It’s best to delay developing the aspect and fluid-fluid network interfaces until after you’ve tuned the network, since you’re going to have to disconnect them all before tuning anyway.

Using its GunnsDraw shape data and the input file, a GunnsFluidExternalDemand link can be initialized to create a constant-pressure/temperature/mixture boundary condition without hooking it up to a GunnsFluidExternalSupply.

Temperature affects density and pressure, which affects flow rate. Changing temperature will throw off your tuning, so best to avoid it. It is possible to set up networks with constant and controlled temperatures.

• All thermal effects can be removed by zeroing their heat transfer coefficients. In run-time, the terms to set are:
  • In GunnsFluidHeatExchanger, this is done for each segment in its mSegHtcDefault term.
  • In GunnsFluidValve and similar links that define thermal diameter & length, etc, you zero the mThermalSurfaceArea term.
  • In GunnsFluidTank, you zero its mSurfaceArea term.
• Conversely, it is possible to force the exit flow of links that do convection a desired constant temperature. This is useful when you have design points you are tuning for that are at different temperatures in different locations around the system:
  • In GunnsFluidValve and similar, set mWallTemperature and give it a very large HTC (see above).
  • The GunnsFluidHeatExchanger has a mTemperatureOverride term that, when set to > 0, forces the exit temperature.

Before you start tuning flows & pressures, look at all the node temperatures (In Trick View, display the entire mNodes.mContent.mTemperature array) and make sure they’re stable at the values you want. Find the links that are causing the wrong temperatures and do the above tricks to control them.

Replace all GunnsGasFan and GunnsLiquidCentrifugalPump links with their base class GunnsFluidPotential. Configure the GunnsFluidPotential to have the same conductance, and set their mSourcePressure term to create a constant pump/fan pressure rise for the design point that you are tuning for.

Set all valve positions to the configuration that you are tuning for. All GunnsFluidValve links will stay at their current mPosition unless driven by some external model, so you can set mPosition since you haven’t interfaced them to their controller models yet. For the self-actuating pressure-sensitive valves like regulators & check valves, you have to use their mMalfFailTo malfunction to force them to the desired position. For these, you’ll usually want to tune your system with them in the full-open position.

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