The simulation of engine cooling circuits by coupling Flowmaster with other simulation tools Dr. B. Beyer / W. Maister / Dr. C. Lund Volkswagen AG

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1 The simulation of engine cooling circuits by coupling Flowmaster with other simulation tools Dr. B. Beyer / W. Maister / Dr. C. Lund Volkswagen AG 1/18

2 Overview 1. Using Excel and VBA-scripts for automated Flowmaster calculations and result analysis 2. Using VBA-scripts for coupling Flowmaster with other simulation tools 3. Coupled simulation of an engine cooling system with Flowmaster and a Kuli air side model 4. Comparison of simulation results and measurements 2/18

3 Automation of Flowmaster calculations Flowmaster calculations can be controlled by using Visual Basic Scripts. Example: Controlling Flowmaster with an all-purpose Excel script which uses GUI automation. Program steps: 1. Open a Flowmaster network 2. Transfer the input values from the Excel sheet to Flowmaster 3. Create a new results list entry in Flowmaster 4. Run Flowmaster 5. Transfer the desired results from Flowmaster to Excel for evaluation purposes 3/18

4 Controlling FM with Excel: Defining input values Element definition Project name Network name Parameter definition Columns: Individual input values for each Flowmaster run (overwriting original values) 4/18

5 Controlling FM with Excel: Reading results Number of the results list entry Specifying results which shall be transferred to Excel Columns: Results for each of the Flowmaster runs 5/18

6 Example: Polo 1,9l TDI 74 kw coolant cycle Main components of the coolant cycle: radiator pump pressure losses of all components cabin heater oil cooler engine pipes, bends, T-pieces thermostat pump expansion tank thermostat 6/18

7 Comparison of measurement and simulation coolant flow / flow at rated speed [%] simulation measurement pump radiator simulation measurement coolant flow / flow at rated speed [%] simulation measurement cabin heater simulation measurement engine oil cooler rotational speed / rated speed [%] rotational speed / rated speed [%] Polo 1,9l TDI 74 kw coolant cycle 7/18

8 Thermal management of a vehicle grill servo steering charge air inlet gear oil cooler engine oil cooler oil pump waterpump thermostat engine passenger compartment TC gear box engine compartment evaporator heater exhaust pipe air outlet Domains involved in thermal management: coolant cycle air conditioning / heating charge air exhaust gas air flow through the engine compartment servo oil cooling engine oil cooling gear oil cooling Many systems are influencing each other Interaction should be considered in the simulation An automatic coupling of the simulation tools for the miscellaneous systems would simplify the analysis of the whole system 8/18

9 Flowmaster automation by using the COM interface Flowmaster provides two main areas of automation: 1. GUI automation Allows to control Flowmaster by scripts very similar to the way it is used manually. Advantage: All input values and output values can be easily accessed, calculation results are stored in the result list as usual. Disadvantage: The iteration process itself can t be influenced. 2. Analysis automation Allows to acces the analysis while it is running. Advantage: The script can interact with Flowmaster in each iteration step. Hence it is possible to provide external calculated values within the iteration process. Disadvantage: It is more difficult to access input values and results. Calculation results can be stored in the result list by overwriting old results only. 9/18

10 Coupling Flowmaster to other programs For coupling Flowmaster with other software it is often necessary that the programs are interacting within the iteration steps. Intervention within the iteration steps is possible only if analysis automation is used. The intricate setting of input values and reading of results when using analysis automation can be eliminated by combining both analysis methods and doing the pre-/postprocessing with GUI automation. 10/18

11 Process of a coupled Flowmaster calculation Start the Flowmaster iteration with start values for the variables Perform a Flowmaster iteration step Did Flowmaster converge? no Transfer of parameters yes Transfer of results Perform a complete external calculation Result analysis 11/18

12 Example: Coupling of Flowmaster and Kuli Heat rejection of the engine, oil cooler etc. heat Coolant cycle heat Air Experimental datas from vehicle or engine test bench *) 1D-Flowmaster model of the whole coolant cycle 1D-Kuli model of the engine compartment *) may be replaced by calulation results 12/18

13 Flowmaster model for a coupled simulation oil heat radiator Values read from Flowmaster and values written to Flowmaster during the iteration process: reading inlet temperature cabin heater oil cycle engine heat pump reading inlet pressure writing heat duty writing pressure loss reading coolant mass flow expansion tank thermostat 13/18

14 Kuli model for a coupled simulation Kühlwasserkreislauf inlet pressure coolant mass flow COM COM Druck Massenstrom inlet temperature COM fan speed (fan 1) COM 345 mm Antriebsdrehzahl P Ein radiator type Dateiauswahl COM heat flow 1.Rechenglied Wärmeleistung IM pressure loss Ein 1 Eintrittsdruck IM trittsdruck IM Ein 2 - Ein COM Kühlluftmassenstrom (Summe der Beträge) COM air flow blue = value set before calculation red = data written to Kuli during iteration green = data read from Kuli during iteration black = result read from Kuli after calculation Antriebsdrehzahl COM Simulationsparameter COM Air side model fans SP cp-value grill Fahrgeschwindigkeit ambient temperature Ein Ein 290 mm vehicle velocity Temperatur fan speed (fan 2) Ein KF COM 1.P-Regler Wasserkühler Ein Umgebungstemperatur press. loss of engine radiator comp. COM cp-values condenser 14/18

15 Calibration of the air side model 1. Determination of the radiator heat duty for a choosen operating point by measuring the radiator inlet and outlet temperature as well as the coolant flow rate in a vehicle. heat duty / ITD 2. Determination of the corresponding air flow rate in the radiator performance map. constant coolant flow rate air flow rate pressure difference 3. Determination of the engine compartment pressure loss which leads to this air flow rate. 1 pressure loss of the engine compartment air flow rate Pressure rise of fan and airstream Pressure loss sum for all known components Pressure loss of the entire air path 15/18

16 All-purpose Excel sheet for a coupled simulation Setting the transfer direction Value name used in FM and Kuli Definition of values transferred during iteration Setting start values of Flowmaster Setting start values of Kuli Flowmaster results Kuli results 16/18

17 Comparison of measurement and coupled simulation Velocity [km/h] v max v max Hill climbing [%] Fans off/on off/on off/on on on off Modifications - upper grill closed 40% reduction of lower grill area Radiator inlet temperature: used for model calibration Deviation of the simulation from measurement [K] /18

18 Conclusions The COM interface allows an interactive coupling between Flowmaster and other software which is providing a corresponding interface. When Excel is used for programming the coupling it is possible to define input tables which allow an easy modification of the data exchange between the programs (no change of the source code necessary). A 1D-simulation of the coolant cycle and the air flow through the engine compartment has shown that the coupling is working reliably and that accurate results can be obtained. Other tools may be coupled to Flowmaster additionally (e.g. engine process simulation). 18/18