Virtual disk: Advance ratio report

a.gmira · May 17, 2023, 08:03

Good afternoon,

I am running selfpropulsion simulations for a ship with virtual disk model and Body Force Propeller method. As the operation point input option I am selecting Thrust. Also, I am running in model scale and adding a Skin Friction Correction Force as a force CM (DFBI).

The values I get for Thrust deduction fraction and Wake fraction (with Thrust Identity method)are reasonable. However, the advance ratio (J) report from the simulation is lower than the one I calculate as J=V/(n*D), where V is the velocity of the farflow. The one I get in the simulation is 0.50 and the calculated one by me is 0.58.

Does anyone know if I should get J=0.58 from this type of report? or how that report calculates the advance ratio?

Thank you in advance!

Kind regards,

A.gmira

fluid23 · May 17, 2023, 09:44

The report pulls velocity from the inflow plane so I would assume that your inflow velocity and far-field velocity are not the same.

a.gmira · May 19, 2023, 07:33

Do you know exactly which velocity in the inflow plane is it using to calculate the advance ratio? Because I am taking the average of the axial velocity, velocity (i), etc., to calculate it but they dont give me the same value as the report.

fluid23 · May 19, 2023, 07:55

According to the help files:

"The velocity components and the density of the fluid approaching the virtual disk are volume-averaged over the inflow velocity plane. The averaged velocity components are then projected onto the normal plane of the virtual disk to yield one average velocity vector value."

May 17, 2023, 08:03	Virtual disk: Advance ratio report	#1
a.gmira New Member ale Join Date: Mar 2023 Posts: 22 Rep Power: 3	Good afternoon, I am running selfpropulsion simulations for a ship with virtual disk model and Body Force Propeller method. As the operation point input option I am selecting Thrust. Also, I am running in model scale and adding a Skin Friction Correction Force as a force CM (DFBI). The values I get for Thrust deduction fraction and Wake fraction (with Thrust Identity method)are reasonable. However, the advance ratio (J) report from the simulation is lower than the one I calculate as J=V/(n*D), where V is the velocity of the farflow. The one I get in the simulation is 0.50 and the calculated one by me is 0.58. Does anyone know if I should get J=0.58 from this type of report? or how that report calculates the advance ratio? Thank you in advance! Kind regards, A.gmira

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[FSI] Having trouble installing FSI_4.0 on foam-extend 4.1 and Ubuntu 16.04	Aliiiii	OpenFOAM CC Toolkits for Fluid-Structure Interaction	11	May 26, 2022 05:00
Virtual Disk Model-Report	afarkas	STAR-CCM+	2	July 7, 2017 05:29
Install/compile fireFoam 1.6-1.0 in Openfoam 2.1.1	hz283	OpenFOAM Programming & Development	19	April 1, 2013 08:35
Propeller thrust at diff. advance ratio (CFX 5.7)	Zoltan	CFX	9	April 27, 2005 08:23
Problem of Turbulent Viscosity Ratio Limited	David Yang	FLUENT	3	June 3, 2002 06:13

May 17, 2023, 09:44		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	The report pulls velocity from the inflow plane so I would assume that your inflow velocity and far-field velocity are not the same.

May 19, 2023, 07:33		#3
a.gmira New Member ale Join Date: Mar 2023 Posts: 22 Rep Power: 3	Do you know exactly which velocity in the inflow plane is it using to calculate the advance ratio? Because I am taking the average of the axial velocity, velocity (i), etc., to calculate it but they dont give me the same value as the report.

May 19, 2023, 07:55		#4
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	According to the help files: "The velocity components and the density of the fluid approaching the virtual disk are volume-averaged over the inflow velocity plane. The averaged velocity components are then projected onto the normal plane of the virtual disk to yield one average velocity vector value."