"INTRODUCTION The pressure loss caused by a body obstructing a duct or pipe can be estimated from a knowledge of the drag force on the body. However@ the presence of the duct or pipe walls confines the flow around the body and increases the drag force on it above the value applicable to unconfined flow or ""free-air"" conditions@ which is the value that is usually known. This Item gives values of a correction factor ??(based on wind-tunnel blockage correction data from Derivation 8)@ and ""free-air"" drag coefficients (based on data from Derivations 1 to 7) from which the pressure loss can be estimated for a range of body shapes as shown in Tables 6.1 and 6.2. The drag force on the body can also be estimated if required. The Item is applicable for incompressible flow of gases@ and for liquid flow in which cavitation does not occur@ at Reynolds numbers. Ref@ greater than about 103. The uncertainty in the accuracy of pressure losses estimated using this Item cannot be quantified. However@ except at low blockage ratios ( S/A<0.05)) it will be greater than for pressure-loss data derived from direct pressure difference measurements in duct or pipe flows@ such as the data presented in other Items in the Internal Flow Sub-series. Some of the factors contributing to the uncertainty and their contribution to blockage effects are briefly discussed in Appendix A."
ESDU 81021-1981 history
1981ESDU 81021-1981 PRESSURE LOSSES CAUSED BY OBSTRUCTIONS IN DUCTS AND PIPES