The inlet air velocity for a turbojet engine refers to the speed of the incoming air at the entrance of the engine’s inlet. In a turbojet engine, air is compressed, mixed with fuel, and burned to produce high-speed exhaust gases. The nozzle at the rear of the engine accelerates these gases, creating thrust.
The continuity equation is based on the principle of conservation of mass, stating that the mass flow rate remains constant in an incompressible flow. For a turbojet engine, this means that the mass of air entering the engine is equal to the mass of exhaust gases leaving it.
The continuity equation is based on the principle of mass conservation, and Bernoulli’s equation expresses the conservation of energy.
The continuity equation is given by:
where:
-  and  are the cross-sectional areas at the nozzle entrance and exit, respectively,
-  and  are the velocities at the nozzle entrance and exit, respectively.
which gives
where,
- A1 is the Cross-Sectional Area of Nozzle Inlet in m2
- A2 is the Cross-Sectional Area of Nozzle Exhaust in m2
- V1Â is the Inlet air Velocity in m/s
- V2Â is the Exhaust Air Velocity in m/s