水洞中的流动可视化：观察三角翼前缘涡流

Delta wings have a small aspect ratio and high sweep angle, which reduce drag at high subsonic, transonic, and supersonic flight regimes. The aspect ratio is the wingspan divided by average chord length. These geometric features make delta wings ideal for high-speed aircraft where conventional rectangular wings would experience excessive drag.

Vortex lift occurs when a delta wing operates at higher angles of attack, causing flow separation at the leading edge rather than downstream. The roll-up of leading-edge vortices induces low pressure on the upper wing surface, creating a pressure differential that enhances lift. This mechanism allows delta wings to maintain lift at angles where conventional wings would stall.

Vortex breakdown occurs when adverse pressure gradients cause the leading-edge vortex to burst, eliminating its ability to induce low pressure. At low angles of attack, breakdown occurs downstream of the trailing edge. As angle of attack increases, breakdown moves upstream until it covers most of the wing surface, reducing lift and causing stall.

Dye containers connected to injection taps on the delta wing model disperse colored dye at different wing regions. By observing surface dye flow visualization qualitative method observe streakline patterns, researchers can track vortex development and identify the vortex core. Multiple colors enable simultaneous observation of vortex interactions across different wing sections.

Researchers measure the distance from the wing apex to vortex breakdown, labeled LB, at each angle of attack increment. This distance is expressed as a percentage of chord length from the trailing edge. By tracking how vortex breakdown location moves upstream as angle of attack increases, the stall angle can be estimated and wing performance characterized.

Aspect ratio, defined as wingspan divided by average chord length, is a key design parameter for delta wings. Delta wings have a small aspect ratio, typically half the root chord length, compared to rectangular or swept-tapered wings. This low aspect ratio contributes to reduced drag at high speeds and enables the enhanced lift characteristics that make delta wings suitable for transonic and supersonic flight.

In the water tunnel experiment, the delta wing experiences full stall at approximately 40 degrees angle of attack. At this attitude, vortex breakdown occurs at 96 percent of chord location from the trailing edge, nearly reaching the wing apex. This represents a total loss of lift as the leading-edge vortex can no longer sustain the pressure differential needed for enhanced lift.