Abstract: We consider stochastic (inviscid) fluid dynamical equations perturbed by multiplicative noise of transport type. Under a suitable scaling of the noises, we show that the solutions converge weakly to the unique solution of the deterministic viscous equation; moreover, stronger noise intensity gives rise to larger viscosity of the limit equation. Recent progress on quantitative convergence rates will also be mentioned. This talk is based on joint works with Professor Franco Flandoli and Lucio Galeati.