This thesis presents an experimental investigation into a compressible turbulent wall jet issuing from a slot, and flowing over a surface with streamwise curvature, followed by a plane wall recovery region. The purpose of this data was to provide suitable test cases to aid in the design and validation of turbulence models used for curved flow situations in computational fluid dynamics. The presence of streamwise curvature provides an extra rate of strain to the flow which effects both the mean flow field and the turbulence structure. The effects of curvature are dependent on the ratio of the slot width to the radius of curvature. The effects are increased with the magnitude of this ratio. Hot film anemometry was used to measure the mean flow and Reynolds stresses under six different flow regimes. Four experiments were performed using a constant slot to radius ratio, and the supply pressure ratio was varied. Two further experiments were performed at a constant pressure ratio, but at differing slot to radius ratios. In all cases, the extra rate of strain was found to increase the jet growth and velocity decay rates beyond those of a plane wall jet. 'History effects' were apparent where there was a change from flow with streamwise wall curvature to that without. The turbulence structure was found to require a finite distance along the recovery section before it reverts to a plane wall turbulence structure. The presence of the extra rate of strain, and the history effects at sudden changes in surface curvature, make strong demands on any turbulence model. Various turbulence models have been tested, and although no one turbulence model has proved robust enough for all flow situations, a number of models have been identified to provide superior performance under certain conditions. The use of a higher order numerical scheme has also been found to reduce the effects of numerical diffusion, leading to improvements in the predictions of the flow shock cell structure and the breakaway performance of the jet.

Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10° and 20° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1° to 27° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case. / Master of Science

The subsonic wind tunnel facility at Mississippi State University has been converted to an open test section configuration. An experimental setup was developed which is easily configurable to allow for further research. Measurements of flow quality over select portions of the test section were made to attain a basic understanding of the performance of the new configuration. A program was developed in LabVIEW to control a 3-axis traverse and perform necessary data reduction. The traverse control program was developed to perform data acquisition using a hotilm probe to facilitate the necessary measurements. Data was gathered at two wind tunnel velocity settings over several test section locations. Results of the testing program yielded recommendations on the use of the open configuration. This paper documents the procedure and setup of the testing program to include discussion of the control/data acquisition program and a discussion of the findings and recommendations.

This thesis investigates the use of hot-film thermal anemometers to align a plate on a wind tunnel at Hill Air Force Base that is used to calibrate Angle of Attack Transmitters on F-16s. A reoccuring problem with this wind tunnel is that no two instruments can verify an angle reading of the the mounting plate for the Angle of Attack Transmitters to the air stream in the wind tunnel. Multiple thermal anemometer calibration methods, such as Jorgensen’s equation and a look-up table are implemented to attemp to achieve consistent measurements between multiple probes. The results show that it is neccessary to have conditions match between calibration and measurement when attempting to achieve high accuracy with angle measurements.

In this study, novel lamination techniques are introduced for the coating of fabrics in order to enhance their ballistic/needle penetration resistance properties. Pressure sensitive adhesive (PSA) was used to create flexible ballistic composite panels with ultra-high molecular weight polyethylene (UHMWPE) fabric. An increase in processing pressure from 0.1 to 8 MPa significantly improved the ballistic performance against 9 mm FMJ ammunition of UHMWPE composite. The number of layers required to stop the bullet were reduced from 45 to 22 layers after lamination without a significant increase in stiffness. The backface signature (BFS) was reduced from 19.2 mm for the 45 layer neat samples to 11.7 mm for the 25 layer laminated samples pressed at 8 MPa. The second lamination technique used patterned thermoplastic hot film to create flexible UHMWPE composite laminates. Hexagonal patterns were cut through a heat transfer vinyl carrier sheet using a vinyl cutter and was used as a mask between the UHMWPE fabric and hot film during heat treatment in order to have the fabric coated only on those regions. The patterns had a nominal diameter of 27.9 mm with a 1 mm gap between each region. A significant improvement in the ballistic performance of UHMWPE fabric is observed after coating each individual layer with patterned hot film and 25 layers of laminated fabric were sufficient to stop a .357 magnum FMJ ammunition compared to unlaminated neat fabric which required 45 layers to stop the bullet. Patterning of the hot film did not negatively affect the ballistic performance of the composite laminates whilst increasing their flexibility in relation to using plain hot film with no patterning involved. It resulted in a 21% increase in bending angle of the 25 layer samples v and 9.5% reduction in bending length of the single plies which both relate to greater flexibility because a higher bending angle and lower bending length correlates to more flexibility. The same technique of patterning of hot film is used in the lamination of woven cotton fabric to enhance needle penetration resistance properties whilst maintaining the flexibility. Patterns used in this study were either hexagonal or a combination of hexagons and triangles and the nominal diameter ranged from 2.6-13.5 mm. The lamination significantly improved the 25G hypodermic needle penetration resistance of the fabric. By increasing the number of laminated fabric plies from 1 to 2, the needle resistance force increased by up to 150%. However, in comparison to just one layer, the flexibility decreased by about 12% to 26% for two and three layers, respectively. It was observed that reducing the sizes of the patterns improved the flexibility of the samples by up to 30% without compromising the needle penetration resistance. / Thesis / Master of Applied Science (MASc)

Flow measurements were made on two highly loaded, low pressure turbine blade configurations in a low-speed, linear cascade facility. The L1M blade has a design Zweifel coefficient of 1.34 with a peak cp near 47% cx (mid-loaded) and the Pack B blade has a design Zweifel coefficient of 1.15 with a peak cp at 63% cx (aft-loaded). Flow velocity and surface pressure measurements were taken for Rec=20,000 and 3% inlet freestream turbulence. For these operating conditions, a large separation bubble forms on the blade suction surface, beginning at 59% cx and reattaching at 86% cx on the L1M blade and a non-reattaching bubble beginning at 68% cx on the Pack B. A spanwise row of discrete vortex-generating jets located at 59% cx on the Pack B and 50% cx on the L1M were used as a separation control device and were pulsed at a frequency of 5 Hz with a duty cycle of 25%. The Pack B with its open separation bubble proved to be a better candidate for VGJ control than the L1M with its closed separation bubble. Further studies were made on the Pack B blade comparing wake and VGJ effects. A wake generator was used to simulate the periodic passing of upstream wakes through the blade passage for the Pack B configuration. The wake passing frequency of 4.5Hz was set to match a typical engine flow coefficient for a low pressure turbine. Data were taken using PIV and a hot-film anemometer mounted on a blade following device. Velocity, turbulence, and intermittency measurements were made along the suction surface of the blade to characterize the bubble dynamics and transitional behaviors for both the presence of unsteady wakes and pulsing VGJs. The wakes caused early breakdown of the separated free shear layer resulting in a thinning of the separation region. The VGJs caused an upstream disturbance which convects downstream, temporarily pushing off the separation bubble. Overall, both wakes and VGJs suppress the size of the steady-state separation bubble, though through different mechanisms. Three-dimensional aspects of the jet disturbance are studied by investigating the effects of the VGJs at two spanwise locations.

Aerodynamic measurements were taken over models of the Boeing 777 high fidelity isolated landing gear in the 6- by 6-foot Virginia Tech Stability Wind Tunnel (VT-SWT) at a free-stream Mach number of 0.16. Noise control devices (NCD) were developed at Virginia Tech [9] to reduce noise by shielding gear components, reducing wake interactions and by streamlining the flow around certain landing gear components. Aerodynamic measurements were performed to understand the flow over the landing gear and also changes in the flow between "Baseline" and "NCD" configurations (without and with Noise Control Devices respectively). Hot-film, Pitot-static measurements and flow visualization using tufts were performed over an isolated 26% scale-model high fidelity landing gear for the "Baseline" and "NCD" configurations. Contours of turbulence intensity, normalized wake velocity and normalized total pressure loss for both configurations are compared. The "Baseline" configuration was also compared with the NASA Ames study conducted by Horne et al [7]. Hot-film measurements are also compared to Microphone Phased Array results which were acquired at Virginia Tech by Ravetta [8]. A novel technique for processing hot-film measurements by breaking turbulence into octave bands as acoustic measurements is presented. Particle Image Velocimetry (PIV) measurements were taken at six different locations over the 13% scale-model landing gear with no door and at a truck angle of zero degrees. Results are compared to PIV measurements taken over the wheels of a four-wheel landing gear by Lazos [10-12]. PIV results such as average velocity contours and vectors, streamlines and instantaneous velocity contours and vectors are presented. Results presented from PIV and flow visualization are in good agreement with results from Lazos [10-12]. / Master of Science

Vortex generator jets (VGJs) have proven to be effective in minimizing the separation losses on low-pressure turbine blades at low Reynolds numbers. Experimental data collected using phase-locked particle image velocimetry and substantiated with a hot-film anemometer were used to answer fundamental questions about the influence of VGJs on a separated boundary layer. The data were collected on the suction surface of the Pack B blade profile, which has a non-reattaching separation bubble beginning at 68% axial chord. Two VGJ pulse histories were created with different frequencies, jet durations, and duty cycles. The mechanisms responsible for boundary layer separation control were shown to be a combination of boundary layer transition and streamwise vortical structures. Jet duration and relaxation time were important VGJ characteristics in determining the extent of control. The unsteady environment characterisitic of the low-pressure turbine section in a gas turbine engine effectively reduces the time-averaged separation zone by as much as 35%. Upstream blade rows create unsteady flow disturbances (wakes) that transition the flow. This transitioned flow propagates downstream, re-attaching the separation bubbles on the subsequent blade row. Phase-locked PIV and hot-film measurements were used to document the characteristics of this separation zone when subjected to synchronized unsteady wakes and VGJs. The phase difference between VGJ actuation and the wake passing, blowing ratio, and VGJ duration were optimized to achieve the greatest time-averaged control of the separation zone. The experimental data were used to identify the important characteristics of the wake/jet interaction. Phase-locked PIV measurements were taken to isolate the wake event (wake only), the VGJ event (jets only), and the synchronized combination of unsteady wakes and jets. The synchronized conditions achieved maximum separation bubble control. The presence of wake and jet induced calmed zones are also noted.

The skin friction and cross-flow separation location on a non-body-of-revolution (non-BOR) ellipsoidal model performing constant-yaw turns and a pitch-up maneuver, each with roll oscillation were studied for the first time. The detailed, low uncertainty, flow topology data provide an extensive experimental database on the flow over non-BOR hull shapes that does not exist anywhere else in the world and serves as a crucial tool for computational validation. The ellipsoidal model was mounted on a roll oscillation machine in the Virginia Tech Stability Wind Tunnel slotted wall test section. Hot-film sensors with constant temperature anemometers provided skin friction magnitudes on the body's surface for thirty-three steady flow model orientations and three unsteady maneuvers at a constant Reynolds number of 2.5 million. Cross-flow separation locations on the model were determined from span-wise minima in the skin friction magnitude for both the steady orientations and unsteady maneuvers. Steady hot-film data were obtained over roll angles between ±25° in 5° increments with the model mounted at 10° and 15° yaw and at 7° pitch with respect to the flow. The roll oscillation machine was used to create a near sinusoidal unsteady roll motion between ±26° at a rate of 3 Hz, which corresponded to a non-dimensional roll period of 5.4. Unsteady data were obtained with the ellipsoidal model mounted at 10° and 15° yaw and at 7° pitch during the rolling maneuver. Cross-flow separation was found to dominate the leeside flow of the model for all orientations. For the yaw cases, the separation location moved progressively more windward and inboard as the flow traveled downstream. Increasing the model roll or yaw angle increased the adverse pressure gradient on the leeward side, creating stronger cross-flow separation that began further upstream and migrated further windward on the model surface. For the pitch flow case, the cross-flow separation remained straight as the flow moved axially downstream. The strongest pitch cross-flow separation was observed at the most negative roll angle and dissipated, moving further downstream and inboard as the model's roll angle was increased. The unsteady flow maneuvers exhibited the same flow topology observed in the quasi-steady conditions. However, the unsteady skin friction and separation locations lagged their quasi-steady counterparts at equivalent roll angles during the oscillation cycle. A first order time lag model and sinusoidal fit to the separation location data quantified the time lags that were observed. / Ph. D.

Hot wire anemometers have been used in several wind velocity sensors deployed in Mars. They are based in keeping the temperature of a surface at a constant value, above the ambient. This is done by means of a heater controlled with an electronic system. The cooling rate of each point at the sensor surface can be used to calculate the wind velocity and direction. However, due to turbulent fluctuations, the cooling rate is not constant even in the case of constant velocity. Moreover, RANS simulations cannot estimate such fluctuations as they only provide an estimation of the averaged flow field. The goal of this work has been to estimate such fluctuations and the e↵ect they might have on the sensor readings. To do so, the turbulent cooling rate (Nusselt number) of a sensor with a generic shape, under the typical conditions to be find in Mars, has been simulated using high performance LES (Large Eddy Simulation) simulations and compared with RANS and URANS simulations.