Don’t worry, I’m even newer We’ll learn and solve along the way.
While you may be able to supposedly get the values out. I do not think that individually calculating both values and adding them up will give you a proper representation of the drag and lift on the body. This is due to (referring to the animation) water and air both “mixing” together and its very difficult to quantify exactly the lift and drag forces due to each medium. Fortunately, there is no need to do that. You can simply just obtain results directly from the body regardless of water or air and produce a lift and drag force value out. However, due to the nature of the results right now, this also may not accurate which brings me nicely to my next point which you already have kind of identified.
I suspect your outlet seems to be “blocking” the flow of water, hence the presence of a “back wave” occurs which will significantly affect your results. If the water were to instead “flow normally” per say and no backflow occurs then you can obtain direct results of lift and drag directly. As for how to fix this issue I am not exactly sure how. On one hand increasing the outlet velocity is one way, but referring to the sample case, the flow doesn’t behave like this despite the same outlet conditions. The backflow likely occurred due to the very strange sudden flow speed increase at around the 7s which is very strange. I suggest maybe increasing the area of the bounding box significantly to mitigate the effects of the wall and if this still continues, we’ll probably have to look into the side wall conditions.
Do let me know how it goes! Cheers.