HPAC (Heating Plumbing and Air Conditioning) magazine is taking several proactive strides to keep the reader well-informed about contemporary developments in the mechanical as well as energy industry. Its editorial is aimed at management level mechanical industry personnel who have documented training in their fields of work.
Known to cover a multitude of topics from Controls and Hydronics to HVAC systems and Solar, HPAC conducted a webinar together with SimScale regarding an industrial duct design analysis. Essentially, ducts are passages or conduits used to deliver or extract air. Most often, they find applications in Heating, Ventilation and Air Conditioning (HVAC). 
In this project, we shall draw a comparison between 3 similar ducts with different blade configurations. With the results obtained, we aim to arrive at an optimized design for the duct.
The 3 configurations have 1, 2 or 3 guide vanes in the critical section of the duct. By performing a CFD analysis of the airflow through the duct, we intend to study the effect of varying the number of guide vanes as well as find methods to eliminate or at least mitigate recirculation regions.
A basic geometry is constructed, keeping in mind the following parameters:
Low pressure loss
Minimum scope of recirculation (smooth edges)
Uniform velocity at outlet
The 3 configurations are basically just modifications of the basic design. The geometry used for the current project can be observed in the images below. The end with the rectangular cross section is the inlet and the one with the circular cross-section is the outlet.
Isometric view of duct geometry
A hex-dominant parametric (only CFD) mesh is mapped onto the geometry with 8 computing cores and 4 types of mesh refinements, which as listed as follows:
Inflated Boundary layer
The final mesh is displayed in the images shown below:
Final Mesh (Isometric)
The fluid is chosen to be air and initial boundary conditions are set as follows:
Inlet: Velocity inlet with a constant velocity of 4 m/s.
Outlet: Pressure outlet at atmospheric pressure
Walls: All the other surfaces of the duct are assigned as walls with zero temperature gradient
In total, 4 simulations are carried out:
Design case 1: 1 guide vane
Design case 2: 2 guide vanes
Design case 3: 3 guide vanes
All the analyses are steady state incompressible, with the a turbulence model of k-omega SST. The simulations are carried out using the solver SIMPLE and take approximately 15 minutes to run,
Results and Conclusion
Flow Analysis of original design:
The image below depicts the relative pressure and velocity contour of the base case.
As can be seen from the image above, a low pressure region is formed just outside the critical section. This leads to an area of recirculation as shown in the velocity streamline diagram. Our aim is to minimize this region as much as possible.
Results for Optimized Design variations
The images below represent the pressure and velocity contours for all the 4 cases, thereby making it easy to perform a comparative study.
The low pressure region significantly decreases in size as guide vanes are added to the critical section. Also, the velocity at outlet is much more uniform for cases with guide vanes as compared to the base case.