#navierstokes

Through studying fluid dynamics this semester, I have become more aware of the ubiquitous presence of fluids in our daily lives. In addition to the air we breathe and the water we drink, there are many fluids that we come across daily that we do not always consider to be examples of transport phenomena. For example, the ketchup I eat with my breakfast every morning is a complex fluid that can only flow with a certain amount of shear stress. Prior to this semester, my intuition for explaining why toothpaste does not flow as easily as water was simply believing that it was “thicker.” With my newly acquired knowledge, I can proudly explain that toothpaste is more viscous than water and only flows in response to stress because is it a non-Newtonian fluid. This is only a mere insight into what I have learned this semester and what I can share with you. Let’s explore some of the fundamentals of fluid dynamics and their relation to current issues!

           I watched the video about Rheological Behavior of Fluids from the National Science Foundation mere hours after my first Transport Phenomena I class with Professor McNeill and I must say that this video helped solidify key concepts of fluid through live experiments and real life examples.  The video introduced me to new vocabulary such as rheology, inviscid fluid, and memory fluid, all topics that we touched on briefly during class. The narrator presents the material in a clear and concise way that assumes that people watching it, like myself, have little to no prior knowledge of fluids. The flow of content progresses gradually especially at the beginning of the video where the narrator explains the basic assumptions of behind the stress deformation relation and their accompanying models such as Euler’s and Navier-Stokes’s Equation.

          The theories and concepts around inviscid and Newtonian fluids explained in the video were fairly straightforward and needed little to no experimental elaboration; however, for the “non-Newtonian” fluids that did not adhere to the aforementioned models. Luckily, he offered numerous demonstrations for “non-Newtonian” fluids that had larger molecules. The demonstrations were extremely helpful in his examination of viscosity, elasticity, and memory fluids. The narrator defined “non-Newtonian”  (or Memory Fluids) as having a fading memory as illustrated by the ball and the hand crank experiment. The ball exhibited characteristics of an elastic solid but in actuality it was a fluid because after 45 minutes it turned into a puddle. Similarly with the hand crank and can of “non-Newtonian” fluid, the crank was turned and the fluid acted as best it could on its memory of its “solid state”. However, when the crank was turned and held in that position longer, the fluid adjusted a lot less. These two experiments along with the other few illustrated how the yield value of a material and the history of the deformation gradient lead to the stress being a non-linear function. 

           The second half of the video left the more challenging topics with less explanations and demonstration that were difficult to interpret in black and white. The narrator briefly touched on shear thinning (pseudo-plastic) and shear-thickening (dilatant) before diving into the effects of non-linearity of normal stress. The more complicated experiment in last few minutes offered not so detailed information regarding further understanding of the material because the narrator was stating facts and not explaining them. However, end of the video drives home the point that the degree to which “non-Newtonian” fluids occur depends on material and flow situations. Overall, I found the video extremely helpful in visualizing introductory fluid concepts.