本研究利用FLUENT計算流力軟體來模擬垂直軸風車之流場，求解三維非穩態不可壓縮紊流的Navier-Stokes方程式。 使用NACA-ls0421以及NACA0024做為計算垂直軸風車的葉片，分別是四葉片以及三葉片，先利用Gambit繪製外型以及建構非結構網格並給定邊界條件，以及運用不同的紊流模式計算，在驗證的過程中，發現每次的時間步階大概需要疊代200次，且收斂條件需調整成較嚴格，才能把時間步階放大。 本文裡有利用二維計算三種不同直徑的垂直軸風車，採用k-ε standard模式計算在不同尖速比下的扭力，其結果與實驗所得趨勢吻合，誤差在20%。 結果發現，不同紊流模式所計算出的扭力值極為不同，且從原本計算二維流場到三維，所需計算時間增七倍多，不符合效率。雖說二維的數值解已與實驗值相近，但是在三維時；卻還需要改進，再找較符合的紊流模式來計算之。 This study used the commercial CFD software, FLUENT, to simulate the flow field of VAWTs. The governing equations are the two-dimensional, unsteady, incompressible, turbulent Navier-Stokes equations. The results show that the residual values should be set small enough to allow at least 200 iterations within a time step in order to obtain a converged solution. This is due to the highly unsteady and turbulent flow of VAWTs. The time step can be set larger to speed up the calculation if 200 iterations requirement is satisfied. The performance data of three small VAWTs were also measured in a low speed wind tunnel to validate the numerical results. The discrepancy between experimental and two-dimensional numerical results is about 20%. The trends of the performance curves predicted numerically match that obtained experimentally. Three-dimensional effects need to be further investigated. A two-dimensional simulation takes about 12 hours in a desk top computer with an Intel-I7 cpu. But a corresponding three-dimensional simulation takes about 8 days. Therefore, two- dimensional simulation is a good preliminary design tool. Our study also demonstrates that different turbulence models affect the numerical results significantly. The application of turbulence models in VAWTs need to be investigated extensively.