A significant area of development in recent years has been around pressure-sensitive paint (PSP) technologies and techniques and as a result of this ARA has teamed with the US-based research and development company ISSI (Innovative Scientific Solutions Inc).
ARA has extensive PSP capabilities and test experience including:
- A large scale multi-camera ISSI Lifetime PSP System capable of capturing PSP images of a complex model for mapping to the 3D geometry for pressure and loads analysis.
- A Binary PSP system, ideal for low speed tunnels or smaller coverage in the ARA Transonic Wind Tunnel.
- A two camera High frequency PSP system for dynamic flows capable of capture at up to 10KHz (Dynamic PSP).
- Fast Responding PSP for capturing pressure distributions on fast moving objects such as rotating blades.
- Miniature PSP cameras for internal flow investigations such as cavities and nacelles.
Lifetime Pressure-Sensitive Paint (LPSP)
The ARA Lifetime Pressure-Sensitive Paint (PSP) system has been developed from the ISSI (Innovative Scientific Solutions Inc) PSP systems. ARA has developed a highly productive and flexible system that can offer simple visualisations of surface pressures up to fully calibrated pressure distributions mapped onto a 3D mesh. The ARA system is capable of providing full 3D coverage of complex wind tunnel models within the ARA Transonic Wind Tunnel (TWT).
The system has also been designed to be portable for use in other facilities, either at ARA or at customer sites. Academic papers on the application of this system in the ARA TWT are available from the document download area of this website. Lifetime PSP measurements are captured by taking two images, one of the direct illumination of the painted surface and the second capturing the emission from the paint during its decay period or lifetime. The surface pressure affects the intensity of the emission from the paint, these intensity variations can then be calibrated to real pressure values.
Binary Pressure-Sensitive Paint (BPSP)
As with the ARA Lifetime Pressure-Sensitive Paint (PSP) system, the Binary PSP system is based around the paints and associated technologies from the US company ISSI (Innovative Scientific Solutions Inc). ARA has experience with both systems in its own Transonic Wind Tunnel (TWT), as well as in other facilities and both are available for hire or demonstration purposes. ARA is also the sole European agent for these systems on ISSI’s behalf, providing paint, hardware and software as well as full system design, installation, training and support.
The main difference between the two systems is in the chemical property of the paints, with the Binary PSP having two luminophore components instead of the single luminophore found in the Lifetime PSP. This requires the signal and reference images to be obtained from the Red and Green emissions of the paint in order to capture the intensity variations caused by the surface pressure. This can be captured either by using a CCD camera and separating out the Red and Green channels or by using a monochrome camera with a filter wheel containing the appropriate filters.
Dynamic Pressure-Sensitive Paint (DPSP)
As with the ARA Lifetime Pressure-Sensitive Paint (PSP) system, the Dynamic PSP system is based around the paints and associated technologies from the US company ISSI (Innovative Scientific Solutions Inc). ARA has experience with both systems in its own Transonic Wind Tunnel (TWT), as well as in other facilities and both are available for hire or demonstration purposes. ARA is also the sole European agent for these systems on ISSI’s behalf, providing paint, hardware and software as well as full system design, installation, training and support.
The Dynamic PSP system is used to capture pressure changes due to either unsteady flow conditions or on fast-moving components such as propeller blades. This requires a paint with a response time significantly faster than the expected pressure change, as well as high power illumination and sensitive cameras with high frame rates and fast exposures.
The images show a sequence that was captured at 2KHz of a 50ms gust impacting the wing of a civil aircraft model in the ARA TWT operating at M=0.8. The gust was generated by the new gust generation rig recently developed for the ARA TWT. Dynamic PSP was used alongside more traditional wind tunnel data acquisition systems to provide verification of the gust rig’s capabilities.
Fast Response Pressure-Sensitive Paint (FPSP)
Fast response pressure-sensitive paint is used to capture the surface pressure on a moving object, such as a rotating blade. ARA uses the ISSI TurboFIB PSP which has a response time of <1-ms and a pressure sensitivity of 0.8% per kPa. The excitation range is between 380nm to 550nm and often a laser is used in order to get sufficient power into the paint.
Miniature Pressure-Sensitive Paint (MPSP)
Camera technology is rapidly advancing and smaller cameras used in the machine vision field have improved to the point that they can be effectively used for PSP. Along with the advances in LED design it enables areas that are normally challenging to access optically to be imaged.
ARA has tested several of these cameras in combination with new LED arrays to capture PSP for applications such as; comparisons with traditional PSP data on civil aircraft wings, internal PSP of weapons bay walls and PSP inside a thrust reverser engine model (in conjunction with Manchester University).
Photo showing PSP camera and LED setup inside a cavity research model, looking at the rear wall of the cavity. Data plot compares miniDPSP data with Kulite transducer data.