Continuum microhaemodynamics modelling using inverse rheology

Modelling blood flow in microvascular networks is challenging due to the complex nature of haemorheology. Zero- and one-dimensional approaches cannot reproduce local haemodynamics, and models that consider individual red blood cells (RBCs) are prohibitively computationally expensive. Continuum approaches could provide an efficient solution, but dependence on a large parameter space and scarcity of experimental data for validation has limited their application. We describe a method to assimilate experimental RBC velocity and concentration data into a continuum numerical modelling framework. Imaging data of RBCs were acquired in a sequentially bifurcating microchannel for various flow conditions. RBC concentration distributions were evaluated and mapped into computational fluid dynamics simulations with rheology prescribed by the Quemada model. Predicted velocities were compared to particle image velocimetry data. A subset of cases was used for parameter optimisation, and the resulting model was applied to a wider data set to evaluate model efficacy. The pre-optimised model reduced errors in predicted velocity by 60% compared to assuming a Newtonian fluid, and optimisation further reduced errors by 40%. Asymmetry of RBC velocity and concentration profiles was demonstrated to play a critical role. Excluding asymmetry in the RBC concentration doubled the error, but excluding spatial distributions of shear rate had little effect. This study demonstrates that a continuum model with optimised rheological parameters can reproduce measured velocity if RBC concentration distributions are known a priori. Developing this approach for RBC transport with more network configurations has the potential to provide an efficient approach for modelling network-scale haemodynamics.

Airborne Atmospheric Measurements with the Max Planck CloudKites

<p>To investigate cloud microphysics and turbulence in clouds and in the atmospheric boundary layer, we specially developed airborne platforms, one Max-Planck-CloudKite + (MPCK+) and two mini-Max-Planck-CloudKites (mini-MPCK). They are deployed aboard balloon-kite hybrids conducting <em>in situ</em> measurements of meteorological and cloud microphysical properties with high spatial and temporal resolution. During the EUREC4A-ATOMIC field campaign in the Caribbean January-February 2020, the MPCK+ and one mini-MPCK sampled clouds aboard a 250 m<sup>3</sup> aerostat launched from the R.V. Maria S. Merian where both instruments were operated between MSL and 1500m MSL. In addition, one mini-MPCK profiled the atmosphere between MSL and 1000 m MSL aboard a 74 m<sup>3</sup> aerostat launched from the R.V. Meteor. In total, we acquired 145 h of flight-data on RV Maria S. Merian and 52 h of flight-data on RV Meteor. For the MPCK+, this included 5 hr of Particle Image Velocimetry data and 3 hr of inline holography data inside clouds and near the cloud edges. We present <em>in situ</em> data measured by the MPCKs during the EUREC4A-ATOMIC field campaign and report on preliminary assessment of turbulence features.</p>

Tuna robotics: hydrodynamics of rapid linear accelerations

Fish routinely accelerate during locomotor manoeuvres, yet little is known about the dynamics of acceleration performance. Thunniform fish use their lunate caudal fin to generate lift-based thrust during steady swimming, but the lift is limited during acceleration from rest because required oncoming flows are slow. To investigate what other thrust-generating mechanisms occur during this behaviour, we used the robotic system termed Tunabot Flex, which is a research platform featuring yellowfin tuna-inspired body and tail profiles. We generated linear accelerations from rest of various magnitudes (maximum acceleration of 3.22 m s − 2 at 11.6 Hz tail beat frequency) and recorded instantaneous electrical power consumption. Using particle image velocimetry data, we quantified body kinematics and flow patterns to then compute surface pressures, thrust forces and mechanical power output along the body through time. We found that the head generates net drag and that the posterior body generates significant thrust, which reveals an additional propulsion mechanism to the lift-based caudal fin in this thunniform swimmer during linear accelerations from rest. Studying fish acceleration performance with an experimental platform capable of simultaneously measuring electrical power consumption, kinematics, fluid flow and mechanical power output provides a new opportunity to understand unsteady locomotor behaviours in both fishes and bioinspired aquatic robotic systems.

Interactional Aerodynamic Analysis of an Asymmetric Lift-Offset Compound Helicopter in Forward Flight

Recently, an asymmetric lift-offset compound helicopter has been conceptualized at the University of Maryland with the objective of improving the overall performance of a medium-lift utility helicopter. The investigated form of lift-compounding incorporates an additional stubbed wing attached to the fuselage on the retreating side. This design alleviates rotor lift requirements and generates a roll moment that enables increased thrust potential on the advancing side in high-speed forward flight. In this study, a numerical model was developed based on the corresponding experimental test case. Three-dimensional unsteady Reynolds-averaged Navier–Stokes equations were solved on overset grids with computational fluid dynamics–computational structural dynamics (CFD–CSD) coupling using the in-house CPU–GPU heterogeneous Mercury CFD framework. Simulations were performed at high-speed, high-thrust operating conditions and showed satisfactory agreement with the experimental measurements in terms of the cyclic control angles, rotor thrust, and torque values. CFD results indicated that for an advance ratio of 0.5 with a collective pitch of 10.6°, a vehicle lift-to-equivalent-drag ratio improvement of 47% was attainable using 11% wing-lift offset. The CFD-computed flow fields provide insights into the origin of a reverse flow entry vortex that was observed in particle image velocimetry data, and they characterize the wing–rotor interactional aerodynamics.

Investigations of Ship Airwakes Using Concurrent Computations and Experiments

Using computational techniques established in previous full-scale dynamic interface simulations, small-scale large eddy simulations of Embry-Riddle Aeronautical University's Boundary-Layer Wind Tunnel were conducted. The ultimate goal of the study is to serve as a useful point of validation for full-scale airwake data provided to flight simulators used to develop flight software and train rotorcraft pilots for shipboard operations. Cowdrey rods were used in the wind tunnel to develop the turbulence and sheared inflow similar to an atmospheric boundary layer. Hot-wire anemometry and particle image velocimetry data were compared to OpenFOAM large eddy simulation data. In uniform inflow conditions, it was found that despite the reduced Reynolds number of the scaled setup, the computational airwake data agreed quite well with larger-scale wind tunnel experiments and full-scale large eddy simulations of the same ship model, but showed less asymmetry spanwise across the flight deck. Comparisons of the experimental and computational simulated atmospheric boundary-layer inflow show good agreement in the time-averaged velocity profile and velocity contours along the ship's centerline. It was further found that the computations while capturing the major flow structures, overpredict the turbulence intensities and turbulent kinetic energy in the ship airwake. The present study provides some confidence that full-scale coupled atmospheric boundary layer/ship airwake solvers are accurate and can assist in improving dynamic interface simulations.

Numerical Study on Flow Field in a Peripheral Ported Rotary Engine Under the Action of Apex Seal Leakage

Apex seal leakage is one of the main defects restricting the performance improvement of rotary engines. The aim of this study is to study the airflow movement in a peripheral ported rotary engine under the action of apex seal leakage. For this purpose, a 3D dynamic calculation model considering apex seal leakage was firstly established and verified by particle image velocimetry data. Furthermore, based on the established 3D model, the flow field in the combustion chamber under the four apex seal leakage gaps (0.02, 0.04, 0.06 and 0.08 mms) and the three engine revolution speeds (2000, 3500, and 5000 RPMs) was calculated. By comparing with the flow field under the condition without leakage, the influences of the existence of apex seal leakage on the velocity field, the turbulent kinetic energy and the volumetric efficiency in the combustion chamber were investigated. Thereinto, the influences of the existence of apex seal leakage on the velocity field is that at the intake stroke, a vortex formed in the middle of the combustion chamber under the condition without apex seal leakage, was intensified by the apex seal leakage action. At the compression stroke, irrespective of the condition with or without apex seal leakage, all vortexes in the combustion chamber are gradually broken into a unidirectional flow. However, there is an obvious "leakage flow area" at the end of combustion chamber due to the existence of apex seal leakage.