7.2.1. Hele-Shaw Experiment

So, let us start with the experimental setups which we call Hele-Shaw apparatus, okay where we can generate a constant flow and there are the patterns of the colour dye we can inject it, as we injected the colour dye from this; this colour dyes are follows the path lines or the streak lines, as we make the flow in steady, so the stream line and streaks line the when you look it, if I put the colour dye, so these what will be show me the streak lines or the path lines, if I tracing on that okay, path line or streak line.

The Hele-Shaw experiment is set up using an apparatus that generates a constant flow of fluid. In this setup, colored dye is injected into the fluid to visualize the flow patterns. When the dye is injected, it follows the paths of fluid particles, creating streak lines or path lines, especially in steady flow conditions. Streamlines, which are the same as streak lines in steady flows, can also be observed, allowing for the mapping of how fluid moves around objects.

Think of swimming in a pool and watching how the water moves around your hand when you push it through the water. The path that your hand creates in the water can be thought of as the path line. By adding a few drops of food coloring to that area, you would see the color following the water's motion, showing exactly how the fluid moves at various positions.

Or since it is a steady flow, I can tell it that it is streamlines, so many of the times we are very much familiarize with the streamlines but when you look it, so what are these lines; is that the streamlines, different colours flow passing over this object, so we can see that how the streamline patterns are happening it, as we change the flow Reynolds numbers this pattern changes it.

In the Hele-Shaw experiment, the injection of dye into a continuously flowing fluid helps in visualizing the flow behavior. Steady flows mean that the fluid's characteristics remain constant over time, allowing us to observe the behavior of streamlines clearly. As different colored dyes are used, we can track various streamlines and how they interact with objects in the flow. The pattern of these streamlines is influenced by the flow conditions, such as the Reynolds number, which measures the flow's turbulence. A higher Reynolds number typically indicates a more turbulent flow.

Imagine sprinkling multiple colors of glitter into a river. If the current of the river is calm (low Reynolds number), the glitter will move smoothly. However, if the river is rushing fast (high Reynolds number), the glitter swirls and mixes chaotically, illustrating how turbulence can affect the flow patterns.

As we control the flow, we will have a different velocity, different the distance, you will have it the change of the flow patterns that what we do using Hele-Shaw apparatus setup which is there in IIT Guwahati.

The Hele-Shaw apparatus allows researchers to manipulate different parameters of the fluid flow, such as velocity and the distance the fluid travels. By making adjustments to these factors, we can observe how the flow patterns evolve. The apparatus is particularly useful for studying laminar flow, where fluid moves in parallel layers, as compared to turbulent flow where mixing occurs. This experimentation helps in understanding how fluids behave under various conditions.

Think about testing different kinds of juices in a blender. If you adjust the speed of the blender, you will notice how the juice blends differently depending on the speed. Similarly, in the Hele-Shaw experiment, modifying the flow speed gives insights into how the fluid reacts under different velocities.

Now, if you look it is very interesting experiment numerically, it is done by professors Amaresh Dalal and the Ph.D. Scholar who develop the CFD solvers and they have very unique lab which called Anupravaha CFD lab, so I acknowledge there, these PPT to that okay, let us understand what is this PPT is, if you look in these colourful things. What it happens is that there is a triangular cylinders are there and there is a uniform flow and there just looking in to vorticity.

The Hele-Shaw experiment also has computational aspects, where numerical simulations are used to complement the physical experiments. Researchers in the Anupravaha CFD lab study how flow interacts with triangular cylinders under uniform flow conditions. They observe the generation of vortices, which are swirling movements of fluid that form behind objects in the flow. This phenomenon, known as vortex shedding, highlights how fluid dynamics can produce complex flow patterns, which can lead to significant engineering challenges such as drag on vehicles and structures.

Imagine riding a bicycle and feeling the wind shifting behind you as you pedal faster. The air creates swirls (vortices) around your bike, which can slow you down. Similarly, when fluids flow past shapes like triangular cylinders, they create vortex patterns that can significantly impact performance and efficiency.

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