17.2. Slip Drag and Lift

Good morning, let us have a today class on drag and lift which is the last class of this course okay. This is lecture number 36 and drag and lift. I think discussion of the drag and lift I started from the lecture number 2 where we illustrated how we can estimate it what will be the drag and lift forces of the towers, the And also we talk about this how the bars drag and lift forces in linear momentum equations. So if you look at that we have really remarkably progressed in experimental fluid mechanics or we talk about wind tunnel testings or water flow testings as well as we also remarkably improved in numerical experiments using computational fluid dynamic software as we demonstrated many cases.

This introduction sets the stage for a discussion on drag and lift forces, fundamental concepts in fluid mechanics. Drag refers to the force opposing an object's motion through a fluid, while lift is the force acting perpendicular to the direction of motion. The speaker emphasizes the progress made in measuring these forces through experimental and numerical methods, which are key for designing efficient structures, vehicle aerodynamics, and energy systems like wind turbines.

Consider a cyclist racing in an Olympic event. As they lean forward, they reduce drag, allowing them to move faster through the air. This illustrates how understanding drag and lift is crucial for maximizing performance in sports.

So that basically this coefficient drags we can get it from experiment basically conducting wind tunnel test or we can do numerical experiment. We can do the numerical experiments to estimate what will be the CD value or we can do a wind tunnel physical experiments to estimate the CD because CD is a function of velocity, functions of rho density of the fluid. It depends upon the velocity which we can say that is a free stream velocities and it also depends upon the frontal area, the shape, size and orientations.

The drag force is influenced by various factors, including the coefficient of drag (CD), which can be determined through experiments. CD is influenced by the object's velocity, the fluid's density (rho), and the object's frontal area and shape. This means that optimizing any of these factors can lead to a reduction in drag force, thus improving performance.

Imagine designing a new race car. Engineers would conduct wind tunnel tests to find the optimal shape that minimizes drag, ensuring the car can move faster while using less fuel. This process is similar to how aircraft wings are designed to ensure efficient flight.

So the basically a cyclist who participates like very competitive racings like Olympics and all he tried to reduce this a value he will try to reduce this a value or will be trying to reduce the CD value that is 2 things he can reduce it so that drag force will be that minimum and he can increase the velocity.

Cyclists use body positioning and streamlined clothing to minimize drag. By reducing their frontal area and optimizing their posture, they can achieve lower CD values during races, which in turn enables them to ride faster with less effort.

Think of a swimmer who reduces drag by cutting through the water with a streamlined form. Just as the swimmer focuses on minimizing resistance, cyclists do the same on the road to gain an edge in competitions.

So just normal to that components we can say that is that lift okay. So if in a flow directions okay this is the flow directions in these directions If there will be a force acting this because of the boundary layer formations because of the pressure difference all details we are not going it which we already discussed in boundary layer concept.

Lift is created as a result of pressure differences in fluid flow over an object. It occurs perpendicular to the direction of motion and is influenced by the shape of the object and how well it disrupts the fluid’s boundary layer. This concept is crucial for understanding how wings of aircraft generate lift.

When an airplane takes off, its wings are designed to create lower pressure on top and higher pressure below, allowing the plane to rise. This is similar to how a bird flaps its wings to generate lift against gravity.

So as you know it, how the boundary layer formations happens, how the flow separation happens, all we discuss in the class in boundary layers. The component of the pressures and the wall strips in the direction normal to the flow tend to move the body in that directions. Their sum is called the lift.

The coefficient of drag (Cd) relates the drag force to the dynamic pressure and frontal area. Form drag, which is a type of drag, is influenced by the shape of the object and how it interacts with the flow of fluid. Understanding these concepts is essential for engineers designing structures that need to withstand wind forces.

Consider designing a tall building. Architects must choose between circular or rectangular designs based on which shape has a lower Cd, meaning less drag force against the building's structure during high winds, similar to how aerodynamic cars are designed.

More details you can understand it in higher classes but if you look at the wind turbines you can talk about the cyclist, we talk about swimmers or you talk about any gymnastics okay. If you just look at the beautiful part of the gymnastics that he here trains himself with a lift and drag force such a way that he knows that how to change the body shapes, and also the wind speed such a way that he can really perform these gymnastics very well.

The principles of drag and lift apply not only in engineering applications like wind turbines but also in sports scenarios. Athletes often train to optimize their form to maximize lift and minimize drag, which can significantly enhance their performance in various sports.

Think of a high jumper who arches their back while going over the bar. This arching isn't just about style; it minimizes drag and maximizes lift, allowing them to jump higher—the same principles are at work in various athletic disciplines.

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