In Part I & II of this series were concerned with rotation of near axisymmetric type bodies. What if the rotating body is not close to axisymmetric, like a radar dish or antenna? No problem…The sliding mesh rotation functionality extends to non-axisymmetric bodies [Refer to the validation case in Part II]. As before (Part I & II), the rotation is defined by simply creating a cylindrical component around the rotating body and defining it as the Rotating Region as illustrated in Figure 1 below.
We have discussed FloEFD’s CAD geometry handling and meshing functionalities in Part I & II, thus we will not duplicate the discussion here again. Instead, let’s discuss the topic of Goals within the FloEFD frame of reference. The purpose of Goals in FloEFD is two-fold. Goals are user-selected parameters of interest to monitor during solving and since we are interested in specific parameters, we don’t want the solver to stop until these goals have converged to within a prescribed tolerance. So we use Goals for convergence control primarily. Another use of Goals is to track parameter values especially during transient analyses to have the time history data available afterwards.
With such rotating equipment as dishes or antennae it is of particular interest to investigate the additional torque required to rotate the dish in a cross-wind situation. It would also be required to predict the variations in torque with respect to the rotation angle in order to account for the range of loads that the structure could be exposed to. A further consideration may be to predict the drag versus time or angle of rotation in order to detect peak drag forces that may be underestimated when performing quasi-steady analyses with the dish in discrete angular positions. Consider the graphs below illustrating the variations in Drag force and Z-Torque versus time as recorded during solving.
The Animation post-processing feature in FloEFD allows one to easily create animated videos of the transient fluid behaviour caused by the rotation of the radar. Take a look at the video below. A surface plot shows the pressure variations on the dish surface as it rotates in the cross wind. The horizontal cut-plot shows the velocity contours and streamlines dynamically changing as the flow separates behind the radar.
This blog article is Part III of a series of blog articles on the CFD simulation of complex rotor equipment.
Part I: LEGO Technic Aero Hawk
Part II: Apache Helicopter
Part III: Rotating Radar Dish
Part IV: KJ-66 Micro Gas Turbine Thrust Prediction
Part V: Diffusor Shock Waves in a Centrifugal Compressor