welcome to aerodynamics this is a field that has existed for thousands of years since humans started designing wind-driven sailboats and chased the aspect of flight this course will serve as an introduction to all things aerodynamics covering the basic fluid dynamics principles modern modeling techniques and application the word aerodynamics comes from a combination of the greek prefix arrow meaning air and dynamics which is the study of motion due to forcing put simply this is the study of how air moves around objects and forces them from a theoretical mechanics perspective aerodynamics is a subset of fluid dynamics which is the study of how all fluids move due to forcing from an engineering perspective aerodynamic serves as the foundation of aerospace engineering both aeronautics and astronautics which is a field that specializes in the development of aircraft and spacecraft people that specialize in aerospace engineering are usually familiar with aerospace materials flight mechanics aero elasticity and propulsion among other things for those of you familiar with fluid mechanics your first question might be why just air doesn't what we learn in fluids apply here of course it does the theory behind fluid mechanics does not change when we specifically focus on air but there are reasons for the distinction due to the composition of the planet throughout history humans have learned to traverse through two major fluids air is the dominant gas and the study of air is aerodynamics water is the dominant liquid and the study of how water moves is hydrodynamics the fundamental equations are the same there is no difference in the conservation of momentum for water and air however water comes with the added benefit of being assumed incompressible meaning the density is constant everywhere in the field and that significantly simplifies the math error however is often compressible especially in high speed flight and this can make the math more difficult and causes us to need more equations like the conservation of energy in the equation of state to find all the variables second water is quite heavy compared to air this means that in order to be held up in the water it is easier to use the buoyancy force but in order to stay up in air we need to generate a vertical force which is known as lift think of it this way a neutrally buoyant fish really needs to only worry about using its fins to move forward a bird however needs to worry about generating lift to stay up while simultaneously generating force to move forward so these unique aspects of moving through air and the usefulness of air transportation are the reason we have specific courses dedicated to it and once you've learned aerodynamics there's a ton you can do with it obviously aerodynamics experts are needed in the design of aircraft commercial aircraft uncrewed area vehicles fighter jets all foundationally operate on aerodynamic principles automobiles heavily rely upon lowering air resistance to decrease fuel consumption or improve race time rockets and ballistics often reach hypersonic speeds and rely on aerodynamics to know where they are going and to get there accurately aerodynamic forces show up in countless sports including the cycling to lower air drag or golf and baseball to manipulate the flight dynamics of the ball some people use aerodynamics to save the planet by designing technologies to harvest wind energy and lastly in order to get to the vacuum of space you have to travel through the atmosphere which can be tough with such high altitudes and low air density so knowing and specializing in aerodynamics opens up a wide variety of interesting career opportunities now that i've hopefully convinced you we should want to study aerodynamics how do we do it specifically let's consider how studying aerodynamics is different than how we would approach fluid mechanics let's consider an object in an airflow in this case an airfoil first aerodynamicists are generally concerned with the global body forces that the flow causes consider the way a fluid mechanism would study this type of flow they would be very concerned with defining the exact flow field as it develops over the object in general they would seek a mathematical definition of the entire flow and aerodynamicists would approach things a bit differently their primary concerns are the body forces produce things like the overall lift and drag the moments produced specifically if body forces are generated from away from the center of gravity and the pressure distributions that produce these body forces and moments in order to get to these body forces you do need to know something about the flow itself but you can do more estimating and modeling to predict these forces as a result aerodynamics is much less exact than how we approach fluid mechanics in fluid mechanics the conservation equations are solved exactly or approximately given a very simple geometry like a channel a pipe or a flat plate boundary layer in aerodynamics we generally can't arrive at exact solutions the geometries are much more complex there are a wide variety of airfoils of arbitrary shape spheres with three-dimensional separation and a wide array of ground vehicles that can change the flow behavior so we do a lot more looking things up in documented tables that have empirical values for example let's say we have a plane flying at some velocity and angle of attack that we know how could we know what lift it's generating and making sure it can stay in flight in this case there's way too much going on to solve the flow field everywhere so what we do is we mark down the meaningful parameters like flow speed angle of attack and what type of airfoils we're dealing with then i take out a reference that has pages of tables where people have documented what forces they found when they put an object like this in the flow you then find the table with the parameters that matter for you like the airfoil type and flow speed and you look up the approximate lift you would expect to see at that angle of attack with some work you can then apply this to the entire plane and ensure that your lift is sufficient to maintain flight while we care about the body forces generated by the flow we're also interested in the entire force balance of a vehicle much like a free body diagram when an object like a plane moves through the air it experiences a number of forces in various spots generally our goal is to move steadily meaning no acceleration or deceleration in any direction in order to maintain steady flight we need to counter the forces from the air consider a wing attached to a plane as the plane moves through the air it experiences lift which is perpendicular to the flow velocity in order not to fall out of the sky the lift must equal the vehicle weight similarly the air force along the flow direction is the drag force to counter the drag we need thrust often the thrust is produced by a turbine a propeller or burning propellant if the drag and thrust are not equal we either speed up or we slow down in the flow direction additionally the central location where the body forces act on the foil can change depending on the flow conditions this causes issues because then the lifting force produces a moment about the plane center of gravity inducing rotation if we want to maintain steady flight and not do backflips we need to create a force that counters this moment which can often be done at the tail of the aircraft the tail has a different airfoil with different lift force so you can see how aerodynamicists need to know a bit about the fluid mechanics but they also need to keep the forces on the entire vehicle in the back of their mind as they do their analysis and finally in aerodynamics we end up needing to solve for more flow variables the velocity field and the pressure field are the main players in introductory fluid mechanics courses in order to solve for the velocity and pressure the two unknowns you need two equations which end up being conservation of mass and momentum for the majority of fluid mechanics until you explore compressible flow that's about it however in aerodynamics we often need a few more flow variables especially in high speed or high altitude flight first the density in air can vary a lot more easily than it can with other fluids so that means we have an additional variable to solve for and need another equation this equation is generally the conservation of energy unfortunately when we introduce this new equation we get more unknown variables specifically we add in the unknown of internal energy and temperature two more unknowns means needing two more equations and that leads us to the equation of state in the perfect gas equation in the end we have five unknowns and five equations and solving for all of the unknowns becomes a bit more difficult outside of the equations it's important to note that from an engineering perspective knowing the temperature in a lot of aerodynamic vehicles is absolutely critical re-entry vehicles get super hot so hot in fact that we have to design specific lightweight materials that don't disintegrate so knowing the max temperatures we can expect tells us how to design the vehicle and better predictions lead to more efficient and cost effective designs to summarize in aerodynamics we take a slightly different perspective than we did in fluid mechanics we focus a bit more on the body forces generated by the fluid and oftentimes these bodies have complex geometry then once we know about the aerodynamic forces we need to think of the vehicle as a whole and consider a force balance to maintain steady flight we use previous observations to tell us about the forces we can expect because more often than not we can't solve for the flow field entirely and we often have to work with more variables than we did in fluid mechanics and more equations to solve for those variables so that wraps up the first lecture i hope you enjoyed it and now we can put our aerodynamicist hats on and move forward i'll see you next time