Generation of Polystyrene Latex Spheres with Incorporated Fluorescent Dyes

Instrumentation
Generation of Polystyrene Latex Spheres with Incorporated Fluorescent Dyes (LAR-TOPS-295)
Use in wind tunnel experiments to monitor airflow
Overview
Polymeric particles are used extensively for seeding airflows in wind tunnels, biological and histological staining, among other applications. For wind tunnel applications, particle image velocimetry is often used to determine the interaction of various models and surfaces with surrounding airflows. Measurements near the wall are particularly relevant and unfortunately exceptionally challenging due to the large level of background noise arising from reflection of incident light off the surface of the model being studied. Thus, the ability to seed the airflow with a material that can be used to accurately portray the airflow properties (i.e., minimal particle lag) while enabling near wall measurements with improved signal to noise ratio is of high interest to wind tunnel researchers.

The Technology
Although polystyrene microspheres are often the seed material of choice for subsonic airflow studies. These seed materials, however, do not provide any benefit for near wall measurements compared to other state-of-the-art seed materials. Consequently, in this innovation NASA scientists have developed this method of generating dye-doped polystyrene microspheres using novel synthetic approaches. The novel features of this invention are the utility of specific chemical functionalities, monomeric species, environmental additives (buffers), and polyelectrolytes to promote incorporation of dye molecules into developing polystyrene microspheres while enabling control of the spectral properties of the dye relative to pH dependence. These particles will have great utility for wind tunnel measurements near the wall where the state-of-the-art seed materials are not able to collect data. Additionally, the incorporation of these dyes will offer other avenues of data collection including temperature and pressure of the airflows and wind tunnel regions. Likewise, the ability to selectively filter the data collected from these dye-doped polystyrene microspheres can have further applications including the direct visualization of 2 or more fluid flows mixing, among other applications.
Laser air flow shown with micro-spheres. Image Credit: NASA
Benefits
  • Enables measurements closer to surfaces
  • Enables simultaneous measurement of velocity and temperature
  • Enables simultaneous measurement of pressure
  • Direct visualization of 2 or more fluid flows mixing

Applications
  • Seed materials for wind tunnel applications
  • Staining of histological or other biological sample
  • Time-delayed drug release
  • A broad variety of government-sponsored research projects and high impact academic research to new product development and process innovation in industry, across a wide variety of applications and disciplines
Technology Details

Instrumentation
LAR-TOPS-295
LAR-18344-1 LAR-18344-2
Similar Results
An aircraft design that could reduce fuel use, emissions and noise is set up for a test in a wind tunnel at NASA's Ames Research Center in California in which pink-colored pressure-sensitive paint is applied to the vehicle. The pink paint shines when exposed to blue light, glowing brighter or dimmer depending on air pressure in the area.
Calculation of Unsteady Aerodynamic Loads Using Fast-Response Pressure-Sensitive Paint (PSP)
Traditionally, unsteady pressure transducers have been the instrumentation of choice for investigating unsteady flow phenomena which can be time-consuming and expensive. The ability to measure and compute these flows has been a long-term challenge for aerospace vehicle designers and manufacturers. Results using only the pressure transducers are prone to inaccuracies, providing overly conservative load predictions in some cases and underestimating load predictions in other areas depending on the flow characteristics. NASA Ames has developed a new state-of-the-art method for measuring fluctuating aerodynamic-induced pressures on wind tunnel models using unsteady Pressure Sensitive Paint (uPSP). The technology couples recent advances in high-speed cameras, high-powered energy sources, and fast response pressure-sensitive paint. The unsteady pressure-sensitive paint (uPSP) technique has emerged as a powerful tool to measure flow, enabling time-resolved measurements of unsteady pressure fluctuations within a dense grid of spatial points on a wind tunnel model. The invention includes details surrounding uPSP processing. This technique enables time-resolved measurements of unsteady pressure fluctuations within a dense grid of spatial points representing the wind tunnel model. Since uPSP is applied by a spray gun, it is continuously distributed. With this approach, if the model geometry can be painted, viewed from a camera, and excited by a lamp source, uPSP data can be collected. Unsteady PSP (uPSP) has the ability to determine more accurate integrated unsteady loads.
Firefighters
Multi-Parameter Aerosol Scattering Sensor
Originally developed to demonstrate a highly accurate, low-false-alarm, early fire detection system in space, this advanced technology level system utilizes a durable, low-cost, compact laser source and detector array, similar to CD/DVD player technology, to analyze the interaction of light with particles. The smart system is ideal for detecting a diverse range of particles found in pollution, emissions, fire and other atmospheric toxins while introducing a flexibility that enables its use in multiple environments, especially when coupled with UAVs or other remote platforms. The MPASS contains a number of features that allow users to make the most of its pioneering capabilities. The self-contained system is lightweight and has been miniaturized and packaged to easily fit into the palm of your hand. A USB port enables the system to be powered, configured, and accessed through its onboard central processing unit. The advanced graphical user interface, custom software, and optimized algorithm allows the user to select known properties when applicable, and to program the system for maximum performance. The dashboard also provides visual feedback through graphical displays, making it easy to analyze the data and make real-time decisions. The system is designed with Bluetooth expansion capability, adding flexibility and communication through potential custom cellular phone applications. Once programmed, the battery-powered wireless sensor system opens the door to monitoring remote areas and extreme environments never thought possible.
Front Image
Airborne Background Oriented Schlieren Technique
This invention is an imaging method that requires very simple optics on an airborne vehicle, a camera with an appropriate lens, and an area on the ground that provides visual texture. The complexity with this method is in the image processing and not as much with the hardware or positioning, making Background Oriented Schlieren (BOS) an attractive candidate for obtaining high spatial resolution imaging of shock waves and vortices in flight. First, images are obtained of a visually textured background pattern from an appropriate altitude. Next, a series of images are collected of a vehicle in flight below the observer vehicle and over the same spot on the ground that serves as a background pattern. Shock waves are deduced from distortions of the background pattern resulting from the change in refractive index due to density gradients. The invention requires special software to create the schlieren images. The schlieren image is a contour plot of a two-dimensional data array of measured distortions, in pixel units. The results are used by researchers to help understand the flow phenomenon and compare to computational models. The BOS method also yields measured deflection distances, which can be used to determine the strength of a given density gradient. The system design and flight planning were based on the camera characteristics, airplane coordination, and airspace limitations.
Source is Free NASA Image library
Projected Background-Oriented Schlieren Imaging
The Projected BOS imaging system developed at the NASA Langley Research Center provides a significant advancement over other BOS flow visualization techniques. Specifically, the present BOS imaging method removes the need for a physically patterned retroreflective background within the flow of interest and is therefore insensitive to the changing conditions due to the flow. For example, in a wind tunnel used for aerodynamics testing, there are vibrations and temperature changes that can affect the entire tunnel and anything inside it. Any patterned background within the wind tunnel will be subject to these changing conditions and those effects must be accounted for in the post-processing of the BOS image. This post-processing is not necessary in the Projected BOS process here. In the Projected BOS system, a pattern is projected onto a retroreflective background across the flow of interest (Figure 1). The imaged pattern in this configuration can be made physically (a pattern on a transparent slide) or can be digitally produced on an LCD screen. In this projection scheme, a reference image can be taken at the same time as the signal image, facilitating real-time BOS imaging and the pattern to be changed or optimized during the measurements. Thus far, the Projected BOS imaging technology has been proven to work by visualizing the air flow out of a compressed air canister taken with this new system (Figure 2).
Image from internal NASA presentation developed by inventor and dated May 4, 2020.
Reflection-Reducing Imaging System for Machine Vision Applications
NASAs imaging system is comprised of a small CMOS camera fitted with a C-mount lens affixed to a 3D-printed mount. Light from the high-intensity LED is passed through a lens that both diffuses and collimates the LED output, and this light is coupled onto the cameras optical axis using a 50:50 beam-splitting prism. Use of the collimating/diffusing lens to condition the LED output provides for an illumination source that is of similar diameter to the cameras imaging lens. This is the feature that reduces or eliminates shadows that would otherwise be projected onto the subject plane as a result of refractive index variations in the imaged volume. By coupling the light from the LED unit onto the cameras optical axis, reflections from windows which are often present in wind tunnel facilities to allow for direct views of a test section can be minimized or eliminated when the camera is placed at a small angle of incidence relative to the windows surface. This effect is demonstrated in the image on the bottom left of the page. Eight imaging systems were fabricated and used for capturing background oriented schlieren (BOS) measurements of flow from a heat gun in the 11-by-11-foot test section of the NASA Ames Unitary Plan Wind Tunnel (see test setup on right). Two additional camera systems (not pictured) captured photogrammetry measurements.
Stay up to date, follow NASA's Technology Transfer Program on:
facebook twitter linkedin youtube
Facebook Logo Twitter Logo Linkedin Logo Youtube Logo