Combined Flow Field Research Articles

Fabric filtration with integral particle charging and collection in a combined electric and flow field: Part I. Background, experimental work, analysis of data, and approach to the development of a mathematical engineering design model

The application of electrostatics to fabric filtration improves performance by decreasing the pressure drop across the collected dust layer. Electrostatics is applied by precharging the particles, or collecting the particles in an electric field, or a combination of both. A system of integral particle charging and collection in a combined electric and flow field has been developed which provides pressure drop reductions that are larger than previously reported in electrifield fabric filtration. A mathematical model has been developed that predicts the non-uniform deposition that results and the relative pressure drop as compared to conventional (non-electrified) filtration. This work is reported in two parts. This part presents the background in the application of electrostatics to fabric filtration. The technique for integral particle charging and collection in a combined electrical field is discussed. An experimental program is described that would provide the data needed to prepare a mathematical engineering design model. Measurements of areal density, drag, thickness, and dust cake bulk density were made upon particle layers deposited on fabric filters with integral particle charging and collection with a combined electric and flow field. The application of charging resulted in a non-uniform deposition, with areal density, thickness, and drag decreasing from the inlet to the top of the bag. No consistent relationship was found between drag and dust cake bulk density. Local charges in the electrical conditions, such as non-uniform corona, caused discontinuities in the dust layer.

Fabric filtration with integral particle charging and collection in a combined electric and flow field: Part II. Development and verification of the mathematical engineering design model

A mathematical engineering design model is developed to predict the nonuniform deposition of particulate matter and the relative pressure drop, compared to conventional filtration, of fabric filtration with integral particle charging and collection. For the model the bag length is divided into a number of increments for each of which collections for the ESP and porous flow are computed separately. Turbulent flow within the bag requires the use of the Deutsch-Anderson relationship for the ESP collection. The relative pressure drop is calculated by first relating the computed areal density in each increment to the drag, which is a resistance to flow. By use of the relationship for parallel resistance, the total drag is determined; the relative pressure drop is the ratio of the drag for the nonuniform flow to that for an equivalent quantity of particulate matter uniformly deposited by conventional filtration. The predictions for small test bags, whose operation was outside the range of assumptions used for the development of the model, were qualitatively correct. For large fabric filtration bags of the size used in practical industrial applications, whose operation is within the range of assumptions, the model provides reasonably well-quantified predictions.

A Modified Inertial Dissipation Method for Estimating Seabed Stresses at Low Reynolds Numbers, with Application to Wave/Current Boundary Layer Measurements

Abstract The inertial dissipation method for estimating seabed friction velocities from near-bed turbulence spectra requires few measurements; it is relatively insensitive to errors in sensor orientation and measurement of mean flows. However, the method is only valid if turbulence spectra are measured at a height above the seabed that is small enough to be within the constant stress layer but large enough to produce an inertial subrange. It is shown that such a height exists only if the friction velocity exceeds a critical value (typically 0.8 cm s−1 for a midlatitude ocean). Recent measurements from combined wave and mean flow conditions on the continental shelf do not satisfy this requirement. However, an empirical modification to the inertial dissipation method is suggested to allow estimation of the friction velocity even when a true inertial subrange does not exist. The modified method is applied to the combined wave and mean flow field data; it virtually removes an increase in estimated friction ve...

Heat transfer enhancement in a convective field with corona discharge.

An experimental study was conducted to examine the heat transfer enhancement in forced convective channel flow by means of the ionic wind induced between the plate wall and plural negative wire electrodes, which were put at the center line of the channel. A theoretical analysis was also performed on electric, flow, and temperature field taking account of the interactions among these fields. Firstly, the combined flow field where the cellular secondary motion occured owing to the field's interaction was characterized in conjunction with the bulk flow velocity and the electric field strength. Secondly, the enhancement of convective heat transfer rate was recognized, especially under low Reynolds number, and its mechanism was clarified. On the basis of these results, the heat transfer performance was shown in connection with the amount of electric power and pumping power.

Experimental Studies on the Combined Flow Field Formed by a Moving Wall and a Wall Jet Running Parallel to It

In order to make more clear the flow field when manufacturing a film or a sheet cooled by a wall jet, fundamental studies on the combined flow field formed by a moving wall and a two-dimensional wall jet running parallel to it were performed experimentally. The existence of a critical distance, where the gradient of the velocity profile at the surface of the moving wall was changed from positive to negative, was ascertained, and factors influencing the critical distance were identified. It becomes clear that there are some cases where the combined flow field can not be treated by a widely employed relative velocity of the respective reference velocities of the moving wall and the wall jet. Some practical data on the critical distance were given.

Experimental Studies on the Combined Flow Field Formed by a Moving Wall Jet Running Parallel to It

Experimental Studies on the Combined Flow Field Formed by a Moving Wall Jet Running Parallel to It

Aerodynamic analysis of tube vehicle systems.

A general description of the aerodynamics of tube vehicles is presented. The advantages of dividing the flowfield into a far flowfield away from the vehicle and a near flowfield close to the vehicle are discussed. Solutions for the near flowfields and asymptotic short- and long-time solutions for the far flow are presented. Combined flowfield solutions are then presented along with predictions of thrust and power requirements. The effects of the vehicle propulsion system and of flow velocities reaching M = 1 about the vehicle are shown to be of fundamental importance.

Strongly radiating hypersonic flow over a sphere - An asymptotic sketch.

14 Pridmore Brown, B. N. and Franks, W. J., A method of characteristics solution in three independent variables/' Northrop Norair Rept NOR 65-42 (1965); also Aerospace Research Laboratories Rept. ARL 65-124 (1965). 15 Sauerwein, H. and Sussman, M., Numerical stability of three-dimensional method of characteristics, AIAA J. 2, 387389 (1964). 16 Heie, H. and Leigh, D. C., Numerical stability of hyperbolic equations in three independent variables, AIAA J. 3, 10991103 (1965). 17 Heaslet, N. A. and Lomax, H., Supersonic and transonic small perturbation theory, General Theory of High Speed Aerodynamics, edited by W. R. Sears (Princeton University Press, Princeton, N. J., 1954), p. 330. 18 Der, J., Jr., Niemann, A. F., Jr., Powers, S. A., and Pridmore Brown, B. N., The determination of combined viscid-inviscid flow fields over hypersonic lifting reentry configurations, Wright Patterson Air Force Base RTD-TDR-64 (1964). 19 Chu, C. W., Numerical integration by modified spline fit, Northrop Norair Rept. NOR 65-316 (1965).

Hypersonic aircraft and their aerodynamic problems

The paper is concerned with a selection of problems of fluid mechanics which are related to one another by their relevance to a possible hypersonic aircraft. This is regarded as a new type of aircraft, still to be developed, in a series of existing types (classical, swept, and slender). Its main aerodynamic characteristics are that the means for providing volume, lift, and propulsion, all produce shock waves in the air during the high-speed phase of flight, and that the type of flow changes with flight speed. Flow fields of lifting bodies with contained shock waves are considered; they are generally of the mixed type in the sense that they contain elliptic and hyperbolic regions. Friction, heating and transition effects in the generally three-dimensional boundary layers are particularly important. Propulsion by heat addition to an airstream is another characteristic feature and the combined flow field of a lifting propulsive body travelling at hypersonic speeds is discussed with a view to recognizing the aerodynamic problems that matter most. It appears that there is a large field of work with possible and promising practical applications, in which the emphasis lies on problems of perfect-gas-dynamics. The relevant Mach-number range extends up to another as yet unknown, boundary beyond which energy-consuming real-gas effects dominate the flow; it probably extends far enough to cover all that may be required for global transport operations.

Addendum-"Effect of Diffusion Fields on the Laminar Boundary Layer"

these conditions, the concept of the combined flow field was used. This consists of superimposing the flow fields of the for­ ward and reversed motions. In this note, it is shown how these conditions may be derived using the standard methods of calculus of variations and the general reverse flow theorem.2 The method will be illustrated for the case of given lift. In addition it is shown that the necessary condition actually yields a mini­ mum for the drag. Linearized theory is assumed throughout. Let p and a denote the local lift and angle of attack distribu­ tions in forward flow. These are defined on the projection of the wing surface on a mean plane. This area is denoted by 5 and all integrations are over this area. As in reference 3, two types of reverse flow are considered. In the first, the lift in re­ verse flow p = p, and a is determined from linearized theory. In the second, the angle of attack in reverse flow a. — —a., and p is determined from linearized theory. The reverse flow theo­ rem states that J* padS = fpadS

The Minimum Drag of Thin Wings in Frictionless Flow

The assumptions of the thin airfoil theory are found to provide certain necessary conditions for the minimum drag of airfoils having a given total lift, a given maximum thickness, or a given volume. The conditions are applicable to steady or unsteady motions and to subsonic or supersonic speeds without restriction on the planform. The computation of drag and the statement of the conditions for minimum drag depend on the consideration of a combined flow field, which is obtained by superimposing the disturbance velocities in forward and reversed motions. If the planform of the airfoil and its total lift are given, it is found that, for minimum drag, the lift must be distributed in such a way that the downwash in the combined field is constant over the entire planform. If the planform is given and the thickness of the airfoil is required to contain a specified volume, then the thickness must be distributed over the planform in such a way that the pressure gradient of the combined field in the direction of flight is constant at all points of the wing.