| With the continuous development of the automobile industry,vehicles are con-stantly requiring higher and more complex heat dissipation capability of power compartment thermal management system.The application of numerical simula-tion method to analyze the flow and heat transfer is a common means to analyze and optimize the thermal management system of the power compartment.In the power compartment,heat exchangers and cooling fans are the most critical components,and they are also difficult to simulate.In order to further improve the computational accuracy and efficiency of the simulation of heat exchangers and cooling fans,this paper studied the simulation methods for heat exchangers and cooling fans,and proposed some numerical methods and modeling strategies to simulate the flow and heat transfer process in the power compartment.This study can provide useful references for flow and heat transfer simulation in the power compartment.The main contents of this study include:1)Proposed two methods for obtaining characteristic parameters of heat exchang-ersThe first method calculates the characteristic parameters of the size-adjusted heat exchanger based on the test data of the original size heat exchanger.Calcu-lation formula of the heat exchanger wind resistance Firstly,the heat exchanger wind resistance characteristic calculation formula is derived from the resistance coefficient formula and empirical formula of Fanning friction factor.Then,a two-dimensional numerical model is established by MATLAB to calculate the heat transfer characteristics.It has been verified that the maximum wind resistance error obtained by the proposed calculation method is-4.5%,and the maximum error of heat flux is 2.2%.This method can provide a reliable and convenient op-tion for obtaining the characteristic parameters of size-adjusted heat exchangers.The second method directly extracts the flow and heat transfer characteristics of the heat exchanger by numerical simulation of the flow and conjugate heat transfer of the heat exchanger micro-unit.It has been verified that the maximum wind resistance error obtained by the proposed calculation method is-1.5%,and the maximum error of heat flux is-6.6%.This method can obtain relatively accurate heat exchanger characteristic parameters without test data.2)Proposed an improved blended wall function for air-side fin passagesIn order to obtain accurate characteristic parameters of the heat exchanger by numerical calculation,an improved blended wall function for gas-side fin passages is proposed to achieve better simulation of the flow and conjugate heat transfer of the heat exchanger micro-unit.By introducing the mixing coefficient and the pressure gradient which are ignored by the standard wall function,the calcula-tion accuracy and efficiency of numerical simulation of radiator unit is improved.Compared to the simulation using standard wall function,the results with wall function could reduce the maximum error of wind resistance from-10.9%to-1.5%,and the maximum error of heat flux from-19.4%to-6.5%..In addi-tion,the simulation with IBWF could save more than half of the solution time.Hence,IBWF is a more economical and reliable near wall treatment method in heat exchanger unit numerical simulation.3)Research on physical equivalent modeling methods of heat exchanger module in power compartmentThe simple effectiveness model can consider the phase change that cannot be modeled using the commonly used ?-NTU method.It simulates the heat transfer of the complete heat exchanger based on the heat transfer of every micro control unit.The calculation accuracy depends on the accurate value of the effectiveness of micro control unit.By analysis of modeling theory of the simple effectiveness model,it is found that the model uses ?/NC as the local effectiveness of the mi-cro control unit when calculating the heat flux of each micro control unit.This will introduce errors into the calculation results.To fix this problem,the paper proposed a corrected simple effectiveness model by previously using MATLAB to establish a two-dimensional algorithm for obtaining the effectiveness of micro control unit.In order to verify the correctness of the modified model,the sim-ulation results obtained by the corrected effectiveness model are compared with the test results and the simulation results calculated by the simple effectiveness model and ?-NTU method.The results tells that the corrected simple effective-ness model reduces the calculation error of heat exchanger heat flux by 20.3%compared with the simple effectiveness model,and the accuracy of the corrected simple effectiveness model is close to the commonly used ?-NTU method,that fulfills general requirements of engineering calculations.4)Research on simulation strategy and error compensation of MRF-based cooling fan simulationBased on different MRF partitions,this paper conducts a cooling fan simula-tion over a wide flow range.The results show that when the flow is uneven on the MRF rotor-stator interface,the simulated static pressure of the fan is lower than the experimental value.Hence,non-uniform flow on the interface should be avoided by optimization of MRF partitions.To compensate the error introduced by non-uniform flow on the interface,a MRF interface error correction method is proposed.Firstly,the non-physical total pressure change caused by the MRF interface is calculated by evaluating the total pressure drop between the inner and the outer envelope surfaces of the MRF interface.Then,the non-physical total pressure change at the interface is compensated by adding an extra axial momentum source term.After the correction,the calculation accuracy under dif-ferent partition strategies and different flow rates have been improved to different extent,and the maximum absolute error has been reduced from-324 Pa to-116 Pa.5)Application research of 3D fan model in cooling fan simulationCompared with the MRF model,the 3D fan model consumes less computa-tional resources,which is suitable for power compartment simulation with mul-tiple fans.The accuracy of 3D fan modeling highly depends the validity of fan pressure curve input.By comparison and analysis of the measurement method of the test fan pressure curve and the application of the fan pressure rise curve in 3D fan model,two problems which could bring extra errors are found.First,the definition of the regional flow rate in 3D fan model is different from the flow rate definition in the fan full pressure curve test.Second,3D fan model would repeatedly consider the system pressure loss effect generated by fan accessory when using the test fan pressure curve input.Both the above two problems will introduce the simulation error in fan effect evaluation.In order to correct these errors,the paper proposes a PtFIC method to derive the input parameters of the 3D fan model based on the test fan pressure curve.By applying the PtFIC method,a corrected fan pressure curve is obtained.The relation between flow rate and pressure rise of test fan pressure curve has been adjusted and repeated considered system pressure loss has been compensated.Compared with directly applying test fan full pressure curve in 3D fan curve,the corrected fan curve would bring down the simulation error from 282.6 Pa to 0.7 Pa.The validity of the PtFIC method is verified. |
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