Civil Engineering Reference
In-Depth Information
Figure 7.8
Manifolds for pressure averaging.
Figure 7.8 shows the types of parallel tube and manifold arrangement that have been
commonly used in wind engineering work. Provided that the inlet tubes are identical in
length and diameter, such a system should provide a true average in the manifold, of the
fluctuating pressures at the entry to the input tubes, assuming that laminar flow exists in
them. Usually, flatter amplitude response curves to higher frequencies can be obtained
with the multi-tube-manifold systems, compared with single-point measurements using
the same tube lengths, due to the reinforcement of the higher frequencies in the input
tubes. However, once the number of input tubes exceeds about five, there is little change
to the response characteristics. The response is also not greatly sensitive to the volume of
the averaging manifold.
The assumption that the average of discrete fluctuating point pressures, sampled
within a finite area of a surface, adequately approximates the continuous average
aerodynamic load on the surface requires consideration (Surry and Stathopoulos, 1977;
Holmes and Lewis, 1987b).
Figure 7.9
Discrete and continuous averaging
of fluctuating pressures.
