Browsing by Author "Brock, Jerry S."

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    A consistent direct-iterative inverse design method for the Euler equations
    Brock, Jerry S. (Virginia Tech, 1993-04-05)
    A new, consistent direct-iterative method is proposed for the solution of the aerodynamic inverse design problem. Direct-iterative methods couple analysis and shape modification methods to iteratively determine the geometry required to support a target surface pressure. The proposed method includes a consistent shape modification method wherein the identical governing equations are used in both portions of the design procedure. The new shape modification method is simple, having been developed from a truncated, quasi-analytical Taylor's series expansion of the global governing equations. This method includes a unique solution algorithm and a design tangency boundary condition which directly relates the target pressure to shape modification. The new design method was evaluated with an upwind, cell-centered finite-volume formulation of the two-dimensional Euler equations. Controlled inverse design tests were conducted with a symmetric channel where the initial and target geometries were known. The geometric design variable was a channel-wall ramp angle, 0, which is nominally five degrees. Target geometries were defined with ramp angle perturbations of J10 = 2 %, 10%, and 20 %. The new design method was demonstrated to accurately predict the target geometries for subsonic, transonic, and supersonic test cases; M=0.30, 0.85, and 2.00. The supersonic test case efficiently solved the design tests and required very few iterations. A stable and convergent solution process was also demonstrated for the lower speed test cases using an under-relaxed geometry update procedure. The development and demonstration of the consistent direct-iterative method herein represent the important first steps required for a new research area for the advancement of aerodynamic inverse design methods.
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    A modified Baldwin-Lomax turbulence model for turbomachinery wakes
    Brock, Jerry S. (Virginia Tech, 1991-01-08)
    A critical evaluation of the Baldwin-lomax (Bl) turbulence model for shock/shear layer interactions, reversed flow, and curved, asymmetric wakes is made. No general definition for reference line is available for wakes, and difficulties exist for length scale prediction in complex flows. An entropy envelope for shear layers, and the locus of maximum entropy to define the wake centerline is proposed. The range of the Bl model is limited to the entropy envelope. This provides all relevant modeling data, and allows general application of existing reversed flow corrections. The total enhancements are flow adaptive and form the Dynamic Bl model. This robust model is more accurate in complex boundary layers and wakes. The Dynamic Bl model is applied to a supersonic fan cascade at the design incidence. Sharp differences in turbulent viscosities were seen between the the original, Baseline Bl, and Dynamic Bl models. Only slight differences exist in the overall cascade solutions. This includes loss factors which were produced by different mechanisms. The Baseline BL model predicted separation on the SS surface and larger standing vorticies off the TE. The Dynamic Bl model predicted attached boundary layers, smaller standing vorticies off the TE, but uniformly higher skin friction. The shock structure in the cascade may reduce the flow field dependence on specific viscosity profile characteristics, so these may be less important than overall turbulence levels.