A method of solving the equations for the three–dimensional, incompressible laminar and turbulent flow along the intersection of two planes at ninety-degrees has been developed. The Alternating Direction Implicit (ADI) finite-difference method was applied for both types of flow. The turbulent stresses in the corner region were modeled with an eddy-viscosity model which was obtained from mixing length theory. The method was compared with other types of solutions for the laminar case and good agreement was achieved. For the turbulent case, the method was compared with experimental data and good agreement was obtained. The three momentum equations were solved simultaneously and the continuity equation was used to verify the method. The method appeared to predict the velocity components correctly since the continuity equation residual approached zero as the solution proceeded from the leading edge in the mainstream flow direction. No analysis was presented for the convergence or stability of the finite-difference equations and no convergence or stability problems solved were encountered when the finite-difference equations were solved. The method predicted symmetry about the corner bisector in all cases and gave the expected u-velocity profile along the bisector for both the laminar and turbulent cases. / Ph. D.

The laminar boundary layer over a semi-infinite flat plate which is impulsively set in motion in an incompressible fluid and which has a simultaneous step change in surface temperature was studied. An approximate method was derived which can be used to determine the thermal boundary layer thickness as a function of the distance from the leading edge and of time. From the thermal boundary layer thickness the temperature of the fluid can be determined at any position in the boundary layer and at any time. The local Nusselt number can also be determined from the thermal boundary layer thickness. The approximate solution was compared with exact steady-state and infinite-plate solutions of the energy equation and with a finite-difference solution of the unsteady continuity, momentum and energy equations. Agreement between the solutions was close enough to indicate that the approximate solutions for the temperature in the boundary layer and for the Nusselt number approximate the actual situation with reasonable accuracy. / Master of Science

This paper deals with three problems, (1) laminar incompressible viscous flow past a cylinder and a sphere, (2) laminar incompressible viscous flow past a finite flat plate (second-order solutions), and (3) laminar viscous past a sphere at a high Mach number. These problems are solved by using an implicit finite-difference method. The first problem (flow past a sphere and a cylinder) involves the classical boundary-layer equations which are the first approximation to the Navier-Stokes equations in a region near to the body surface for high Reynolds number. The computational results were obtained for the distribution of velocity components in the boundary-layer, and the variation of skin-friction and displacement-thickness along the body. The second problem (second-order flow past a finite flat plate) involves the second-order boundary-layer equations which introduce only the effect of the displacement-thickness in the case of flow past a flat plate. An assumption is made that the displacement-thickness is constant in the wake behind the flat plate. The adequacy of this assumption is checked from solutions based on the calculated displacement-thickness in the wake. The wake behind the finite flat plate is assumed laminar, and its displacement-thickness and the velocity distribution are computed downstream, by using the implicit finite-difference method. In the third problem (high Mach number flow past a sphere), constant density is assumed in the shock layer. This is nearly true in the stagnation-point region, especially if the flow is hypersonic and the temperature of the sphere is nearly the same as the stagnation-temperature. It is also assumed that the shock is nearly spherical, even though it is not spherical as it is in the inviscid case. The numerical results will show that the assumption of a spherical shock will, however, nearly be true. This problem involves the solution of the complete Navier-Stokes equations. These equations are solved for various Reynolds numbers by two methods; namely the truncated series method and the implicit finite-difference method. The solutions by the implicit finite-difference method are in excellent accord with those obtained by the series solutions in the stagnation-point region. As the computation by the finite-difference method proceeds downstream, the deviation of the finite-difference solution from the series solution increases. This is due to the fact that the series is valid only around the stagnation-point, and is thus expected to give inaccurate solutions downstream. The finite-difference method has no such restrictions, however, and gives accurate results in the whole flow field. In conclusion, solutions by the implicit finite-difference method have proven not only to be accurate but also to be stable in all examples computed. / Ph. D.

An oscillating-hot-wire system is developed to allow mean-flow velocity measurements in separated flows. Disturbance velocities can also be measured in regions of interest. An oscillating-arm assembly provides a directional bias to the hot-wire probe, and a linear-step assembly steps the probe through the boundary layer. These assemblies are mounted to a positioning plate which allows profiles to be taken at a discrete number of chord locations. Data sampling is computer regulated using a trigger pulse from an exterior source. A distance proximity probe gives the distance of the hot-wire probe from the model. Series of mean-velocity profiles over an airfoil are measured for R_C 150,000, 200,000, 250,000, and 300,000 with a= 14° and for R_C = 200,000 and 250,000 with α= 12°. / M.S.

M.S.

Yes / Cystic fibrosis (CF) is an inherited multi-system disorder characterised by chronic airway infection with pathogens such as Pseudomonas aeruginosa. Acquisition of P. aeruginosa by patients with CF is usually from the environment, but recent studies have demonstrated patient to patient transmission of certain epidemic strains, possibly via an airborne route. This study was designed to examine the survival of P. aeruginosa within artificially generated aerosols. Survival was effected by the solution used for aerosol generation. Within the aerosols it was adversely affected by an increase in air temperature. Both epidemic and non-epidemic strains of P. aeruginosa were able to survive within the aerosols, but strains expressing a mucoid phenotype had a survival advantage. This would suggest that segregating individuals free of P. aeruginosa from those with chronic P. aeruginosa infection who are more likely to be infected with mucoid strains may help reduce the risk of cross-infection. Environmental factors also appear to influence bacterial survival. Warming and drying the air within clinical areas and avoidance of humidification devices may also be beneficial in reducing the risk of cross-infection.

Following the concepts of stability analysis, a study is made of the pre-breakdown stage of transition to turbulence in boundary layers. The first step consists of a ’decoupling’ of the primary and secondary instabilities. A perturbation method is used to solve for the primary wave, in the absence of any secondary disturbances. Once the wave is calculated, it is decomposed into a basic flow portion and an interaction portion. The basic flow portion acts as a parametric excitation for the secondary wave. The interaction portion then captures the resonance effects of the secondary back onto the primary. A perturbation method is also used for the secondary and interaction components. The results obtained are in three principal forms: Landau constants, amplitude growth curves, and velocity functions. While in good agreement with experiments and simulations, these results offer new explanations to the observed processes. In addition, a physically-based transition criteria is established. / Ph. D.

The linear stability equations which govern the growth of small periodic disturbances for compressible, three-dimensional laminar boundary layer flow are derived in an orthogonal curvilinear coordinate system. The parallel flow assumption is utilized in the derivation. The system of equations is solved using a finite difference scheme similar to that in a current state-of-the-art stability analysis code, COSAL. The LR method and the inverse Rayleigh iteration procedure are used to calculate the eigenvalues. The stability of the three-dimensional compressible laminar boundary layer including the effects of streamline and surface curvature for flows past swept wings where crossflow type disturbances dominate is calculated. A parametric study is performed varying Reynolds number and sweep angle on an airfoil with a concave cutout in the leading edge region of the lower surface. It is known that convex curvature has a stabilizing effect on the laminar boundary layer. Conversely, concave curvature has a destabilizing effect. The magnitude of these effects for swept wing flows is determined. Non-stationary as well as stationary disturbances are calculated, and the most amplified frequencies are identified. N-factor correlations at the measured location of transition are made utilizing flight test data. Results indicate that amplification rates and hence, N-factors, for swept wing flows over convex surfaces are reduced by about 30 to 50 percent when curvature effects are included in the linear stability analysis. In addition, comparisons are made with some experimental results on a swept concave-convex surface. Calculated velocity vector plots show good agreement with observed disturbances in the laminar boundary layer over the concave surface. The results of the calculations show that concave curvature destabilizes "crossflow” type disturbances with a 30 percent increase in amplification rate. / Ph. D.

The aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn rate and increasing range. In addition to environmental benefits, the economic implications of improved fuel efficiency could be substantial due to the upward trend of fuel prices. This is especially true for the commercial aviation industry, where fuel usage is high and fuel expense as a percent of total operating cost is high. Transition from laminar to turbulent flow can be caused by several different transition mechanisms, but the crossflow instability present in swept-wing boundary layers remains the primary obstacle to overcome. One promising technique that could be used to control the crossflow instability is the use of spanwise-periodic discrete roughness elements (DREs). The Flight Research Laboratory (FRL) at Texas A&M University has already shown that an array of DREs can successfully delay transition beyond its natural location in flight at chord Reynolds numbers of 8.0x10^6. The next step is to apply DRE technology at Reynolds numbers between 20x10^6 and 30x10^6, characteristic of transport aircraft. NASA's Environmentally Responsible Aviation Project has sponsored a transonic laminar-flow wing glove experiment further exploring the capabilities of DRE technology. The experiment will be carried out jointly by FRL, the NASA Langley Research Center, and the NASA Dryden Flight Research Center. Upon completion of a wing glove design, a thorough computational evaluation was necessary to determine if the design can meet the experimental requirements. First, representative CAD models of the testbed aircraft and wing glove were created. Next, a computational grid was generated employing these CAD models. Following this step, full-aircraft CFD flowfield calculations were completed at a variety of flight conditions. Finally, these flowfield data were used to perform boundary-layer stability calculations for the wing glove. Based on the results generated by flowfield and stability calculations, conclusions and recommendations regarding design effectiveness were made, providing guidance for the experiment as it moved beyond the design phase.

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