Backflow turbulent intensity?

Jongmin Choi · January 10, 2016, 23:50

Hi, I'm beginner of ansys fluent.

As doing tutorials I have a question about backflow turbulent intensity.

I haven't learned any knowledge about that so I couldn't understand it.

Could you explain about backflow turbulent intensity?
How could I decide that value for ansys fluent???

LuckyTran · January 11, 2016, 14:41

When there is backflow, your outlet is an inlet. Thus you need to specify back-flow conditions in the event that there is any back-flow. Just as you might specify pressure, temperature, turbulence, etc at inlets, you need to do the same for outlets.

Just take your best guess as to what a suitable value is. If you knew what the backflow turbulence was, then you would already know the flow field and wouldn't be doing CFD in the first place.

Jongmin Choi · January 27, 2016, 02:17

Thank you for your sincere ansewering

ama294 · September 7, 2016, 14:49

Quote:

Originally Posted by LuckyTran

When there is backflow, your outlet is an inlet. Thus you need to specify back-flow conditions in the event that there is any back-flow. Just as you might specify pressure, temperature, turbulence, etc at inlets, you need to do the same for outlets.

Just take your best guess as to what a suitable value is. If you knew what the backflow turbulence was, then you would already know the flow field and wouldn't be doing CFD in the first place.

Hi LuckyTran,

First of all, thanks for your answer and could you please specify if the turbulence intensity affected by the application. for example if it is a rotor then the turbulence intensity will be higher than if it is a static object facing the flow. And in case of airfoil, should the turbulence intensity at the inlet be little larger than at the outlet.

Thanks
Aziz

LuckyTran · September 7, 2016, 15:00

The backflow turbulence intensity is affected by everything. Yes, it depends on each individual application.

The turbulence intensity is a local variable. It may locally decrease or increase depending on the local details of the flow. The turbulence intensity in the freestream can decrease because of decaying turbulence whereas the turbulence intensity can be enhance by the wake of a rotor/stator.

nawres · January 11, 2024, 02:53

Backflow Turbulent Intensity (BTI) is a measure of the turbulence intensity in the backflow region of a fluid flow. It is defined as the ratio of the root-mean-square (RMS) velocity of the backflow to the mean velocity of the main flow. BTI is an important parameter in the design of fluid systems, as it can affect the performance and efficiency of the system.

BTI is typically caused by a sudden change in the flow direction, such as a bend or a valve. When the flow encounters a sudden change in direction, it can create a region of recirculation, or backflow, behind the obstruction. The backflow region is characterized by high levels of turbulence, which can lead to a number of problems, including:

Increased pressure drop
Reduced flow efficiency
Noise and vibration
Cavitation
Erosio

January 10, 2016, 23:50	Backflow turbulent intensity?	#1
Jongmin Choi New Member Jongmin Choi Join Date: Jan 2016 Posts: 14 Rep Power: 10	Hi, I'm beginner of ansys fluent. As doing tutorials I have a question about backflow turbulent intensity. I haven't learned any knowledge about that so I couldn't understand it. Could you explain about backflow turbulent intensity? How could I decide that value for ansys fluent??? Vinay94 likes this.

January 11, 2016, 14:41		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	When there is backflow, your outlet is an inlet. Thus you need to specify back-flow conditions in the event that there is any back-flow. Just as you might specify pressure, temperature, turbulence, etc at inlets, you need to do the same for outlets. Just take your best guess as to what a suitable value is. If you knew what the backflow turbulence was, then you would already know the flow field and wouldn't be doing CFD in the first place. ama294, Jongmin Choi and Vinay94 like this. Last edited by LuckyTran; January 27, 2016 at 02:41.

September 7, 2016, 15:00		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	The backflow turbulence intensity is affected by everything. Yes, it depends on each individual application. The turbulence intensity is a local variable. It may locally decrease or increase depending on the local details of the flow. The turbulence intensity in the freestream can decrease because of decaying turbulence whereas the turbulence intensity can be enhance by the wake of a rotor/stator. ama294 likes this.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Problem with divergence	TDK	FLUENT	13	December 14, 2018 06:00
Question regarding Reynolds Number and Turbulent Intensity	maxj	Main CFD Forum	4	March 5, 2013 06:16
k-epsilon: Defining turbulent intensity and length scale?	klausb	OpenFOAM	0	January 23, 2011 07:28
Turbulent intensity	swe704	Main CFD Forum	0	November 13, 2009 03:42
setting value of turbulent intensity and turbulent viscosity ratio in wind tunnel	nuimlabib	Main CFD Forum	0	August 4, 2009 00:05

January 27, 2016, 02:17		#3
Jongmin Choi New Member Jongmin Choi Join Date: Jan 2016 Posts: 14 Rep Power: 10	Thank you for your sincere ansewering

January 11, 2024, 02:53		#6
nawres New Member nawres Join Date: Feb 2023 Posts: 2 Rep Power: 0	Backflow Turbulent Intensity (BTI) is a measure of the turbulence intensity in the backflow region of a fluid flow. It is defined as the ratio of the root-mean-square (RMS) velocity of the backflow to the mean velocity of the main flow. BTI is an important parameter in the design of fluid systems, as it can affect the performance and efficiency of the system. BTI is typically caused by a sudden change in the flow direction, such as a bend or a valve. When the flow encounters a sudden change in direction, it can create a region of recirculation, or backflow, behind the obstruction. The backflow region is characterized by high levels of turbulence, which can lead to a number of problems, including: Increased pressure drop Reduced flow efficiency Noise and vibration Cavitation Erosio