report: Computational Fluid Dynamics Modelling of the Vortex Ventilator MK4 Rev 2 PrePAreD for: Ventrite International
D O C U men t C O N trol Any questions regarding this document should be directed to: Mr Stephan Schmitt Qfinsoft (Pty) Ltd Postnet Suite #274 Private Bag X8 ELARDUSPARK 0047 Tel : +27 12 345 1917 Mobile: +27 72 766 8051 E-mail : stephan@qfinsoft.co.za DOCUMENT HISTORY Version Number Revision Date Pages/ Section Amendment Summary Author 1.0 30/03/2010 All Creation Stephan Schmitt 1.1 03/08/2010 All Added throat discharge Stephan Schmitt DISTRIBUTION LIST Version Name Organisation Date 1.0 Thomas Kingsley Qfinsoft (Pty) Ltd 30/03/2010 1.0 Mark van Biljoen Ventrite International 30/03/2010 1.0 David Spilkin Ventrite International 30/03/2010 1.1 Thomas Kingsley Qfinsoft (Pty) Ltd 03/08/2010 1.1 Mark van Biljoen Ventrite International 03/08/2010 Approved by: Date: 03/08/2010 Company Reg. No. 99/17078/07 Directors: Dr J A Visser, Dr D J de Kock Page 2 of 14
C O N ten ts 1. EXECUTIVE SUMMARY...4 2. INTRODUCTION...5 3. MODELLING SETUP...6 4. RESULTS...9 5. CONCLUSION... 14 6. REFERENCES... 14 Page 3 of 14
1. e x e CUt IVe SUmmA ry Qfinsoft is pleased to provide this report to Ventrite International on the completion of the CFD (Computational Fluid Dynamics) consultancy service. This document provides results on the Computational Fluid Dynamics Modelling of the Vortex ventilator. The results of the analyses can be summarised as follows: There are some dead zones around the deflector plates in the ventilator The discharge coefficient based on the duct area is calculated to be 0.347. The discharge coefficient based on the open throat area is calculated to be 0.469. The current design is a large improvement from the initial design. Page 4 of 14
2. INtrO D U C t I O N The study involves the analysis and characterisation of the Vortex ventilator. The flow patterns through the Vortex ventilator are examined and the discharge coefficient is calculated. Page 5 of 14
3. m ODe L L I N G S etu p This section provides an overview of the modelling techniques used in the study. ANSYS Fluent [1] was used to solve the CFD simulation. The geometry was prepared in ANSYS pre-processor GAMBIT [2]. A CAD drawing of the ventilator geometry was supplied by Ventrite. Figure 1 displays the geometry used in this CFD study. Air enters the ventilator from the bottom (blue edge, flows through it, and exits at the top (red edge). The yellow edge represents the symmetry line. A representative section of the mesh can be seen in Figure 2. The mesh consisted of 500 000 quadrilateral elements. Open throat area Duct area Figure 1: Modelled domain Page 6 of 14
Figure 2: Representative section of the mesh The model was simplified to a 2-dimensional section with the ventilator inside a duct. A symmetry boundary along the centre of the ventilator (yellow edge) was also used in the simulation. A zero slip condition was applied to the walls of the duct to ensure that there are no losses in the model, except through the ventilator. Table 1 below shows the material properties used in this study. Several runs with different inlet velocities were solved to determine a representative discharge coefficient. The boundary conditions used in this simulation are summarised in Table 2. Property of air Table 1: Material properties Value Density 1.225 [kg/m 3 ] Viscosity 1.7894e-5 [kg/m.s] Page 7 of 14
Table 2: Boundary conditions Boundary Zone Condition Centreline on ventilator Symmetry Duct wall No friction Velocity inlet 0.5 1.0 1.5 [m/s] Pressure outlet Atmosphere Turbulence was accounted for with the two-equation SST k-ω turbulence model. Four steady state simulations were solved. The case with an inlet velocity of 1.5 m/s has been solved with two different solvers to determine the effect the solver has on the simulation. It was found that the solver does not influence the solution significantly. Page 8 of 14
4. r e s u l t s This section covers the results for the Vortex ventilator. The results include contours and vectors of velocity, contours or pressure, and path lines through the ventilator. The case with an inlet velocity of 0.5 m/s is used for all images. Figure 3 and Figure 4 show contours of total pressure through the ventilator. There is a slight low pressure area above the ventilator. Figure 3: Contours of static pressure [Pa] Page 9 of 14
Figure 4: Close-up of contours of static pressure [Pa] Contours of velocity magnitude are displayed in Figure 5 and Figure 6. The maximum velocity through the ventilator is four times the inlet velocity. Figure 7 displays velocity vectors coloured by velocity magnitude on the ventilator cross section. Path lines coloured by velocity magnitude is shown in Figure 8. The path lines indicate dead areas in the flow. The path line plots and velocity vectors show some areas in the ventilator where the air is circulating as well as some dead zones around the deflector plates at the top of the ventilator. Page 10 of 14
Figure 5: Contours of velocity magnitude [m/s] Figure 6: Close-up of contours of velocity magnitude [m/s] Page 11 of 14
Figure 7: Vectors of velocity, coloured by velocity magnitude [m/s] Figure 8: Path lines released at the inlet, coloured by velocity magnitude [m/s] Page 12 of 14
Table 3 summarises the pressures determined from the CFD simulations, as well as the calculated discharge coefficients based on the duct area. The discharge coefficient gives a relation between the pressure drop and the flow rate through equipment, in this case the ventilator. The equation which represents this relationship is shown below: [1] where P : Pressure drop across the ventilator [Pa] C : Discharge coefficient ρ : Density [kg/m 3 ] V : Normal velocity on ventilator throat area [m/s] Table 3: Discharge coefficient data based on duct area Velocity Average inlet pressure (determined form CFD) Discharge coefficient 0.5 [m/s] 1.3 [Pa] 0.343 1.0 [m/s] 5.1 [Pa] 0.346 1.5 [m/s] 11.3 [Pa] 0.349 The average discharge coefficient based on the duct area is 0.347. The average discharge coefficient based on the open throat area is 0.469. Figure 9 displays a graph of the measured CFD data together with Equation 1 calculated with the average discharge coefficient. Page 13 of 14
Pressure drop [Pa] 25 Vortex Ventilator MK4 Rev2 20 15 10 5 CFD Equation 0-5 0 0.5 1 1.5 2 2.5 Normal duct velocity [m/s] Figure 9: Measured CFD data and equation graph 5. C O N C L U S I O N There are dead zones around some of the deflection plates at the top of the ventilator. The discharge coefficient based on the duct area is calculated to be 0.347. The discharge coefficient based on the open throat area is 0.469. The current design is a large improvement from the initial design. 6. r e f e r e NCe S [1] ANSYS Release 12.1, ANSYS.Inc, Canonsburg, Pennsylvania, USA. www.ansys.com [2] GAMBIT 2.4, ANSYS.Inc, Canonsburg, Pennsylvania, USA. www.fluent.com Page 14 of 14