In flight mechanics, the term “instantaneous value” refers to a measurement or characteristic of an aircraft or its motion at a specific point in time. It represents the value of a parameter or variable at an exact moment during the flight, as opposed to an average or cumulative value over a period.
Instantaneous value= U-bar+u(t)
- “u-bar” (pronounced as “u-bar”): This term typically represents the steady or average velocity component of the airflow around an aircraft or an airfoil. It is also known as the freestream velocity or the undisturbed airspeed. The u-bar represents the mean or average airflow velocity and is used as a reference velocity in many aerodynamic calculations.
- “u(t)”: This term represents the fluctuating or perturbation component of the airflow. In fluid mechanics, the flow around an object is often composed of a steady component (u-bar) and small variations or disturbances (u(t)) from that steady state. These fluctuations in the velocity field are essential in understanding the aerodynamic behavior of the aircraft.