Flow Through a Convergent Nozzle — Lesson 2

This lesson covers the concept of flow through a convergent nozzle, which can be established in two ways: by pulling or pushing the flow through the nozzle. The lesson explains the process of pulling the flow, where the upstream stagnation conditions are fixed and the downstream ambient pressure is varied. It also discusses pushing the flow, where the ambient pressure downstream is fixed and the inlet stagnation condition is varied. The lesson further elaborates on the concept of sonic speed, under-expanded and over-expanded flow, and the impact of these conditions on the nozzle's performance. For instance, in propulsion applications, a convergent-divergent nozzle is used to prevent loss of thrust due to external expansion.

Video Highlights

01:40 - Discussion on the isentropic process in the nozzle
04:13 - Explanation of how to increase the stagnation pressure
06:44 - Explanation of how the fluid reaches the sonic state at the exit of the nozzle
14:48 - Explanation of how the jet diameter is constant when the flow is correctly expanded
18:40 - Explanation of why propulsion applications tend to have convergent diversion nozzles

Key Takeaways

- Flow through a convergent nozzle can be established by either pulling or pushing the flow.
- In pulling the flow, the upstream stagnation conditions are fixed and the downstream ambient pressure is varied.
- In pushing the flow, the ambient pressure downstream is fixed and the inlet stagnation condition is varied.
- The flow through the nozzle can reach sonic speed under certain conditions.
- The flow can be under-expanded or over-expanded, affecting the nozzle's performance.
- In propulsion applications, a convergent-divergent nozzle is used to prevent loss of thrust due to external expansion.