It’s a fan/unofficial designation for the engine that was fitted to later batch of J-16.
It was known that early J-16 used WS-10A, but later batch had notably different engine nozzle and was more similar to what we know is on WS-10B, but since WS-10B’s oil cooler position is off to the side, like AL-31FN, WS-10D was given to what we think is WS-10B but for the Flanker platform, aka different oil cooler.
Does anyone have the in-game weight of the J-11B and the Su-27 or J-11? Saw a report saying the plane is too heavy, I’ve got the sources to report this if somebody has the in-game data on the weight.