本文使用三維逆向計算流體力學配合最小平方法進行封閉空腔內具一被加熱物之暫態自然對流特徵研究，並選定適用於在不同時間點的流動模型，並提出修正之經驗公式，最後探討Ra數、Nu數、熱傳遞係數以及速度與時間的關係。結果顯示，在流場之Ra數小於10^6時，所有計算使用的流動模型，以層流的計算結果最為精準，在熱傳遞係數以及最大速度的預測也最為接近，當Ra數超過10^6後，流場開始進入過渡流，數值計算的結果變為Zero-eq.較為精準。此外，在熱傳遞係數的部分，因為熱羽流(Thermal Plume)的發展以及回流影響對流效應，在本文所獲得的結果為先上升後下降，後續持平與穩態之計算結果相符。在最大速度方面，則是持續上升，並隨著Ra數趨緩而趨緩，後續漸漸持平並與穩態之結果相符。因此本文建議在自然對流之暫態分析應考慮在不同的Ra數下使用不同的流動模型進行計算，並且在封閉空腔中需考慮熱羽流回流發展所影響的對流強度，進行經驗公式的修正以適配各種不同的狀況，並且在過渡流的時候可以使用層流與紊流的經驗公式進行內插修正。

In this study, the three-dimensional inverse computational fluid dynamics(CFD) combined with the least square method(LSM) to investigate the transient natural convection characteristics in a cavity with a block. Appropriate flow model is determined for different time interval. The results indicate that Laminar flow model yields the most accurate prediction across all flow models when the Rayleigh number is below 10^6. As the Rayleigh number exceeds 10^6, the flow enters transitional rigime. The zero-equation provides higher accuracy in predicting the heat transfer coefficient and maximum velocity in flow field. Regarding the heat transfer coefficient, due to the development of thermal plumes and the influence of recirculation on convective effects, the heat transfer coefficient initially increases, then decreases, and eventually stabilizes—consistent with the steady states result. In contrast the maximum velocity continuously increases and gradually levels off as the Rayleigh number grows, eventually aligning with steady-state values. Therefore, this study recommends that inverse transient natural convection analyses account for varying flow models based on different Rayleigh number. Additionally, the development of thermal plume recirculation in closed cavities should be considered when evaluating convection strength. Modified empirical correlations should be applied to accommodate different flow regime, and the interpolation between laminar and turbulent correlations is advised during transitional flow conditions.

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