3 Replies Latest reply on Jun 21, 2013 10:55 AM by Hannah Liang

    How to set the operation point of a fan?

    Henrique Yamashiro

       

      I am conducting a study of ventilation in a railway tunnel.

       

      I have not found a fan with features I need, so I created one using the manufacturer's data sheet.

       

      I am initially using a cylinder with the diameter of the fan, 2.5 meters and a length of 100 meters. I have created a body in the middle of the cylinder and insert the fan on it, using the internal fan configuration. In both cylinder ends I've add lids and utilized as boundary condition static pressure (at 30 °C and atmospheric pressure).

       

      The initial conditions are: Internal study, initial temperature of 30 °C, adiabatic wall and air as the fluid.

       

      The operating point that is defined by the system curve and the characteristic curve of the fan is: flow of 115 m³/h and pressure of 600 Pa.

      Teste  Ventilador - Static Pressure.jpg

      After running the simulation I cannot reach these values. The values of the goals of pressure and flow are close to the characteristic curve of the fan, but not at the point of operation.

       

      Is there a way to set the operating point of the equipment?

       

      How the program defines where in the curve the fan will operate?

       

      Thanks

        • Re: How to set the operation point of a fan?
          Jared Conway

          in your setup, it looks like you've set static pressure at both ends of 101325? a better choice would be environmental pressure at both ends if you're trying to simulate them being open to atmosphere. take a look at the help for more info on static pressure vs environmental pressure. in an ideal situation, you could make this an internal/external analysis where those ends are open to environement completely. (a worthwhile test to compare your boundary conditions against)

           

          I don't fully understand this comment:

           

          The operating point that is defined by the system curve and the characteristic curve of the fan is: flow of 115 m³/h and pressure of 600 Pa.

           

          But what I can tell you is how flow simulation is solving the problem. The simplest way your curve is defined is if there is zero pressure difference on either side, your fan will perform at full volume flow rate. If it is completely choked, you'll get zero volume flow rate. As the software is solving your problem, it is solving for the pressure on both sides of your fan and comparing the difference against your curve to generate the flow rate. It is an iterative process.

           

          So what you might want to do is create a goal on both sides of your fan for static pressure (or total pressure depending on how you defeined it) and then an equation goal for the difference. Compare that against your fan curve. it should match the flow rate leaving your fan. if it isn't, it could be a mesh issue or it could be a reference density issue.

           

          so in essence, there is no way to set the operating point. your systme defines what the operating point is. just like in the physical situation. if you wanted to set the operating point, you would simply set a volume flow rate.