Travis S. Kocian

Boundary-layer instability and transition on a flared cone in a Mach 6 quiet wind tunnel

Measurements of boundary-layer transition location and boundary layer profiles on a sharp-tipped 5o-half-angle flared cone were made in a low-disturbance Mach 6 wind tunnel. Uncalibrated boundary-layer profiles of mean and fluctuating voltage representative of mass flux are obtained using constant temperature hot-wire anemometry at several axial locations, and are notionally compared with preliminary simulations. Spectral energy content is observed between 250 and 310 kHz – the first measurements of frequencies typical of the second mode instability at Texas A&M. Growth of this high-frequency content is compared with N-factor results from linear parabolised stability equation (LPSE) computations. Possible sources of disagreement between the experimental and computed frequencies for second-mode growth are discussed, as are future improvements to the hotwire anemometry technique. Nevertheless, the successful measurement of high-frequency content highlighted here constitutes an important step toward acquisit...

Hypersonic Stability Analysis of a Flared Cone

The JoKHeR computational tool is used to provide linear and nonlinear parabolized stability equation analysis of the Langley 93-10 flared cone. The second-mode instability mechanisms and their response to slight angle of attack changes and temperature variation is explored and compared to experiments in the Mach 6 Quiet Tunnel located at Texas A&M University. The most-amplified second-mode frequency is found to be sensitive to small incidence angles. In an effort to better model broadband initial conditions, the effects on boundary-layer stability are compared for multiple discrete and single discrete primary modes and their harmonics. The inclusion of multiple primary modes results in a noticeable difference in N-factors when compared to the single primary mode case. The multiple mode interactions were found to increase the nonlinear stabilization effect and may be affecting the flow of energy into the primary modes from the mean flow. Mean flow distortion widens and compresses the boundary layer and is tuning lower and higher frequencies respectively.

EPIC: NPSE Analysis of Hypersonic Crossflow Instability on Yawed Straight Circular Cone

The purpose of this paper is to provide nonlinear parabolized stability equation (NPSE) analysis of stationary crossflow vortices within a hypersonic boundary layer. EPIC is a new NPSE capability developed within the Computational Stability and Transition Laboratory at Texas A&M. Results for the 7 half-angle straight cone geometry at 6 angle of attack are presented in this paper. Comparisons with the experimental results of Craig & Saric (2014) in the Texas A&M Mach 6 Quiet Tunnel are provided. Techniques for modeling stationary crossflow vortex paths and the evolution of spanwise wavenumber derived solely from the basic state solution are presented and verified via the DNS solution of Balakumar & Owens (2010).

Stability of Hypersonic Compression Cones

Our activities focus on the identification and understanding of the second-mode instability for representative configurations in hypersonic flight. These include the Langley 93-10 flared cone and the Purdue compression cone, both at 0o angle of attack at Mach 6. A nonlinear parabolized stability equation (NPSE) capability, called JoKHeR (Kuehl et al. 2012), is applied. Steady basic-state calculations are obtained with Pointwise and GASP. Verification studies are provided. Then, second-mode instabilities are modeled on the Langley 93-10 flared-cone model, and progress in validation with the experimental findings of Hofferth et al. (2012) is discussed. Through application of NPSE and linear parabolized stability equations (PSE) to both geometries, it is concluded that mean-flow distortion tends to amplify frequencies less than the peak frequency and stabilize those greater by modifying the boundary-layer thickness. As initial disturbance amplitude is increased and/or a broad spectrum disturbance is introduced, direct numerical simulations (DNS) or NPSE appear to be the proper choices to model the evolution, and relative evolution, because these computational tools include these nonlinear effects (mean-flow distortion).

Bandwidth Effects on Mack-Mode Instability

Hypersonic Mack-mode instability on the Purdue compression cone is investigated by means of the nonlinear parabolized stability equations method. To date, most nonlinear stability analyses have considered a single frequency primary mode, however experimental observations find a finite-bandwidth of disturbances. To determine the effects of disturbance bandwidth on Mack-mode stability, the nonlinear evolution of different numbers of primary Mack-modes is considered. It is found that disturbance bandwidth has a negative feedback effect, suppressing the growth of the primary Mack-modes. A novel methodology is introduced to isolate nonlinear saturation effects from other nonlinear mechanisms. In addition to nonlinear saturation, a separate mechanism, “nonlinear detuning,” is found to have a significant influence on Mach-mode growth. These results suggest that bandwidth should be accounted for when studying the later stages of transition and developing hypersonic laminar flow control schemes.

Fuel efficiency and laminar flow control

The International Air Transport Association has reported that 27.5% of the operating budget for a co…