Measuring and testing – Fluid flow direction – Relative to aircraft or watercraft
Patent
1999-01-26
2000-05-23
Oen, William
Measuring and testing
Fluid flow direction
Relative to aircraft or watercraft
A63B 5300, G01P 1300, G01W 100
Patent
active
060653345
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an device according to the preamble of claim 1.
A device of this type is disclosed in report IW-94079-R of August 1994 by the Institute for Wind Energy, the Technical University of Delft, entitled: `Visualisation of the Stagnation Point: First Results of a new Method`.
In this report it is proposed to fit one or more flaps, each having a width of approximately 1 metre, at the front, that is to say the zone close to the stagnation line (that is to say the stagnation point where flow ceases), of a wing-like surface. Such flap or flaps is/are fitted at an angle with respect to the so-called stagnation line and is/are of a width such that the stagnation line remains between the ends of each flap for all positions to be expected and certain conclusions relating to the flow are drawn from the shift in the turn-over point along the flap surface.
A construction of this type replaces constructions known in the prior art consisting of a number of preferably woollen threads, or jetting smoke or the like in the vicinity of the surface. Such a change has been made in particular because, especially when woollen threads are used on relatively large surfaces, the visibility of the position of the threads constitutes a problem.
If, for example, it is desired to obtain a general impression of the flow distribution in the case of wind turbines, it is not uncommon to take photographs thereof from a distance of 75 metres away from the vanes thereof. Small woollen threads are not visible on these photographs. Visibility remains poor even if use is made of technically sophisticated aids, such as stroboscopes. Large threads are influenced to a greater extent by the centrifugal force and give more flow disruption. Under certain flow conditions, the threads make rapid fluttering movements. As a consequence of this, blurring due to movement can become so severe that the position of the threads becomes invisible.
For these reasons electrical devices for rendering the flow direction visible by electrical means have been proposed in the prior art. However, these devices require vulnerable electrical connections for the power supply or signals. Moreover, these can affect the flow. An appreciable installation space in the object to be studied is also required. Consequently a long preparation time is necessary and the construction of the object can be weakened and a method of this type cannot be used in all locations.
This still takes no account of problems such as lightning strikes. Finally, woollen threads tend to be influenced by centrifugal force, that is to say to move outward.
The flap according to the abovementioned report solves these problems due to the effect of centrifugal force and the electrically complex construction.
However, visibility remains a problem at greater distances. After all, with a flap height of, for example, 5 mm it will be not be simple to detect (partial) turning over from a distance of a few tens of metres. The position at which the flap points towards the observer is visualised and, as a result, this position is dependent on the direction from which the observer views the flaps. This gives rise to systematic errors. The flap surface is stretched relatively severely close to the turn-over point for each flap. This is a disadvantage because permanent deformation can occur and because rapid response of the flap to a different flow condition is hindered by the hysteresis of the flap material. Moreover, the region close to the turn-over point is virtually perpendicular to the profile and, as a result, can easily give rise to flow disruption.
This problem is exacerbated when stalling is found. After all, the transition from one state to another then takes place gradually over a larger region.
The aim of the present invention is to avoid this disadvantage and to provide an improved device for detecting and rendering visible the fluid over a surface.
This aim is achieved with a device as described above having the characterising features of claim 1 or 2.
`Optically covered` is alwa
REFERENCES:
patent: 4567760 (1986-02-01), Crowder
patent: 4730488 (1988-03-01), David
U. Herzke et al., "Visualisation of the Stagnation Point: First Results of a New Method", 7 pages, TU Delft, Institute for Wind Energy, Aug. 1994.
Oen William
Stichting Energieonderzoek Centrum Nederland
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