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Historically, the addition of polymers to turbulent flows of Newtonian fluids has been known to effectively reduce turbulent friction drag by up to 80 %. Conducted in the Hydrodynamics Laboratory in Virginia Tech, this research presents a comprehensive analysis into drag reducing effects through experimental, theoretical, and computational analyses. A major focus of this research was the evaluation of one of the newest viscoelastic Reynolds Averaged Navier-Stokes (RANS) turbulence models. Based on the k−ε−v 2−f framework, this model describes the viscoelastic effects of polymer additives using the Finitely Extensible Nonlinear Elastic-Peterlin (FENEP) constitutive model. To evaluate its accuracy, multiple simulation scenarios were benchmarked against Direct Numerical Simulation (DNS) data. Results indicated, that the viscoelastic RANS turbulence model shows a high accuracy against DNS percentages of drag reduced when dealing with higher solvent viscosity to polymer viscosity ratios, but revealed inconsistencies at lower ratios. Additionally, our theoretical and empirical flow rates from the inclined channel were closely aligned. The results of this study highlight the significant capacity of polymer additives to improve energy efficiency in industries that heavily rely on fluids / Master of Science / In fluid dynamics, understanding the behaviour of fluids under different conditions can unlock solutions to many engineering challenges. An area of much interest is the introduction of polymers to turbulent flows. The addition of polymers to turbulent flows can effectively dampen turbulence, leading to reduced drag. Our research, conducted at Virginia Tech's Hydrodynamics Laboratory, engaged in further study regarding this phenomena. We employed one of the latest viscoelastic computational models to predict drag reduction in polymer additive flows. This advanced model operates on the foundation of certain mathematical constructs, taking into account various parameters associated with polymeric solutions. By comparing our model's predictions with high-end direct numerical simulations (DNS), we found it to be highly accurate, especially when the base fluid had a much higher viscosity than the polymer additives. But, it's worth noting that the model showed some deviations in cases where this viscosity difference was less pronounced. Furthermore, our tests also showcased a close alignment between predicted and observed flow rates in an inclined channel setup. Our findings underscore the potential of polymers to revolutionize industries, enhancing energy efficiency in processes that involve fluid flows

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The primary objective for this work was to evaluate the reliability of computational fluid dynamics (CFD) tools in the prediction of upstream surface pressure disturbance and pressure drag of various instrument excrescence shapes for a small aircraft flight test device called the Boundary Layer Data System (BLDS). Insights on pressure disturbance will serve as a guide for the placement of BLDS probes/sensors, and pressure drag can be used to ensure sufficient adhesive is used to install BLDS instrumentation. The Mach number for all CFD cases was 0.12 and the Reynolds number based on excrescence height varied from 4 x 104 to 1 x 105. Excrescences studied have height to local boundary layer thickness ratios 0.75 < h/d < 1.9 and width to height ratios 3 ≤ w/h < 4. Wind tunnel tests were first conducted in the Cal Poly Fluids Lab’s 2 x 2-foot wind tunnel to obtain measurements of the upstream pressure disturbance created by a blunt BLDS housing and a streamlined BLDS fairing. Upstream surface pressure data was measured for two-dimensional excrescences and for three-dimensional models of the blunt and streamlined housings. A rake measurement of the undisturbed boundary layer profile at the leading edge location of each excrescence was also obtained to compare to the computed boundary layer. Prior to viscous modeling with CFD, potential flow theory was used to compute the inviscid upstream pressure disturbance for a generic excrescence on a smooth surface. A Rankine oval was generated using superposition, and a MATLAB program was written to evaluate ovals of varying chord and height. The potential flow results for the pressure distribution upstream of a Rankine oval were found to agree quite well with 2-D measurements and viscous CFD. Ansys ICEM CFD and FLUENT were used for computational modeling. A viscous CFD model was first created in two-dimensions and validated by comparing the upstream pressure disturbance results to the two-dimensional experimental measurements. The validated FLUENT case set-up was extended to three-dimensions, and three-dimensional models were created for blunt and streamlined BLDS excrescences. ICEM CFD was used to generate meshes for 2-D and 3-D models and FLUENT was used to solve the Reynolds-Averaged Navier Stokes (RANS) equations in conjunction with the Spalart-Allmaras turbulence model. Mesh independence studies and evaluation of discretization error were conducted to ensure that the final mesh employed provided adequate spatial resolution. The computed flow features, and results for dimensionless pressure and drag, were compared to experimental measurements and classic aerodynamic principles to evaluate the CFD solutions. It was concluded that CFD can accurately compute upstream pressure disturbances and pressure drag for excrescences mounted to a smooth surface. The viscous calculations showed that the effect of excrescence shape on upstream pressure field is only significant within 6 body heights of the leading edge. Beyond that, no significant difference in the pressure disturbance was observed between different excrescence configurations. Additionally, the spanwise pressure disturbance was found to become negligible at about 1-1.5 housing widths away from the upstream centerline of each excrescence regardless of its shape. Finally, all computed blunt housing models resulted in a pressure drag coefficient of about 0.5 which corroborates past experimental drag measurements. This thesis has set-up a working FLUENT CFD case that can be used for future computational studies related to the BLDS and provides detailed guidance for existing BLDS housing shapes beyond the rules of thumb currently used for informing housing designs.

A validation of parallel TURBO, an unsteady RANS turbomachinery solver, is performed for Rotor 35. Comparisons of the rotor's operational range for computational and experimental data as well as comparisons of its spanwise performance characteristics for a single blade passage provide depth to the validation and show a very favorable agreement. Further operational and performance comparisons against experiment are used for multiple blade passage simulations. Multiple blade passage simulations are shown to demonstrate noticable gains over the single blade passage simulation in solution accuracy against experiment. Also demonstrated are the asymmetric flow features that develop at the near stall operating condition for multiple blade passages. These single and multiple blade passage simulations are presented as groundwork for future research examining the effect of periodic boundary conditions on the growth of computational stall cells within a rotor or stage configuration.

The purpose of this dissertation is to develop a methodology for designing active control laws in a computational aeroelasticity environment. The methodology involves employing a systems identification technique to develop an explicit state-space model for control law design from the output of a computational aeroelasticity code. The particular computational aeroelasticity code employed in this dissertation solves the transonic small disturbance equation using a time-accurate, finite-difference scheme. Linear structural dynamics equations are integrated simultaneously with the computational fluid dynamics equations to determine the time responses of the structural outputs. These structural outputs are employed as the input to a modern systems identification technique that determines the Markov parameters of an "equivalent linear system". The eigensystem realization algorithm is then employed to develop an explicit state-space model of the equivalent linear system. Although there are many control law design techniques available, the standard Linear Quadratic Guassian technique is employed in this dissertation. The computational aeroelasticity code is modified to accept control laws and perform closed-loop simulations. Flutter control of a rectangular wing model is chosen to demonstrate the methodology. Various cases are used to illustrate the usefulness of the methodology as the nonlinearity of the computational fluid dynamics system is increased through increased angle-of-attack changes. / Ph. D.

This research concerns the development and validation of simulation of the beam-target interaction to determine the target temperature distribution as a function of time for a given target geometry, surface radiation intensity and free stream flow condition. The effect of a turbulent supersonic flow was investigated both numerically and experimentally. Experiments were in the Virginia Tech supersonic wind tunnel with a Mach 4 nozzle, ambient total temperature, total pressure of 160 psi and Reynolds number of 5 × 10⁷/<i>m</i> . The target consisted of a 6.35 mm stainless steel plate painted flat black. The target was irradiated with a 300 Watt continuous beam Ytterbium fiber laser generating a 4 mm Gaussian beam at 1.08 micron 10 cm from the leading edge where a 4 mm turbulent boundary layer prevailed. An absorbed laser power of 65, 81, 101, 120 Watts was used leading to a maximum heat flux between 1035 to 1910 <i>W/cm</i>². The target surface and backside temperature was measured using a mid-wave infrared camera. The backside temperature was also measured using eight type-K thermocouples. Two tests are made, one with the flow-on and the other with the flow-off. For the flow-on case, the laser is turned on after the tunnel starts and the flow reaches a steady state. For the flow-off case, the plate is heated at the same power but without the supersonic flow. The cooling effect is seen by subtracting the flow-off temperature from the flow-on temperature. This temperature subtraction is useful in cancelling the bias errors such that the overall uncertainty is significantly reduced. A new conjugate heat transfer algorithm was implemented in the GASP solver and validated by predicting the temperature distribution inside a cooled nozzle wall. The conjugate heat transfer algorithm was used to simulate the experiments at 81 and 65 Watts. Most computations were performed using the Spalart-Allmaras turbulence model on a 280, 320 cell grid. A grid convergence study was performed. At 65 Watts, good agreement was found in the predicted surface and backside temperature. On the surface, cooling was underpredicted close to the center and better agreement was seen away form the center. On the backside, good agreement was found for the temperature and temperature difference. Compared to the 65 Watt case, the 81 Watt case displays more asymmetry and a region of increased cooling is found upstream. The increased asymmetry was also seen on the backside by both the thermocouple and infrared temperature measurements. The computation underpredicts the surface temperature by 7% for the flow-off case. Again, cooling is underpredicted at the surface near the center. For all power settings, convective cooling significantly increases the time required to reach a given temperature. / Ph. D.

A new unsteady rotor/fuselage interactional aerodynamics model has been developed. This model loosely couples a Generalized Dynamic Wake Theory (GDWT) to a Navier-Stokes solution procedure. This coupling is achieved using a newly developed unsteady pressure jump boundary condition in the Navier-Stokes model. The new unsteady pressure jump boundary condition models each rotor blade as a moving pressure jump which travels around the rotor azimuth =and is applied between two adjacent planes in a cylindrical, non-rotating grid. Comparisons are made between predictions using this new model and experiments for an isolated rotor and for a coupled rotor/fuselage configuration. / Ph. D.

A numerical investigation of the performance of two candidate designs for injection into supersonic flow, including a comparison of two renormalized group theory (RNG) based k-epsilon turbulence models with a more conventional k-epsilon model. The chosen designs were an unswept ramp injector with four injection ports and a novel nine-hole injector array. The objectives of the investigation were to provide reliable computational solutions to the flowfields in question using both RNG and standard k-epsilon turbulence models and to compare the solutions to experiment, thereby to judge the relative performance of the turbulence models. A second objective of the investigation was to use the computed data to provide design insights for the nine-hole injector array. This investigation made use of GASP(tm) version 2.2, a commercial computational fluid dynamics code that was augmented by the addition of one RNG-based k-epsilon turbulence model derived by Zhou, et. al. and one variant of Zhou's model, which was derived by the author. Mesh sequencing studies were performed to measure solution quality, with the fine mesh for the injector array containing roughly one million grid nodes and the fine mesh for the ramp injector containing more than six million grid nodes. Results of these studies indicated that the injector-array solution was significantly under-resolved in the farfield, though the quality was better in the vicinity of the injector itself. The ramp-injector solution, while not perfectly grid-resolved, showed much better grid convergence in both the nearfield and farfield. Accordingly, comparison with experiment was better for the ramp injector than for the injector array. For both injectors, the differences between solutions generated with RNG-based k-epsilon and standard k-epsilon turbulence models were negligibly small." Despite inadequate grid resolution in the farfield, the computational investigation of the nine-hole injector array did yield several important design insights. Particularly, the significance to mixing and losses of the placement of the outer injectors of the second and third rows was determined. / Ph. D.

Several different time-integration algorithms for the Euler equations are investigated on two distributed-memory parallel computers using an explicit message-passing paradigm: these are classic Euler Explicit, four-stage Jameson-style Runge-Kutta, Block Jacobi, Block Gauss-Seidel, and Block Symmetric Gauss-Seidel. A finite-volume formulation is used for the spatial discretization of the physical domain. Both two- and three-dimensional test cases are evaluated against five reference solutions to demonstrate accuracy of the fundamental sequential algorithms. Different schemes for communicating or approximating data that are not available on the local compute node are discussed and it is shown that complete sharing of the evolving solution to the inner matrix problem at every iteration is faster than the other schemes considered. Speedup and efficiency issues pertaining to the various time-integration algorithms are then addressed for each system. Of the algorithms considered, Symmetric Block Gauss-Seidel has the overall best performance. It is also demonstrated that using parallel efficiency as the sole means of evaluating performance of an algorithm often leads to erroneous conclusions; the clock time needed to solve a problem is a much better indicator of algorithm performance. A general method for extending one-dimensional limiter formulations to the unstructured case is also discussed and applied to Van Albada’s limiter as well as Roe’s Superbee limiter. Solutions and convergence histories for a two-dimensional supersonic ramp problem using these limiters are presented along with computations using the limiters of Barth & Jesperson and Venkatakrishnan — the Van Albada limiter has performance similar to Venkatakrishnan’s. / Ph. D.