UFR 4-19 Evaluation

Converging-diverging transonic diffuser

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References

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.

All the turbulence models capture the pressure coefficient distribution in the converging and the diverging part of the diffuser with a very good accuracy.However,in the region near the shock-wave (the region where the minimum pressure value is computed),the good level of accuracy is not maintained. The EVMs compute a less intense shock-wave,as it can be concluded from fig.11. Regarding the RSM,it computes a shock-wave with a greater value for the maximum Mach number,giving a lower pressure coefficient value.

The static pressure (Pa) and the Mach number contours for all the turbulence models are presented in figs.12 and 13. The flow field representation is almost the same for all the models with the RSM providing the largest Mach number value in comparison with the EVMs.

Figure 12: Weak shock wave case: Contours of static pressure

Figure 13: Weak shock wave case: Contours of Mach number

The strong Mach number case

The computed velocity distributions for the EVMs and RSM in comparison with the experimental data are shown in fig.14.

---

Contributed by: Z. Vlahostergios, K. Yakinthos — Aristotle University of Thessaloniki, Greece

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References

© copyright ERCOFTAC 2024