Bleed Tapping

A bleed tapping device is a special kind of orifice (Figure 77), used to divert part of the main stream flow. The geometry can be quite complicated and the discharge coefficient should be ideally determined by experiments on the actual device.

Figure 77: Geometry of the bleed tapping fluid section

The discharge coefficients provided by CalculiX are merely a rough estimate and are based on [35]. For this purpose the bleed tapping device must be described by the following constants (to be specified in that order on the line beneath the *FLUID SECTION, TYPE=BLEED TAPPING card):

• the cross section $A$.
• the ratio of the upstream static pressure to the upstream total pressure $p_{s_1}/p_{t_1}$.
• the number of a curve.

Right now, two curves are coded: curve number 1 corresponds to a tapping device with lip, curve number 2 to a tapping device without lip. More specific curves can be implemented by the user, the appropriate routine to do so is cd_bleedtapping.f. Alternatively, the usr can enter an own curve in the input deck listing $Y=C_d$ versus $X=(1-p_{s_2}/p_{t_1})/(1-p_{s_1}/p_{t_1})$. In that case the input reads

• the cross section $A$.
• the ratio of the upstream static pressure to the upstream total pressure $p_{s_1}/p_{t_1}$.
• not used
• $X_1$.
• $Y_1$.
• $X_2$.
• $Y_2$.
• ..