The basic structure of vortex flowmeter
Published on：2014-12-17 8:54:29 Hits：
The basic structure of vortex flowmeter
In deriving the frequency and velocity relationship, use a stable condition Vortex: The spacing ratio h /, which shows the frequency of vortex generated by the impact of a certain space vortex structure, and spatial structure of the vortex and vortex shape about the body.
Further, in the preceding discussion, we should also note that:
① In the above derivation, are under the condition of the one-dimensional flow. However, the flow in the pipe, is a three-dimensional axisymmetric flow distribution.
② There upstream pipeline conditions exist, there will be an additional distortion of the velocity distribution, swirl, fluctuations instability.
These two will have a significant impact on the stability of the vortex and regularity. Therefore, within the vortex phenomenon found after a long time, has not been able to measure the flow rate, in addition to signal detection techniques, the above two points is important. In order to overcome the impact of these factors brought vortex shape must have certain requirements, so that the occurrence of vortex flow tube as close to the body of the two-dimensional flow, in order to control the three-dimensional vortex flow in the vortex phase body issued happen, so vortex line bending becomes minimal.
Thus, the shape of the vortex has a decisive influence on the issue vortex.
Basic Requirements 1. shaped vortex shedder
The shape of the vortex are already a variety of patterns occur, but they must have some of the same basic requirements:
① a blunt (ie non-streamlined) cross-sectional shape - this is the condition of a vortex;
② up and down the same cross-sectional shape and symmetrical - flow close to two-dimensional flow conditions;
③ boundary layer separation point is fixed - Strouhal number St constant conditions.
Meanwhile, the vortex of the mounting position in the pipeline must be strictly symmetrical. Upstream vortex D body must have more than 10 times straight, there must be five times the D downstream straight pipe.
2. The basic structure of the vortex
Vortex has a cylindrical shape, the triangle to, T-column, four corner posts, etc. The following describes both cylindrical and triangular prism type.
Body (1) cylindrical vortex
Content on the front part of the vortex theory is discussed as an example to the cylinder. Although this type of use earlier, but strictly speaking, at high flow rates it Strouhal number St is not stable. Therefore, it will be the improvement to open a slit or hole in the form of impulse.
Figure 3-9 cylindrical vortex generator Figure 3-10 capacitive triangular prism bluff body
1- pressure guide hole; 2- cavity; 3- wall; 4- platinum edge
Enlighten cylindrical hole pressure vortex generator shown in Figure 3-9. Because pressure guide hole exists, when the alternating vortex lift simultaneously emitted disturbs the flow of fluid through the pressure guide hole, generating a suction side, while blowing effect. When the fluid boundary layer separation is initiated in the cylindrical surface, in the suction side, separation is suppressed; in blown example, were isolated promotion occurs. This allows the fluid separation point position fixed, it can make the Strouhal number St is relatively stable.
Body (2) triangle columnar vortex
Currently used more vortex generating body is triangular prism shape, which shape is generally determined experimentally. It not only can be more intense than the vortex cylinder, and its boundary layer separation point is fixed, i.e. it Strouhal number St is relatively constant, about St = 0.16. Thus, the relationship between vortex frequency and flow rate was f = 0.16 u / d, where d is the width of the bottom edge of the triangular prism. Shape seen in Figure 3-10.
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