Impingement pressure characteristics of swirling and non-swirling turbulent jets

For low swirl flows, the coefficient of pressure (Cp) shows a non-swirl like behaviour with maxima at the stagnation point. For medium-to-high swirls, maximum Cp shifts radially outward from the stagnation point and becomes relatively flat with increasing S. The stagnation pressure reduces nonlinearly with increasing swirl intensity and follows a quadratic relationship for a given Re. For any S, the pressure distribution is found to be independent of Re for low swirl numbers (up to S = 0.3), but it varies up to r/D = 2 for larger swirl numbers. A negative Cp (flow separation) occurs near the stagnation region for H = 1D, however, vanishes at larger H. For very high swirl number (S = 1.05) and at H = 1D, three different regions are recognised on the impingement surface from the stagnation point: a rotating, reversed inward flow at r/D ⩽ 0.5, a transition and less stable region at 0.5 < r/D ⩽ 0.75 and an outward flow with stronger tangential component at r/D ⩾ 1.0. These surface pressure results may significantly affect the heat transfer characteristics as well as wall shear stresses for future impinging jet studies.