Characterization of a MEMS acoustic/pressure sensor

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76702/1/AIAA-1999-520-510.pd

Experiments on identification and control of inflow disturbances in contracting streams

Vorticity from all surfaces and isolated objects in the vicinity of the fan intake, including the outside surfaces of the fan housing, were identified as the major sources for disturbances leading to blade passing frequency noise. The previously proposed mechanism based on atmospheric turbulence is refuted. Flow visualization and hot wire techniques were used in three different facilities to document the evolution of various types of disturbances, including the details of the mean flow and turbulence characteristics. The results suggest that special attention must be devoted to the design of the inlet and that geometric modeling may not lead to adequate simulation of the in flight characteristics. While honeycomb type flow manipulators appear to be effective in reducing some of the disturbances, higher pressure drop devices that generate adequate turbulence, for mixing of isolated nonuniformities, may be necessary to suppress the remaining disturbances. The results are also applicable to the design of inlets of open return wind tunnels and similar flow facilities

The hunt for the K\'arm\'an "constant'' revisited

The logarithmic law of the wall, joining the inner, near-wall mean velocity profile (MVP) to the outer region, has been a permanent fixture of turbulence research for over hundred years, but there is still no general agreement on the value of the pre-factor, the inverse of the K\'arm\'an ``constant'' or on its universality. The choice diagnostic tool to locate logarithmic parts of the MVP is to look for regions where the indicator function $\Xi$ (equal to the wall-normal coordinate $y^+$ times the mean velocity derivative \dd U^+/\dd y^+) is constant. In pressure driven flows however, such as channel and pipe flow, $\Xi$ is significantly affected by a term proportional to the wall-normal coordinate, of order \mathcal{O}(\Reytau^{-1}) in the inner expansion, but moving up across the overlap to the leading $\mathcal{O}(1)$ in the outer expansion. Here we show, that due to this linear overlap term, \Reytau's of the order of $10^6$ and beyond are required to produce one decade of near constant $\Xi$ in channels and pipes. The problem is resolved by considering the common part of the inner asymptotic expansion carried to \mathcal{O}(\Reytau^{-1}), and the leading order of the outer expansion, which is a \textit{superposition} of log law and linear term L_0 \,y^+\Reytau^{-1}. The approach provides a new and robust method to simultaneously determine $\kappa$ and $L_0$ in pressure driven flows at currently accessible \Reytau's, and yields $\kappa$'s which are consistent with the $\kappa$'s deduced from the Reynolds number dependence of centerline velocities. A comparison with the zero-pressure-gradient turbulent boundary layer, henceforth abbreviated ``ZPG TBL'', further clarifies the issues

Wall-bounded turbulent flows at high Reynolds numbers: Recent advances and key issues

Wall-bounded turbulent flows at high Reynolds numbers have become an increasingly active area of research in recent years. Many challenges remain in theory, scaling, physical understanding, experimental techniques, and numerical simulations. In this paper we distill the salient advances of recent origin, particularly those that challenge textbook orthodoxy. Some of the outstanding questions, such as the extent of the logarithmic overlap layer, the universality or otherwise of the principal model parameters such as the von Kármán “constant,” the parametrization of roughness effects, and the scaling of mean flow and Reynolds stresses, are highlighted. Research avenues that may provide answers to these questions, notably the improvement of measuring techniques and the construction of new facilities, are identified. We also highlight aspects where differences of opinion persist, with the expectation that this discussion might mark the beginning of their resolution

Application of streamline simulation to gas displacement processes

Performance evaluation of miscible and near-miscible gas injection processes is available through conventional finite difference (FD) compositional simulation. Streamline methods have also been developed in which fluid is transported along the streamlines instead of using the finite difference grid. In streamline-based simulation, a 3D flow problem is decoupled into a set of 1D problems solved along streamlines. This reduces simulation time relative to FD simulation, and suppresses the numerical dispersion errors that are present in FD simulations. Larger time steps and higher spatial resolution can be achieved in these simulations. Thus, streamline-based reservoir simulation can be orders of magnitude faster than the conventional finite difference methods. Streamline methods are traditionally only applied to incompressible flow processes. In this paper, the method is adopted and assessed for application to compressible flow processes. A detailed comparison is given between the results of conventional FD simulation and the streamline approach for gas displacement processes. Finally, some guidelines are given on how the streamline method can potentially be used to good effect for gas displacement processes

Visualization of Unsteady Flow Over Oscillating Airfoils

This study is concerned primarily with the complex nature of leading edge flow separation occurring on airfoils oscillating in a uniform flow field at low Reynolds numbers. The flow field past an oscillating airfoil and a fixed airfoil with an oscillating flap were investigated using various visualization techniques in water. The role of mean flow velocity, instantaneous angle of attack, mean angle of attack and amplitude and frequency of oscillation as well as the location of the support point are examined. The results which were obtained over a range of parameters substantially beyond previous studies include new information regarding the effect of these parameters on the nature and onset of separation. Two basic forms of leading edge separation have been observed. At low values of reduced frequency (ω* \u3e 0.5) the separation resembles leading edge separation on stationary airfoils with the separated flow remaining detached from the upper surface. At higher values, beyond ω*cr, a strong vortex (roller) is formed at the leading edge with the flow reattaching downstream from it. In addition to these two flow regimes, a third regime made its appearance at extremely high values of frequency and amplitude where the flow around the airfoil has collapsed. The frequency of oscillation is found to govern the angle, αcr, at which leading edge separation occurs at low reduced frequencies (ω* \u3c 0.2); at higher frequencies αcr occurs at the portion of the cycle where d2 α/dt2 is near its maximum

Influence of sonication and in vitro evaluation of nifedipine self‑nanoemulsifying drug delivery system

In order to develop a self-nanoemulsifying system, three components, olive oil, Tween 80, and Capmul, were used to construct a ternary phase diagram that helped to find the optimum formulation, which was loaded with nifedipine. The effect of sonication on drug loading was also evaluated. After that, measurement of the droplet size, size distribution, zeta potential, and scanning electron microscopy were conducted for evaluation and characterisation of the formulations. The phase diagram of four formulations showed nanosizes below 200 nm; however, only one was selected to be loaded with nifedipine. The selected formulation had the lowest droplet size of 98 nm and size distribution 0.192, and was composed of 48% Tween 80, 32% Capmul, and 20% olive oil. The nifedipine self-nanoemulsifying drug delivery system (SNEDDS) showed a significant change in the particle size (97 nm) and size distribution (0.257) after sonication. Its zeta potential was -32.3 mV indicating good stability. The SEM photographs of nifedipine showed particles with spherical shape and smooth surface. Finally, a self-nanoemulsifying formulation containing nifedipine, loaded in olive oil, was successfully prepared by mixing the oil with various types of surfactants and co-surfactants. A significant nifedipine self-nanoemulsifying system was developed and significantly improved accordingly

Effect of construction joints on the splitting tensile strength of concrete

AbstractThe purpose of this study is to experimentally correlate the compressive strength (f′c) of concrete to the splitting tensile strength (T) for plain concrete in the existence of a construction joint, and formulate an empirical equation relating T to f′c. Both the American Concrete Institute code (ACI 318-08 (ACI Committee 318, 2008)) and the American Society for Testing and Materials (ASTM (ASTM Standard C496, 2002; ASTM Standard C192/C192M, 2002; ASTM Standard C39/C39M, 2005; ASTM Standard C617, 2002)) provide the testing methods and standards, as well as the applicable theoretical and experimental formulas for the correlation between T to f′c for concrete specimens, which are monolithic, indicating that the specimens lack any construction joints. Providing a useful reduction factor in the splitting tensile strength of concrete due the existence of a construction joint is essential. It is a well known fact that construction joints are used in every concrete structure, which indicates that engineers would definitely benefit from an equation that could relate the splitting tensile strength of concrete in function of its compressive strength.The results suggest that the reduction in the splitting tensile strength in the presence of a construction joint is not as much as most engineers tend to believe. Due to that belief, most engineers tend to overdesign for steel reinforcement at those joints to compensate for this reduction. The objective of the study is to better the understanding of the effects of a construction joint on the splitting tensile strength. Thus provide an empirical equation to assist engineers in their design calculations, therefore reducing the amount of steel reinforcement at the construction joints. Thus also leading to cost saving on projects

Introduction to the dossier: Brazilian cinema in the neoliberal age (O cinema brasileiro na era neoliberal)

Introdução ao dossiê

PRODUCTIVITY AND QUALITY OF QUINOA YIELD (CHENOPODIUM QUINOA, WILLD) AS AFFECTED BY PLANTING DATE AND PLANT SPACINGS

A field experiment was conducted at the nursery of ornamental plants, Faculty of Agriculture, Minia University during 2018/2019 and 2019/2020 seasons to study the effect of three planting dates (November 1st, November 15th and December1st) and three plant spacings (10, 15 and 20 cm) on growth, yield and chemical composition of quinoa plants to obtain the best agricultural transactions under the conditions of Central Egypt. The results showed significant effects of planting dates on all the studied traits, except for plant height, weight of 1000 seeds and protein% in both seasons, with the planting date of November 15th being the best date. The effect of plant spacing was significant for all studied characters, except for weight of 1000 seeds and protein % in the first season. Planting quinoa seeds at 15 cm. was superior to the other spacings in most cases. The interaction between planting dates and plant spacing between plants was insignificant except for number of panicles/plant and yield of seeds/plant (g) in both seasons and the weight of 1000 seed (g) and seed yield/fed (ton) in the second season. Therefore, it is recommended to cultivate the quinoa on November 15th at a distance of 15 cm apart under the conditions of Central Egypt because it gave the best values ​​for economic characteristic