2. in orifice meters, a flat disk with a central opening of diameter do is set across a pipe of diameter d, and the pressure drop is p across the opening is measured. it is postulated that p is a function of the average fluid velocity in the pipe v, the density of the fluid , the fluid viscosity , and the diameters of the pipe and the opening, d and do, respectively. thus, p = (v, , , d, do) find an acceptable set of dimensionless groups which relate these various factors.