Digital Schlieren for Flow Visualization in Hypersonic Wind Tunnels

Schlieren visualization, an important imaging method in aerodynamic testing for viewing density gradients caused by turbulence, shock waves, and temperature gradients, has seen few changes in over 100 years. The schlieren systems at AEDC, with near-perfect optics and vibration isolation, are extremely sensitive when properly aligned, which also makes existing systems difficult and expensive to use and maintain. The age of digital and computational optics produced a revolution in this technology, removing limitations, expanding capability, and enabling new, improved methods. The MetroLaser/Spectabit team, building upon new digital schlieren system research and commercialization proposes to incorporate the new technology into the AEDC schlieren capability. Our overall objective is to update and add to the schlieren technology currently existing in Von Karman Gas Dynamics Facility (VKF) tunnels by integrating methods made available with new age digital optics, beginning with designing and installing a direct, flexible, optical interface with digital cameras to replace existing frosted glass imaging interfaces. The updated interface will open the way for employing many other types of cameras, lighting, and software solutions. In addition, we propose to examine other digital schlieren, optical configurations that can add to the facility capability. We will develop and install a high-speed digital schlieren system that can demonstrate the technology to replace or augment the existing schlieren systems. An optimal digital schlieren system has the potential to provide improved, more useful, and easier to use schlieren data for AEDC customers. Such data could enable more detailed visualization of boundary layer turbulence, shock layers, shock-boundary layer interactions and locations of interesting aerodynamic flow features. Other potential benefits are better flexibility in data output such as variable sensitivity, focusable fields, higher speed video, better temporal resolution. The proposed work will consist of adaptation of MetroLaser’s patented digital technology using new age digital optics, illumination sources and high-frame rate cameras for application to the AEDC wind tunnels. Further, the research will determine and select optimal components to satisfy the digital schlieren design for potential implementations for wind tunnel flow visualizations in a potential Phase II program.