Abstracts Category : Other

NUMERICAL ANALYSIS OF FLUID MOTION AT LOW REYNOLDSNUMBERS

by Gonzalez Jesus Garcia

At low Reynolds number flows, the effect of inertiabecomes negligible and the fluid motion is dominated by the effectof viscous forces. Understanding of the behaviour of low Reynoldsnumber flows underpins the prediction of the motion ofmicroorganisms and particle sedimentation as well as thedevelopment of micro-robots that could potentially swim inside thehuman body to perform targeted drug/cell delivery and non-invasivemicrosurgery. The work in this thesis focuses on developing anunderstanding in the mathematical analysis of objects moving at lowReynolds numbers. A boundary element implementation of the Methodof regularized Stokeslets (MRS) is applied to analyse the lowReynolds number flow field around an object of simple shape (sphereand cube). It also showed that the results obtained by a boundaryelement implementation for an unbounded cube, where singularitiesare presented in the corners of the cube, agrees with more complexsolutions methods such as a GBEM and FEM.A methodology foranalysing the effect of walls by locating collocation points on thesurface of the walls and the object is presented. First at all,this methodology is validated with a boundary elementimplementation of the method of images for a sphere at differentlocations. Then, the method is extended when more than one wall ispresented. This methodology is applied to predict the velocityfiled of a cube moving in a tow tank at low Reynolds numbers fortwo different cases with a supporting rod similar to anexperimental set-up, and without the supporting rod as in the CFDsimulations based on the FVM. The results indicate a good matchbetween CFD and the MRS, and an excellent approximation between theMRS and experimental data from PIV measurements.The drag, thrustand torque generated by helices moving at low Reynolds numbers inan unbounded medium is analysed by the resistive force theory, aslender body theory, and a boundary element method of the MRS. Theresults show that the resistive force theory predict accurately thedrag, thrust and torque of moving helices when the resistive forcecoefficients are calculated from a slender body theoryapproximation by calculating independently the resistive forcecoefficients for translation and rotation, because it is observedthat the resistive force coefficients depend also of the nature ofmotion. Moreover, the thrust generated by helices of differentpitch angles is analysed calculated by a CFD numerical simulationbased on the FVM and a boundary element implementation, an comparedwith experimental data. The results also show an excellentprediction between the boundary element implementation, the CFDresults and the experimental data. Finally, a boundary elementimplementation of the MRS is applied to predict swimming of abiomimetic swimmer that mimics the motion of E.coli bacteria in anunbounded medium. The results are compared with the propulsivevelocity and induced angular velocity measurement by recording themotion of the biomimetic swimmer in a square tank. It isAdvisors/Committee Members: ALONSO RASGADO, TERESA TM, Alonso Rasgado, Teresa, Zhong, Shan.