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    Field Survey on Aquatic Environment and "Ayu" Habitat in Urban River
    (2006) Higashino, Makoto; Takami, Tohru; Onitsuka, Kouki; Akiyama, Juichiro; Nagaya, Takayuki; Shiraishi, Yoshiki; Ohtsuka, Noriharu
    Field measurements were performed to investigate "Ayu" habitat in the Gokase (Ose) river in Miyazaki. "Ayu" is famous and popular, and hence, one of the most important fish in Japan. There has been substantial river engineering for flood control, e.g. dredging of bed, especially near urban areas. This engineering work can damage the fish habitat. In order to protect "Ayu" habitat, it is necessary to predict how the fish respond to habitat damage in the river, i.e. an environmental assessment. The water quality e.g. DO (Dissolved Oxygen), BOD, COD, SS, the temperature, and the discharge are all significant for the fish habitat. The abundance of algae attached to the surface of bed material, e.g. stones, is also significant because it is a food source for the fish. The water quality, the temperature, and the velocity of flow were measured at the several points in one of the artificial spawning beds "Ogura-shita rapid" in the Ose river. Material attached to the river bed was collected, and TR (Total Residue) and Chl.a (Chlorophyll.a) were smaller in summer, and larger in winter, which is different from what is generally expected. The growth rate of algae in the Ose river was found to depend on the velocity of flow, i.e. the value of Chl.a was increased as the velocity was increased, became the largest at a velocity of 0.4 to 0.5m/s, and decreased with increasing velocity above 0.5m/s.
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    Vortex Roll-Up from an Elliptic Wing at Moderately Low Reynolds Numbers
    (AIAA Journal, 1987-12) Higuchi, Hiroshi; Quadrelli, Jose C.; Farell, Cesar
    An experimental investigation of tip-vortex roll-up was undertaken at moderately low Reynolds numbers for an elliptic wing with a NACA 66_2 - 415 section. Flow visualization and laser Doppler velocimetry measurements were carried out to examine the flow in the vortex core and the tangential velocity distributions around the core. Separation was observed on both sides of the foil for Reynolds numbers up to 5X10^5. The observed changes in the location of separation and reattachment with angle of attack and Reynolds number were adequately predicted by laminar boundary-layer calculations. Axial and tangential velocity profile measurements were made at Reynolds numbers up to about 5X10^4. The vortex core radius was found to grow with increasing angle of attack, increasing downstream distance, and decreasing Reynolds number. A comparison of the experimentally-determined velocity distributions and core sizes, with the results of inviscid, laminar, and turbulent vortex models, is presented.
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    Headrace Design Studies for the Jim Falls Hydro-Redevelopment Project
    (St. Anthony Falls Laboratory, 1987-08) Stefan, Heinz G.; Voigt, Richard L. Jr.; Lindblom, Karen L. C.; Ainsworth, Bruce; Colgan, Patrick
    The 48 MW Jim Falls Hydropower Redevelopment project on the Chippewa River, Wisconsin, required extensive model studies to facilitate the debris sluicing and to prevent intermittent vortex formation in front of the powerhouse intake. Debris, consisting mainly of natural materials from a forested and agricultural watershed, had to be directed to a gated spillway adjacent to the powerhouse (Fig. 1). To accomplish that goal, the surface circulation in the headwater pool had to be reversed. Vortices formed preferentially at two locations near the ends of the powerhouse, and were highly unstable in space and time. The highly irregular headrace geometry, in terms of width and depth, was found to be the cause of the undesirable flow features. A series of headrace modifications resulting in a more symmetrical approach channel configuration provided a debris flow pattern away from the powerhouse intake, and reduced frequency and strength of vortex formation to acceptable levels. A description of effective and ineffective design changes will be given.
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    Independent Turbine Testing and Research
    (St. Anthony Falls Laboratory, 1987-08) Voigt, Richard L. Jr.; Gulliver, John S.; Wetzel, Joseph M.; Arndt, Roger E. A.
    The St. Anthony Falls Hydraulic Laboratory (SAFHL) is presently upgrading their Turbine Test Facility. Completion of the upgrade, including checkout tests, is scheduled for Fall 1987. This paper will discuss the improvements being made to the Facility. The upgrades include enclosure of the upper portion of the test loop (head tank, tail tank, and dynamometer), to enable year-around operation. A temperature control system is being constructed and installed in the test loop which will provide temperature stability, necessary for cavitation testing, and required by IEC model test codes. Installation of additional instrumentation will provide for simpler, more efficient, data acquisition. The Facility is being connected to the Laboratory compressed air and vacuum facilities for pressure control. The existing Laboratory deaeration equipment will be incorporated to allow accurate dissolved gas content control not generally available in turbine test facilities. The SAFHL Turbine Test Facility will be available to undertake specific projects for the hydropower community funded by a variety of industries, agencies, and organizations. Projects might include performing model tests for small manufactures, prototype tests of micro-turbine units, model acceptance tests, comparative model tests, as well as a wide range of basic research experiments. The Facility will also be used as a demonstration tool in the instruction of students and hydropower engineers as part of SAFHL's active hydropower education program.
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    Jet Noise at Low Reynolds Numbers
    (American Institute of Aeronautics and Astronautics, 1981-10) Long, D.; Van Lent, T.; Arndt, R.E.A
    There is considerable interest in the question of whether coherent structures that govern the mixing process in turbulent jets also affect the radiation of acoustic energy. This study indicates that below a Reynolds number of 10^5, where coherent structures are most easily observed, the spectral properties of jet noise change significantly. The relative acoustic power is lower in this Reynolds number range and the noise spectra scale with Helmholtz number rather than Strouhal number. There appear to be definite compressibility effects on the large scale structure and flow development. Similar Mach number effects on the fine scale turbulence are not noted.
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    Modelling Stream Braiding Over a Range of Scales
    (New Zealand Hydrological Society, 2001-01) Paola, Chris
    Modelling of fully developed braiding using conventional PDE techniques has been hindered by the difficulty of solving a nonlinear system of equations on a complex, constantly deforming domain. Simplified cellular models can reproduce many of the main features of braiding but their parameters are difficult to constrain. These two approaches are examples respectively of reductionism and synthesism, two approaches to modelling complex systems whose relative merits are being debated across a range of fields. Future research should aim at a marriage of these approaches, and at developing models capable of handling the full range of natural river types from braided to meandering. Another important parallel goal is the development of models for the mean behaviour of braided river systems. The first goal is to predict mean slope, depth, velocity, etc. from total water and sediment fluxes, and grain-size distribution. One can average the shallow-water and sediment-flux equations in a manner analogous to Reynolds averaging. This produces viable models, but just as for turbulence, adds new parameters that must be measured or estimated from physical arguments. Application of such averaging techniques to modelling rivers is only just beginning.
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    Self-Aerated Flow in Open Channels
    (St. Anthony Falls Laboratory, 1960) Straub, Lorenz G.; Anderson, Alvin G.
    Measurements of distribution of air concentration in self-aerated flows are presented. The experiments were made in a rough channel of sand-grain type surface at various slopes and discharges, and the data were used as a basis for study of the mechanism of entrainment of air and to relate the air content and distribution to the characteristics of the flow. The analysis of the data shows that the air distribution can be adequately described by relationships based on a simplified concept of turbulent transport and thus are functions of the flow characteristics. The maximum depth and the mean velocity are both shown to increase above those of a corresponding nonaerated flow.
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    Jet Noise at Low Reynolds Numbers
    (2014-05-02) Long, D.; Van Lent, T.; Arndt, R.E.A.
    There is considerable interest in the question of whether coherent structures that govern the mixing process in turbulent jets also affect the radiation of acoustic energy. This study indicates that below a Reynolds number of 10^5, where coherent structures are most easily observed, the spectral properties of jet noise change significantly. The relative acoustic power is lower in this Reynolds number range and the noise spectra scale with Helmholtz number rather than Strouhal number. There appears to be definite compressibility effects on the large scale structure and flow development. Similar Mach number effects on the fine scale turbulence are not noted.
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    Abrupt Transition from a Circular Pipe to a Rectangular Open Channel
    (St. Anthony Falls Hydraulic Laboratory, 1969-07) Blaisdell, Fred W.; Donnelly, Charles A.; Yalamanchili, Kesavarao
    The development of criteria and a generalized procedure for the design of an abrupt transition from a circular pipe to a rectangular open channel are presented. The rectangular channel must be 1.0 pipe diameters wide. Wider channels cause high waves which reflect from the channel sidewalls, may overtop the sidewalls, and produce severe disturbances in the channel. To permit the pipe to expand, the channel may be widened for a distance not exceeding 0.5 pipe diameters downstream from the pipe exit, and the floor of the channel may be lowered. The equations developed describe the locations of the water surface elements to within an average of 0.11 pipe diameters of their correct locations. The maximum anticipated location error is +/- 1.4 pipe diameters. The equations for the envelope curves covering the crests of the sidewall waves, which determine the channel sidewall height, provide an average freeboard of 0.08 pipe diameters and a maximum freeboard of 0.31 pipe diameters. When the envelope equations are used only 2 percent of the wall waves will overtop the sidewalls, the maximum overtopping being 0.04 pipe diameters. The average depth of flow-the depth at the wave nodes-is predicted by the equations to within a maximum deviation of +0.13 and -0.06 pipe diameters of the observed depths. The average depth at the nodes is predicted by the equations within 0.01 pipe diameters of the observed average depth.
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    On the Existence of Zero Form-Drag and Hydrodynamically Stable Supercavitating Hydrofoils
    (St. Anthony Falls Hydraulic Laboratory, 1965-11) Oba, R.
    The linearized complex acceleration potential is obtained for a hydrofoil of arbitrary shape in steady motion beneath a free surface with cavity of infinite length in simple and compact form. Under appropriate limiting conditions, it is shown that the solutions obtained from this potential reduce to the known solutions of Green for a planing foil, and of Auslaender and Hsu for a flat plate foil with or without flat flap near the free surface. Using some numerical results obtained from the complex potential, it is shown that there exists theoretically a supercavitating hydrofoil with finite lift coefficient and zero form drag. It is also shown that there exists theoretically a supercavitating hydrofoil with stable characteristics when shallowly submerged; that is, the lift coefficient increases as the submergence increases. Possible shapes for these hydrofoils are suggested so that the free streamlines from the leading edges do not. intersect the foil surface (the hydrofoils are physically real) and so that the pressure on the pressure surface is everywhere greater than cavity pressure and less than stagnation pressure (except near the leading and trailing edges).
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    Supercavitating Flat-Plate with an Oscillating Flap at Zero Cavitation Number
    (St. Anthony Falls Hydraulic Laboratory, 1965-11) Song, C. S.
    The results of experimental and theoretical investigations on a supercavitating flat-plate with an oscillating flap at zero cavitation number are presented. The experiment was carried out in a vertical free-jet water tunnel using 3 in. chord and 2 in. chord flat-plate hydrofoils, both having flap-chord ratios of 0.29. Various relative locations of the free surfaces were used and the reduced frequency range of zero to four was covered. Amplitude and phase angle of lift, drag, and moment as well as the surface wave speed were measured. The problem was also solved, analytically by means of a first order perturbation theory using complex acceleration potential. Numerical values were obtained for the cases of infinite fluid, symmetrical jet, and zero spray thickness using three flap-chord ratios (0.25, 0.30, 0.40). Fairly good agreement between the experimental data and the analytical results was obtained.
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    Performance of Supercavitating Hydrofoils with Flaps, with Special Reference to Leakage and Optimization of Flap Design
    (St. Anthony Falls Hydraulic Laboratory, 1965-05) Oba, R.
    A modified linearized theory was developed for supercavitating, flapped foils of arbitrary form in which effects of fluid leakage through the flap hinge were considered. It was found that the performance at conditions other than design conditions was improved with the use of trailing edge flaps. The drag-lift ratio may be reduced by a factor of 1/2 to 1/3. The foil performance is dependent on the flap-chord ratio, e, and the flap deflection, performance increasing with small e. Effects produced by leakage through the flap hinge were significant in their influence on velocity distribution and flap effectiveness (increment in lift coefficient per unit change in flap angle). The effect of hinge leakage on the overall performance, i. e., lift, drag, and moment, was small and may be neglected in most cases.
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    Tandem Interference Effects for Noncavitating and Supercavitating Hydrofoils
    (St. Anthony Falls Laboratory, 1965-01) Wetzel, Joseph. M.
    Experimental studies had previously been made at this Laboratory to determine the tandem interference effects for noncavitating hydrofoils. The results are compared with theory in this report, and good agreement is shown to exist. The experimental studies have now been extended to include fully submerged, ventilated foils of finite span. Both forced and naturally ventilated foils were employed in various configurations. The surface wave generated by the ventilated foil and the total interference effect of the forward foil on the force and cavity characteristics of the aft foil were of particular interest. The surface wave generated by the forward foil had relatively little influence on the force and cavity characteristics of the aft foil. For forced-ventilated foils, considerable change due to interference effects was observed in the cavity pressure of the aft foil. For long initial cavities on the forward and aft foil, the interference effect on the forces was relatively small, whereas for small initial cavities, the interference effect was much larger. Similar trends were observed for the naturally ventilated foils. Lateral separation of the forward foils reduced the interference effects to essentially negligible values.
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    Measurements of the Unsteady Force on Cavitating Hydrofoils in a Free Jet
    (St. Anthony Falls Hydraulic Laboratory, 1964-06) Song, C. S.
    Experimental data concerning force and other related quantities associated with unsteady super cavitating flow about bodies tested in a free-jet water tunnel are reported herein. Three types of unsteady flows were studied -- those due to pitching oscillation, sudden ventilation, and sudden angle of attack change. All test bodies were of such geometrical configuration that separation could occur only at two or three fixed points. The first type of unsteady flows was subdivided into three categories, each having different characteristics. When a flat plate was oscillated about a large mean angle of attack at small cavitation number and without ventilation, the cavity pressure remained unchanged. When air was supplied to the cavity for ventilation, the cavity pressure oscillated with the same frequency as that of the body oscillation. When the plate was oscillated about a small mean angle of attack, there was a change in the cavity configuration even without ventilation and the resulting flow was quite irregular. The plate was oscillated at the maximum reduced frequency of 0.03. The second phase of the experiment involved measurements of cavity pressure, cavity length, and the force on the body following a sudden ventilation of an otherwise steady cavity. It was found that the change in cavity length and the change in the force lagged behind the cavity pressure change. Furthermore, the rate of cavity increase never exceeded the free-stream speed. An attempt was also made to measure the response of the flow to a sudden angle of attack change. It was concluded that, due to the oscillatory nature of the cavity, a faster angle of attack change than was attained in the experiment is needed to obtain a useful unit function response curve.
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    Studies of the Flow Characteristics of a Compressible, Bubbly Mixture about Supercavitating Bodies and in a Converging-Diverging Nozzle
    (St. Anthony Falls Hydraulic Laboratory, 1964-04) Schiebe, F. R.; Wetzel, J. M.; Foerster, K. E.
    Experimental studies have been made to determine the effect of a compressible, air-water mixture on the drag characteristics of a cavitating body. Data are reported for a series of conical bodies of various slenderness ratios for free stream Mach numbers up to 0.7. Results indicate that the drag coefficient increases with Mach number, although in general not as rapidly as for a non-cavitating body. It was possible to apply Gothert's rule to adequately predict the drag coefficient up to Mach numbers of about 0.6. A brief study was also conducted to study the flow characteristics of an air-water mixture in a converging-diverging nozzle. Supersonic flow was obtained and shock waves were observed downstream of the throat. Measured throat pressures for choked flow were somewhat higher than those calculated from homogeneous mixture theory.
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    Two-Dimensional Supercavitating Plate Oscillating Under a Free-Surface
    (St. Anthony Falls Hydraulic Laboratory, 1963-12) Song, C. S.
    The problem of a super cavitating flat plate at non-zero cavitation number oscillating under a free surface is analyzed by a linearized method using the acceleration potential. The flow is assumed two-dimensional and incompressible. The flow field is made simply connected by using a cut along the wake. The flow field is then mapped on to an upper half plane and the solution is expressed in an integral form by using Cheng and Rott's method. Equations for the cavity length, total force coefficient, moment coefficient and the frequency response function are expressed in closed form. Numerical results for some special cases are also obtained and presented graphically. When the flow is steady, the present theory agrees with experimental data and other existing theories. For the special case of infinite fluid and infinite cavity the present theory agrees with Parkins' original work. For the special case of zero submergence, the present theory indicates that the total force coefficient is one half that of the value for fully wetted flow in an infinite fluid for both steady and unsteady cases. An alternate analysis is also carried out for the infinite fluid case and the result shows that the effect of the wake assumption is of order of the square of the cavitation number when the cavitation number is small. The effect of the gravity field is also discussed qualitatively. It is also concluded that the effect of the free-surface is to shorten the cavity and to increase the total force coefficient. The steady part of the force coefficient at an arbitrary submergence is obtained by multiplying the value at infinite submergence by a correction factor, whereas the unsteady part is given by a more complicated function. Even with the presence of a free-surface and oscillation of the foil, the total force coefficient at small cavitation number is approximately equal to the corresponding value at zero cavitation number multiplied by a factor (1 + σ).
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    Experiments on a Jet Flap in Supercavitating Flow
    (St. Anthony Falls Hydraulic Laboratory, 1964-01) Silberman, Edward
    Experiments on a fully-cavitated, flat-plate hydrofoil equipped with a pure jet flap were conducted in the free-jet water tunnel at the St. Anthony Falls Hydraulic Laboratory. The foils were of 2-in. and 2.75-in. chord and were tested in 6-in., 10-in., and l4-in. wide free jets. Data were obtained on the increments in lift, drag, and moment coefficients and on the shift in center of pressure as a function of jet momentum coefficient C_j, cavitation number, and other variables.
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    Hydraulics of Closed Conduit Spillways Part XI. Test using Air
    (St. Anthony Falls Hydraulic Laboratory, 1966-01) Blaisdell, Fred W.; Hebaus, George G.
    The use of air instead of water to evaluate the full flow entrance loss coefficients and pressure coefficients for closed conduit spillways is the subject of this paper. The paper explains that air cannot be used as a substitute for water when the spillway is only part full, gives reasons for using air instead of water, presents background information, compares the water and air equations, develops the compressible flow equations required to analyze the data, and describes the test apparatus and procedure. Verification tests show that identical results can be obtained using either air or water.
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    A Quasi-Linear and Linear Theory for Non-Separated and Separated Two-Dimensional, Incompressible Irrotational Flow about Lifting Bodies
    (St. Anthony Falls Hydraulic Laboratory, 1963-05) Song, C. S.
    A general theory is developed for calculating lift, form drag, and moment applicable to thin bodies at small angles of attack without separation or with separation at an arbitrary number of given points. The separated flows are related to fully cavitated and partially cavitated flows by making use of the concept of free streamlines. The closure condition of free-streamline theory is replaced by a boundedness condition. Unique solutions are thereby obtained for a large variety of problems. The mathematical solution involves a Riemann-Hilbert mixed boundary value problem in an upper-half plane. The general solution for this problem is given in the Appendix and is applied to various kinds of mixed boundary conditions. The method is exemplified by means of four illustrative calculations. As may be expected when the boundary profile is truly linear, the solution agrees with the classic exact solution.
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    Studies of the Reduction of Pipe Friction with the Non-Newtonian Additive CMC
    (St. Anthony Falls Hydraulic Laboratory, 1963-04) Ripken, John F.; Pilch, Meir
    This study extends existing data to better clarify the manner in which the addition of a small quantity of long-chain polymer chemical additive to water can remarkably reduce the frictional resistance to flow. The material sodium carboxymethylcellulose was added to fresh water and subjected to pipe friction tests under a wide range of shear rates, additive concentration, and temperature conditions. The frictional data are characterized by application of the power law expression for non-Newtonian fluids.