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Flow optimization, heat transfer analysis of a burning chamber using-CFD.

Objectives

To carry out flow analysis of a gas turbine burning combustion chamber[2] and to propose the best possible design of primary and secondary holes, to achieve optimal primary to secondary air flow ratio at cold flow conditions.

Methodology

All the computational chain from the numerical definition of the variables values to the results handling was automated by means of

(1) A parametric CAD model of the device

(2) A robust hexahedral multi-block meshing (ICEM CFD)

(3) A batch--mode use of the CFD solver[2], with automatic post-processing (Fluent).

The software has been developed from fundamental principles of fluid flow and heat transfer. Fluent 6.0 has been used for present simulations. Governing equations solved are.

Continuity equations, Momentum balance equations, Total energy balance equation and Thermal energy balance equation.

Geometry for inside domain thickness has been created by ICEM software so as to put the structured mesh.

Because of limitation of computational resources, mesh dependency study has not been done and a mesh of 1.1 million nodes has been used.

We have incorporated all the possible ways to optimize the primary to secondary hole ratio's[3], which includes performing analytical calculations which was referred as an baseline for the CFD calculations. Performing meshing, solver setting activities and tabulating the post processed results to study the effect of all possible options such as variation of inlet velocities, effect of temperature (which leads to buoyancy effect in flow), effect of number of secondary holes in the burning chamber, effect of opening area of primary holes, Location of secondary holes etc.,

Thermal analysis has been carried out for the optimized options to see the effect of temperature on the primary to secondary flow ratio's. Results have shown that there was no significant effect of temperature on the flow split between the primary and secondary flow area. Effect of flow and physical parameters on the primary to secondary flow distribution ratio.

* Effect of mass flow rate at the main inlet (velocities).

--0.1 m/s, 0.25 m/s, 0.5 m/s

* Effect of primary inlet opening area.

--fully, 1/3rd, 1/4th, 1/6th & 1/8* opened

* Effect of secondary hole diameter.

--3 mm, 5 mm & ?? mm dia.

Boundary Conditons

Main Inlet: Velocity inlet.

Outlets: Atmospheric outlet (static pressure 1bar), Primary holes:

Results and Discussions

Fig.1 and 2 shows the velocity contours of the flow (along the plane) through the secondary holes of the burning chamber. For 1/4th and 1/8th primary opening area, 6mm Secondary holes and for the inlet velocity of 0.5m/s.

It is observed that the flow is independent of temperature and found that these is no significant change in the velocity of the fluid due to the raise in temperature.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Total mass flow entering the burning chamber with hot flow condition is dependent on draft or pressure drop available. Which is resultant of buoyancy effect.

Results with 1/8th opening primary area & all rows of secondary holes meeting the theoretical primary to secondary air flow ratio of 4.0 & above. It has been observed that primary to secondary air flow ratio is almost independent on the inlet mass flow rates.

Fig 3 and 4 shows the path lines flows for 1/4th and 1/8th primary opening area.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Table.1 shows the tabulation for Mass flows for Primary openings for 0.1 m/s of inlet velocity for 6mm secondary holes.

Conclusions

It has been observed that primary to secondary air flow ratio is less dependent on cold and hot flow conditions. Total mass flow entering the burning chamber with hot flow condition is dependent on draft or pressure drop available. Which is resultant of buoyancy effect.

Results with 1/8th opening primary area & all rows of secondary holes meeting the theoretical primary to secondary air flow ratio of 4.0 & above.

Best theoretical primary to secondary air flow ratio of ~5.5 has been obtained with 1/8th opening primary area and all rows of secondary holes and clearance outlet closed.

Nomenclature

Symbol Discription

V Velocity

m Mass flow rate

L Length

D Diameter burning chamber

d Dia of secondary holes

A Opening area at primary hole

T Temperature

[rho] density of air

References

[1] Reed, T.B., Walt, R. Ellis, S.,Das, a. and Deutch, S, Superficial Velocity-the Key to Downdraft Gasification, ibid.

[2] A F Bicen, J J Mc guirk and J M L M Palma. " Modelling gas turbine combustor flow fields in isothermal flows experiments" Proceedings of Institution of mechanical engineers, part A: Journal of power energy, vol 203,1989,pp 113-122.

[3] J F Carrote and S J stevens " The Influence of dilution hole geometry on jet mixing" ASME Transactions, Journal of engineering gas turbine power, vol 112, 1990, pp 73-79.

[4] Fluent INC, Fluent 6 User Manual, Fluent INC:2003 pp.8-1

(1) S. Gowreesh, (2) V.K Pravin, (3) K. Rajagopal and (4) Veena PH.

(1) Infotech Enterprises Ltd, Hyderabad, India

(1) E-mail: gowrish.subbu@gmail.com

(2) Professor and Dean, PG Co-ordinator PDACE, Gulbarga, India

(3) Former VC-JNTU University, Hyderabad, India

(4) Professor, Women's college, Gulbarga, India
Table 1: Mass flows for primary and secondary opening.

 Mass flow kg/s

Primary opening Main Primary Secondary Clearance
 inlet opening opening outlet

 Full 2.55E-02 1.66E-02 5.62E-03 3.24E-03
 1/3rd 2.55E-02 1.07E-02 7.91E-03 6.90E-03
 1/4th 2.55E-02 8.29E-03 8.38E-03 8.83E-03
 1/6th 2.55E-02 6.40E-03 9.43E-03 9.67E-03
 1/8th 2.55E-02 9.95E-03 9.95E-03 1.07E-02

 Mass flow kg/s

 Primary Main Primary Secondary Clearance
 inlets inlet opening opening outlet

 Full 2.55E-02 1.66E-02 5.62E-03 3.24E-03
 1/8th Cold 2.55E-02 1.07E-02 7.91E-03 6.90E-03
 flow@inlet
 0.5m/s &
 outlet:1bar
 1/8th Hot 2.55E-02 8.29E-03 8.38E-03 8.83E-03
 flow@inlet
 0.5m/s &
 outlet:1bar
 1/8th Hot 2.55E-02 6.40E-03 9.43E-03 9.67E-03
 flow@inlet
 1bar &
 outlet:1bar

Primary opening Primary to
 secondary
 air flow
 ratio

 Full 1:0.388
 1/3rd 1:0.74
 1/4th 1:1.01
 1/6th 1:1.47
 1/8th 1:2.04

 Primary Primary to
 inlets secondary
 air flow
 ratio

 Full 1:0.388
 1/8th Cold 1:0.74
 flow@inlet
 0.5m/s &
 outlet:1bar
 1/8th Hot 1:1.01
 flow@inlet
 0.5m/s &
 outlet:1bar
 1/8th Hot 1:1.47
 flow@inlet
 1bar &
 outlet:1bar
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Author:Gowreesh, S.; Pravin, V.K.; Rajagopal, K.; Veena, Ph.
Publication:International Journal of Dynamics of Fluids
Date:Jun 1, 2010
Words:1097
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