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Particle Image Velocimetry (PIV)
The original concept of PIV was to create a plane of light with a Nd/Yag pulsed laser and photograph the motion of particles within it.
The objective of the current work has been to image sub-micron particles so as to produce a whole-field visualisation of a transonic flow. The work is directed towards the development of a new type of optical diagnostic suitable for operation with a transient running blow-down transonic testing facility. The initial part of the study, completed at MIT 1989-90, has shown that it is possible to map, with an accuracy of 1%, flow through a normal shock disc of 2mm in diameter. The shock was generated by a 10mm diameter nozzle.
The technique has now been developed further, (at RAE) to measure a whole two-dimensional field, instantaneous quantitative map of the velocity and flow direction within a transonic annular turbine cascade. Experiments have shown that with the use of a diffraction limited optical system the low light levels which restrict the working distance associated with many conventional measurements do not apply in the application of PIV. Within a transonic wind tunnel at ARA (Aircraft Research Association, Bedford) it has been possible to use PIV to image 1 micron particles, travelling at transonic speeds, at a stand-off optical distance of 2.5m. This work is the result of innovative research performed by the Warwick Optical Engineering group.
Results have been obtained which show the following whole-field velocity data:-
The supersonic flow from a 10mm nozzle The transonic flow within the passage of an annular turbine cascade flow. The transonic flow around the leading edge region of a 1/20th scale wing at an optical stand-off distance of 2.5m. The visualisation of the fuel injection cycle of a diesel engine.
Turbulent Boundary Layer Flow
The free stream velocity and the Reynolds number are 12.65 ms-1 and 2.94 x104 respectivley. The flow media of the experiment was air.
Fig. 1 Turbulent boundary layer PIV picture.
Fig. 2 Raw sparse velocity vectors map.
2015 velocity vectors have been extracted by particle image tracking
Fig. 3 Instantaneous fluctuating velocity vectors map.
This was obtained by interpolating the random sparse velocity vectors in fig.2 and then subtracting the ensamble average velocity.
Fig. 4 Instantaneous vorticity map
Fig. 5 Instantaneous vorticity map overlaid with instantaneous fluctuating velocity vector map.
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