Shock Waves on Transonic Airfoils: Pressure Distribution and Wave Drag

What the pressure plot does

Past the critical Mach number the upper surface carries a supersonic pocket. The flow returns to subsonic speed through a shock, unless the section is designed so the recompression is nearly isentropic, which is a special and fragile case. In the Cp plot the shock is a steep jump: suction collapses over a short distance. Ahead of the jump, Cp is more negative than the sonic value. Behind it, the recovery continues subsonically to the trailing edge. A supercritical section tries to keep that jump weak and far aft, after a long rooftop, instead of a strong jump right behind a nose spike.

The jump is a rise the boundary layer must climb. A weak shock may leave the layer attached. A stronger shock separates it. Shock-induced separation is the usual source of transonic buffet: the separation and the shock move, and the lift and moment oscillate. The buffet boundary on an airplane is a wing result, but the section shock is the seed.

Wave drag

A shock raises the entropy of the air that passes through it. In the force accounting that loss appears as a streamwise pressure drag, called wave drag. It is not skin friction, and it is not induced drag. It shows up in CD once the shock is strong enough to matter, which is the drag rise around Mdd. A method without a shock cannot report wave drag. It can only apply a correction that grows large and then becomes meaningless. An Euler solution can show the shock and a wave-drag-like pressure integral, and it still misses the viscous thickening that moves the shock. A viscous transonic solution is the first tool that has both the jump and the layer.

What to read off a transonic Cp curve

Quote Mach, CL and whether the solution was viscous. A shock location from an inviscid mesh and a shock location from a wind-tunnel oil-flow picture are allowed to disagree, and the disagreement is the boundary layer.

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Where this sits in the series

In simple words: what this page is for

A transonic shock is a sudden pressure rise on the upper surface. Wave drag is the momentum lost through that shock. If the rise is too sharp, the boundary layer separates and the moment breaks.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Shock Waves on Transonic Airfoils: Pressure Distribution and Wave Drag helps you keep a clean trail from shape to polar to choice.

Why the topic matters

Engineers lose time when a title sounds clear but the page only sketches the idea. This article expands Shock Waves on Transonic Airfoils: Pressure Distribution and Wave Drag so you can answer three questions without jargon: what is the idea, when do you use it, and how do you check it in a HENDOI product.

Read the sections above for the core definitions. Use the steps below to move from reading into a real project trail you can share with a teammate.

How to apply this in HENDOI

In practice: create a HENDOI account or log in, open HENFOIL, bring a section in (create, import DAT, or digitize), pass the geometry gate, climb the analysis ladder only as far as the decision needs, then compare and archive. Every calculated number should keep its method label.

When the section choice is ready for the aircraft, continue in HENSYNTH for mission, compliance and trades. Same account. Same plans.

What this page will not claim: a teaching polar or geometry note is not a flight-Re certificate. HENFOIL labels methods so you know what you bought. Tunnel data and professional judgement still sit outside any single software run.

Checklist before you leave this page

• Can you state the idea of Shock Waves on Transonic Airfoils: Pressure Distribution and Wave Drag in one sentence?
• Do you know which product owns the next action — HENFOIL or HENSYNTH?
• Will every number you keep carry a method label or a stored-run source?
• If you are new here, have you opened Register or Login?

Related reading on this site

• Active Flow Control on Airfoils: Suction, Blowing and Synthetic Jets
• How Adverse Pressure Gradients Affect Airfoil Boundary Layer Separation
• What Is the Aerodynamic Center of an Airfoil? Location, Meaning and Applications
• What Is Airfoil Aerodynamic Efficiency Across a Range of Flight Conditions?
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
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• Index: all HENFOIL airfoil lessons

These pages teach the ideas. They are not wind-tunnel data and not a certification analysis. When a number matters, compute it at a stated Reynolds number, Mach number and transition setting, and keep the method label on the result. In HENFOIL that production polar is a VIC polar — see the analysis ladder and the polar field guide.