CFD modeling and simulation in hydraulics

Hydraulic modeling: definition

The term hydraulics refers to the study of liquids in the broadest sense. It has a number of industrial applications:

Free-surface hydraulics, relating to the study of flows where a marked liquid/gas interface exists, as in rivers and canals, for example,
Pipe flow, where the focus is on flow in closed conduits. Examples include water flow in the primary circuit of a nuclear power plant, or oil flow in a hydraulic distributor.
Hydraulic machines, exploiting the energy of pressurized liquids, notably for lifting systems

Hydraulic modeling aims to describe the flow in these different types of problem. Flow characteristics can be calculated mathematically using the Navier-Stokes equations. The system studied can then be recreated on a numerical model, and these equations can be solved to obtain the velocity, pressure, water head or turbulence of the flow at any point in space and at any time.

Depending on the problem, hydraulic modeling can be three-dimensional, two-dimensional or one-dimensional. 1D and 2D models are generally preferred for studying flood risks or river heights under different scenarios.

For systems that are spatially smaller but need to be characterized in greater detail, 3D modeling enables the precise description of the effect of geometric singularities, the interaction of the flow with its environment, and provides a complete overview of the problem. As a result, applications such as spillway design, dam penstocks and fish ladders, as well as sewage treatment plants and storm water basins, are made possible by hydraulic modeling.

CFD consultancy for the hydraulics sector

Hydraulics is one of the earliest fields of study in fluid mechanics, and CFD hydraulic modeling is a natural fit. Optifluides’ scope of action in the field of hydraulics is one of the widest: from the simple calculation of head losses in single-phase liquid flow to the propagation of seismic waves in the penstock of dams, from the dimensioning of Panama Canal locks to the quantification of thermohydraulic loads in the primary circuit of nuclear power plants. Hydraulic modeling is at the heart of our business. OptiFluides specializes in 2D and 3D modeling.

Here are some examples of CFD applications for hydraulic infrastructures.

Turbomachinery

Whether the machine receives energy or generates it, CFD can be used to model the behavior of fluids in different types of turbomachinery, analyze head losses and propose design modifications to maximize performance.

Reducing energy losses: simulation enables us to precisely quantify hydraulic load consumption zone by zone, and to target and optimize critical zones with high pressure drops, to ultimately improve performance.
Cavitation prevention: CFD helps to predict and minimize the risk of cavitation, thus increasing pump durability and efficiency.
Optimizing turbine control: Francis turbines usually have a set of guide and stay vanes at the spiral casing outlet, to direct the flow towards the impeller. The three-dimensional models implemented by OptiFluides enable us to analyze the influence of the angle of incidence of these vanes to maximize efficiency, avoid cavitation and turbulence generation.

Optimization of hydraulic dams and infrastructures

In dams and hydraulic infrastructures, CFD simulation can be used to optimize flows to improve water resource management.

Flood management: CFD simulation enables us to model various flood scenarios on a 1:1 scale, in order to validate the design of discharge systems. In particular, OptiFluides studies gated spillways, as well as the flutter-type instabilities that can develop in them, and quantifies their structural impact.
Spillway modifications: open-channel spillways can also be used to discharge excess flow. Simulation can be used to model them to determine discharge coefficients, linking flow and upstream water level. This is particularly useful when modifications to the crest are required, as the usual correlations can no longer be used. For instance, OptiFluides simulates spillways equipped with Fusegates, designed to raise the dam’s level and increase production in the event of high flows, and automatically evacuated when the limit level is reached.
Siphons: another discharge device, also used to provide reserve flow during low-water periods, the priming phase and flow rate of siphons can be simulated by OptiFluides.
Currents: Using bathymetry of the watercourse, OptiFluides performs three-dimensional simulations of free-surface flow, enabling precise determination of the velocity field upstream of the installation, its impact on water intake, water level fluctuations and flood discharge.

Lubrication and cooling of rotating machines

Cooling critical components: Simulating and optimizing the cooling of moving parts is another application. Good thermal management is essential to avoid overheating, reduce wear, and guarantee machine reliability.
Reducing friction losses: by modeling the interactions between moving surfaces and lubricating fluids, CFD can quantify and reduce friction losses, extending component life and improving efficiency.
Optimization of lubrication flow: CFD helps to adjust the flow of lubricants to ensure that they effectively reach all bearings.

Wastewater treatment

Flow rate and facility design: Wastewater treatment plants rely on various processes to purify wastewater: physical (screening, settling, etc.), physico-chemical (flocculation), chemical or biological. Simulation can be used to characterize the flow at each of these stages, and even to quantify and improve their efficiency, as well as the hydraulic head required to treat the desired flow. CFD thus plays a decisive role in the design of WWTPs, pump sizing, etc.
Optimization of settling basins: In settling basins, low velocities enable the sedimentation of suspended solids that need to be separated. Homogeneity of velocities, absence of overspeed and control of turbulence are essential parameters that CFD simulation can help to understand in order to model sediment behavior and maximize efficiency.
Ozonation processes: water treatment also involves multiphase flows such as ozonation, a process in which ozone (gaseous bubbles) is injected into the wastewater to be treated (liquid). These complex multiphase flows can be simulated with CFD software, enabling verification that the flow is correctly treated, effectively neutralizing pathogenic viruses and bacteria.
Biological reactors: CFD simulation can be used to model flows in biological reactors, ensuring better aeration and even distribution of nutrients for more effective purification.

Conclusion

CFD simulation is an essential tool in the hydraulics sector. The applications are numerous, and will provide you with important elements to better understand, control and improve your hydraulic equipment or installations.