Tetrahedral Mesh At Lower Velocities

sam

Hello fluent users, i have a question regarding my problem, i am doing cfd of underwater vehicle and when i compared my drag coefficient data with the experimental data, at lower velocities the drag coefficient has not very good aggreement with the experimental data, although the trend is same of both curves.Please tell me that is there limitation in fluent that at lower velocities it underpredict the drag or there is something wrong with my problem setup.