The UFAST case consists of a naturally growing turbulent boundary on the floor of a wind tunnel interacting with the tunnel’s normal recovery shockwave (Figure 1). It has been experimentally investigated by Bruce and Babinsky (2008) in the framework of the FP6 UFAST Europen project (Doerffer et al., 2011). Measurements data, obtained by Bruce and Babinsky (2008), are available for steady and unsteady shock waves for three different flow conditions (M = 1.3 and Reδ* = 14770, M = 1.4 and Reδ* = 13600, M =1.5 and Reδ* = 13000 where Reδ* is the Reynolds number based on the displacement thickness δ* and M is the Mach number). The test section free stream Mach number is adapted by changing convergent-divergent nozzle liner configurations. Shock wave excitation can be achieved by rotating an elliptical shaft mounted in the tunnel downstream of the interaction to form a second throat with a continuously varying cross sectional area. Measurements data include Schlieren images and movies, LDA measurements, pressure measurements and unsteady shock dynamics data.
Figure 1: Overview of the wind tunnel test section.
Figure 2: Oil visualisation of the flow pattern at the shock location on the wind tunnel lower wall for the steady case at M = 1.4.
The main features of the flow are the interaction of the shock with the boundary layer and the corner recirculating flows as well as the shock-induced separation. The modelling challenges faced when simulating this flow are pressure-induced separation, shock-induced separation and corner separation, shown in Figure 2 for the steady case at M = 1.4. Numerical investigations carried out during the FP6 UFAST European project (Doerffer et al., 2011) by Bruce et al. (2010) demonstrated that RANS eddy-viscosity models have significant weaknesses in predicting this case, because of their inability to predict properly the corner flow separation. This inability leads to asymmetric flow predictions whose intensity varies depending on the model selected. More complex RANS models, such as those investigated in the FP7 ATAAC European project, which have anisotropic capabilities, are expected to provide more accurate predictions, compared to the eddy-viscosity RANS models. The development of models being able to correctly represent this case will directly improve the predicting capabilities of the tools used, as an example among many, in the aerospace industry for the design of airframes. A number of complex cases (denominated Applications Challenges - AC) considered in ATAAC are directly related to this example and include wing-body civil aircraft configurations at transonic speed (AC02: DLR-F6 and AC03: HiRETT), a UAV (AC05) configuration and a generic combat aircraft configuration (AC06).
- Bruce, P.J.K., Babinsky, H. (2008) “Unsteady Shock Wave Dynamics”, J. Fluid Mech., vol. 603, pp. 463-473.
- Bruce, P, Babinsky, H., Tartinville, B, Hirsch, C. (2010) “An Experimental and Numerical Study of an Oscillating Transonic Shock Wave in a Duct”, AIAA 2010-0925.
- Doerffer, P., Hirsch, C., Dussauge, J.-P., Babinsky, H., Barakos, G.N. (eds) (2011) “Unsteady Effects of Shock Wave induced Separation”, Notes on Numerical Fluid Mechanics and Multidisciplinary Designs, vol. 114, Springer (to appear in 2011).