We have devised a method and an apparatus for multidirectional flow speed measurement. The apparatus consists of a cylindrical container with a hemi-spherical cap at one end, a pressure transducer with a pair of pressure inlets, and a signal and data processing unit One of the pressure inlets is open to a cylindrical chamber; the pressure P_p at the center of the hemi-spherical cap is introduced in this chamber via a perpendicularly perforated hole. The second pressure inlet, which is the reference pressure inlet, is placed at a distance from the hemi-spherical cap in order to measure the static pressure P of the free air flow.The pressure transducer detects the differential pressure between the two inlets. The pressure difference thus detected is then converted to the wind speed U using the following relationship: P_p-P=(1/2)ρU²(1-C²), where C is equal to 1.5 for this particular apparatus. The method was tested in the field. The wind speeds U obtained from the proposed method were compared to the speeds measured with a standard propeller anemometer. A satisfactory agreement between the measurements and predictions from the above relation demonstrates the capability of the present method as a means of measuring the average speed of the flow of varying direction. When the cylindrical container is held parallel to the flow with the hole directed upstream, the constant C in the equation becomes zero, and the equation is reduced to the principle of the standard Pitot tube measurement. The flow sensor (probe) in the present method is robust because of its simple structure with no external moving parts. Thus, it is advantageous over conventional rotation meters in adverse conditions, for example, those in which heavy snowfall or freezing conditions could hamper the proper functioning of conventional instruments.

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[in Japanese]

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