| Monohull is a type of high-speed ship.In order to meet the needs of higher speed,more than two sets of propulsion devices are often arranged.Water jet propulsion devices have been widely used in high-speed ships due to their good noise performance,high efficiency,and high speed.Due to the special principle of the water jet propulsion device,when two or more units are arranged,mutual interference may occur,which affects the normal operation of the device and may not reach the designed speed.To this end,this paper adopts CFD(Computational Fluid Dynamics)technology,takes monohull as the final application object,successively develops piping systems,water jet propulsion devices with propulsion pumps,and applies the devices to monohulls The analysis and research of the interference characteristics of two adjacent units of the "hull-device" system have concluded as follows:(1)Only consider the piping system,and carry out analysis and research on the interference characteristics of two adjacent units.Aiming at the piping system of the water jet propulsion device,the interference of the unit arrangement spacing and the advance speed ratio on its hydraulic flow characteristics is studied,and the flow tube characteristics and hydraulic performance are analyzed.The research results show that:①When the unit spacing B<2.0D,The flow pipes of the two units interfere with each other obviously,and the flow pipes are extruded each other.As the distance between the units increases,the mutual extruding effect is constantly weakened.When the unit spacing is 2.0D,the inlet surface begins to separate to form a separate inlet flow.surface.The larger the unit arrangement distance,the larger the uniformity of axial flow velocity distribution and the speed-weighted average angle.②With the continuous increase of the speed ratio,the width and depth of the inlet surface of the unit increase.The larger the feed speed ratio,the more obvious the extrusion of the inlet surface.The mutual interference of the depth,width and area of the flow tube increases with the increase of the speed ratio.The larger the speed ratio,the smaller the uniformity of axial flow velocity distribution and the speed-weighted average angle.When only considering the piping system,it is recommended that unit spacing is greater than 2.0D,and the corresponding IVR should be less than 1.0(2)Considering the propulsion pump,carry out analysis and research on the interference characteristics of two adjacent units of the complete set of water jet propulsion equipment.The hydraulic performance,flow tube characteristics,and thrust performance of the two water jet propulsion devices at different spacings and speeds are studied.The results show that:①The small space between units will cause flow tube squeeze.Increases,the squeezed flow tube begins to recover.When the unit spacing is 2.5D,the flow tube almost returns to its original shape,which indicates that the rotation effect of the impeller has a greater impact on the characteristics of the flow tube;depth interference deformation coefficient and unit layout The spacing is negatively correlated,while the width and area interference deformation coeficients increase monotonically with the random arrangement spacing;the uniformity characteristics of the runner outlet section are positively correlated with the unit arrangement spacing.When the unit spacing is 2.75D,the section uniformity characteristics are optimal.The uniformity of axial speed distribution is 75.94%,and the weighted average angle of speed is 81.8°;although the unit efficiency and head are positively correlated with the unit arrangement spacing,the amplitude is small,and the unit efficiency is up to 83.76%;thrust and system efficiency are randomly grouped The increase of the arrangement spacing increases.In short,improper unit spacing will adversely affect the normal operation of the water jet propulsion device.②Due to special reasons,the rotational speeds of two adjacent units may be inconsistent.This article keeps the rotational speed of unit 2 unchanged,adjusts the rotational speed of unit 1,and calculates the rotational speed ratio based on the rotational speed of unit 2,and analyzes the effect of different rotational speed ratios on the device.The influence of hydraulic performance,flow tube characteristics and thrust performance.The more the speed ratio deviates from 1,the more obvious the squeezing effect of the flow tube is.The flow tube of the low-speed unit is relatively more disturbed.When the speed ratio is 1,that is,symmetrical operating conditions,the hydraulic loss,efficiency,uniformity characteristics of flow rate and thrust of the two units are almost the same.At this time,the efficiency is the highest,exceeding 72%,the flow velocity distribution uniformity can reach 75.86%,and the speed weighted average angle can reach 81.54°.When the speed ratio is less than 1,the hydraulic loss of the two units is negatively correlated with the speed ratio.The change rate of unit 1 is larger,and the change rate of unit 2 is smaller.The flow rate uniformity characteristics and efficiency of the two units are positively correlated with the speed ratio,and the rate of change is consistent with the hydraulic loss.When the speed ratio is greater than 1,the change trend and rate of change of the hydraulic loss of each unit are completely opposite to those when the speed ratio is less than 1.Different from the trend of other parameters,the thrust of unit 1 increases monotonically with the increase of speed,while the system efficiency does not change monotonously.The overall trend is to increase first and then decrease;the thrust of unit 2 and system efficiency increase with the increase of speed.Decrease monotonously,when the speed ratio is less than 1,the rate of change is small,and when the speed ratio is greater than 1,the rate of change is greater.When considering the propulsion pump,there is no water grab under each unit spacing.To ensure the device operate under the optimal conditions and maximum thrust,it is recommended that the unit spacing be greater than 2.25D.In addition,priority should be given to ensuring that the rotation speeds of adjacent water jet propulsion devices of the same model are consistent.If the rotation speed cannot be guaranteed due to special circumstances,the rotation speed ratio range should not exceed 0.87～1/0.87.(3)Considering the monohull ship model,the research on the interference characteristics of two adjacent units of the "hull-water jet propulsion device" system is carried out.Based on the CFD numerical simulation technology,the effect of unit arrangement spacing on the hydraulic performance,flow tube characteristics and thrust performance of the "hull-device" system is studied.The research results show that when the unit arrangement spacing is small,the two units are close to each other.There are undesirable flow patterns such as obvious backflow near the elbow of the inlet flow channel on the side of the unit.As the arrangement spacing of the units increases,the backflow gradually weakens and the water flow becomes smoother.When the unit spacing is less than 2.2D,the inlet surface of the two units has no obvious limit,and the center of symmetry is concave toward the water surface.When the unit spacing exceeds 2.2D,the inlet surface has an obvious limit.The depth interference deformation coefficient is negatively correlated with the unit layout spacing,and the rate of change is small,while the change trend and rate of change of the width and area interference deformation coefficients are completely opposite to it.With the increase of unit arrangement spacing,the hydraulic performance and thrust characteristics are improved.When the unit spacing is 2.2D,the uniformity of the axial speed distribution of the two units is about 74%,the speed-weighted average angle is close to 81°,and the efficiency exceeds 74%.The loss is 0.538m.Considering the "hull-water jet propulsion device" system,it is recommended that the unit spacing should be greater than 2.0D.The results of carrying out this research not only have certain engineering guidance and reference significance for the layout of water jet propulsion devices,but also can further enrich the theory of water jet propulsion devices by summarizing the interference characteristics of dual water jet propulsion devices. |
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