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10.1 Data Exchange Module and Tutorial

Data exchange module in Simerics-MP+ is used to simulate heat transfer between fluid and solid in a coupled manner. Traditionally, Conjugate Heat Transfer (CHT) simulation is followed in which fluid and solid are modelled together. The heat flux and the wall temperature across the conjugate interface are predicted as part of the solution and no separate treatment is required. However, the CHT approach for certain practical applications (For example, Emotor cooling and Piston cooling) is computationally expensive due to heat transfer time scale difference between fluid and solid. Usually, temperature changes in solids occur over a much slower time-scale due to their higher thermal inertia compared to faster convective and diffusive heat transfer in fluid.

The barrier of time scale difference is addressed by using data exchange module in Simerics-MP+. The module synonymously is also called as mixed-time scale module. In the approach, fluid and solid domains are modelled separately. The heat flux and temperature boundary conditions are exchanged between the domains during the progress of the simulation. Both steady and transient heat simulations can be performed using the module. Data exchange module is not limited to conjugate heat transfer but can be used for any heat transfer simulation. A pictorial representation of the module is shown in Figure 10.1.

 

 

To activate the Data Exchange module: Click Select Modules in the Model Panel. The Physical Model Selection dialog box opens. See, Figure 10.2. Select Data Exchange module under Heat in the Available Modules and click Add.

Figure 10.2 - Adding module

 

´	Note: Data Exchange module must be added in both solid and fluid models separately.

 

The module is explained as follows:

• Controller Parameters: Parameters used in Data Exchange module for fluid and solid models.
• Output Variables: Outputs from the Data Exchange module.

 

The list of parameters available under Data Exchange module in the Properties Panel is different for fluid model and solid model.

 

Conditions for the Fluid Model The Data exchange conditions, and associated parameters for fluid model boundaries are specified as follows: Geometric Entities Panel > Boundaries > Desired Boundary Properties Panel > Model Tab > Data Exchange

Figure 10.3 - Fluid Coupling Conditions

 

The two options available under Data Exchange drop-down list, as shown in Figure 10.3 are:

• Wall: This is the default boundary condition for the Data Exchange in the Properties Panel. This implies no temperature field and heat flux are exchanged at this selected boundary.
• Mixed Scale Coupling: This boundary is selected to exchange the boundary conditions between fluid and solid models. It has the following more sub-options as shown in Figure 10.4.

 

Options

The list of boundary conditions available under Options are shown in the Figure 10.4. This allows to define the thermal boundary condition for the fluid model received from the solid model.

Receive Temperature: This is the default boundary condition assigned for a Boundary under Options. It receives the wall temperature of the solid boundaries in contact with fluid. Usually, this boundary condition is selected for fluid boundary. The other options are used for solid model, which is explained in Conditions for the Solid Model section in the solid side.

Figure 10.4 - Assigning Boundary condition

 

Geometry Type This is used to specify coupled boundary either as stationary wall or rotating wall. Wall: This is the default option for Geometry Type. This corresponds to a stationary fluid exchange boundary. Rotor: This corresponds to rotating fluid exchange boundary. The selection of the boundary type ensures correct spatial averaging of the exchanging variable and axi-symmetric distribution.

Figure 10.5 - Assigning Geometry type

 

The Rotor option has additional parameters as shown in Figure 10.6.

Number of Pockets: It defines the amount of rotation based on the angle between the two blades. Rotational Axis Vector: Rotational axis vector is used to specify the axis of rotation. Rotational Centre: Rotational centre is specified as {} coordinate lying on the Rotational Axis Vector.

Figure 10.6 - Geometry type parameters

 

 

Exchange Output

The output from the fluid model is exchanged with the solid model by selecting the options as given in Figure 10.7. The default exchange output with the solid model is Auto Exchange Coefficient.

Heat Flux: It exchanges the heat flux with solid model. Local Exchange Coefficient: It exchanges the time averaged heat transfer coefficient and the corresponding near wall reference temperature with the solid model. The heat transfer coefficient is averaged based on the cycle computational interval (Refer Cycle Computation Interval in the Common module). Auto Exchange Coefficient: It exchanges the time averaged heat transfer coefficient with automated temperature change for the calculation of reference temperature. The heat transfer coefficient is averaged based on the Cycle Computation Interval.

Figure 10.7 - Exchange output with Solid

 

Upper Limit Temp. Change

This is the maximum allowable temperature change. If oscillations are observed in flux balance, this parameter can be varied. For example, from default value of 20K to 10K.

 

Lower Limit Temp. Change

This is the maximum allowable temperature change. If flux convergence is slow, this parameter can be increased. For example, from default value of 1K to 2K.

 

Start Factor

Initial jump in the flux imbalance can be controlled using this parameter. Initial jump in flux is directly proportional to Start Factor.

 

Sensitivity

If flux is converging slow in the simulation, this parameter can be increased for a faster convergence. For example, from default value of 1K to 3K. Conversely, if the flux balance shows oscillations, the value can be lowered. For example, from 1K to 0.1K.

 

Conditions for the Solid Model The data exchange conditions, and associated parameters for solid model boundaries are specified as follows: Geometric Entities Panel > Boundaries > Desired Boundary Properties Panel > Model Tab > Data Exchange

Figure 10.8 - Solid Coupling Conditions

 

The two options available under Data Exchange drop-down list, as shown in Figure 10.8 are:

• Wall: This is the default boundary condition for the Data Exchange in the Properties Panel. This implies no temperature field and heat flux are exchanged at this selected boundary.
• Mixed Scale Coupling: This boundary is selected to exchange the boundary conditions between fluid and solid models. It has the following more sub-options as shown in Figure 10.9.

 

Solid Options

The list of boundary conditions available under Options are shown in the Figure 10.9. This allows to define the thermal boundary condition received from the fluid model.

Receive Temperature: This boundary condition is only applicable for fluid model. Refer Figure 10.4. Receive Flux: It receives the heat flux from the fluid model. Heat transfer co-efficient is calculated from the Max Temperature Change provided as sub-option under this boundary condition. See, Figure 10.10. Receive and Fix Flux: It receives the heat flux from the fluid model, and it is directly used as the boundary condition for the solid model. Receive Exchange Coefficient: It receives exchange coefficient from the fluid model.

Figure 10.9 - Assigning Boundary condition   Figure 10.10 - Receive Flux Boundary condition

Output Variables

The outputs available from the Data Exchange module are:

• Solid Flux: This plots the exchange of heat flux from solid to fluid at the solid/fluid mapped boundaries.

• Fluid Flux: This plots the exchange of heat flux from fluid to solid at the solid/fluid mapped boundaries.
• Flux Imbalance: This plots the difference between solid and fluid flux every iteration/timestep.