### Author Topic: Particle injection rate at a frequency less other then every time step.  (Read 5137 times)

#### pitney1

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• Searching for solution ##### Particle injection rate at a frequency less other then every time step.
« on: May 11, 2012, 10:40:05 PM » How do I set a particle injection rate at a frequency less other then every time step in a transient simulation?

#### william

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• Know it, share it. ##### Re: Particle injection rate at a frequency less other then every time step.
« Reply #1 on: May 11, 2012, 10:40:40 PM »
In this case, particles are not injected at every time step, but are injected at every nth timestep or some other frequency. In order to accomplish this, the particle mass flow rate should be specified as a function of time using an expression ( step function will have to be used ), and then set the number of particles per unit time dependent on the mass flow rate. (That is why this option exists.) Alternatively, you may wish to use a particle injection region with User Fortran.

For example, if we are running a transient case with time step of 0.01 s and we want a particle to be injected at t = 0.1 s and t = 0.2 s the setup would appear as follows:

##------------------------------------------------------------------------------
#
# Creating an expression to turn the particle injection on and off
#
##------------------------------------------------------------------------------

LIBRARY:
CEL:
EXPRESSIONS:
particle mass flow = 0.0037418 [kg/s]* \
(step((t-0.099)/1)*step((0.101-t)/1)\
+step((t-0.199)/1)*step((0.201-t)/1))total time = 0.5
tstep = 0.01
END
END
END

##------------------------------------------------------------------------------
#
# Using the CEL expression for particle mass flow:
# particle mass flow = 0.0037418 [kg/s] @ t = 0.01 , 0.02
# otherwise, particle mass flow = 0 [kg/s]
#
# Note 0.0037418 kg/s is equivalent to 100 copper particles per second.
#
##------------------------------------------------------------------------------

FLOW:
SIMULATION TYPE:
Option = Transient
INITIAL TIME:
Option = Automatic with ValueTime = 0
END
TIME DURATION:
Option = Total Time
Total Time = total time
END
TIME STEPS:
Option = Timesteps
Timesteps = tstep
END
END
DOMAIN: Domain 1
Domain Type = Fluid
Fluids List = Water
Particles List = Copper
BOUNDARY: In1
Boundary Type = INLET
Location = in1
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Normal Speed = 1 [m s^-1]
Option = Normal Speed
END
TURBULENCE:
Option = Medium Intensity and Eddy Viscosity Ratio
END
END
FLUID: CopperBOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Zero Slip Velocity
END
PARTICLE MASS FLOW RATE:
Mass Flow Rate = particle mass flow
END
PARTICLE POSITION:
Option = Uniform Injection
##------------------------------------------------------------------------------
#
# One particle will be injected:
# Since there will be 100 injection points per kg:
# - when the flow rate is 0 kg/s, there will be no injection points
# - when the flow rate is 0.0037418 kg/s, at a timestep of 0.01
# 3.7418e-5 kg will be injected. So the number of injection points will be
# 100 points/kg * 3.7148e-5 kg = 0.0037148 injection points. Since the
# number of injection points is rounded up to the nearest integer,
# a value of 1 is assigned to the number of injection point.
#
##------------------------------------------------------------------------------
NUMBER OF POSITIONS:
Number per Unit Time and Mass Flow Rate = 100 [kg^-1]
Option = Proportional to Mass Flow Rate
END

END
END
END
END
BOUNDARY: Outlet
Boundary Type = OUTLET
Location = outBOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Average Static Pressure
Relative Pressure = 0 [Pa]
END
PRESSURE AVERAGING:
Option = Average Over Whole Outlet
END
END
END
FLUID: Copper
FLUID MODELS:
MORPHOLOGY:
Option = Dispersed Particle Transport Fluid
##------------------------------------------------------------------------------
#
# 1 [mm] particle injected
#
##------------------------------------------------------------------------------
PARTICLE DIAMETER DISTRIBUTION:
Diameter = 1 [mm]
Option = Specified Diameter
END
END
END
END
END
END