# "constant power" inlet?

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 January 30, 2015, 12:07 "constant power" inlet? #1 New Member   Join Date: Jan 2015 Location: Berlin Posts: 2 Rep Power: 0 Another newbie hits the pavement: Hello cfd-community I searched the forum (and outside) but couldn't get a thourough answer: I'm working on an aerodynamic structure that is driven by a fan and produces lift (very vague, but i wouln't like to go into further details about it). Now I'm hoping to optimize this a bit through cfd. Therefore I want to compare the lifting force of several slightly modified versions against each other. To make the lift-values comparable, i need to ensure that the flow through my models is driven by an equal amount of power - like i did in my real-world experiments by controlling the input power to the fan. In my first attempt I simply used a constant-velocity inlet, but looking at the inlet pressure values in paraview revealed that there is a huge spread in average inlet pressure amongst the models. At constant velocity this would mean different power-levels for a (hypothetical) fan driving the flow. My first (real newbie) question: Is it ok to look at pressure values directly at an inlet-patch to calculate power, or should this be done a bit downstream on internal cells? I already realized that the TotalPressure BC would be more in my favour, but what I really need is some kind of "constant pumping power" inlet. So here's my second question: Is there an "open-foam-way" to achieve this? I don't ask you to solve this problem for me, just a hint if I'm simply overseeing something. I had a look at the various derived BCs in the code - none of them seemed to fit directly. Maybe the fan-patch could be used for it with an apropriate function for the pressure-drop.

 March 29, 2015, 10:38 #2 New Member   Join Date: Jan 2015 Location: Berlin Posts: 2 Rep Power: 0 As it turned out, I already gave the answer myself, just in case somebody stumbles across teh same problem: The solution for me was to use the pressureFan bc for p on the inlet while using pressureInletVelocity for U. To achieve what i called 'constant-power-inlet' I wrote a simple script to calculate a fan-curve for a given input-power and inlet-area using the following formula: input_power = fan_pressure_drop_total * rate_of_volume where: fan_pressure_drop_total = fan_pressure_drop_static + fan_pressure_drop_dynamic (fan_pressure_drop_dynamic = 0.5 * density * square_of(U)) In this nomenclature the fan-curve would be: fan_pressure_drop_static = f (rate_of_volume) leading to: input_power = ( f (rate_of_volume) + fan_pressure_drop_dynamic ) * rate_of_volume which finally can be resolved for: f (rate_of_volume) = (input_power / rate_of_flow) - 0.5 * density * square_of(rate_of_flow / A) (with A beeing inlet-area) As p in icoFoam is not simply pressure but (pressure / density) the pressure-values from that formula (or the fomula itself) would have to be divided by density.

 Tags fan bc, inlet bc

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post cfdonline2mohsen OpenFOAM 6 November 26, 2013 03:59 preetam69 FLUENT 0 September 28, 2013 04:51 Ozgur_ FLUENT 2 August 3, 2012 05:54 aeroman CFX 12 August 6, 2009 18:42 Balaji FLUENT 2 August 8, 2005 07:37

All times are GMT -4. The time now is 01:10.

 Contact Us - CFD Online - Top