| Engine cooling water pump(ECWP), a critical component in the cooling system, is always used at the condition of high temperature, large flow and changed rotational speed, which leads to its earlier cavitation. At the same time, cavitation occurs together with thermodynamic effect because heat exchange makes material temperature and parameters changed. In this study, cavitation mechanism under thermodynamic effect is researched based on the ECWP and the main work and conclusions are as follows:1. Research status of ECWP and cavitation background under thermodynamic effect were summarized.2. The impeller was optimized based on the consideration of cavitation performance and three impellers with different blade outlet widths were numerically simulated. From the performance curves, we knew that, with the increase of impeller blade outlet width, the investigated ECWP’s head increased gradually, and best efficiency point(BEP) moves into large flow, and the bubble volute distribution at the BEP was increasing slowly. Compared with the internal flow field, we found that the areas of high turbulence kinetic energy appeared mainly in the impeller inlet and blade passage near the throat.3. A modified cavitation model under thermodynamic effect was established and certificated. The basic features of common turbulence models were analyzed and RNG k-? turbulence model was finally chosen based on the experimental data. The evaporation and condensation source terms of cavitation model were summarized, and the method of user defined cavitation model by CEL language was proved. Four cavitation models under thermodynamic effect were modified based on the Rayleigh-Plesset, Taylor and Clapeyron equation, as well as three sets of evaporation and condensation coefficients(50 and 0.01; 10 and 0.002; 1 and 0.0002) were given to combination. One of four modified cavitation models(TCM2) was finally verified after comparison with the test datum of NACA0015 airfoil surface pressure coefficient at the temperature of 70℃. Therefore, RNG k-? turbulence model and modified cavitation model TCM2 were used to do the simulation.4. Hydrofoil and ECWP were simulated based on the modified thermodynamic cavitation model. For hydrofoil, the bubble areas were similar at different temperatures. With the increase of temperature, the bubble volute fraction of NACA0015 was larger amount. Cavitation development both the hydrofoil and NACA0015 was becoming obvious at higher temperature. For ECWP, we found that there was 0.9% head error, 2.5% power error and 3% efficiency difference when the temperature was at the range of 25℃~70℃. With the increase of temperature, the cavitation in the ECWP occurs preferentially and develops rapidly. Temperature had an important influence on cavitation process, so cavitation under thermodynamic effect should be taken into consideration when the medium parameters were changing.5. Experimental study of ECWP was carried out. The hydraulic performance trend between numerical results and experimental datum was fully consistent, but the simulation results required to be appropriately revised. From the performance curves, with the increase of rotational speed, the head increased gradually; and the BEP moved to lager flow; and critical NPSH was becoming larger. Meanwhile, the pump similar law at different rotational speed was certificated. The inlet pressure was becoming larger at the higher temperature and the cavitation performance was worse. With the increase of flow coefficient at the same speed, bubbles were growing up and more and more bubbles would be appeared. Meanwhile, cavitation thermodynamic effects in the engine cooling water pump within the temperature range of 25℃~70℃was becoming positive, and the area of bubble distribution in the impeller was becoming large at higher temperature. Reliability tests showed that experimental hydraulic error was less than 1%, which indicated that the investigated ECWP met the reliability requirements. |
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