Converging-diverging transonic diffuser

Confined flows

Underlying Flow Regime 4-19

Evaluation

Comparison of CFD Calculations with Experiments

For both "weak" and "strong" Mach number cases,for comparison with the calculations, experimental data for four measurements stations after the shock-wave (h₁, h₂, h₃, h₄) are selected for the longitudinal velocity as well as pressure distributions along the bottom and the top wall of the diffuser. A representative figure of the shock-wave positions and the measurement stations is shown in fig.9.The x-location of the axial measurement stations are non-dimensionalized with the diffuser throat height,resulting in the following four stations: h₁ = 2.822, h₂ = 4.611, h₃ = 6.340 and h₄ = 7.493.

Figure 9: Shock-waves positions and experimental measurements

The weak Mach number case

The modelling results of the three adopted turbulence models are compared with the available experimental data for the "weak" Mach number case in figs.10 and 11.

All three turbulent models are able to capture the maximum velocity value. The main differences are observed in the boundary layer in the wall regions. The EVMs have similar behavior as they underpredict the axial velocity,especially in the top wall region of the diverging part of the diffuser. On the other hand,the RSM overpredicts the axial velocity on both walls providing thinner boundary layers. The pressure coefficient distributions along both walls of the diffuser are plotted in fig.11.