##### Posted by: william

«**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

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

+step((t-0.199

tstep = 0.01

END

END

END

##------------------------------------------------------------------------------

#

# Using the CEL expression for particle mass flow:

# particle mass flow = 0.0037418 [kg/s] @ t = 0.01

# 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