JP2000088870A - Evaluation method for fluid turbulence - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a quantitative evaluation of a fluid in a flowing field as a plane by evaluating a fluid turbulence based on a turbulence strength average M represented by a specific formula. SOLUTION: A turbulence strength obtained by dividing a square average of a deviation from an average flowing speed by the average flow speed can only grasp a turbulence of a field having a flow speed distribution at a point. However, a weighted coefficient Sij at each point represented by the formula I here is determined. The weighted coefficient Sij is also called as a flow speed ratio. In each coordinate in a direction of an object to be evaluated, one-dimensional turbulence strength Mj in an orthogonal direction is calculated based on the formula II. A turbulence strength average M is calculated as defined in the formula III and a flowing turbulence having the flow speed distribution can be grasped not at a point but at a plane if it is used. Since a flowing analysis in the flowing field is carried out based on the turbulence strength average M, an analysis of a numerical value capable of grasping a stirring state in the flowing field can be carried out while corresponding to the numerical value of the turbulence strength average M. The flow analysis in the flowing field can be carried out based on an object numerical value without using a qualitative expression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating turbulence of a fluid in a flow field.

[0002]

2. Description of the Related Art As a method of evaluating turbulence of a fluid in a flow field, there is a method of analyzing a flow field by visualizing a flow using a model of the flow field relating to an evaluation object. For example, using a model of a flow field, a thread called a tuft is installed in an area where observation is desired, and air is circulated through the model of the flow field so that the same wind as the actual flow field passes. Because the tuft moves violently in the place where the wind is stirred and mixed,
The state of stirring and mixing in the flow field is observed. In addition, when a two-dimensional flow channel model of the flow field is used, flow observations such as floating aluminum powder on the water surface and examining the movement of the aluminum powder, and flowing ink on the water surface and observing the flow of ink are required. Is being done. Aluminum powder or ink floating on the water surface is called a tracer. It can be understood that mixing and agitation are promoted where the tracer is violently swirled and disturbed on the water surface.

[0003]

However, only flow observation by visualization as a flow analysis method for a flow field is, for example, such as "the stirring is intense" or "the mixture is well mixed". There is a problem that this method cannot be adopted when the analysis of the flow can be grasped only qualitatively and quantitative evaluation is required. On the other hand, the turbulence intensity obtained by dividing the root mean square of the deviation from the average flow velocity in the flow field by the average flow velocity, which is used in fluid dynamics, etc., is often used as an indicator of the turbulence of the field, but it is understood at the measurement point There is a problem that the method cannot be applied to the case where a quantitative evaluation is performed only in the entire flow field or in a certain area.

An object of the present invention is to provide a method for evaluating fluid turbulence that can quantitatively evaluate fluid turbulence in the entire flow field or in a certain region.

[0005]

According to the present invention, there is provided a method for evaluating a turbulence of a fluid, comprising: a flow in a two-dimensional plane defined by a direction to be evaluated and a direction orthogonal to the direction to be evaluated; In the field, at any time t, any point P
flow rate of the evaluation direction component in _ij and u _ij (t),
When the average flow velocity of the evaluation target direction component at the arbitrary point P _{ij at} time t is U _ij , and the deviation of the evaluation target direction component from the average flow velocity U _ij of t at time t is v _ij (t),

[0006]

(Equation 5)

[0007] The turbulence intensity T _ij defined by

[0008]

(Equation 6)

A weighting coefficient S _ij is obtained for the turbulence intensity T _{ij at} each point defined by the following equation. At each coordinate in the evaluation target direction, a one-dimensional turbulence intensity M _j in the orthogonal direction is calculated.

[0010]

(Equation 7)

And the obtained one-dimensional turbulence intensity M _j

[0012]

(Equation 8)

An object of the present invention is to obtain a turbulence intensity average M defined by the following equation, and to evaluate fluid turbulence based on the turbulence intensity average M.

[Operation] The turbulence intensity (or turbulence intensity) obtained by dividing the root mean square of the deviation from the average flow velocity by the average flow velocity, which is used in fluid dynamics or the like, is given by
_Let u be the flow velocity of the directional component to be evaluated at an arbitrary point P _ij
ij (t), the average flow velocity of the evaluation target direction component at the arbitrary point P _{ij at} time t is U _ij , and the deviation of the evaluation target direction component from the average flow velocity U _ij of t at time t is v _ij (t). In this case, it is expressed by Expression 5. This turbulence intensity can only grasp the turbulence of the field having the flow velocity distribution at a point. However, here, the weighting coefficient S _ij of each point expressed by Expression 6 is obtained. This weighting coefficient S _ij is also called a flow velocity ratio. Then calculated based on the one-dimensional turbulence intensity M _j over the perpendicular direction to the number 7 in the coordinates of the evaluation direction.
Next, the turbulence intensity average M is calculated as defined by Expression 8, and by using this, the turbulence of the flow having the flow velocity distribution can be grasped not as a point but as a surface. Also, the turbulence intensity average M
The flow analysis in the flow field is performed on the basis of the numerical value of the turbulence intensity average M, so that the numerical value that can grasp the stirring state in the flow field can be analyzed, and objective analysis can be performed without using a qualitative expression. The flow analysis in the flow field can be performed based on the numerical values.

[0015]

As described above, the fluid in the flow field can be quantitatively evaluated as a surface, not as a point, and it is possible to easily examine the turbulence of the fluid in the flow field.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a case where an embodiment of the present invention is applied to the design of a secondary combustion zone of a municipal waste incinerator will be described. Thorough reduction of dioxins discharged from municipal solid waste incinerators is required due to its toxicity and domestic pollution situation.To reduce dioxins, complete combustion is considered important. This is because promoting the mixing and stirring in the secondary combustion region is an important factor for achieving complete combustion. In order to consider the mixing and stirring state in the secondary combustion zone of the incinerator, it is important to consider the furnace shape of the incinerator and the method of blowing the secondary air. For example,
Furnace shapes that allow a sufficient amount of secondary air to penetrate into the gas from properly positioned nozzles and that promote turbulent agitation of the gas and air tend to contribute to complete combustion. It has been pointed out since ancient times.

In the present invention, Q1, Q as shown in FIG.
2. A continuous stoker furnace (230 t / d × 2) with measures against mixing and agitation by blowing secondary air from three locations Q3
Furnace) was used as a reference furnace, and a two-dimensional water channel model 1 having a size 1/10 that of the reference furnace formed of an acrylic plate and styrene foam was used. Water flows from the stoker of the two-dimensional waterway model 1 and the portion corresponding to the secondary air Q1, Q2, Q3, and polystyrene particles having a specific gravity almost equal to water (φ2 × 3 mm)
Was used as a tracer, and the flow field was observed from the movement of the tracer. As shown in FIG. 2, the flow field includes a two-dimensional water channel model 1 attached to a predetermined base 5 via a flow type 4 for flowing water from a predetermined water tank 2 through a pump 3 and maintaining a constant amount of water.
To the water tank 2 again. Further, the two-dimensional waterway model 1 is configured such that water flows in from places corresponding to the primary air and the secondary air Q1, Q2, Q3. A camera 6 is mounted above the gantry 5 so that the state of water flowing through the two-dimensional channel model 1 can be observed.

Regarding the similarity rule of the flow in the flow field, the total water amount was determined so that the Reynolds number at the furnace outlet coincided with the reference furnace and the two-dimensional channel model 1. In addition, the amounts of water were distributed such that the mass flow rate ratio of the water supplied from each zone of the primary air and the secondary air Q1, Q2, and Q3 was the same between the reference furnace and the two-dimensional channel model 1. Further, the area of the secondary air protruding was changed so that the flow velocity ratio between the under-furnace air and the secondary air coincided between the reference furnace and the two-dimensional channel model 1.

The observation of the flow field was performed by using the camera 1
By digitally converting images at 60-second intervals, working on a computer, and tracking successive tracers,
This was done by finding the velocity distribution over the flow field. Camera 6
As a method of calculating the instantaneous velocity distribution in the plane from the image captured in the PTV, PTV calculation (Particle tracking ve
locimetry) was used. The PTV calculation is performed by measuring the coordinates of the center of gravity of the tracer particles on a captured moving image, and calculating vector data by tracking the coordinates of the tracer particles by a fixed time pattern matching method.

In the present invention, the three-time pattern matching method is used in the PTV calculation. The three-time pattern matching method is a method of transferring coordinate data for two or three times from the first time to the second time and from the second time to the second time. This is an arithmetic method for tracking coordinate data to three times. Since the PTV only measures the coordinates of the tracer particles on the image and tracks the coordinates, the amount of calculation can be relatively reduced. The search for tracer particles by the three-time pattern matching method is performed in the following procedure. Tracking from the first time to the second time First, as the tracking from the first time to the second time, the tracking of the particle of interest at the first time exists in a first search area (search radius) centering on the particle of interest. The candidate particles at the second time are listed, and the “matching degree” between the target particle and each candidate particle is calculated, and the top three are left. Tracking from the second time to the third time Next, as tracking from the second time to the third time, the vector from the particle of interest to the three candidate particles is extended, the position of the third particle is estimated, and the position is defined as the center. The third time particles present in the second search area thus obtained are listed, and the “matching degree” between the particles at the second to third times is calculated in the same manner as in the first to second time tracking, and the top three Leave a candidate. Determination of Optimal Pair If only one pair at the first-second-third time is found, it is determined as the optimal pair, and if there are a plurality of combinations (maximum 3 × 3 = 9), The “three-time matching degree” is calculated for each combination, and the largest one is determined as the optimal pair. The “3 time matching degree” is calculated based on the following formula. “3 time matching degree” = (first-second time matching degree) × (second-third time matching degree) × (third-first time)
(Time Matching Degree) At this time, an optimum pair is determined only when the maximum three time matching degree is 1.5 times or more that of the second or lower one, and only the one having the maximum matching degree is surely recognized as the optimum pair. If the particles at the second and third times are included in the optimal pair two or more times, only the pair having the maximum three-time matching degree is retained and the others are rejected. Iterative processing The above processing is repeated until no optimum pair is found. In the second and subsequent times, the processing is performed excluding particles already included in the optimum pair. Rejection of low matching degree pairs The three-time matching degrees are compared for all the optimal pairs obtained by the above processing, and those whose values are included in the lower 3% are rejected as having low reliability.

FIG. 3A shows a visualized photograph of the movement of the tracer taken by the camera 6. FIG. 3B shows the flow velocity distribution obtained by the PTV analysis. FIG. 3C shows a schematic diagram of the turbulence intensity distribution. The appearance that the flow of the combustion gas is bent at two places by the secondary air Q1 and Q2 is not only a visualized photograph taken by the camera 6 but also a schematic diagram of a velocity distribution and a turbulent flow intensity distribution obtained by PTV analysis. It turns out that it is well caught.

The average turbulence intensity is calculated by the following procedure. For example, as shown in FIG. 10, in a flow field in a two-dimensional xy plane defined by an evaluation target y direction and an x direction orthogonal to the evaluation target y direction, that is, first, at an arbitrary point P _ij in the flow field Flow velocity u of the evaluation target y-direction component
_ij (t) is obtained. Then, at the arbitrary point P _ij , the deviation v from the average flow velocity U _ij of the y-direction component at time t is calculated.
_The turbulence intensity T _ij is obtained by dividing the mean square of _ij (t) by the average flow velocity U _ij of the y-direction component at time t. This turbulence intensity T _ij
Shows how much the flow is disturbed at the point P, and is shown by Expression 5. Next, the average flow velocity U _ij of the arbitrary point P _{ij at} the time t of the y-direction component is calculated using the y coordinate j
Determining a weighting factor S _ij divided by the sum of the average flow velocity in the y-direction component definitive in all points of the flow field is. The weighting coefficient S _ij is represented by _Expression 6. Next, a one-dimensional turbulence intensity M _j is obtained by summing a value obtained by multiplying the turbulence intensity T _ij by the weighting coefficient S _ij at all points in the flow field whose y coordinate is j. The one-dimensional turbulence intensity M _j is shown by Expression 7. Finally, the sum of the one-dimensional turbulence intensities M _j at all y-coordinates in the flow field can be divided by the number of y-coordinates in the flow field to obtain the average turbulence intensity M of the entire flow field. The average turbulence intensity M is
Indicated by

In the two-dimensional waterway model 1, the flow rate ratio of the amount of water blown from three locations is (Q1: Q2: Q3) = (5:
4: 1), (5: 3: 2), and (5: 1: 4). Further, in the reference furnace shown in FIG. 1, the flow rate ratio of the secondary air blown from three places is (Q1: Q2: Q3) = (5: 4: 1),
The carbon monoxide concentration in the flue gas of the flue gas when the ratio was changed to (5: 3: 2) and (5: 1: 4) was measured. And the result of having compared those values is shown in FIG.
It can be seen that the carbon monoxide concentration decreases as the turbulence intensity average M increases.

On the other hand, FIG. 5 shows that the flow rate ratio of the secondary air blown from three places in the reference furnace is (Q1: Q2: Q3) =
The secondary combustion region oxygen concentration, the secondary combustion region residence time, the secondary combustion region entrance temperature, and (5: 4: 1), (5: 3: 2), and (5: 1: 4). It is a figure which shows the secondary combustion zone furnace exit temperature. Even if the flow rate ratio of the secondary air was changed, the oxygen concentration in the secondary combustion zone, the residence time in the secondary combustion zone, the inlet temperature of the secondary combustion chamber, and the outlet temperature of the secondary combustion zone hardly changed. It is considered that the decrease in carbon concentration is caused by mixing and stirring of the combustion gas and the excess air. Accordingly, the turbulence intensity average M can be used as an indicator of mixing and stirring. If the turbulence intensity average M is high, the mixing and stirring is promoted. Conversely, if the turbulence intensity average M is low, the mixing and stirring proceeds. I could prove it wasn't.

An attempt was made to determine the shape of the new furnace using the turbulence intensity average as an index of the promotion of mixing and stirring. As shown in FIG.
With the stoker surface, the first pass of the boiler and the volume of the primary combustion area fixed, two-dimensional water channel models of furnaces with different drawing positions were prepared. The furnace shape shown in FIG. 6A is furnace shape 1 and the furnace shape shown in FIG. Here, FIG.
Furnace shape 2 shown in (b) is obtained by moving the throttle position to the drying zone side and increasing the height of the outlet of the secondary combustion chamber from furnace shape 1. Turbulence intensity averages corresponding to furnace shapes 1 and 2 were calculated. FIG. 7 shows the results together with the average turbulence intensity in the reference furnace. It is understood that the average turbulence intensity, which is an index of the mixing and stirring, does not differ between the furnace shapes 1 and 2, and is smaller than when the secondary air is not blown in the reference furnace.

For furnace shapes 1 and 2, secondary air was blown into the opposed type and the zigzag type. FIG. 8 shows this blowing. FIG. 8 (a) shows a case where secondary air is blown in a facing type, and FIG. 8 (b) shows a case where secondary air is blown in a zigzag type. FIG. 9 shows a case where secondary air was blown into the opposed type and zigzag type of the furnace shapes 1 and 2 together with the average turbulence intensity in the reference furnace. Regardless of the furnace shape 1 or 2, the turbulence intensity average is larger when the secondary air is blown into the opposed type than when the secondary air is blown into the zigzag type. When secondary air is blown into the opposed type, there is almost no difference in the average turbulence intensity between the furnace shapes 1 and 2, but in each case, the average is larger than the reference furnace.
Since the secondary combustion outlet is lower in the furnace shape 1 than in the furnace shape 2, it is considered that the method of blowing the secondary air in the facing shape in the furnace shape 1 is optimal.

[Alternative Embodiment] In the above embodiment, the flow analysis in the secondary combustion region of the incinerator has been described. However, the present invention is not limited to this. Can also be used. In the carrier fluidization tank of the septic tank, it is desirable that the microorganisms are brought into contact with air and the microorganisms are brought into contact with sewage sludge. Therefore, it is desirable that the water in the carrier fluidization vessel be stirred.

As a method of calculating an instantaneous velocity distribution in a plane from an image captured by a camera, a PIV operation (Partic
le imaging velocimetry). PIV operation is a tracer (Part
This is an operation for focusing on a certain part in the image data obtained by photographing the icle) and calculating where the part has moved on the image at the next time. The calculation is performed by calculating a vector component of the entire image by executing the calculation on an equally-spaced mesh set on the image. In the PIV operation, the movement amount at each point on the image is obtained by comparing the images themselves.

In the above embodiment of the present invention, the turbulence intensity average is calculated by obtaining the flow velocity of the y-direction component as the evaluation target direction among the flow velocities in the flow field, but the present invention is not limited to this. The average turbulence intensity can also be calculated using the flow velocity of the x-direction component, the scalar amount of the flow velocity, the angle of the flow velocity, and the like as the evaluation target direction among the flow velocities in the flow field. In addition, even if the turbulence intensity average is calculated using the flow velocity of the y-direction component, the flow velocity of the x-direction component, the scalar amount of the flow velocity, the angle of the flow velocity, etc. among the flow velocity in the flow field, the flow analysis is performed equally. be able to.

Although the two-dimensional flow analysis has been described in the embodiment of the present invention, the present invention is not limited to this, and it is considered that the present invention can be applied to a three-dimensional visualization experiment and a simulation.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a reference furnace.

FIG. 2 is a schematic diagram of an experimental apparatus.

FIG. 3 is a diagram showing a state of water flowing through a two-dimensional waterway model. Among them, (a) is a visualized photograph taken by a camera.
(B) is a flow velocity distribution chart obtained by PTV analysis. (C) Schematic diagram of turbulence intensity distribution

FIG. 4 is a diagram showing the relationship between the average turbulence intensity and the concentration of carbon monoxide.

FIG. 5: Secondary air flow rate ratio and temperature, residence time,
Diagram showing the relationship between oxygen concentrations

FIG. 6 is a diagram showing a new furnace shape.

FIG. 7 is a diagram showing an average turbulence intensity in a new furnace shape.

FIG. 8 is a diagram showing a state of blowing secondary air.

FIG. 9 is a diagram showing a relationship between a secondary air blowing method and a turbulence intensity average in a new furnace shape.

FIG. 10 is a diagram showing the flow velocity in the y direction on the xy plane.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Two-dimensional water channel model 2 Water tank 3 Pump 4 Flow rate type 5 Mount 6 Camera 7 PTV analysis system

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[Procedure amendment]

[Submission date] September 14, 1998 (1998.9.1)
4)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

Claims (1)

[Claims] 1. An evaluation target direction is orthogonal to the evaluation target direction.
In a flow field in a two-dimensional plane defined by the directions_ijEvaluation target in
U_ij(T), the arbitrary point P_ijIn
The average flow velocity of the evaluation target direction component at time t is U_ijAnd said
Average flow rate U at t time of the directional component to be evaluated_ijDeviation from
v_ij(T),Turbulence intensity T defined by_ij, And in a direction orthogonal to the evaluation target direction,Turbulence intensity T at each point defined by_ijWeighting factor for
S_ijAt each coordinate in the evaluation target direction,
Barrel one-dimensional turbulence intensity M _jIs given byAnd the obtained one-dimensional turbulence intensity M_jAgainst
Then,Turbulence intensity average M defined by
How to evaluate body turbulence.