Convective Flow Patterns of a Three Generation Bifurcation Model

Download or read book Convective Flow Patterns of a Three Generation Bifurcation Model written by Andrew C. Shupe and published by . This book was released on 2012 with total page 478 pages. Available in PDF, EPUB and Kindle. Book excerpt: To experimentally study the convective flow patterns of the human lung, a large scale symmetric model was built to model branching airways that air passes through during respiration. The model used in this experiment goes through three symmetrical 70¿¿ bifurcations before terminating at the model exits. The model not only demonstrated in-plane flow but was rotated to represent out-of-plane flow after each bifurcation. In the latter case the model was rotated 90¿¿ at each of the bifurcations, which allowed a more realistic study of the three-dimensional branching flow inside the lung. For each case the flow was studied at inlet Reynolds numbers of 750 and 1500. The airflow was studied using a parabolic inlet condition and was only representative of inspiratory flow. In order to visualize the flow in the model a laser was expanded though a cylindrical lens to produce a laser sheet that was directed through the exit plane flow field of each bifurcation. When shining the laser sheet through the flow-field, the size, shape, and location of vortices could be visually identified. A Laser Doppler Anemometer (LDA) was used to measure the velocity patterns in the model. The LDA was used to measure both the primary (normal) velocity component and the secondary (tangential) velocity components of the flow at the entrance and at the exits of each bifurcation. This data was then used to reveal the flow field for each model configuration. When considering the in-plane (non-rotated) model, the flow development after one bifurcation was fairly predictable and developed into two distinct vortices at each exit. The two vortices were symmetrical and were located toward the inner wall of curvature. The formation and position of the vortices were in agreement with many previous curved flow studies and could be predicted from curved pipe simulations. Numerically this was also calculated, for example by Soriropoulos (26), for a non-bifurcating curved tube. At the in-plane second bifurcation, the flow at the exits developed two different patterns. The two lower exit points developed into four equal vortices. At the upper two exits, the flow pattern developed into two vortices again. This was similar to the flow after the first bifurcation. The two vortices at the upper two exits were located toward the inner wall of curvature. This was the same location in relation to the radius of curvature as in the first bifurcation. When the second bifurcation was rotated 90¿¿ or out-of-plane, the flow development changed from that of the in-plane patterns. At each exit there were two main vortices that were split at roughly a 45¿¿ angle. Inside one of the two main vortices, two smaller vortices were beginning to develop. The flow patterns at these two exits at 90¿¿ rotation were mirror images of one another. After the third bifurcation, the flow development was different at each exit point for the in-plane model. When the second bifurcations were rotated 90¿¿, the flow developed into three distinct vortices, regardless of the rotation position of the third bifurcation. The location of the three vortices was, however, affected individually by of the third bifurcation rotation. The flow patterns after the third bifurcation were also mirror images of one another at each individual branch when considering the out-of-plane flow. When each section of the third bifurcation was rotated independently, they showed no apparent effects upon the other exit points. It was also evident that the initial orientation and angle of rotation of the second bifurcation had a major impact on the downstream flow. When all of the bifurcations were at the in-plane rotation the flow patterns at each exit point still had noticeable differences from each other. When the second bifurcation was in the out-of-plane rotation, the exits at the third bifurcation all contained three distinct vortices. From these observations, it can be concluded that the orientation and the angle of rotation of initial or upstream bifurcations had a significant effect on the exit flow patterns. However, the effect diminishes for the exit flow passing through a multi-generation model. The effect was further diminished when the flow passed out of the initial flow direction plane (out-of-plane). The more bifurcations the flow passed through, the more uniform the exit flow became. While the initial flow bifurcation did affect the final exit flow, the immediately previous bifurcation flow conditions play a much stronger role in the whole process. Finally, it was reasonably inferred that after 4 or 5 out-of-plane bifurcations, all the exit flows will all be nearly identical.