Wind Tunnel Design Basics - Supersonic Wind Tunnels — Lesson 4

This lesson covers the detailed understanding of supersonic wind tunnels, focusing on the intermittent blow-down type tunnel and its components. It explains how the tunnel operates, the role of the compressor, the storage tank, and the significance of the Converging-Diverging (CD) nozzle in accelerating the flow to supersonic speeds. The lesson also discusses the challenges of maintaining a normal shock at the end of the tunnel and the benefits of using a supersonic diffuser. It concludes with a brief overview of a continuous closed circuit supersonic wind tunnel. For instance, to achieve a Mach 2.5 flow, a pressure ratio of 17.09 is required, which can be challenging and expensive to maintain. However, by using a supersonic diffuser, this pressure requirement can be significantly reduced.

Video Highlights

00:52 - Explanation of the process of running the compressor and filling up the storage tank.
05:13 - Explanation of the process of creating a supersonic free jet exhausting into the atmosphere.
14:35 - Discussion on the problems associated with having a normal shock at the end of the constant area section.
26:33 - Introduction to the concept of a continuous closed return supersonic wind tunnel.

Key Takeaways

- Supersonic wind tunnels, specifically the intermittent blow-down type, are complex systems comprising a compressor, storage tank, and a Converging-Diverging (CD) nozzle.
- The CD nozzle plays a crucial role in accelerating the flow from near stagnation conditions to supersonic speeds.
- Maintaining a normal shock at the end of the tunnel can be challenging due to instabilities causing the shock to move and fluctuate constantly.
- The use of a supersonic diffuser can significantly reduce the pressure requirements, making the operation of the tunnel more efficient and cost-effective.
- Continuous closed circuit supersonic wind tunnels offer an alternative solution, allowing for longer duration runs.