Doyle Knight

Advances in CFD prediction of shock wave turbulent boundary layer interactions

Abstract The paper presents a summary of recent computational fluid dynamics (CFD) simulations of shock wave turbulent boundary layer interactions. This survey was prepared as part of the activity of NATO RTO Working Group 10 which was established in December 1998, and considers results obtained subsequent to the previous survey paper on the same topic by Knight and Degrez (“Shock Wave Boundary Layer Interactions in High Mach Number Flows—A Critical Survey of Current CFD Prediction Capabilities”, AGARD Advisory Report AR-319, Volume II, December 1998). Five configurations are considered: 2-D compression corner, 2-D shock impingement, 2-D expansion–compression corner, 3-D single fin and 3-D double fin. Recent direct numerical simulations (DNS), large eddy simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) simulations are compared with experiment. The capabilities and limitations are described, and future research needs identified.

Large-Eddy Simulation of a Supersonic Boundary Layer Using an Unstructured Grid

A Mach 3 adiabatic flat plate turbulent boundary layer is studied using large-eddy simulation (LES). The filtered compressible Navier-Stokes equations are solved on a three-dimensional unstructured grid of tetrahedral cells. A compressible extension of the rescaling-reintroducing process of Lund et al. is developed to generate the inflow conditions. The effect of the subgrid-scale motion is incorporated using two approaches, namely, monotone integrated LES (MILES) and the Smagorinsky subgrid-scale model. A detailed grid refinement study is performed

Survey of Aerodynamic Drag Reduction at High Speed by Energy Deposition

A selected survey of aerodynamic drag reduction at high speed is presented. The dimensionless governing parameters are described for energy deposition in an ideal gas. The types of energy deposition are divided into two categories. First, energy deposition in a uniform supersonic flow is discussed. Second, energy deposition upstream of a simple aerodynamic body is examined. Both steady and unsteady (pulsed) energy deposition are examined for both categories, as well as the conditions for the formation of shock waves and recirculation regions. The capability of energy deposition to reduce drag is demonstrated experimentally. Areas for future research are briefly discussed.

Control of Edney IV Interaction by Pulsed Laser Energy Deposition

An experimental investigation was conducted to examine the effect of a pulsed Nd:YAG laser energy addition on the shock structures and surface pressure in a Mach 3.45 flow past a sphere. Two configurations were considered: 1) a sphere in a uniform freestream and 2) an Edney IV interaction generated by impingement of an oblique shock on the bow shock of the sphere

Laser Energy Deposition in Quiescent Air

Laser energy deposition in quiescent air has been studied experimentally and numerically. The study is focused on the gasdynamic effects of the laser energy spot on the e ow structure. A Gaussian proe le for initial temperature distribution is proposed to model the energy spot assuming the density is initially uniform. A e ltered Rayleigh scattering technique has been used for obtaining the experimental results. These consisted of e ow visualization of the blast wave, and simultaneous pressure, temperature, and velocity measurements. Good agreement has been achieved between numerical and experimental results for shock radius vs time. The comparison of computed and experimental density, pressure, temperature, and velocity outside the laser spot show good agreement as well.

A hybrid explicit-implicit numerical algorithm for the three-dimensional compressible Navier-Stokes equations

A hybrid explicit-implicit numerical algorithm has been developed for the three-dimensional mean compressible Navier-Stokes equations. The algorithm combines the explicit finite difference algorithm of MacCormack and an implicit algorithm for the viscous sublayer and transition wall regions of the turbulent boundary layers. The algebraic turbulent eddy-viscosity model of Baldwin and Lomax is employed. A bodyoriented coordinate transformation is utilized to facilitate treatment of arbitrary flow regions. The hybrid algorithm has been vectorized on the CDC CYBER 203 computer using the SL/1 vector programming language developed at NASA Langley. The accuracy of the numerical algorithm, established previously for twodimensional flows with strong viscous-inviscid interaction (including flow separation), is validated for threedimensional flows. The algorithm is applied to the interaction of an oblique shock wave with a turbulent boundary layer in three dimensions. The computed results generally are found to be in close agreement with the experimental data. The hybrid algorithm is shown to provide a substantial improvement in computational efficiency compared to a vectorized MacCormack explicit algorithm alone.

Polymer-drug interactions in tyrosine-derived triblock copolymer nanospheres: a computational modeling approach.

A combination of molecular dynamics (MD) simulations and docking calculations was employed to model and predict polymer-drug interactions in self-assembled nanoparticles consisting of ABA-type triblock copolymers, where A-blocks are poly(ethylene glycol) units and B-blocks are low molecular weight tyrosine-derived polyarylates. This new computational approach was tested on three representative model compounds: nutraceutical curcumin, anticancer drug paclitaxel and prehormone vitamin D3. Based on this methodology, the calculated binding energies of polymer-drug complexes can be correlated with maximum drug loading determined experimentally. Furthermore, the modeling results provide an enhanced understanding of polymer-drug interactions, revealing subtle structural features that can significantly affect the effectiveness of drug loading (as demonstrated for a fourth tested compound, anticancer drug camptothecin). The present study suggests that computational calculations of polymer-drug pairs hold the potential of becoming a powerful prescreening tool in the process of discovery, development and optimization of new drug delivery systems, reducing both the time and the cost of the process.

Insights in Turbulence Modeling for Crossing-Shock-Wave/Boundary-Layer Interactions

The impact of turbulence modeling on the numerical simulation of the crossing-shock-wave/boundary-layer interactionsoccuringinaMach4e owon7 ££ 7deg,7 ££ 11deg,and15 £ 15degdouble-sharpe nplatesisanalyzed. The full Reynolds-averaged Navier ‐Stokes equations are solved with linear and weakly nonlinear formulations of the k‐! turbulence model, on grids up to 4 ££ 10 6 cells. The overpredicted heat transfer on the bottom plate is shown to be closely related to the main three-dimensional features developing in these e ows. The stronger the interaction, the more the numerical solutions violate the realizability principles. By introducing a dependence of cµ on the velocity gradients, realizable solutions are obtained and analyzed. The heat-transfer coefe cients are effectively lowered but not sufe ciently to meet the experimental data. The expected impact of other corrections, based on a limitation of the turbulent length scale or some compressibility effects, is evaluated and shown to be insufe cienttoe llthegapbetweencomputedandmeasuredheat-transfercoefe cients.Thestreamlinesarriving near the wall in the regions of overpredicted heat transfer are shown to originate from the very narrow regions close to the e n leading edges, in the upper part of the incoming boundary layer, and to be associated with an increase of turbulent kinetic energy when approaching the bottom wall, rather than when crossing the shock waves.

Calculations of laminar viscous flow over a moving wavy surface

The steady, laminar, incompressible flow over a periodic wavy surface with a prescribed surface-velocity distribution is found from the solution (via Newtons method) of the two-dimensional Navier–Stokes equations. Validation runs have shown excellent agreement with known analytical (Benjamin 1959) and analytico-numerical (Bordner 1978) solutions for small-amplitude wavy surfaces: For steeper waves, significant changes are observed in the computed surface-pressure distribution (and consequently in the nature of the momentum flux across the interface) when a surface orbital velocity distribution, of the type found in water waves, is included.

High-Performance Supersonic Missile Inlet Design Using Automated Optimization

A multilevel design strategy for supersonic missile inlet design is developed. The multilevel design strategy combines an efe cient simple physical model analysis tool and a sophisticated computational e uid dynamics (CFD) Navier ‐ Stokes analysis tool. The efe cient simple analysis tool is incorporated into the optimization loop, and the sophisticated CFD analysis tool is used to verify, select, and e lter the e nal design. The genetic algorithms and multistart gradient line search optimizers are used to search the nonsmooth design space. A geometry model for the supersonic missile inlet is developed. A supersonic missile inlet that starts at Mach 2.6 and cruises at Mach 4 was designed. Signie cant improvement of the inlet total pressure recovery has been obtained. Detailed e owe eld analysis is also presented.