Recent Advancements in the Infrared Flow Visualization System for the NASA Ames Unitary Plan Wind Tunnels

Abstract

The following details recent efforts undertaken at the NASA Ames Unitary Plan wind tunnels to design and deploy an advanced, production-level infrared (IR) flow visualization data system. Highly sensitive IR cameras, coupled with in-line image processing, have enabled the visualization of wind tunnel model surface flow features as they develop in real-time. Boundary layer transition, shock impingement, junction flow, vortex dynamics, and buffet are routinely observed in both transonic and supersonic flow regimes all without the need of dedicated ramps in test section total temperature. Successful measurements have been performed on wingbody sting mounted test articles, semi-span floor mounted aircraft models, and sting mounted launch vehicle configurations. The unique requirements of imaging in production wind tunnel testing has led to advancements in the deployment of advanced IR cameras in a harsh test environment, robust data acquisition storage and workflow, real-time image processing algorithms, and evaluation of optimal surface treatments. The addition of a multi-camera IR flow visualization data system to the Ames UPWT has demonstrated itself to be a valuable analyses tool in the study of new and old aircraft/launch vehicle aerodynamics and has provided new insight for the evaluation of computational techniques.

A Qualitative Investigation of Selected Infrared Flow Visualization Image Processing Techniques

“…An image processing routine must enhance features of interest with minimal artifacts. Additionally, the production wind tunnel test environment demands that these processed images are made available in a real-time, automatic fashion [1,4]. Therefore, any image processing routine must be computationally economical and enhance the image data with minimal input from a human operator.…”

“…There are several implementations of this method, some reduce noise in uniform regions by limiting contrast, CLAHE, but most reduce compute time by equalizing within fixed sub regions and interpolating look-up-table values between [5,6,7]. With high dynamic range images, the interpolated AHE implementations can cause artifacts in regions with sharp pixel value gradients [1]. The implementation of AHE discussed here is non-interpolated (the equalization sub windows are convolved pixel by pixel across the entire image) to avoid these artifacts.…”

“…he deployment and integration of high-sensitivity infrared (IR) cameras in a transonic wind tunnel test environment has resulted in a unique capability to image aerodynamic phenomena in real-time. Multi-camera IR flow visualization data systems are now routinely utilized [1] at the NASA Ames Unitary Plan Wind Tunnel (UPWT). The small flow-induced temperature gradients on the surface of the wind tunnel test article coupled with the high bit-depth of the IR camera sensor makes the processing of the image data critically important.…”

Investigation on Transition Characteristics of a Modified RAE5243 Airfoil

“…Many aerodynamics research institutions have regarded infrared thermography as the primary technique for surface flow regime observations and temperature field measurements. The NASA Ames Research Center [19] utilizes infrared thermography to measure boundary layer transition, shock/boundary layer interference, and corner flow. However, it is not easy to use infrared thermography to detect transition locations in subsonic and transonic wind tunnel tests.…”