Flow straighteners are arrays of narrow ducts placed in wind tunnels to remove swirl and other in-plane secondary velocities. They can be idealized as square boxes constructed by vertical and horizontal plates, as in Fig. P7.28, the cross section is a by a, and the box length is L. Assuming laminar flat-plate flow and an array of N × N boxes, derive a formula for
(a) The total drag on the bundle of boxes and
(b) The effective pressure drop across the bundle.

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