Oblique shock waves occur at an angle to the flow, compressing the fluid and increasing its density, pressure, and temperature, while reducing flow speed downstream. Expansion waves, in contrast, allow fluid to expand and accelerate without shock formation. The discussion highlights the relationship between shock waves and drag on aircraft, noting that oblique shocks convert kinetic energy into thermal energy, potentially increasing drag. The participant is researching how the speed of sound affects drag and has found resources like John D. Anderson's "Fundamentals of Aerodynamics" helpful. Overall, the conversation emphasizes the importance of understanding these concepts for aerodynamics research.
