# Sig Turbulence / Dellenback Abrupt Expansion

## 1 Testcase description and experimental results

The OpenFOAM case-study was developed by:

Håkan Nilsson, Chalmers University of Technology, Gothenburg, Sweden

The turbulent swirling flow in an abrupt expansion was experimentally investigated by Dellenback, Metzger, and Neitzel . The geometry is illustrated in Figure 1. The inlet is located at the smaller diameter, where either a pure axial, or swirling flow at different swirl and Reynolds numbers is imposed.

Figure 1: Dellenback Abrupt Expansion geometry. Inlet at the small diameter.

The geometric data used in this case-study are the following:

 Inlet diameter $D_{in} = 50.78 mm$ Outlet diameter $D_{out} = 98.5 mm$ Expansion ratio $D_{out}/D_{in} = 1.94$ Inlet length $2*D_{in}$ Outlet length $10*D_{in}$

Dellenback presented 9 cases: 3 with purely axial flow, and 6 with swirl: $Re = \frac{U_{b,in}D_{in}}{\nu}$ $S = \left. \frac{\int_0^{R_{in}}V_\theta V_zr^2dr}{R_{in}\int_0^{R_{in}}V_z^2rdr}\right|_{z/D_{in}=-2.00}$ 30,000 0.00, 0.60, 0.98 60,000 0.00, 1.16 100,000 0.00, 0.17, 0.74, 1.23

The measurements were taken at the cross-sections shown in figure 2.

Figure 2: Measurement cross-sections. Numbers refer to Z/D, where D is the inlet diameter, and Z=0 at the abrupt expansion.

At each cross-section the following data is available:

• Axial mean velocity profiles.
• Tangential mean velocity profiles.
• Axial RMS velocity profiles.
• Tangential RMS velocity profiles.
• Most data sets show measurements on both sides of the centerline as a check for symmetry.
• Only some of the experimental data are arranged for the automatic post-processing. Please help arrange the rest in a similar way!

The case-study is thoroughly described in  (Slides), where there are also some preliminary results.

Future work using this case-study should refer to Gyllenram and Nilsson , Nilsson and Gyllenram , and Nilsson .

## 2 Published computational results

Computations have been performed by Schluter et al. , Gyllenram, Nilsson and Davidson , Gyllenram and Nilsson [4,5,8], Gyllenram , and Nilsson . Gyllenram and Nilsson  validated the filtered k-omega SST model using the Dellenback Abrupt Expansion case. Gyllenram and Nilsson  determined the optimal filter width ( $\alpha=3$). Nilsson and Gyllenram  implemented the kOmegaSSTF model in OpenFOAM, and validated it in the Dellenback Abrupt Expansion case. The OpenFOAM case-study was developed and first presented by Nilsson , at the 4th OpenFOAM Workshop in Montreal.