Numerical Investigations of the Nonlinear Transition Stages in Boundary Layers for High Mach Numbers
Abstract
Compressibility effects decrease the growth rates of instability waves in hypersonic boundary layers according to linear stability t,heory (small disturbance amplitudes) compared to incompressible boundary layers. In particular, for larger boundary-layer edge Mach,numbers (roughly beyond Mach 5), the growth rates of both the first and second mode decrease with increasing edge Mach number. In ad,dition, from our previous research (M = 5 to 6) we found that compressibility also has a profound dampening effect on the nonlinear,transition regime. As a consequence, the nonlinear transition regime becomes considerably extended in the downstream direction. Our,preliminary simulation results suggest that this effect becomes even more pronounced with increasing Mach number. Thus, the nonlinea,r transitional flow may cover a very large downstream extent of actual hypersonic flight vehicles, such as for Hypersonic Glide Vehi,cles (HGVs). Our previous research has also shown that for a Mach number range 3.5 M_ 7, nonlinear interactions in the transit,ion regime can lead to the development of streamwise streaks of locally very high skin friction and heat transfer (hot streaks) th,at far exceed the turbulent values. This may negatively affect the aerodynamic performance and compromise the structural integrity o,f flight vehicles. The extended nonlinear transition region, combined with the various instability modes that exist in hypersonic bo,undary-layers, creates a situation where a wide range of instability modes can nonlinearly interact. Furthermore, our numerical inve,stigations, and experimental measurements carried out by others, have provided clear evidence that in the nonlinear regime the wall,pressure fluctuations on the model can be in excess of 35-45% of the mean wall pressure due to the large amplitudes that the instabi,lity waves can reach. Again, this may have very detrimental structural and aerodynamic implications, and in addition may be challeng,ing the guidance and control systems of hypersonic vehicles. Therefore, the overall objective of the proposed research is the unders,tanding of the fundamental physics in the nonlinear stages of hypersonic boundary layer transition for high Mach numbers. The main i,nvestigative tools will be high-fidelity Direct Numerical Simulations (DNS) in combination with stability investigations for both th,e primary and secondary instability region. For the proposed research, the sharp cone with a 7o half angle and the flow conditions o,f the experiments at the Hypervelocity Wind Tunnel 9 (T9) at the Arnold Engineering Development Complex (AEDC) for M=10 and M=14 (Ma,rineau et al. 2014, 2015, 2017) will be used. Furthermore, the effect of angle of attack on the nonlinear transition stages and brea,kdown will be investigated for several representative angles of attacks from the T9 experiments. The main focus of the proposed rese,arch is to explore if and how larger Mach numbers affect the nonlinear transition physics for asharp cone, including the effects of,angles of attack. Moreover, in order to understand the role of the free-stream-stream disturbances on the nonlinear transition stage,s, DNS will be carried out with realistic free-stream disturbance environment as in the wind-tunnel experiments.This abstract is app,roved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 08, 2022
- Source ID
- N000142212138
Entities
People
- Hermann Fasel
Organizations
- Office of Naval Research
- United States Navy
- University of Arizona