The fan performance curve shown under Adjusting the Momentum Source is for a specific fan speed and air temperature. If a different fan speed and/or air temperature is to be analyzed, a fan performance curve is needed for those conditions. Fortunately, "fan laws" exist which allow fan curves to be easily scaled from one set of conditions to another, as per Eqns. (12) and (13).
Therefore, when you specify a fan performance curve, an associated fan speed and air temperature are also specified in the Data Rotation Rate and Data Temperature properties, respectively. In addition, you specify a desired operating speed in the Operating Rotation Rate property. Then, during the analysis, STAR-CCM+ automatically scales the user-supplied fan curve to the specified fan speed and the computed average air temperature.