Application of Reichardt's hypothesis for multiple coflowing jets

The efficacy of Reichardt's momentum transfer hypothesis for turbulent jets in a stagnant ambient is well documented. Application of the same hypothesis for a coflowing jet needs some modifications. Most integral methods assume the velocity excess and the concentration distribution to follow the normal distribution. In the modified approach, the distribution of uΔu is considered as Gaussian. This assumption is in consonance with the available data. The governing equation of motion being linear in uΔu, it provides the necessary theoretical basis for superposition. In applying the principle of superposition, a new characteristic width of the jet, b, is needed. The variation of b with x is non-linear and depends on the local flow conditions. Based on the modified large eddy hypothesis of spread and the conservation of the excess-momentum flux, the decay of the maximum momentum flux, umΔum, with distance x was computed for a single jet. Using the method of superposition, the velocity field and the dilution downstream of multiple round jets in coflowing streams have been predicted. Experimental data agree with the predictions based on the modified spread hypothesis and Reichardt theory.