Experimental investigations were conducted with and without the presence of the surface-mounted obstacle to quantify its effects on the far wake. The obstacle chosen for this study was a 3:2 elliptical nose NACA 0020 tail wing-body (Rood body), approximately of height equal to the boundary layer thickness at one of the measurement locations of the flow. The experiments were performed by varying the Reynolds number of the flow and manipulating the pressure gradient distributions using a NACA 0012 airfoil placed within the wind tunnel test section. The measurements were acquired utilizing a spanwise traversing boundary layer rake and a point pressure sensing microphone array. The findings reveal that the presence of the obstacle introduces disruptions in the flow, such as vortex and jet regions in the wake. However, the overall flow behavior remains consistent with that of an undisturbed turbulent boundary layer, for varying Reynolds numbers and pressure gradients. Notably, an adverse pressure gradient and lower Reynolds number both accentuate the prominence of the jet and vortex region within the wake, with the trend reversing towards the other end of the spectrum. This behavior is akin to the larger turbulent boundary layer under adverse pressure gradients and lower Reynolds numbers. Furthermore, the presence of obstacles induces an increase in the overall level of the wall pressure spectrum by approximately 2 dB, regardless of the flow condition. Additionally, it leads to a deviation in the slope of the mid-frequency range of the autospectra compared to the smooth wall case. Specifically, the mid-slope frequency of an undisturbed turbulent boundary layer is steeper than that observed in the disturbed wake flow caused by the obstacle. / Master of Science / The interaction between turbulence and aerodynamic surfaces gives rise to wall-pressure fluctuations, which in turn induce structural vibrations and acoustic noise. On surfaces turbulent flows meet, antennae, flaps, and other frequently mounted measuring devices. The flow in their wake is impacted by the coherence of a turbulent boundary layer being disrupted by these impediments mounted on aerodynamic surfaces. They also alter the nature of the pressure fluctuations that are generated on the surface of interest. The far wake of a Rood Body obstacle was studied using a point pressure sensing microphone array and a spanwise traversing boundary layer rake. Experimental measurements were taken for a range of Reynolds numbers and pressure gradient environments at the Virginia Tech Stability Wind Tunnel. Results show that the boundary layer rake measurements resolve the presence of the obstacle wake successfully, by characterizing the wake structures and confirming the presence of jet and vortex regions in the wake of the obstacle. Surface pressure measurements reveal that the presence of the obstacle causes the low-frequency content of the wall pressure to be less dominant than the no obstacle case, while the high-frequency content becomes more dominant in the presence of the obstacle. The presence of obstacles also increases the overall levels of the wall pressure spectrum by approximately 2 dB.

Turbulent boundary layers flowing over a smooth surface were studied to understand the influence of varying pressure gradients and flow Reynolds number on the boundary layer growth and mean turbulent properties. The test was conducted in the Virginia Tech Stability Wind Tunnel with a 0.914 m chord length, NACA 0012 Airfoil in the test section. This airfoil was rotated to different angles of attack to induce varying pressure gradients on the boundary layer developing on the test section walls. Mean pressure measurements, boundary layer pressure measurements, and time-resolved, wall-normal, stereoscopic particle image velocimetry (TR-PIV) measurements were made. The TR-PIV data was acquired at a chord-based Reynolds number of 1.2 million, 2 million, and 3.5 million, at a sampling rate of 1 kHz, in two different camera configurations. The boundary layer pressure measurements were acquired at different flow Reynolds numbers ranging between 0.76 million and 3.5 million. Both adverse and favorable pressure gradients of varying intensities were imposed on the boundary layer by rotating a 0.914 m chord NACA 0012 airfoil to angles of attacks between -{10}^o and {12}^o. Measurements at varying streamwise locations enabled the study of boundary layer flow development under changing pressure gradients. The pressure gradient influences were observed in the boundary layer characteristic properties, on the mean velocities, and on the Reynolds stresses present in the flow. The pressure gradient influences were found to be consistent at varying Reynolds numbers, but the intensity of their effects was influenced by the flow Reynolds number. Moreover, the influence of pressure gradients and flow Reynolds numbers was evident in both outer and inner scales. The test data acquired was also validated with previous works. / M.S. / The interaction of turbulent boundary layers and smooth surfaces is prevalent in our world. It plays a vital role in various phenomena, such as, aircraft stall, cabin noise, and structural vibrations. Varying flow conditions influence the behavior of boundary layers and the extent of their implications. The effects of pressure gradients and the level of turbulence, described by the Reynolds numbers, on turbulent boundary layer flow was studied. This was done through an experiment conducted at the Virginia Tech Stability Wind Tunnel facility. The test data was acquired through boundary layer pressure measurements and Time-Resolved, Stereoscopic Particle Image Velocimetry (TR-PIV) at varying streamwise locations in the test section. A 0.914 m chord, NACA 0012 airfoil was placed in the test section and its angle of attack was varied to -{10}^o,0^o,\ \ and\ {12}^o to induce a favorable, minimum, and an adverse pressure gradient, respectively. The TR-PIV measurements were acquired at a sampling rate of 1 kHz and in two different camera configurations. The flow Reynolds number was based on the airfoil chord length (Re_c) and was varied to 1.2 million, 2 million, and 3.5 million for the TR-PIV tests. The boundary layer pressure measurements were acquired using an array of 30 Pitot probes placed in the boundary layer of the flow. The flow Reynolds number for these test runs ranged between 0.76 million and 3.5 million. The acquired data was used to analyze the mean statistical properties of turbulent boundary layers primarily focusing on the mean velocities, boundary characteristic parameters, Reynolds normal stresses, and Reynolds shear stresses. The results showed that the nature of pressure gradient influences on the mean properties of turbulent boundary layers remained consistent regardless of the flow Reynolds number. However, the intensity of the pressure gradient effects was influenced by the flow Reynolds number. These observations were made at various streamwise data acquisition locations through which the evolution of the flow was also studied. Lastly, the results obtained in this experiment were validated with previous works.