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How can it possible to change by itself in volumetric flow rate of velocity inlet BC

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Old   November 23, 2016, 06:56
Default How can it possible to change by itself in volumetric flow rate of velocity inlet BC
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Hi all,

I just wonder how to change volumetric flow rate in face cell of velocity inlet boundary condition ?

velocity and temperature has been specified together with hydraulic diameter in velocity_inlet BC

It has changed by itself following 50. iterations. Then, temperature of some regarding faces has not been steady as well.

I am confusing how can it possible?
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Old   November 23, 2016, 23:35
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Hi all,

I just wonder how to change volumetric flow rate in face cell of velocity inlet boundary condition ?

velocity and temperature has been specified together with hydraulic diameter in velocity_inlet BC

It has changed by itself following 50. iterations. Then, temperature of some regarding faces has not been steady as well.

I am confusing how can it possible?
Is there anyone who help me with out this issue?
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Old   November 24, 2016, 04:06
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Has the size of the inlet changed? Because then the velocity could remain constant while the volumetric flow rate changes. Second, are there any UDFs or profiles hooked to the boundary?
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Old   November 24, 2016, 04:23
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Has the size of the inlet changed? Because then the velocity could remain constant while the volumetric flow rate changes. Second, are there any UDFs or profiles hooked to the boundary?
that is relevant to flow of outlet_pressure. Backflow has occured side of inlet_velocity. How can I surpass it?

velocity inlet and pressure outlet are boundary conditions.

Velocity inlet :

Velocity magnitude: 1.4m/s,
Supersonic/Initial Gauge Pressure (pascal) : 150000 Pa (1.5 bar)
Temperature 300K ,
Operating pressure :101325 Pa (reference pressure location X,Y,Z=0, gravity is deactivated )


Pressure outlet :

Gauge Pressure (pascal) =0
Backflow Total Temperature :323.15K
Operating pressure :101325 Pa (reference pressure location X,Y,Z=0, gravity is deactivated )
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Old   November 24, 2016, 05:13
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Has the size of the inlet changed? Because then the velocity could remain constant while the volumetric flow rate changes. Second, are there any UDFs or profiles hooked to the boundary?
velocity must be constant, wet area is constant, rho as well.

mass flow rate : rho x A x V ; (from continuity) equals to outlet_pressure

all of them must be constant. Because I have specified that face as velocity_inlet BC.

Volumetric flow rate need to be constant as well.
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Old   November 24, 2016, 07:24
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Moreover, the problem always happen whenever I activate energy equation.
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Old   November 25, 2016, 03:28
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Are you modelling compressible flow? Where are you measuring the volumetric flow rate (inlet and/or outlet boundaries?), and what are the values?
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Old   November 25, 2016, 03:41
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flow is defined as ''incompressible ideal gas ''. Well it is associated with density change . it arises from continuity equation.

But the thing I couldnt understand is that I have given a velocity and temperature inputs in velocity_inlet boundary condition.

Well, coming from mass conservation, mass flow rate= rho x Wetted area x velocity,

wetted area like velocity has been specified in velocity_inlet bc.

Remaining is rho, it is just comply with temperature,So, temperature is constant as well. (because of giving in BC)

I am really really confused what is going on during calculation ?

I will be really appreciated if you help me out

by the way I couldnt check inlet and outlet mass flow rate for this reason I have told you above
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Old   November 25, 2016, 04:14
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Remaining is rho, it is just comply with temperature,So, temperature is constant as well. (because of giving in BC)
Have you checked the temperature field? Are your initial temperature values, inlet and wall boundaries all the same temperature? You mentioned this problem occurs when you enable the energy equation; suggesting that the temperature is inadvertently affecting your results. Could the density of the ideal gas change within the domain over time, as a function of temperature?

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by the way I couldnt check inlet and outlet mass flow rate for this reason I have told you above
Why? You can run a UDF over the inlet and outlet boundaries at each time step (DEFINE_AT_END) and compare the fluxes (calculated from the velocity etc).
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Old   November 25, 2016, 04:50
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Have you checked the temperature field? Are your initial temperature values,

inlet and wall boundaries all the same temperature?

You mentioned this problem occurs when you enable the energy equation; suggesting that the temperature is inadvertently affecting your results.

Could the density of the ideal gas change within the domain over time, as a function of temperature?

Why? You can run a UDF over the inlet and outlet boundaries at each time step (DEFINE_AT_END) and compare the fluxes (calculated from the velocity etc).

Well, respectively.

you can find attached whole geometry (consisting of 3 bodies in a part)
Wall boundaries surrounds air inlets and heat flux =0 in wall boundary conditions tab.
Exactly, whenever energy eq. is activated, that situation is to come true.
problem is to solved in steady-state (not time). But yes,exactly, density changes
not used UDF.
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Old   November 25, 2016, 04:54
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Quote:
Originally Posted by oozcan View Post
Well, respectively.

you can find attached whole geometry (consisting of 3 bodies in a part)
Wall boundaries surrounds air inlets and heat flux =0 in wall boundary conditions tab.
Exactly, whenever energy eq. is activated, that situation is to come true.
problem is to solved in steady-state (not time). But yes,exactly, density changes
not used UDF.
You find attached ''model''
Attached Images
File Type: jpg Capture.JPG (146.3 KB, 5 views)
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