The diagrams below show a holographic interferogram of a model of a power station cooling tower.
This demonstrates how an aerodynamic force acting at the top of the tower created the rotation and eventual catastrophic failure of the whole concrete structure.
Holographic Flow Visualisation
Vibrations Experienced by a RB211 1st Stage Compressor Fan
A series of experiments were performed on a RB211 first stage fan. In this case a stationary fan was 'shaken' by attaching a vibrator to a particular blade. The result shows how a resonance effect may occur. The results of these tests were later developed for a rotating blade assembly. They were also used to compare the calculated deflection of the blade assembly with that measured from the holograms.
A three dimensional holographic camera has been constructed to visualise the shock structure found within the first compressor stage of a gas turbine engine. The holograms show the position of the shock. Currently a new configuration of this camera was eventually constructed at Warwick University.
The arrow in Fig.1 points to the 19mm diameter negative lens through which the sample beam of ruby laser was expanded. The opposite side of the casing has been painted white to diffuse and reflect the laser light.
Holographic Visualisation of a Turbine Blade
These holographic visualisations were made using a two dimensional turbine cascade. The picture shows the density gradient around the turbine section as it accelerates from a near stationary point until it reaches transonic speeds at the trailing edge of the blade. The position of the shock waves in the cascade has been visualised as a rapid change in density. It is now possible to make similar three dimensional velocity measurements using other optical diagnostic techniques such as PIV (Particle Image Velocimetry).
More Examples of Holographic Interferometry
Supersonic flow around an isolated airfoil, visualization of constant density lines by Laser Holography. Image produced by Laboratoire de Thermique Appliquee et de Turbomachines, EPF - Lausanne.
The interferogram in the centre shows the flow from the exit of a model gas turbine engine mounted on a wing. The interferogram shows the jet core as it exits from the engine and passes under the wing surface. This technique demonstrates how the unsteady forcer experienced between the engine and wing can be visualised.
Interferogram visualising a supersonic flow approaching a wedge. The strong discontinuities in the fringe pattern show existence of shock waves in the flow field. The shock wave represent a viscous loss in the efficiency in the flow. The flow also shows in detail how the air finds its way around an object at supersonic speeds. As a consequence of the confidence created by this and many similar comparisons between measurement and theory it is now possible to make full three dimensional viscous calculations of this highly complicated flow.
A joint programme has been successfully completed with a US diesel engine manufacturer to visualise the diesel jet spray pattern. This figure is taken from a video print showing the spray pattern
Density gradient within a supersonic boundary layer Ma.=2.5. The
interferogram was formed by taking one exposure before the tunnel ram, the
other during the run on the holographic plate.
Interferogrametric visualisation of a subsonic karmen vortex structure made in the trailing-edge region of a two-dimensional model steam turbine blade at Ecol Polytechnique Federale de Lausanne (EPFL).
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