Dear Kemal,
You can set the fixed wind direction in either TurbSim (HFlowAng) or the InflowWind module of FAST / OpenFAST (PropagationDir), but the latter is preferred because the wind will propagate along the wind direction specified in InflowWind (PropagationDir) regardless of the setting of HFlowAng in TurbSim.
Without changing the source code, there is no way to prescribe a time-varying wind direction of the TurbSim wind field in FAST / OpenFAST. It is standard practice to run many FAST / OpenFAST simulations (each with different wind speed, turbulence intensities, etc.) at fixed wind directions. The design standards (e.g., IEC 61400-1) also specify discrete gust and direction-change events, but these simulations do not involve full-field turbulence.
Best regards,