Unsteady flow in hydraulic turbomachinery generates hydrodynamic pressure fluctuations that are relevant both to acoustic emissions and to the structural excitation of the machine. How hydraulic efficiency, off-design flow topology and fluid-induced source mechanisms relate remains incompletely characterized, yet is central to pump design and operation. This work investigates the fluid-side source mechanisms in a semi-axial multistage pump through unsteady Reynolds-Averaged Navier–Stokes simulations at two rotational speeds (50 Hz and 75 Hz) spanning twelve operating points. Fluid-induced source terms are extracted using two complementary formulations: Lighthill’s quadrupole term and the Perturbed Compressible Equations (PCE). A new volume-averaged metric, the Average Volume Noise (AVN), is introduced to quantify the intensity of the hydrodynamic acoustic-source field. Results show that source intensity exhibits a distinct minimum at the best efficiency point and increases asymmetrically off-design: at high flow coefficients, AVN rises sharply due to stator separation and vortex shedding; at low flow coefficients, the increase is milder, dominated by rotor recirculation. When non-dimensionalized, AVN curves for both speeds collapse onto a single trend versus a non-dimensionalized discharge ( ϕ ), indicating that flow-induced source intensity scales with the same similarity parameter governing hydraulic performance. These findings provide a physically grounded framework for relating operating condition, flow topology and fluid-side source strength in semi-axial turbomachinery, relevant to subsequent vibro-acoustic and fluid-structure-interaction analyses.
Montillo et al. (2026) studied this question.