Circular Cylindrical Model Research Articles

High-Reynolds-number effects simulations for wind effects on a cooling tower model in a wind tunnel based on a statistical approach

The traditional high-Reynolds-number (Re) effects simulation method for wind effects on circular cylindrical models in wind tunnels is fundamentally a trial-and-error practice, which is strongly subjective and laborious. To this end, a mathematically well-founded high-Re effects simulation method is proposed based on the response surface (RS) optimization algorithm in this article. Having the advantages of good considerations of random errors and simplified calculations using the polynomial models, RS method has been widely employed in chemical industry. However, it is seldom employed in physical experiments. Using a case study of Weisweiler cooling tower, it has been proved that model tests using the new high-Re effects simulation method based on RS optimization algorithm can objectively and easily reproduce the mean and the fluctuating wind pressure distributions measured on the spot, and the model-scale spectral characteristics of the wind pressures obtained by using the new high-Re effects simulation method agree well with the full-scale ones. Besides, numerical analyses undertaken on a computational fluid dynamics platform also indicate the validity of the new method.

Experimental study of flow field in geometric Type-I vortex chamber at low water abstraction ratio

ABSTRACTIn this paper, an attempt has been made to critically examine the flow field inside a cylindrical model vortex chamber type sediment extractor with 1.0 m diameter. Data on velocity distribution along tangential and radial directions have been collected by Programmable Electro Magnetic Shunt (PEMS) meter in a circular cylindrical model of vortex chamber in the laboratory. Data were for wide range of flow rate, water abstraction ratios, vertical, radial and transverse spacing. In this paper only result of one lowest water abstraction ratio that is 8% is presented. The results are presented in the form of graphical representation. Also, the segments with similar flow field have been identified.

The effect of combined countermeasures on main local scouring parameters using physical models

Details of an experimental study for 22 clear-water scour tests around bridge piers are presented in three combinations of flow-altering countermeasures against bed erosion. The combined countermeasures are as follows: (1) berm and geometry; (2) berm, geometry, and centered slot; and (3) berm, geometry, and off-centered slots. First, four different cross-sections were selected for the model piers (A series). The results of this group have shown that the lenticular model can decrease the scour depth remarkably. The efficient height of a berm was then determined through B series of tests for circular cylindrical model pier. Then, it was found that the first combination (C series) could not decrease the bed erosion significantly. Also, the second combination (D series) mainly decreased the scour depth only in the circular and round-nosed rectangular geometries. Finally, the third combination (E series) used for the first time with considering its structural aspects can be considered as the most effective countermeasure only for the common geometries of the model piers. The results showed that the combination of different countermeasures would not be an efficient tool for all geometries of model piers.

Determination of the structural properties of a columnar hexagonal liquid crystal by light scattering

In this study we examine a new computer model of light scattering. Light propagation through a columnar hexagonal liquid crystal has been represented by using a cylindrical model. Numerical aspects of the light scattering process, which are based on numerically solving Maxwell's equations, have been calculated for a liquid crystal. We describe in detail the circular cylindrical model for computing light scattering from a columnar hexagonal liquid crystal and present the results of benchmark computations. We report results of extensive calculation for oriented columnar molecular systems. Our results are compared with previous studies on light scattering by other materials.

A new expression for beamwave scattering in the case of various types of arbitrary scattering

A rigorous expression for electromagnetic beam wave scattering by arbitrary conducting and dielectric scatterers is presented in a simple form using the Fourier transform. As numerical models, the B.E.M. and the multiple cylinders method (M.C.M., circular cylindrical model) for the conducting and dielectric rectangular cylinders are used. Scattering patterns and near field distributions are also illustrated. A comparison between the two methods is made.

Electromagnetic beam wave scattering by arbitrary cross-sectional conducting cylinder using N circular cylindrical models

Rigorous expression of the electromagnetic beam wave scattering by N circular cylindrical models is described. To check this method, comparison between exact solution and this model composed of N=24 circular cylinders is presented for a single circular conducting cylinder. Numerical results of conducting square cylinder has been also checked with well-known result (B.E.M).

Use of the field-iteration method in studying the three-dimensional phased array for electromagnetic hyperthermia

The field-iteration method (FIM) is used for simulation of the three-dimensional (3-D) phased array for deep regional hyperthermia at a frequency of 200 MHz. The iterative equation involving the electric field integral equation is derived using the dyadic Green's function with singularities at source paints. The electric field and specific absorption rate distributions in a circular cylindrical model of muscle-like medium and in a model of computerized tomography scans of a liver cancer patient are calculated, respectively, using different amplitudes and/or phases and/or positions of individual applicators of the H-horn phased array. The obtained numerical results compared with the moment method results are analyzed to assess the accuracy of the field-iteration method and also to predict the advantages of the 3-D phased array hyperthermia system.

Analysis of soft and hard strip-loaded horns using a circular cylindrical model

Strip-loaded horns with transverse (soft) and longitudinal (hard) strips are analyzed theoretically. The method is based on a circular cylindrical and uniform waveguide model with a periodic strip structure. The field is represented by an infinite series of space harmonics (Floquet modes) in the air-filled central region and in the dielectrically filled wall region. The tangential field is forced to be continuous across the air-dielectric boundary. The propagation constant and the total field (including the hybrid factor) can be determined by solving the resulting matrix equations. The convergence of the solution has been accelerated by calculating the higher-order terms analytically. It is shown that the soft-strip-loaded horn in principle exhibits the same electrical behavior as a corrugated horn. The horn represents an interesting alternative to the corrugated horn in wide-band or dual-band applications, in particular for millimeter waves and for lightweight applications onboard satellites. The hard-strip-loaded horn has potentially high gain and low cross polarization over a certain frequency range, dependent on the horn dimensions, thickness of the dielectric wall and on how strongly the stripline modes are being excited.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of Blockage on Periodic Pressure Fluctuations and Shock in Cavitating Flow

The intensity of the cavitation shock, the geometry of the cavity and the associated pressure fluctuations in the wake are measured for six different circular cylindrical models. The influence of blockage on these parameters is discussed in detail. In general, with an increase in the blockage ratio, the shock intensity becomes stronger with an increase in the cavitation number. This is noticeable even for small models. With the onset of the shedding-cavity-vortex flow, the shock intensity jumps to a higher value, and the Strouhal number increases. A higher blockage at a given flow velocity or a higher velocity at a fixed blockage tends to accentuate this phenomenon. Shedding of the cavity ceases for λ≥7 (σ≤0.6), however the rear of the cavity shows oscillatory instability resulting in the higher Strouhal number.

A means of controlling bluff body flow separation

Phenomena such as vortex-induced oscillation, high pressure drag and wake buffeting are results of the flow separation which is likely to occur to a bluff body immersed in a fluid stream. One of the effective methods of controlling boundary layer separation is by means of energy exchange, in that energy is extracted from the fluid stream and transported to regions where the flow suffers momentum deficiency and is liable to separation. This concept is incorporated in the design of a flow stabilizing device, which is a passive system relying on the pressure energy derived at the forward part of the body and which provides fluid ejections to invigorate the otherwise debilitated boundary layer. An experimental programme conducted at sub-critical Reynolds numbers was carried out to investigate the performance of such a device fitted on circular cylindrical models. The test results demonstrate the effectiveness of the device in counteracting the above-mentioned adverse effects and, in particular, in suppressing oscillations due to vortex excitation. The degree of effectiveness achieved by the device, regarded as a measure of its ability to control flow separation, is examined in the light of our understanding of the flow handling characteristics of the device in operation.

On vortex excitation of model piles in water

An investigation has been made to determine the nature of flow-induced oscillations in water of circular cylindrical model piles typical of full-scale marine structures. Wind induced oscillations of cylinders usually result in motion normal to the direction of approach flow; in water, oscillations can be excited in the cross-flow and in-line directions. In this paper, a brief review of some of the relevant published literature is followed by a presentation and discussion of the experimental results obtained from the tests at BHRA. Reference is made to full-scale data where appropriate. Fundamental oscillations of free-ended cantilevers were studied in the in-line and cross-flow directions; second normal mode oscillations were also observed in the in-line direction. The second normal mode was of particular practical interest because it approximated the clamped-pinned condition more frequently encountered in full-scale applications. The results showed that two distinct types of instability occurred. These are discussed in some detail and, based on measurements of wake frequencies and pile responses, possible mechanisms of excitation and stability criteria are proposed.