Aeration baffle device and at the end of the cavity length of the cavity opposite the impact

Aeration baffle device and at the end of the cavity length of the cavity opposite the impact Aeration baffle device and at the end of the cavity length of the cavity opposite the impact Abstract: The sudden fall in the sudden expansion of aeration facilities, in order to ensure aeration effect, increasing the length of the end of the cavity, the addition of baffle device is effective engineering measures. Experiment proved that baffle device cavity length of the slope and height of both the impact of the higher increase in cavity length of the baffle device obviously, and so run through the end of the cavity with the side of the cavity is conducive to the end of the cavity fully aerated. Looking back at the end of the cavity flow to make shorter effective cavity length is affecting entrainment effects important factor. In the calculation of cavity length should be considered together, the roof slope angle, or Hom Kok and pick off the impact of converter size, the formula derived from practical applications and theoretical significance. 1 Keywords: aerated baffle device at the end of the cavity side of the cavity jet For the high-head sluice structures, in addition to solve the high-speed water damage caused by the cavity, the gate seal security and optimization problems have become increasingly prominent. Sudden sudden-expansion or the use of aeration facilities, on the one hand to meet the requirements of aeration, on the other eccentric hinge is suitable for use with the curved arc of the door frame seal hydraulic seals can 2 ensure safety and reliability of the gate seal and excellent operation. But the sudden-expansion aerated lack mature engineering experience and theoretical basis for construction projects at home and abroad have already been instances of cavitation damage, its causes have not yet been completely clarified. Therefore, tests to study the sudden expansion by sudden or aerated water law, in additional baffle side walls of the cavity after the device characteristics, pressure distribution, air entrainment caused by the impact of the concentration of practical significance. A pilot program and equipment Experimental Study on the Three Gorges Project deep-hole sudden-expansion suddenly fell on aerated hydraulic model. Gravity model similar to the criteria according to design, model scale is 1:25, the model maximum flow of 350L / s, the export section of a flow rate of 4.5 ~ 7 m / s, Fr = 2.47 ~ 3.59, Re = 1.7 × 106 ~ 2.4 × 106, Wb = 330 ~ 490. model of lateral folding converter shown in Figure 1, the model contract in the 3 width of side-gradient from zero to 2cm, side slope depicting 1:4,1:6,1:8 contraction, baffle device a high degree of depicting the H, 1/2H, 1/3H (H for the aperture height). In the side walls and the floor layout of the time-average pressure on the measured holes, pulse pressure measurement hole, mixed gas concentration sensor chip. Aeration vent holes with hot ball speed anemometer measurements, the concentration of aerated water conservancy and hydropower with the Chinese Academy of Sciences, 848 developed type doped air concentration instrument measurements. To explore the lateral baffle devices of different height and size of the side walls and bottom elements of the various effects of aerated water, experimental study compared the six kinds of programs, such as shown in Table 1. 2 Experimental results and analysis 4 2.1 The sudden expansion flow pattern due to lateral flow of water from the pressurized section of export out of the proliferation after 4 weeks, from two-dimensional flow into a more complex three-dimensional flow. The proliferation of water hit the side walls, the upward spread of water to form water wings, water down the spread of the formation of water curtain. Water-wing back to normal after the water downstream will provoke shock waves, flow pattern more complex wing is too high the water will be the impact of the door hinges. The spread of water curtain down at the end of the cavity back to increase water flow, reduce the length of the end of the cavity. Table 1 Test program Sudden-expansion flow on the sidewall side effects can be broadly divided into four regions, namely the cavity area, 5 sudden change in the pressure area, low-pressure area and stability in the area, as shown in Figure 2, the figure at the end of the cavity length Lb for, Lr effective at the end of the cavity length, Ls for the side of the cavity length. Tests defined in the unit along the side wall of water higher than the same section of the vertical height of the water jet centerline for the water-wing height Hf, part of the level of water higher than the centerline length of water-wing length Lf. Cavity since the flow from the orifice area is Water shares are listed on the downstream side wall until the intersection with the side wall of the horizontal distance. Figure a lateral baffle device to indicate 6 The highest point of water-wing position, with the increase of water level goes down. Maximum height of water with water wings wing length, with the higher water level and significant increase, with the height of baffle device also related to, but with no obvious gradient baffle device of the mutual relations. It is noteworthy that, when the height of baffle device is small, the cavity length of the smaller side, opening in a sudden expansion flow and the impact of sidewall angle larger, generates a stream of white reverse the downward angle of water jet, a direct impact on arc-shaped sealing Road. This phenomenon is usually in the Baffle device height is less than half of the orifice height was a higher incidence of white reverse the impact of water jet off point elevation and height of the converter. 7 Figure 2 sudden-expansion flow patterns indicative of aeration facilities When the converter off when height of more than half of the holes, side cavity longer, the impact of Orifice Flow and sidewall angle smaller, reverse water-jet weakened, this time due to the impact point to the downstream passage of time, reverse water-jet on the arc only side did not constitute any threat to waterways. 2.2 The cavity length of the lateral side of the cavity length is reflected in a stream from the orifice wall orifice until a stream and downstream side walls at the level of the impact of the distance. As the orifice wall in a vertical direction for the arc-shaped, the horizontal spread out along the stream flow direction is gradually strengthened, and therefore the impact of a stream and side wall and the orifice of the distance from the intersection are not equal. Did not increase when the baffle device, usually at the top from the large, the bottom of 8 the range is small, plus baffle device, the top of the range is small, the bottom of the large distance. Take orifice center wall elevation at the end to the outflow orifice and the side wall of the impact of the horizontal distance for the side of the intersection of the cavity length of the test results of all programs shown in Figure 3. As can be seen from Figure 3, the addition of baffle device can be lengthened side of the cavity length of the device with the baffle height. A high degree of more than half of off-hole converter right side of the cavity length of longer obvious effect, on the contrary, a high degree of less than half of the fold-hole converter, converter, compared with non-folding, because of the flow orifice at the bottom of horizontal proliferation constraints affecting the contrary, to shorten the length of the side cavity. 2.3 at the end of cavity length of 9 2.3.1 at the end of the cavity length of the cavity length of the test results the longer the more adequate aeration, reduce erosion, the better, so. The cavity length is a measure of an important indicator of strengths and weaknesses of various programs. Figure 3 Comparison of different options side of the cavity length of Orifice flow down from the threshold, the water along the bottom edge of the tongue turbulent proliferation, increased mixed gas, water and air between the formation of a transitional zone, there is no obvious gas-water interface, which gives at the end of the cavity length of the measurement result difficulties in the water bottom edge of the tongue to determine the different measurement results 10 quite different. Literature [1,2] have been defined along the cavity aeration concentration of 60% of the cavity line such as the concentration of gas-water interface, by measuring the distribution of mixed gas concentration to determine the length of the end of the cavity, apparently this method time-consuming and laborious, Later, by measuring the floor to produce time-average pressure to determine the length of the end of the cavity method, P = 0.4 (Pmax-Pca) to determine the location of the end of the cavity length, where: Pmax is the largest on the floor when you are pressure, the minimum cavity pressure Pca. It was also the direct use of floor are the most stressful time to determine the location of the point at the end of the cavity length. According to this study directly observed at the end of the cavity length of the data with the above-mentioned two methods differed substantially, but not with the following formula to express the bottom time-average pressure match, as shown in Figure 4. 11 P = 0.75Pmax (1) A large number of experiments show that the impact of bottom water after the tongue, resulting in the upstream part of the water along the bottom back to the phenomenon, the actual clearance is much smaller than the length of the cavity at the end of the cavity length (Figure 2, Lrb). Therefore, at the end of the cavity with the length of Lb to illustrate the aeration capacity is not comprehensive, effective cavity length Lr shorter-doped gas decreases, reducing erosion effect is greatly weakened. Fengjiashan and Wujiangdu projects such as the prototype observation data [3] also shows that the prototype water-edge vortex sublingual roll back the strength and water is more serious than the model. Therefore, the introduction of effective cavity length as the basis for the design of aeration facilities are safe. 12 The effective cavity length measurements, and the time-average pressure with the bottom the size of the cavity length to determine the method of comparative analysis found that the effective cavity length value more in line with the following formula expressed in floor time-average pressure values, shown in Figure 5, and Table 2 shows. P = 0.18Pmax (2) Figure 4 at the end of the cavity length of the direct measurement of the value of the pressure conversion value is compared with the bottom 13 Figure 5, the effective cavity length of the value of direct measurement of the pressure conversion Comparison As can be seen from Table 2, the cavity length and the effective cavity length, to a certain extent, subject to discount the impact of converters, the higher the baffle device, the longer the cavity length, there are folding converter program than no folding converter cavity length of the program increased significantly. Baffle device width is from the top to the bottom of the hole-hole gradient from zero to 0.5m, a baffle device is actually a flow orifice at the bottom of the top wide-narrow baffle device played to raise up the role of jet orifice . 2.3.2 the calculation of the length of the end of the cavity there are a variety of computing formula for calculating the cavity lengths, but applies to sudden sudden expansion or aeration facilities at the end of the cavity length of the formula very few can reflect on the cavity length of the baffle device 14 the formula for calculating the impact is even more rare, this article intends to explore in this respect one. Table 2 at the end of the cavity length (bottom pressure conversion value) (unit: m) Is usually calculated at the end of the cavity length of the projectile theory as an important theoretical basis. Coordinate origin on the threshold down to the end of the level of the downstream direction of positive x-axis, y-axis vertically downward, there are Where: Lb for the at the end of the cavity length; y0 for the 15 down Hom Hom and Ming the top to the bottom slope down to extend the line of intersection at the end of the distance; α for the downstream open channel with the angle between the horizontal and downward is positive; β for the actual jet projectile downward angle is positive; u average velocity for the threshold on the water. Using equation (6) calculated at the end of the measured cavity length of the Lb and Lb have greater access must therefore be amended. For the choice of β are different [3], there is pressure directly to the exit hole pressure roof slope angle θ1 as β; literature [4] to consider the introduction of θ1 at the same time the pulse of the largest horizontal velocity calculated β, but did not consider or Hom trajectory angle θ2 of the impact of the calculation error is relatively large; literature [5] considered the trajectory angle θ2 but did not take into account the impact of θ1. Hole pressure or threshold level of exports and the conditions for shorter distances, should also consider the impact of θ1 and θ2. In this paper, β make the following assumptions: 16 Rather, at the end of the cavity gas is doped with an effective cavity length of the vast majority of aeration is the effective cavity achieved. Therefore, estimates of the effective cavity length, for an aeration facility is more meaningful. Assumed impact velocity is equal to Hom top of average velocity, will coordinate origin located at the end of buckets by the equation (3), (4), (10) were jet-slot chassis with out the impact angle γ = arctan (tanβ g’Lb / u2cos2β)-α. (11) Figure 6 at the end of the cavity length Lb experimental 17 values compared with the calculated values Is located at the end of the cavity end of the coordinates y1, vortex go back to the water surface intersects the bottom edge of the tongue point coordinates y2, then: yb = y1-y2. (12) yb generally associated with water tongue thickness (desirable for the exit hole sectional height h), the flow rate u (taking Hom top average velocity), water density ρ, gravitational acceleration g, and the bottom jet impingement angle γ, cavity negative pressure Pca (m water column) of the. Application of dimensional analysis and test results were: The water level in different conditions, the six programs by 18 type (15) The calculation results as shown in Table 3, the calculated values and experimental measurements show the value of comparison in Figure 7. Table 3 at the end of the cavity length and the effective cavity length of the calculated values (unit: m) From Table 3 and Figure 7 can be seen, the experimental data with the calculated values closer comparison. Reposted elsewhere in the paper for free download 3 Conclusion In order to maintain a stable side of the cavity and at the end of the cavity. Baffle device height and slope of the cavity 19 length of the implications and use of the higher baffle device, and can effectively increase the length of underground cavities and side cavity. Moreover, experimental observations have shown that addition of baffle can enable connectivity at the end of the cavity and side cavities, so that the end of the cavity side of the cavity to become an effective ventilation channel, the end of the cavity to ensure adequate aeration. It is noteworthy that, when the baffle device height is less than half the height of orifice, the orifice flow with sudden expansion out of the impact of sidewall angle become larger, resulting in a general downward reverse angle of water jet, only a direct impact on arc waterway, which is a low folding converter program of the state. 20 Figure 7 Experimental values of the effective cavity length of the Lr compared with the calculated values As the back flow effect at the end of the cavity length of the shorter, directly affect the aeration effect. Correctly distinguish and calculation of cavity length and the effective cavity length is evaluation of an aeration program the key. Based on the floor at maximum are two kinds of cavity pressure to determine the length of the experience of relationship (1), (2), for reference. Particularly in view of the top pressure slope angle, or Hom Kok and pick off converter size and other factors derived from a comprehensive calculation of the cavity length of the type (10), (15), there are practical applications and theoretical significance. References: [1] Pan water waves. Ventilation flip bucket capacity of jet aeration [J]. Journal of Hydraulic Engineering, 1980, (5): 25-27. 21 [2] Kai-sui. Ventilation by mechanical problems corrosion pick Kanshui Experimental study [J]. Journal of Hydraulic Engineering, 1984, (3): 33-34. [3] Chang-appointed design institutes hub office. Three Gorges Project sudden down-style deep-hole sudden-expansion of research results aeration facility [R]. Wuhan: Changjiang Water Resources Commission and Design Institute, 1996. [4] Ministry of Water Resources Yangtze River Water Resources Commission. The Yangtze River Three Gorges Project Table-hole and hole shape optimization special report [R]. Wuhan: Changjiang Water Resources Commission, 1996: 22-23. 22 [5] Yu Qi Yang. Bucket-type aeration measures to over-current aeration characteristics of [D]. Beijing: Tsinghua University, 1993. [6] Chanion H. Study of Air Entrainment and Aeration Devices [J]. IAHR, HydrRes 1989, 27: 56-57. Reposted elsewhere in the paper for free download 23