JP2005233170A - Method for reducing disc friction by forming spiral groove - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce frictional loss by forming a side wall of an impeller, an inner wall or a disc surface of a casing a surface which is provided with a number of spiral grooves meeting a logarithm spiral curve taking a stream angle as a variable for disc frictional loss of the impeller of a turbo type fluid machine which performs energy conversion of the fluid or gas, and viscosity frictional resistance of a rotating disc which rotates in the fluid. <P>SOLUTION: The logarithmic spiral of a required radius r taking the stream angle ψ as the variable is formed into a groove shape, and the required number of spiral grooves where n = 150-160 order, are provided on the disc surface at constant intervals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to disc friction loss of a turbo fluid machine that performs energy conversion of fluid such as liquid or gas, and reduction of friction loss of a rotating disc in a fluid flow system.

Background technology

  In recent years, attempts to reduce fluid loss and resistance reduction have attracted a great deal of attention at home and abroad in direct relation to global warming and energy saving. When the fluid flows, the frictional resistance of the solid wall surface in contact with the fluid cannot be ignored in the existing fluid, and its reduction has been a major research and technical problem in fluid engineering.

  On the other hand, the rotating disk frictional resistance is directly related to the mechanical friction loss power of the impeller of a turbomachine, which is a fluid machine that converts energy such as pumps, blowers, blowers and water turbines, such as liquids and gases. Since it is directly linked to improvement, its reduction is very important industrially.

  Usually, the loss power can be calculated and predicted from the analysis of the frictional resistance of the rotating disk in the container and the experimental results. If resistance and loss in the fluid flow are considered to be caused by the interaction between the fluid and the solid wall, there are two methods for reducing the resistance: a method for changing the properties of the fluid and a method for changing the properties of the solid surface. It can be roughly divided.

  As a method of changing the characteristics of the former fluid, a method of adding a resistance reducing agent such as a water-soluble polymer or a surfactant can be raised. However, these can be applied in general turbomachine operating conditions, considering the deterioration problem that the characteristics are lost when flowing in a high shear rate field for a long time and the environmental impact when dumped after flow. Is difficult. Furthermore, it is targeted only for liquids. Therefore, it is considered that the latter method focusing on the characteristics of the solid surface is suitable for application of the resistance reduction effect to the rotating disk in the impeller of a turbomachine and a flow system, and the application range is considered wide.

  As an example of paying attention to the characteristics of the solid surface, there is a method in which a super water-repellent wall that causes fluid slip on the wall surface is applied to the solid surface (see, for example, academic literature 1). However, it is possible to obtain a resistance reduction effect in the laminar flow area, but only for liquids, and in a flow field where a large mechanical shear force acts for a long time such as a pump impeller, the coating film is peeled off or worn. Is inevitable and its effect is lost, so its practical use at the present time is difficult.

  Therefore, a wall surface with excellent durability is required for practical use of a solid surface having a resistance reducing effect. One of the durable wall surfaces is a riblet. (For example, see academic literature 2). A riblet is a groove having a certain regularity provided on a solid surface, and has an effect of reducing fluid frictional resistance in a certain flow region. The application of this resistance reduction effect to a rotating disk can be applied to both gas and liquid, and is considered excellent in terms of durability.

  In connection with this, a fluid machine having a certain surface shape has been proposed (see, for example, academic literature 3). In addition, based on the experimentally clarified aspect of the flow on the disk surface, an application as an impeller with multiple grooves has been proposed. (For example, see academic literature 4).

Academic literature

Academic literature 1

Watanabe, Ogata, and Super water-repellent rotating discs for reducing the frictional resistance of Newtonian fluids, The Japan Society of Mechanical Engineers, B, 63, 612, (1997), p. 2752.

Academic literature 2

Walsh, W .; J. et al. , Ribets as a Viscous Drag Reduction Technique, AIAA Journal, Vol. 21, no. 4, (1982), p. 485.

Academic literature 3

Zenge Prodersen, fluid machinery, Japanese Patent No. 3455586 (2003)

Academic literature 4

Watanabe, a turbomachine impeller having a plurality of narrow grooves on the side wall, JP-A-121316, (1996).

However, the proposed method described above does not fully grasp the characteristics of the turbulent boundary layer and its flow on the surface of the rotating disk. However, the original resistance reduction cannot be obtained. In Academic Literature 3, the target groove structure is S = ⁺ 5 to 25, but when the number of grooves is calculated backwards, it becomes 450 or more, and the groove structure area is on the order of ² μm, which is too small. It is impossible to control the boundary layer of the rotating disk. This is thought to be due to the fact that the shape is simply applied from a circular tube or flat plate of a riblet that has been conventionally used. Furthermore, the optimum and effective disk surface shape that can be reduced to the maximum cannot be specified, and it is difficult to say that the method is actually realized.

  The present invention has been made for the purpose of solving the above-described conventional problems, hydrodynamically captures the flow behavior on the disk surface, and has a surface shape determined based on the result, A surface characterized by reducing frictional resistance in the flow transition region and the turbulent flow region. Originality and novelty that cannot be realized by analogy with the surface structure of the riblet proposed in the past or referring to them. Have

  The visualization of the flow on the surface of the rotating disk, which has been performed conventionally, has revealed the direction of vortices and main flow that stay on the disk surface in laminar and turbulent regions (see, for example, academic literature 5). That is, it can be said that the flow of the boundary layer on the rotating disk is a flow having a certain type of structure having a flow direction of the main flow and a fixed vortex.

Academic literature

Academic literature 5

Kato, Watanabe, Naya, The flow in the vicinity of a rotating disk in a polymer solution is described in Japan Society of Mechanical Engineers, Volume B, Vol. 44, 379 (1978), p. 970.

  Focusing on the flow in the vicinity of the disk, which is clarified from the visualization result, it is considered that the rotational disk frictional resistance can be reduced by performing the flow rectification effect, that is, the control, rather than the riblet effect. The flow control on the disk surface is controlled by a constant number of lines following a logarithmic spiral curve as a function of the flow angle φ, which is the ratio of the tangential and radial wall shear stresses of the spiral disk along the flow on the disk surface. This is possible by attaching grooves at regular intervals.

  These grooves can be manufactured by etching or mechanical processing. If it is of course difficult to process these grooves, a groove with the required spiral shape is pressed into a thin film or film and the target is processed. Needless to say, it can also be realized by bonding to the surface.

  According to the present invention, the viscous loss is reduced by about 15% at maximum by attaching fine spiral grooves to the side wall of the impeller of the turbomachine, the inner wall of the casing, or the surface of the disk rotating in the fluid. Taking a centrifugal pump as an example, the disk friction loss usually occupies 10 to 20% of the total efficiency of the pump, and by this reduction, the performance can be expected to increase by 2 to 3%, and the present invention has an excellent effect. Demonstrate.

ただし、φ＝流れ角（ｒａｄ）、τ_θ＝接線方向の壁面せん断応力（Ｐａ）、τ_ｒ＝半径方向の壁面せん断応力（Ｐａ）、Ｒｅ_Ｌ＝円板の半径を代表寸法とする局所レイノルズ数（・／・）、ｒ＝円板上の任意半径（ｍ）、ｒ_ｌ＝基準となる半径（ｍ）、θ＝円周方向座標（ｒａｄ）Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a logarithmic spiral curve of a spiral groove according to the present invention attached to the disk surface. The flow angle φ is given as a function of the local Reynolds number Re _L with the radius of the disk as a representative dimension, and the radius r of the logarithmic spiral curve is given as a variable.

Where φ = flow angle (rad), τ _θ = tangential wall shear stress (Pa), τ _r = radial wall shear stress (Pa), Re _L = local Reynolds with the radius of the disk as a representative dimension. Number (./.), R = arbitrary radius (m) on the disc, _r.sub.l = reference radius (m), .theta. = Circumferential coordinate (rad)

  As shown in FIG. 2, the above-mentioned logarithmic spiral curve is given to the disc surface or inner wall at equal intervals in the order of 150 to 160. The widths of the spiral grooves according to the spiral curve are automatically determined by giving them equal intervals. 3 to 5 are examples of the spiral groove shape.

The ratio of the gap s between the container of the rotating disk in the container and the side wall of the disk and the radius a (s / a) on the surface of the groove number n = 150 having a depth of about h = 0.2 mm that matches the spiral curve ) when the small frictional resistance moment coefficient of the disc in frictional resistance moment coefficient as shown in the relationship of C _m and the Reynolds number Re, the water compared to the smooth disc in turbulent disc of FIG. 6 ( The mark (●) in the figure was reduced by about 15%.

  The flow visualization at this time is shown in FIG. 7 and FIG. 8 as a result of visualizing the flow in the vicinity of the disk having a smooth surface and the spiral groove. Although the flow on the smooth disk surface in FIG. 7 is outward in the circumferential direction, a large vortex flow is generated. It can be seen from FIG. 8 that the flow is directed and controlled in the circumferential direction by attaching the spiral groove, and the effect can be clearly confirmed.

  The present invention is not limited only to the above-described embodiment, but the viscous friction can be obtained by providing a required surface against the flow of gas such as a rotating disk and air installed in the tank of the fluid stirring system. Of course, various changes can be made without departing from the scope of the present invention.

It is a logarithmic curve figure of one spiral groove used for one Example of the method of this invention. It is an Example of the disc which attached | subjected FIG. 1 to the disc at equal intervals. The cross-sectional shape with respect to the spiral groove of FIG. 2 is an example of a trapezoidal shape. FIG. 2 shows an embodiment in which the cross-sectional shape with respect to the spiral groove of FIG. 2 is U-shaped. FIG. 2 shows an embodiment in which the cross-sectional shape with respect to the spiral groove in FIG. 2 is V-shaped. It is an example of the experimental result of the rotation disk friction moment coefficient with respect to the case where the axial clearance was comparatively narrow manufactured based on this invention. It is an example of the visualization result with respect to the flow in the vicinity of a rotating disk with a smooth disk surface that matches the experimental conditions of FIG. It is an example of the visualization result with respect to the flow in the vicinity of the rotating disk with the spiral groove according to the present invention, which is consistent with the experimental conditions of FIGS.

Claims (3)

A logarithmic spiral curve having a required radius r with a required flow angle φ given by the following equation as a variable is defined as a groove shape, and the required number of n = 150 to 160 orders of the spiral grooves is given to the disk surface at equal intervals. The surface of the impeller of a turbo fluid machine using the liquid or gas as a working fluid, the inner wall of the casing, or the surface of a rotating disk in a fluid flow system.

The surface or inner wall according to claim 1, wherein the depth of the spiral groove is on the order of 0.05 mm to 0.2 mm. The surface or inner wall according to claim 1, wherein the spiral groove has a V-shaped, U-shaped or trapezoidal cross-sectional shape.

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