Pressure-sensitive paint
Encyclopedia
Pressure-sensitive paint (PSP) is a method for measuring air pressure, usually in aerodynamic settings. It is paint which fluoresces in differing intensities depending on the external air pressure being applied to its surface.
s. In these tunnels, models (usually subscale) are subjected to airflows to simulate an actual airplane in free flight. The aerodynamic forces acting on the model are measured, and are used to predict the response of an airplane when subjected to equivalent airflows.
Automobiles are also subjected to aerodynamic testing in wind tunnel
s. Automobile companies use data collected in these tests to measure areas of high and low pressure. This data helps engineers improve designs to increase performance for the vehicles. By changing these designs, engineers can help improve gas mileage and reduce noise.
In order to measure the aerodynamic forces on the whole model, beam balances
are connected to the model. However, it is also imperative to also understand how those forces are distributed across the aerodynamic surfaces of the aircraft, and this understanding is more difficult to obtain. The classic approach has been to drill small holes along the surface, and attach tubes (which run to manometers) to each hole.
The PSP is coming into use as a replacement for the hole-drilling methodology. It can be used to indicate the differing pressure across the aerodynamic surface, so that no holes or other measuring apparatus need be installed on that surface.
Time-resolved PSP applications involve pulsed excitation and delay and gating of the imaging devices. One can thus determine pressure differentials as a function of time. In this case, the imaging devices must be synchronized to the excitation. Multi-channel digital delay/pulse generators provide that synchronization.
Another area of interest has been the measurement of pressure in low-speed wind tunnels. This is possible with the application of PSP. Normally
. The binder is permeable
to oxygen
. This mixture is applied (by spray application) onto the test surface under controlled conditions. This is important because dirt in the paint causes the loss of a data point. When the model is being tested in the wind tunnel, ultraviolet light from a high intensity LED lamp is beamed onto the surface, and the molecules fluoresce in a visible light wavelength. The intensity of the visible light is proportional to the amount of oxygen above the coating. Higher pressures cause more oxygen molecules permiate the binder in the paint. The oxygen interacts with the flourescense in a process called quenching. The result is a dimmer phosporescence where there is high pressure. Photographs of the surface can be obtained from outside the wind tunnel's test section, which means that the model need never be disturbed or touched in order to obtain the pressure distribution. Computer-aided photography can be used to produce false-color images, where the color range corresponds to the pressure variations.
Where it is used
Due to the high cost of constructing airplanes, the first designs of proposed aircraft are usually subjected to aerodynamic testing in wind tunnelWind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
s. In these tunnels, models (usually subscale) are subjected to airflows to simulate an actual airplane in free flight. The aerodynamic forces acting on the model are measured, and are used to predict the response of an airplane when subjected to equivalent airflows.
Automobiles are also subjected to aerodynamic testing in wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
s. Automobile companies use data collected in these tests to measure areas of high and low pressure. This data helps engineers improve designs to increase performance for the vehicles. By changing these designs, engineers can help improve gas mileage and reduce noise.
In order to measure the aerodynamic forces on the whole model, beam balances
Weighing scale
A weighing scale is a measuring instrument for determining the weight or mass of an object. A spring scale measures weight by the distance a spring deflects under its load...
are connected to the model. However, it is also imperative to also understand how those forces are distributed across the aerodynamic surfaces of the aircraft, and this understanding is more difficult to obtain. The classic approach has been to drill small holes along the surface, and attach tubes (which run to manometers) to each hole.
The PSP is coming into use as a replacement for the hole-drilling methodology. It can be used to indicate the differing pressure across the aerodynamic surface, so that no holes or other measuring apparatus need be installed on that surface.
Time-resolved PSP applications involve pulsed excitation and delay and gating of the imaging devices. One can thus determine pressure differentials as a function of time. In this case, the imaging devices must be synchronized to the excitation. Multi-channel digital delay/pulse generators provide that synchronization.
Another area of interest has been the measurement of pressure in low-speed wind tunnels. This is possible with the application of PSP. Normally
How it works
PSP consists of luminescent molecules in a special binderBinder (material)
-See also:*Adhesive or Glue*Cement*Paint...
. The binder is permeable
Permeation
Permeation, in physics and engineering, is the penetration of a permeate through a solid, and is related to a material's intrinsic permeability...
to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. This mixture is applied (by spray application) onto the test surface under controlled conditions. This is important because dirt in the paint causes the loss of a data point. When the model is being tested in the wind tunnel, ultraviolet light from a high intensity LED lamp is beamed onto the surface, and the molecules fluoresce in a visible light wavelength. The intensity of the visible light is proportional to the amount of oxygen above the coating. Higher pressures cause more oxygen molecules permiate the binder in the paint. The oxygen interacts with the flourescense in a process called quenching. The result is a dimmer phosporescence where there is high pressure. Photographs of the surface can be obtained from outside the wind tunnel's test section, which means that the model need never be disturbed or touched in order to obtain the pressure distribution. Computer-aided photography can be used to produce false-color images, where the color range corresponds to the pressure variations.
Advantages
- The greatest advantage of the new technology is its much reduced preparation time compared to installing hundreds of pressure-conducting holes and tubes under the model's surface, as in the pressure tap system.
- The same model can be used for other testing, such as load-bearing tests or radar-reflection tests, since the PSP will not interfere with other preparations or setups.
- There are far more data points than other methods. There is a data point at every pixel instead of at every pressure tap.