A Review of Available Methods for the Assessment of Fluid Added Mass, Damping, and Stiffness With an Emphasis on Hydraulic Turbines

Abstract

Fluid added mass, damping, and stiffness are highly relevant parameters to consider when evaluating the dynamic response of a submerged structure in a fluid. The prediction of these parameters for hydraulic turbines has been approached relatively recently. Complex fluid-structure analyses including three-dimensional flow and the need for experiments during operation are the main challenges for the numerical and experimental approaches, respectively. The main objective of this review is to address the impact of different parameters, for example, flow velocity, cavitation, nearby solid structure, and rotational speed on the fluid added mass and damping of Kaplan/Propeller and Francis turbine runners. The fluid added stiffness is also discussed in the last section of the paper. Although studies related to hydraulic turbines are the main objective of this paper, the literature on hydrofoils is also taken into consideration to provide valuable information on topics such as individual runner blades. In this literature survey, the analytical, numerical, and experimental approaches used to determine fluid added parameters are discussed, and the pros and the cons of each method are addressed.

Added Mass Effects on a Francis Turbine Runner with Attached Blade Cavitation

“…Several works devoted to investigating the modal behavior and dynamic responses of hydraulic turbine runners both in air and water can be found in the literature based on FEM and AFSCM [4][5][6][7][8][9][10][11][12][13][14][15]. In all cases, the numerical results have shown a good agreement with the corresponding measured ones, which fully validates the feasibility of FEM and AFSCM for the current study.…”

“…Finally, the complete finite element discretized equations with assembled form expressed in Equation (14) can be used to solve acoustic fluid-structural coupling problems by considering Equations (12) and (13) simultaneously:…”

“…Many research works have been carried out to predict the dynamic behavior of Francis runners in air and still water based on both measurements and simulations in reduced scale models of Francis runners [10,11] and pump-turbines [12,13]. The final objective is to identify the natural frequencies and the damping ratios of the runner, taking into account the added mass and damping of the surrounding water, because it has been demonstrated that these effects can considerably affect the results [14]. Moreover, additional boundary conditions such as the proximity of walls can also influence the added mass effects, which have been investigated from simple structures like disks [15] to actual prototype structures [16][17][18].…”

The hydroelastic response of a surface-piercing hydrofoil in multiphase flows. Part 2. Modal parameters and generalized fluid forces

“…Robust predictions of the fluid forces in multiphase flows are lacking; thus potentially dangerous instabilities are difficult or impossible to predict with the theoretical or numerical tools presently available. A recent review by Dehkharqani et al (2019) summarizes the challenges facing experimentalists and numerical modellers seeking to quantify fluid forces on vibrating hydraulic systems, with an emphasis on turbine runner blades. Abramson (1969) succinctly summarized three characteristics of hydroelasticity that preclude the application of analyses from the more-mature field of aeroelasticity: the presence of a free surface, the presence of multiple phases (cavitation or ventilation) and low ratios of solid-to-fluid density (relative mass ratio).…”

An Indirect Measurement Methodology to Identify Load Fluctuations on Axial Turbine Runner Blades

“…Runner blades are subjected to two types of loading; static loading due to the turbine head and discharge passing through the turbine and dynamic loading produced by different dynamic phenomena such as rotating vortex rope (RVR), rotor-stator interaction, rotating stall, cavitation, and tip vortex [ 10 ]. These dynamic phenomena are influenced by the turbine operating point in which the contribution of each source on the runner dynamic response varies [ 11 ]. Therefore, dynamic load prediction on the runner is essential to avoid high-pressure fluctuations and mechanical resonance.…”