Waterhammer

Waterhammer, Acoustic Waves, and Other Fast Transients

Waterhammer is an impulse load created by sudden changes such as valve opening or closing. The resulting pressure loads can have catastrophic effects on pumps, pressure transducers, turbines, and valves. Waterhammer events typically occurs over a millisecond time frame, but may spand several seconds in large systems. The ability of SINDA/FLUINT and FloCAD® to capture fast transients allows the modeling of waterhammer and other fast transient events such as acoustic waves propagating through ducts that contain compressible and even two-phase fluids.

Historically, the Method of Characteristics (MOC) was often used to predict wave propagation phenomena, while FloCAD uses a finite difference/volume approach. What is the difference? FloCAD may be optionally used to model wave propagation events, while MOC-based software can't be used for much else. MOC is inapplicable to phenomena such as slow transients (much less steady states), heat transfer, two-phase flows with phase change, mixtures, etc.

Shown below is a comparison between FloCAD and a MOC solution, as documented in Wylie and Streeter's Fluid Transients (1982 edition, Example 3-1). The RMS error is about 1%: on the order of the interpolation error. To enable an "apples to apples" comparison, default FloCAD features had to be turned off such as the automatic inclusion of frictional losses, heating effects, heat transfer, fluid properties, etc.

Chart showing Comparison between FloCAD and a MOC solution

Other validations have included comparisons with column separation events … a flashing phenomenon not easily handled by MOC-based programs. In fact, SINDA/FLUINT is capable of full two-fluid nonhomogeneous phasic nonequilibrium analysis if needed. What does that mean? It means FloCAD is the only commercial off-the-shelf program that is capable of modeling waterhammer and similar oscillations and instabilities in two-phase multiple-component flows.

FloCAD's implicit solution techniques enable it to take large time steps, and the availability of simplifying assumptions means that FloCAD is just as applicable to parametric sweeps of steady-state heat exchanger performance as it is to simulating detailed waterhammer events. In other words, FloCAD doesn't have to concentrate on higher order effects like fast transients. But such capabilities are there if needed.

FloCAD also features flat-front two-phase modeling, a specialized tool for studying waterhammer that occurs when priming evacuated lines, especially when a liquid front strikes a valve or dead end.

Choking and High-speed Flow

Tuesday December 17th, 2pm MST

When flow velocities get big, things gets interesting. Above Mach=0.1, the bulk fluid "sees" a wall that is warmer than the structural temperature due to deceleration within the boundary layer. Above Mach=0.3, kinetic energy changes cease to be negligible. And of course, nothing moves faster than Mach=1.0 for internal flow. When you also add in changes in flow area, or changes in phase ... well, let's just say that doesn't simplify anything.

This webinar will introduce you to the phenomena involved, with a focus on the FloCAD modeling parameters available and their associated correlations and assumptions.

Click here to register

Turbomachinery and Rotating Passages (Secondary Flows)

Thursday December 19th, 2pm MST

Are turbomachines a component in your system, and you'd like to treat them as a "black box"?

Or are they the focus of your work, and the cycle is just a boundary condition to you?

Either way, this webinar will have something to offer you. Each type of turbomachine will be covered: pumps and fans, positive and variable displacement compressors, and turbines (whether gas or hydraulic). Methods for modeling systems like turbochargers and turbopumps will be introduced. Tools for handling spinning flow passages and rotating cavities will be presented.

Click here to register

Starting in 2020, we will begin offering Introduction to Thermal Desktop and Introduction to RadCAD as either in-person training or online training, alternating between online and in-person every three months. The training uses lectures and demonstrations to introduce you to basic Thermal Desktop and RadCAD usage. Hands-on tutorials provide practice building models and interpreting results (tutorials are completed by students outside of the online class time).
 
The next training class will be an online format in January 2020:
  • Introduction to Thermal Desktop (and SINDA) - A three-part series on January 14, 16, and 21 from 9am to 12pm, Mountain time
  • Introduction to RadCAD - January 23 from 9am to 12pm, Mountain time
For up-to-date schedules, fees, and policies, visit our Product Training page. To register for the class above, complete our registration form and select "Online" for the Training Format.
 
If you are interested in product training for your company based on your schedule, please contact us to obtain a quote for training between 8-12 attendees. We can come to your facility or the lectures can be presented online. Descriptions of the available classes can be found in our course catalog.
 
To keep up with our training opportunities, take a look at our new Events and Training Calendar.