Hi I’m Chris and I’m a Fluid Systems Engineer. I didn’t plan on becoming one on graduating from University and didn’t really know what one did but bluffed my way through an interview and got offered a job working for Flowmaster as a support engineer. It can be difficult to explain to friends, family and customers exactly what I do and where a tool such as Flowmaster is used beyond ‘Virtual Plumbing’. I thought my first post on the Fluid Thinking Blog might be a place to start.
When people hear the phrase CFD they immediate think of 3D CFD tools such as FloTherm and FloEFD that are used to model problems in a three dimensional space, this can be either external flow (over and around the object being modelled) or internal flow (confined within the model). A 1D system tool such as Flowmaster is different, to build a model the user builds a system from a selection of components each modelling the internal flow within a component. The components are connected together to form a network and the network is then run through a series of scenarios and the results analysed. The systems modelled are more often than not those you don’t see or think about but don’t want to fail such as the fuel system on an aircraft, the lubrication system in the engine of your car or the cooling system of a power station. It’s the unglamorous downstairs to 3D CFDs glamorous manor house, alot of work happens but it’s largely unseen.
When someone passes me a picture or diagram and asks ‘How can you model that in Flowmaster?’ the first question I’ll ask is what do you want to use the model for? Is it for an initial sizing study to specify a pump or heat exchanger, is it looking at how a model reacts with time to external event or what happens if we run the system with a different fluid? Once I know this I’ll start mentally breaking it down into smaller sections, pipes and valves can be pulled from a catalogue directly but some things may need to be built from a combination of components. The example below shows how the muffler (silencer) in the exhaust of a car modelling the expansions, baffle plates and contractions into the chambers within it.
This breaking things down into elements from lumping everything into a single loss to breaking it down into smaller elements as was done in this example where more detail is required, this often happens as the project progresses. An example here would be modelling an aircraft fuel system where you start with a single tank to represent a wing tank in an initial model then breaking it down into individual tanks to represent cells within the wing and looking at the flow between them through a flight cycle. Talking to colleagues who’ve moved from 3D CFD to system simulation this breaking it down into components is stage that takes longest to get a grasp of.
The second question I’ll ask is where I can get the data to characterise the components. Flowmaster components are pre-loaded with data from Internal Flow Systems that provides a good starting point, however for the best results data for the actual components is needed. This data might come from the manufacturer, test data or more recently CFD with automated tools built into Flowmaster for the import of data.
As a person with little patience and a short attention span one of the attractions of working with a 1D model is the speed at which you can access results. For a steady state simulation the time from pressing run to get a result is usually measured in seconds, for a transient it’s usually minutes rather than hours. This speed of results is one advantage over 3D CFD meaning it’s possible to run through many potential configurations in a short period of time quickly to optimise a model.