

In this work, we investigate the transient electromagnetohydrodynamic (EMHD) flow of non-Newtonian fluid in a narrow/micro-fluidic channel. We consider the couple stress fluid (CSF) model to characterize non-Newtonian behaviour. We present an analytical solution for electric potential and temporal EMHD flow velocity by applying the standard Laplace transform method using physically relevant boundary conditions. We demonstrate the excellent agreement between the present analytical solution for fluid flow with the CSF model and previously reported results for a Newtonian fluid. We analyse the transient flow velocity and volume flow rate for a wide range of flow governing parameters. We notice that the steady-state flow velocity magnitude is higher for magnetic parameter/ Hartmann number values than for the couple stress parameter values, which characterizes the flow’s viscous resistance. We demonstrate that the contribution of couple stresses in the fluid medium is prominent in the combined pressure, magnetic and electroosmotic force to increase the volume flow rate, which contrasts with the EMHD flow of Newtonian fluid. We observe that the critical Hartmann number attains a fixed value (about 1.3) for higher values of the couple stress parameter due to the transverse electric field effect. The present work hold the key towards explaining non-Newtonian behaviour impersonating bio-fluid transport in the narrow/micro-fluidic channel under the combined effect of electromagnetic force and pressure gradient. The results anticipated from the present attempt are useful to develop efficient electro-magneto-mechanical and micro-bio-fluidic devices.

Multifidelity aerodynamic flow field prediction using random forest-based machine learning

In this paper, a novel random forest (RF)-based multifidelity machine learning (ML) algorithm to predict the high-fidelity Reynolds-averaged Navier-Stokes (RANS) flow field is proposed. The RF ML algorithm is used to increase the fidelity of a low-fidelity potential flow field. Three cases are studied, the first two consist of a flow past a backward-facing step, and the third, a subsonic flow around an airfoil. In the first case, the data is generated using ten different inlet velocities, in the second using six different step heights, and in the third using 20 different airfoil shapes parameterized using B-spline curves. Input parameters to RF are case dependent. For the first case, the x and y cell-center locations and the corresponding x and y potential flow velocities, along with the specified inlet velocity, are used. For the second, the cell-center values are nondimensionalized using the step height, and the step height is used in place of the inlet velocity. The remaining two input features used are the same as in the previous case. For the third case, the potential flow stream function and velocity potential along with the B-spline control point values are used as input variables. The outputs of the RF algorithm are the same for all the cases and include the RANS velocities, pressures, and turbulent viscosities. The results in this study are compared to those generated using the tensorFlowFoam (TFF) and from directly solving the RANS equations. To quantify the errors, the absolute error and relative L2 norm error metrics are used. The results show that for the first two cases, RF consistently has two to 30 times lower relative L2 norm compared to TFF, with the only exception being the turbulent viscosities for the second case. For the third case, RF is better at predicting the pressure and skin friction coefficients for the RAE 2822 airfoil compared to the NACA 0012 airfoil. The relative L2 norm error is 1.67 and 1.19 times lower for the pressure and skin friction coefficients, respectively.

Velocity decomposition approach for steady incompressible flow around multiple bodies

The CFD simulations for external flow problems can request high computational costs. To reduce these costs, viscous/inviscid interaction methodology based in the domains decomposition and the Helmholtz velocity decomposition has been developed. The calculation of viscous flow by the Navier–Stokes equations is made on a computational reduced domain. In this work, an interactive methodology is presented, which consists of: calculate the potential flow outside the rotational region, impose the potential flow velocity field as a boundary condition in the reduced domain boundary, calculate the transpiration velocity to correct the potential flow, recalculate the potential flow velocity field outside the rotational region, and update the boundary conditions on the reduced domain. To formulate the transpiration velocity, the velocity decomposition approach was used, but to calculate the transpiration, it is necessary determine the boundary of the rotational region, called rotational boundary, where the vorticity is negligible. For this, negligible vorticity criteria were developed to find that boundary; however, determining it can be a complex task, as is the case of flow around multiple bodies. Some techniques, which may include the use of an auxiliary surface, have been developed to facilitate the determination of the rotational boundary. Thus, two proposals were made in this work, first: the use of an auxiliary surface to determine the rotational boundary to multiple bodies cases; and second: a new negligible vorticity criterion based on the total pressure field. Calculations were performed in the viscous reduced domain for two-dimensional incompressible flow, around a single body and multiple bodies. The use of the present methodology allowed reducing the computational costs. The aerodynamic coefficients and viscous flow fields obtained in the reduced domain were satisfactory for such engineering problems.

Electroosmotic flow of viscoelastic fluid through a microchannel with slip-dependent zeta potential

We investigate flow characteristics for an electroosmotic flow of viscoelastic fluids through a hydrophobic plane microchannel, considering the coupled effect of interfacial slip and zeta potential. We employ a simplified Phan–Thien–Tanner model to describe the constitutive behavior of the fluid. The governing equations are solved analytically to obtain electric double layer (EDL) potential distribution, flow velocity, flow rate, stresses, and viscosity. We have compared the obtained analytical flow field with the established theoretical and experimental works at the limiting cases. We demonstrate that ignoring the effect of the interfacial slip on zeta potential will lead to underprediction of the flow rate, and this underprediction is amplified with the increase in the Deborah number, decrease in the EDL thickness, and increase in the slip coefficient. Moreover, the relative flow rate augmentation by the rheological behavior strictly depends on the range of slip coefficients with the change in the EDL thickness. Accordingly, we have identified three regions of the slip coefficient. In addition, the viscosity near the wall decreases with the slip coefficient for the slip dependent zeta potential model. In contrast, the normal and shear stresses are augmented with the slip coefficient. Outcomes of the present investigation may help one to understand the enhanced flow behavior for the transport of complex fluids through a hydrophobic microchannel.

A velocity decomposition method combining potential and viscous flow for the estimation of submarine's hydrodynamic coefficients

Estimating hydrodynamic coefficients is important in the design of submarines. To enhance the efficiency of the computational fluid dynamics (CFD) method for evaluating the hydrodynamic performance of submarines, we have developed a velocity decomposition solver for the simulation of a moving body based on the open-source CFD platform OpenFOAM. The total velocity is decomposed into potential flow velocity and non-potential flow velocity. The potential flow velocity is further decomposed into unit components, which can be computed by the proposed method with less interpolation cost. Further, the original potential flow velocity can be recovered by linear summation of these unit velocity components. This avoids solving Laplace equation at each time step. The non-potential flow velocity is solved by using a complementary Navier–Stokes equation in a smaller domain as compared to that used in the conventional CFD method. In addition, a buffer source term is introduced for the transition of non-potential flow velocity to potential flow velocity. Oblique towing test and planar motion mechanism test are numerically simulated using the proposed method, which reveal good consistency between the experimental data and simulation results. This validates the efficiency and reliability of the proposed method in estimating the hydrodynamic coefficients of submarines.

Model Identification for Adsorption Dynamics and Suppression Effect of Polyethylene Glycol Using Inverse Analysis Approach

Cu electroplating is important in LSI manufacturing. In the manufacturing process, some additives are added to a copper sulfate solution. The additive that reduces a deposition rate is called suppressor. Polyethylene Glycol (PEG) has been actively studied as a typical suppressor. PEG adsorbs to the electrode in the presence of a chloride ion and suppresses the deposition rate. The dynamics of adsorption and the mechanism of the suppression effect have been studied, and various mathematical models have been proposed from these results. However, the phenomena have not been perfectly understood and the conventional mathematical models cannot fully reproduce these phenomena.[1] Voltammetry is often performed to observe the behavior of the additives. The rotating disc electrode(RDE) is used in order to control the concentration on the electrode surface. The RDE can control and evaluate the concentration on the electrode surface under the assumption for uniform distribution of concentration and current density on the electrode surface. However, it is observed that the adsorption of PEG occurs non-uniformly on the electrode surface.[2] The voltammogram show dynamics of the current density averaged on the working electrode. It is important to know the local current density and its distribution on the working electrode in order to understand the adsorption dynamics of PEG and the suppression of copper deposition. On the other hand, “Inverse Problems” have attracted attention due to the development of numerical simulation. Inverse Problems is a research area dealing with finding out unknown information from external or indirect observation through a system model. In the fields of electrochemical engineering, there are many problems which can have a benefit from the inverse analysis approach. Using an approach of the Inverse Problems, we identify the current density distribution on the electrode surface. Currents are measured by changing potential and PEG concentration with an electrochemical flow cell. Observation data such as potential, bulk concentration, average flow velocity, and current are used for the inverse analysis. From these observation data, we identify the current density distribution with estimating the models that represent the adsorptiondynamics of PEG and the suppression effect of the copper deposition. The figure shows a procedure of the inverse analysis method. The method consists of an experiment and a numerical simulation as shown. In the experiment, observation data are obtained with the electrochemical flow cell. The experimental system consists of two solution supply devices and the electrochemical flow cell.The solution supply device can arbitrarily control a flow rate of the solution supplied to the flow cell. Copper sulfate solutions with different concentrations of PEG are prepared for the solution supply devices. The experimental system can continuously change PEG concentration supplied to the flow cell by changing a mixing ratio of the two solutions. Currents are measured with a linear sweep of potential under constant PEG concentration and a linear sweep of PEG concentration under constant potential. Potential, concentration, average flow velocity, and current are obtained as observation data. In the numerical simulation, the adsorption dynamics of PEG and the suppression of copper deposition are treated in order to express the phenomena related to PEG. Surface coverage of PEG is introduced to express the adsorption dynamics. In this study, the dynamics of the surface coverage is represented by a piecewise linear function with current density, PEG concentration, and surface coverage. The suppression of copper deposition is expressed by the piecewise linear function with surface coverage, copper ion concentration, potential. A velocity field is modeled by the Navier-Stokes equation, and concentration fields of copper ion and PEG are modeled by the advection-diffusion equation. Boundary conditions of the advection-diffusion equation at the electrode are given by the models representing the adsorption dynamics of PEG and the suppression effect of copper deposition. The current density distribution on the electrode surface is evaluated with solving the advection-diffusion equation. The numerical simulation described above can be performed by assuming the parameters of these models. Currents are calculated with solving the advection-diffusion equation under the same potential, concentration, and average flow velocity as the experiment. The parameters of the models can be obtained by minimizing the residual between measured and calculated currents with a nonlinear least squares method. After the model is identified, the currentdensity distribution on the electrodes is easily calculated by the direct analysis. [1]Liu Yang, Aleksandar Radisic, Johan Deconinck, and Philippe M. Vereeckena; J. Electrochem. Soc., 161(5) D269-D276(2014)[2]D. Josell and T. P. Moffat; J. Electrochem. Soc., 163(7) D322-D331(2016) Figure 1

Streaming potential analysis and electrokinetic energy conversion efficiency of two immiscible fluids in a nanochannel

In order to conduct extensive investigation of electrokinetic energy conversion in nanofluidic devices, the analysis of streaming potential of pressure driven flow in the two-layer fluidic system through a nanochannel is investigated theoretically. Under the influences of the interfacial electric potential difference and the interface charge density jump, we first obtain the analytical electric potential distribution in the present two-layer fluidic system with consideration of Debye–Hückel linearization assumption. Then the analytical expressions of streaming potential field and flow velocity are derived. Based on the obtained the streaming potential, we finally give the analytical electrokinetic energy conversion efficiency in two-layer fluidic system and discuss the influences of related physical parameters on it. The theoretical result shows that the streaming potential can be viewed as a criterion to estimate the electrokinetic energy conversion efficiency. The electrokinetic energy conversion efficiency can be enhanced by the viscosity ratio and the interfacial slip length, but be restrained by the permittivity ratio and ion friction coefficient. Comparing to the single-layer fluidic system, the electrokinetic energy conversion efficiency can be augmented obviously in the two-layer fluidic system by selecting optimized flow parameters.

Electroosmotic flow of Phan-Thien–Tanner fluids at high zeta potentials: An exact analytical solution

We present a mathematical model to study the electroosmotic flow of a viscoelastic fluid in a parallel plate microchannel with a high zeta potential, taking hydrodynamic slippage at the walls into account in the underlying analysis. We use the simplified Phan-Thien–Tanner (s-PTT) constitutive relationships to describe the rheological behavior of the viscoelastic fluid, while Navier’s slip law is employed to model the interfacial hydrodynamic slip. Here, we derive analytical solutions for the potential distribution, flow velocity, and volumetric flow rate based on the complete Poisson–Boltzmann equation (without considering the frequently used Debye–Hückel linear approximation). For the underlying electrokinetic transport, this investigation primarily reveals the influence of fluid rheology, wall zeta potential as modulated by the interfacial electrochemistry and interfacial slip on the velocity distribution, volumetric flow rate, and fluid stress, as well as the apparent viscosity. We show that combined with the viscoelasticity of the fluid, a higher wall zeta potential and slip coefficient lead to a phenomenal enhancement in the volumetric flow rate. We believe that this analysis, besides providing a deep theoretical insight to interpret the transport process, will also serve as a fundamental design tool for microfluidic devices/systems under electrokinetic influence.

Design and fabrication of a new compound probe for plasma flux measurement in IR-T1 tokamak

A new compound probe is designed, built, and installed on an IR-T1 tokamak to flow measurements in the plasma edge region. The first results of using this probe on the IR-T1 tokamak are presented. The plasma parameters such as plasma current, loop voltage, floating potential, ion and electron saturation currents, electron temperature, plasma potential, and plasma flow velocities are measured in this work. The results show that the electron temperature and the plasma potential in the edge area are 14 eV and 44 V, respectively. The results indicate that the mean value of a parallel Mach number is 0.5 while the mean value of a perpendicular Mach number is almost zero. The large parallel flow velocity (about 17 km/s) and the negligible perpendicular flow velocity are also seen in this work. The most important advantage of using this compound probe is that it can not only save space and vacuum ports but also measure more physical quantities at the same time, contributing to further physical analysis.

Analytical/Numerical Study of Fluid Flow and Heat Transfer Across In-Line Cylinders

An integral approach to boundary-layer analysis is employed to investigate the effects of the longitudinal-pitch ratio on fluid flow and heat transfer from a longitudinal row of circular cylinders immersed in an infinite medium. The momentum equation is solved using the modified von Kármán–Pohlhausen method, which employs a fourth-order velocity profile within the hydrodynamic boundary layer. The potential-flow velocity is obtained by complex potential theory outside the boundary layer. A third-order temperature profile is used in the thermal boundary layer to solve the energy integral equation for the isothermal boundary condition. Closed-form solution is obtained for the heat transfer coefficient for a longitudinal row of circular cylinders immersed in an infinite medium. In the second part of this research activity, a numerical model based on computational fluid dynamics is developed to validate the closed-form solution. The proposed numerical model has been successfully implemented for simulating the flowfield over a longitudinal row of circular cylinders. Numerical simulations have been carried out for various values of the freestream Reynolds number and longitudinal-pitch ratio. The results obtained from the analytical and numerical models have been found to be in good agreement. The maximum percentage error in values of the average Nusselt number obtained from the numerical and analytical solutions is less than 9% and reduces further to a value of less than 4% with an increase in values of the freestream Reynolds number.

Effects of Hydromagnetic and Thermophoresis of Unsteady Forced Convection Boundary Layer Flow over Flat Plates

In this paper, we analyze unsteady two dimensional hydromagnetic forced convection boundary layer flow of a viscous incompressible fluid along flat plates with thermophoresis. The potential flow velocity has been taken as a function of the distance x and time t. The governing partial differential equations are transformed to ordinary differential equation by applying local similarity transformation. The resulting similarity equations are then solved numerically for unsteady case, applying Nachtsheim-Swigert shooting iteration technique with six order Runge-Kutta method. The variations in fluid velocity, fluid temperature and species concentration are displayed graphically and discussed for different material parameters entering into the analysis. The effects of the pertinent parameters on the skin-friction coefficient, wall heat transfer coefficient and wall deposition flux rate are also displayed in tabulated form and discussed them from the physical point of view. An analysis of the obtained results shows that the flow field is influenced appreciably by the magnetic field parameter and the thermophoresis particle deposition.

Indication of Differential Kinetic Freeze-out at RHIC and LHC Energies

The transverse momentum spectra at RHIC and LHC for A+A and p+p collisions are studied with Tsallis distributions in different approaches i.e. with and without radial flow. The information on the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocities for different particle species are obtained. These parameters are found to show a systematic behavior with mass dependence. It is observed that the heavier particles freeze-out early as compared to lighter particles and freeze-out surfaces are different for different particles, which is a direct signature of mass dependent differential freeze-out. Further, we observe that the radial flow velocity decreases with increasing mass. This confirms the mass ordering behavior in collectivity observed in heavy-ion collisions. It is also observed that the systems created in peripheral heavy-ion collisions and in proton-proton collisions are of similar thermodynamic nature.

Indication of a Differential Freeze-Out in Proton-Proton and Heavy-Ion Collisions at RHIC and LHC Energies

The experimental data from the RHIC and LHC experiments of invariant pT spectra for most peripheral A+A and p+p collisions are analyzed with Tsallis distributions in different approaches. The information about the freeze-out surface in terms of freeze-out volume, temperature, chemical potential, and radial flow velocity for π+, K+, and p and their antiparticles is obtained. Furthermore, these parameters are studied as a function of the mass of the particles. A mass dependent differential freeze-out is observed which does not seem to distinguish between particles and their antiparticles. Furthermore, a mass-hierarchy in the radial flow is observed, meaning heavier particles suffer lower radial flow. Tsallis distribution function at finite chemical potential is used to study the mass dependence of chemical potential. The peripheral heavy-ion and proton-proton collisions at the same energies seem to be equivalent in terms of the extracted thermodynamic parameters.

Autonomous obstacle avoidance for fixed-wing unmanned aerial vehicles

AbstractThis paper investigates a method for autonomous obstacle avoidance for fixed-wing unmanned aerial vehicles (UAVs), utilising potential fluid flow theory. The obstacle avoidance algorithm needs only compute the instantaneous local potential velocity vector, which is passed to the flight control laws as a direction command. The approach is reactive, and can readily accommodate real-time changes in obstacle information. UAV manoeuvring constraints on turning or pull-up radii, are accounted for by approximating obstacles by bounding rectangles, with wedges added to their front and back to shape the resulting fluid pathlines. It is shown that the resulting potential flow velocity field is completely determined by the obstacle field geometry, allowing one to determine a non-dimensional relationship between obstacle added wedge-length and the corresponding minimum pathline radius of curvature, which can then be readily scaled in on-board implementation. The efficacy of the proposed approach has been demonstrated numerically with an Aerosonde UAV model.