Direct numerical simulation of hypersonic transition induced by an isolated cylindrical roughness element

Abstract

Hypersonic boundary layer transition induced by an isolated cylindrical roughness element is investigated using direct numerical simulation method based on a finite volume formulation. To simulate the transition procedure by resolving the generation and evolvement of small-scale coherent structures, and capture the shock wave at the same time, high-order minimum dispersion and controllable dissipation scheme is validated and then applied. The results are compared with the available measurements in the quiet wind tunnel, such as the dominated frequency and root mean square of pressure. The computational dominated frequency of 19.23 kHz is very close to the experimental one, 21 kHz. Also, the disturbances of the roughness are mostly generated by the "jet" just before the roughness, and then they travel and develop downstream with the shear layer and vortex shedding. The transition is mainly dominated by the instabilities of both the horseshoe vortex and the shear layer. hypersonic, boundarry layer transtion, roughness PACS number(s): 47.27.Cn, 47.27.ek, 47.40.Ki, 47.85.ld Citation:Duan Z W, Xiao Z X, Fu S. Direct numerical simulation of hypersonic transition induced by an isolated cylindrical roughness element.

New omega vortex identification method

“…The DNS results in our previous study [13] show that the horseshoe vortex and the shear layer instabilities which come from the "jet" upstream of the roughness, dominate the flow transition procedure downstream. Figure 11 depicts the vortex structures around the cylindrical roughness element, through the Q-criterion with different thresholds and the W-criterion.…”

“…For example, some literature shows vortices visualized by iso-surfaces of Q=50000 (Duan et al [13]) while the vortices is well visualized in Figure 3 by iso-surfaces of Q=0.001. The choosing of threshold seems arbitrary without a framework.…”

“…However, the new threshold of l 2 is 100 times larger than the appropriate l 2 in the DNS case and the new threshold of Q is 500 times larger than the appropriate Q in the DNS case. In addition, some literature shows vortices can be properly visualized by iso-surfaces of Q=50000 (Duan et al [13]). A rather fixed threshold in W-method is one of the major advantages over other vortex identification methods.…”

UQ eSpace

“…• Largest Re in 3D was 6.66×10 6 by Duan et al [40] • Most studies investigate boundary layer phenomena in the presence of a shock and only a few include chemical reactions.…”

“…• Added complexity of extending to higher dimensions Memory requirements are also important because once there are a large number of cells (a few DNS literature studies use more than 100 million nodes), storage becomes a large issue [37], [35], [40].…”