Isothermal Dump Combustor With Swirl

Isothermal confined swirling and non-swirling flows in a dump combustor. The case is a 2D axisymmetric flow with constant temperature.

The considered domain in figure 1 is a portion of a cylindrical combustor chamber. The inlet pipe has a diameter of \(D_i=2R_i =101.6\) mm and a total length of 2850 mm. The combustor chamber has a diameter of \(D=2R=152.4\) mm and a total length of 1850 mm. \(H\) is the height of the step between the inlet pipe and the chamber. A diagram of the experimental arrangement is shown in figure 2.

Fig. 1: Combustor geometry

Fig. 2: Experimental arrangement (from Ref.[2])

The combustor chamber is set up after a cylindrical swirler housing of a smaller diameter which is following a long straight inlet pipe. Downstream from the sudden expansion caused by this difference in diameter, the flow is characterized by a recirculation zone like the one occurring in a corner-type flow and a very slow decay of the swirl intensity in the core of the flow. The corner recirculation zone length decreases from about \(8H\) in the non-swirling case to about \(4.3H\) for a swirl intensity number of \(S=0.3\) and about \(3.2H\) for \(S=0.5\). This decreasing with the swirl intensity is caused by a more rapid expansion of the flow after separation due to the more intense centrifugal forces. Moreover, vortex breakdown occurs for \(S=0.5\), and the central recirculating flow due to this breakdown extends to about \(4.4H\) downstream of the step.

At the last measuring station, the vortex is stabilized in both cases so that the measured mean velocity profiles are rather similar at \(x/H=15\) and \(x/H=24\).

• Air with a kinematic viscosity: \(\nu = 1.56 \times 10^{-5}\) m²/s.
• Centreline velocity in the inlet pipe: \(U_{ref} = 19.2 \pm 0.4\) m/s.
• Inlet Reynolds number (based on pipe diameter and centreline velocity): \(Re = 1.25 \times 10^5\).
• Different axial flow type swirlers provide swirl numbers of \(S=0.3\), \(0.4\) and \(0.5\). The swirl number is defined as:

\[ S = \left( \int_0^R UWr^2\,dr \right) /\left( \int_0^R RU^2r\,dr \right) \]

Upstream of the swirler, the flow corresponds to fully-developed pipe flow conditions. For those wanting to start calculations from downstream of the swirler, measurements of the quantities below are available for a cross-section just downstream from the sudden expansion, at \(x=0.38H\), for 4 different swirl numbers: \(S=0\), \(0.3\), \(0.4\) and \(0.5\).

• Mean velocities
• Second Moments
  • Reynolds stresses: \(\overline{u^2}\), \(\overline{v^2}\), \(\overline{w^2}\), \(\overline{uv}\), \(\overline{uw}\)
  • Turbulent kinetic energy
• Third order moments: \(\overline{uuv}\), \(\overline{uuw}\), \(\overline{uvv}\), \(\overline{uww}\)
• Skewness: \(S_u\), \(S_v\), \(S_w\)

The three-dimensional flow field using was measured using a two component LDV set-up, with measurements taken in the horizontal and vertical planes.

Profiles are available of the following quantities at 12 different \(x/H\) sections for \(r\) ranging from \(0\) (centerline) to \(D/2\):

• Mean velocities
• Second Moments
  • Reynolds stresses: \(\overline{u^2}\), \(\overline{v^2}\), \(\overline{w^2}\), \(\overline{uv}\), \(\overline{uw}\)
  • Turbulent kinetic energy
• Third order moments: \(\overline{uuv}\), \(\overline{uuw}\), \(\overline{uvv}\), \(\overline{uww}\)
• Skewness: \(S_u\), \(S_v\), \(S_w\)
• Stream function for \( 0 < x < 18H\) and \(0 < r < D/2\)

Sample plots of some of the datasets are available.

The data can be downloaded as compressed archive files from the links below, or as individual files by selecting those required from the tables.

• sdc-allfiles.zip
• sdc-allfiles.tar.gz

The raw data is contained in two files, sdc-number1.dat and sdc-number2.dat, together with a readme.txt explanation. The individual profiles below have been extracted and processed from these two files.

S.P. Vanka has calculated the flow field corresponding to these initial conditions using the \(k\)-\(\varepsilon\) model. His results are presented at the end of the referenced paper. Rapid convergence was achieved using the standard \(k\)-\(\varepsilon\) model with a Block Implicit Multigrid Method and a coupled solution of the momentum and continuity equations. His results indicate that the model is able to represent successfully the additional production of \(k\) due to azimuthal swirl.

1. Nejad A.S., Favalord, S.C., Vanka, S.P., Samimy, M., Langenfeld, C. (1989). Application of Laser Velocimetry for Characterization of Confined Swirling Flow. Journal of Engineering for Gas Turbines and Power, Vol. 111, pp. 36-45.
2. Ahmed, S.A., Nejad, A.S. (1992). Velocity Measurements in a Research Combustor Part 1: Isothermal Swirling Flow. Journal of Experimental Thermal and Fluid Science, Vol. 5, pp. 162-174.
3. Ahmed, S.A., Boray, R.S., Nejad, A.S. (1989). An experimental investigation of isothermal swirling flow in a model of a dump combustor, Proc. IX ISABE, Athens.
4. Favalord, S.C., Nejad, A.S., Ahmed, S.A., Miller, T., Vanka, S.P. (1989). An experimental and computational investigation of isothermal swirling flow in an axisymmetric dump combustor, AIAA Paper No. 89-0620.

Indexed data: