Boundary layer characteristics at the trailing edge of a tiltrotor blade model were measured using a flattened pitot probe and a single hot wire. The blade was mounted in Virginia Tech Stability Wind tunnel stationary on a turntable on the wind tunnel's upper wall with the tip pointing down. The measurement point was located at 1 mm behind the trailing edge to make it possible to measure the flow near the blade surface and measure the boundary layer on both sides of the trailing edge in a same run. Mean velocity profiles were measured for a variety of Reynolds numbers and angles of attack. Turbulence intensity and spectral measurements were performed using a single hot wire at the highest Reynolds number. Conclusion was reached that both of the flattened pitot probe and single hot wire are good for boundary layer thickness measurements. Displacement thickness, which is important in trailing edge noise prediction, was calculated from the profile data and fit using an algebra expression against the tip angle of attack. Once the relationship between tip angle of attack and local effective angle of attack is obtained by lifting line theory, the results can be used in the trailing edge noise prediction code. / Master of Science

Francisella tularensis is a highly virulent zoonotic pathogen that is the causative agent of tularemia in humans. Two subspecies of F. tularensis are the most virulent in humans: tularensis (type A) and holarctica (type B), with less than 10 organisms via aerosol of a type A strain having the ability to cause fatal infection. Over the last decade much research has been done on the pathogenesis of this unique intracellular bacterium and many different virulence factors have been identified. The goal of this dissertation has been to identify and characterize the capsule-like complex (CLC) surface antigen of F. tularensis, and to determine its role in virulence and immunoprotection in a mouse model. In addition, I have investigated the role of CLC in biofilm formation. The CLC appears as a negatively staining material surrounding F. tularensis cells during transmission electron microscopy (TEM). I found that the CLC in the type B live vaccine strain (LVS) could be significantly diminished by deleting two glycosyl transferase genes (LVSΔ1423-22) in the putative polysaccharide locus, FTL_1432-FTL_1421. In addition, I determined that the CLC was not a typical polysaccharide capsule, but was in fact composed of over 50 proteins and glycoproteins including known virulence determinants, such as GroEL, DnaK, and ClpB. Upon further evaluation of the CLC, I determined that it was composed of an increase in production of outer membrane vesicles and tubules (OMV/T). These OMV/T appeared to be self-aggregating into what I visualized through TEM as the CLC. LVSΔ1423-22 was attenuated in the mouse model, and BALB/c mice immunized with CLC and adjuvant were protected against challenge with LVS. In addition to virulence, the CLC appears to play a role in biofilm formation and development. F. tularensis type B strains lacking the surface antigens CLC or CLC and O-antigen, develop a 2-7-fold more robust biofilm than the parent strains. The biofilm matrix contains a glucan-like EPS, proteins, and extracellular DNA, and further characterization may lead to determining if the biofilm acts as an environmental survival mechanism for F. tularensis. In summary, the CLC appears to be a novel surface antigen composed of upregulated OMV/T that is present in type A and B F. tularensis. Deficiency in CLC contributes to increased biofilm formation that could contribute to the survival of F. tularensis in a wide range of environmental niches. Furthermore, the CLC contributes to virulence of type B strains and elicits a protective immune response to type B challenge. A CLC-deficient type A strain could be a candidate for a new live vaccine strain, and therefore further investigation of such a mutant is warranted. / Ph. D.

Experimental studies were conducted to obtain direct measurements of skin friction, mean velocity profiles, axial and normal turbulence intensity profiles, and Reynolds stress profiles in the boundary layer on a large diameter, axisymmetric body with a smooth, solid surface; a sandpaper-roughened, solid surface; a sintered metal, porous surface; a"smooth", perforated titanium surface, a solid, rough Dynapore surface made of diffusion-bonded screening, and a porous, rough Dynapore surface. The roughness values were in the low range (k⁺ = 5-7) just above what is normally considered"hydraulically smooth. 11 Measurements were taken at several axial locations and two different freestream velocities corresponding to dynamic pressures of 12.7 and 17.8 cm. of H₂O, which gives a Re_𝓁 range of 2.93 x 10⁶ to 3.38 x 10⁶. For the Law of the Wall, Defect Law, and the turbulence quantities, very good agreement was found between the present results and those from well-established studies for a solid, smooth surface. The sandpaper-roughened, solid wall and solid, rough Dynapore wall tests showed a 20%~30% increment in local skin friction and a slight shift in the log region of the Wall Law, as well as an increase in turbulence quantities over the smooth wall results. These results were in accord with the classical results collected by Clauser for rough, solid surfaces in this range. The effect of porosity can be shown by comparing the sintered metal, porous wall results to the sand-roughened, solid wall results. Although there is a difference in roughness patterns for these two cases, the average k⁺ is in the same range of 5 ~ 7. To check the effect of porosity directly without any interference of different surface roughness patterns, one can compare the results between the 11 smooth 11 perforated titanium wall and the solid, smooth wall, or between the porous Dynapore and solid Dynapore walls. The effect of porosity showed a 30%~40% increment in local skin friction and a marked downward shift of the logarithmic portion of the Wall Law, as well as an increase in turbulence quantities over the smooth wall results. The combined effects of small roughness and porosity could be seen by comparing the results between the sintered metal, porous wall and the smooth, solid wall, or between the porous Dynapore wall and the smooth, solid wall. It was observed that the combined effects of small roughness and porosity are roughly additive. The effect of porosity due to the existence of the penetration of turbulence through the porous surfaces was detected experimentally by a hot-wire underneath the porous walls. All these results demonstrate that a rough, porous wall simply does not influence the boundary layer in the same way as a solid, rough wall. Therefore, turbulent boundary layer models with injection or suction must include both surface roughness and porosity effects. / Ph. D.

An examination of selected two- and three-dimensional turbulent boundary layer data sets was made to determine the consistency of these data sets with their appropriate momentum integral equations. Several turbulent boundary layer experiments were reviewed to determined which of these provided adequate data so that they could be examined using this method. The selected data sets were used to numerically integrate and compare the two sides of the appropriate momentum integral equations in an extension of the Coles' momentum integral (PL-PR) method originally derived for two-dimensional flow. The effects of small three-dimensionality in a nominally two-dimensional flow were also studied. Three-dimensionality due to converging or diverging collateral flow and converging or diverging skewed flow about a plane of symmetry was investigated. The momentum integral examination of two-dimensional and quasi two-dimensional data sets was verified to be a useful and convenient means of data set validation. Very small amounts of three dimensionality in a nominally two-dimensional flow could have large effects on and adversely affect the outcome of a momentum integral validation of the data set. Three-dimensionality of the order of magnitude of experimental uncertainty, in the form of collateral or skewed convergence/divergence of the flow at a plane of symmetry, was shown to have large adverse effects on the momentum integral validation. Investigations of arbitrary.three-dimensional flows were generally found to lack sufficient data to perform an accurate validation using this PL-PR technique extended to such flows. / Master of Science

Yes / Results and analysis from investigations into the behaviour of the interfacial layer (Tribolayer) at the friction interface of a brake friction pair (resin bonded composite friction material and cast iron rotor) are presented in which the disc/pad interface temperature has been measured using thermocouple methods. Using a designed experiment approach, the interface temperature is shown to be affected by factors including the number of braking applications, the friction coefficient, sliding speed, braking load and friction material. The time-dependent nature of the Tribo-Iayer formation and the real contact area distribution are shown to be causes of variation in interface temperatures in friction braking. The work extends the scientific understanding of interface contact and temperature during friction braking.

Three-dimensional wind measurements and temperature measurements were obtained on a 250-foot meteorological tower located near the Atlantic Ocean at Wallops Island, Virginia. The type of flow measured approached the tower from the ocean resulting in a complex three-dimensional type of flow as it sees a change in roughness and a possible change in surface temperature when passing the shoreline. During warm summer afternoons, the stable air is heated from below, and an internal boundary layer (IBL) with an unstable stratification develops within the stable layer which originated over the ocean. As this flow moves inland the IBL grows vertically depending on changes in surface roughness and surface temperature. Eventually, far enough inland, the IBL replaces the original stable layer. The vertical heat flux is positive in the IBL and negative in the overlying inversion. The point where the heat flux changes sign corresponds to the height of the IBL. Measurements of the mean and turbulent flow quantities were made with a special computer-controlled data-acquisition system for the aforementioned type of flow. Data analysis includes the following statistical parameters: mean values, variances, covariances (heat flux and Reynold's stresses), spectra and cospectra. Nine, one-hour runs were analyzed and the results agreed closely with the suggested model. In addition, the spectra and cospectra measured in the IBL, as well as those from the overlying inversion layer, reduce to a family of curves when expressed in appropriate similarity coordinates. These results for moderately, thermally stratified flows compare quite well with the Kansas data which were obtained in the surface layer. The results for very stable flow (z/L > 2.0) do not follow the same trend as was established in the moderately stable range. / Master of Science

A review of the existing, more prominent velocity profile models for two and three-dimensional incompressible flows was presented, with emphasis placed on those that had previously shown their ability to correlate experimental data taken under various conditions. This review included velocity profile models that seemingly could represent flows in which the cross flow velocity vector reverses direction. The various methods of determining a wall shearing stress by semi-empirical considerations for two and three-dimensional flows was discussed. A direct measurement of the wall shearing stress in a three-dimensional flow field was used to infer the most accurate method of applying two-dimensional techniques to three-dimensional conditions in order to obtain reasonable values for the friction losses in a boundary layer. A discussion of the error in the determination of the skin friction coefficient by use of the Glauser Chart was presented. The experimental constants in the law of the wall formulation are shown to be the basis for an error which may be in excess of 15 per cent in the determination of the skin friction coefficient. Finally, a thorough comparison of the previously reviewed two and three-dimensional velocity profile models was made with some of the most complete sets of experimental data available to date. / Master of Science

Presented in this paper are experiments to test the hypothesis that drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and turbulent flows. Quantification of surface drag reduction in rectangular channel flow over walls with specific hydrophobic or hydrophilic properties was obtained with pressure drop measurements along the channel for a range of Reynolds numbers between 350 and 5900. Several commercially available materials and coatings were chosen in order to span a range of contact angles between 30° and 135°. The results are within the bounds of the theoretical values calculated with the Colebrook equation, and do not show any reduction in wall shear stress as a function of material properties or surface chemistry. The differences between this experiment and others measuring pressure drop over hydrophobic surfaces is the macro-scale conditions and the hydrophobic surfaces being fully wetted. These experiments are further proof of the importance of a liquid-vapor interface for increasing the shear free area to produce drag reduction. / Master of Science

The present investigation was undertaken to determine experimentally whether or not instability of the laminar boundary layer on blunt convex bodies exists when the wall-to-stagnation temperature is lowered. It was found that instability existed and theoretical considerations are given to the transition being associated with the formation of ice on the model surface and with an increase in roughness Reynolds numbers due to thinning of the laminar boundary layer at low wall-to-stagnation temperature ratios. The experimental tests were conducted on two-inch diameter spheres at M = 4.95 and free-stream Reynolds numbers per foot of approximately 72. 5 x 10⁶ or 12.1 x 10⁶ based on the model base diameter. Data were obtained tor both the hot wall and cold wall case. The stagnation temperature was approximately 400° F. Initial model wall temperatures were 97°F, for the hot wall test and -320° F for the cold wall tests. / M.S.

The design of the most commonly-used Internet and Local Area Network protocols provide no way of verifying the sender of a packet is who it claims to be. Protocols and applications exist that provide authentication but these are generally for special use cases. A malicious host can easily launch an attack while pretending to be another host to avoid being discovered. At worst, the behavior may implicate a legitimate host causing it and the user to be kicked off the network. A malicious host may further conceal its location by sending the attack packets from one or more remotely-controlled hosts. Current research has provided techniques to support traceback, the process of determining the complete attack path from the victim back to the attack coordinator. Most of this research focuses on IP traceback, from the victim through the Internet to the edge of the network containing the attack packet source, and Stepping-Stone traceback, from source to the host controlling the attack. However, little research has been conducted on the problem of Data-Link Layer Traceback (DLT), the process of tracing frames from the network edge to the attack source, across what is usually a layer-2 network. We propose a scheme called Tagged-fRAme tracebaCK (TRACK) that provides a secure, reliable DLT technique for Ethernet networks. TRACK defines processes for Ethernet switches and a centralized storage and lookup host. As a frame enters a TRACK-enabled network, a tag is added indicating the switch and port on which the frame entered the network. This tag is collected at the network edge for later use in the traceback operation. An authentication method is defined to prevent unauthorized entities from generating or modifying tag data. Simulation results indicate that TRACK provides accurate DLT operation while causing minimal impact on network and application performance. / Master of Science