A ducted propeller hydrodynamic calculation method and its application

Abstract

The present invention relates to the technical field related to propeller hydrodynamic performance simulation, and discloses a ducted propeller hydrodynamic calculation method based on the flow equality principle and its application. The method uses a body force model to replace the effect of the blades, introduces a mass flow correction coefficient λ in the processing of the advance rate, and calculates λ based on the principle that the mass flow of the physical ducted propeller is equal to the mass flow of the duct-matched body force model. The advance rate coefficient is then corrected by the mass flow correction coefficient λ, thereby correcting the low propeller thrust, duct thrust, and mass flow in the duct after the use of body force instead of the physical propeller. Through this improved body force method, the coupled hydrodynamic effects between the duct and propeller can be fully considered on the basis of significantly improving the efficiency of the vehicle's maneuvering motion simulation, thereby obtaining more accurate propeller thrust, duct thrust, and the vehicle's navigation resistance simulation values.

Description

Technical Field

[0001] The present invention relates to the technical field related to propeller hydrodynamic performance simulation, and more specifically, to a ducted propeller hydrodynamic calculation method based on the flow equality principle and its application. Background Art

[0002] Rapid and accurate prediction of underwater vehicle maneuverability is crucial during the ship design phase. Ducted propellers are often used as propulsion systems for underwater vehicles due to their high efficiency under heavy loads, blade damage avoidance, and low noise levels. However, the current numerical simulation method—the body force method—which accurately simulates propeller hydrodynamics and thus rapidly predicts underwater vehicle maneuverability, is not suitable for ducted propellers, which have "internal flow" characteristics.

[0003] Figure 1 The figure shows the simulation-experimental comparison of the traditional body force method applied to ducted propellers. The No. 19A duct, a famous ship model test tank in the Netherlands, was selected as the research object. The No. 19A duct was matched with the Goldstein distributed propeller body force model for numerical simulation. The open water performance curve in the simulation was the open water curve value of the Ka4-70 single propeller, the advance coefficient J was taken from the ducted propeller design range of 0.1-0.7, and the propeller body force model speed n was constant at 25r / s. The simulation results of the open water performance curve are shown below. Figure 1 As shown, the propeller thrust coefficient and the duct thrust coefficient are expressed in K TPG and K TDG Indicates that K TP0 and K TP0 is the corresponding test value, Figure 1 It can be seen that the propeller thrust coefficient is consistent with the test value, with an average relative error of -8%; however, the ducted thrust coefficient is far from the test value. Its inapplicability is manifested in the low predicted values ​​of ducted thrust, propeller thrust, and underwater vehicle body resistance. The reason is that after replacing the physical propeller with body force, the traditional advance coefficient formula without flow correction is still used, resulting in a low mass flow rate in the duct. Therefore, it is impossible to achieve a rapid and accurate prediction of the maneuverability of the underwater vehicle equipped with a ducted propeller.

[0004] Patent CN112464585A proposes a ducted propeller calculation method based on the coupling of viscous flow and potential flow. This method uses a curved surface similar to the propeller's leading edge as the propeller's advance sampling surface and distributes the body force in the viscous flow field in the shape of the blade. This method achieves effective wake flow, achieving an equalization between body force and propeller thrust. However, because it does not include mass flow correction, it cannot accurately calculate ducted thrust and ship / hull resistance. Summary of the Invention

[0005] In response to the defects or improvement needs of the above-mentioned existing simulation technologies, the present invention provides a ducted propeller hydrodynamic calculation method based on the flow equality principle and its application. By correcting the existing body force method technology with mass flow as the entry point, efficient and accurate numerical simulation of the hydrodynamic performance of ducted propellers can be achieved.

[0006] To achieve the above object, the present invention provides a method for calculating the hydrodynamics of a ducted propeller and its application, the method comprising the following steps:

[0007] Step 1: Establish a viscous fluid calculation model based on the RANS equation.

[0008] Specifically, the method includes establishing a three-dimensional model of a ducted propeller and a surface or underwater vehicle (hereinafter referred to as the vehicle), and determining a propeller speed n. The propeller speed n is determined by specific maneuverability tests, such as self-propulsion tests, slewing tests, and Z-type tests.

[0009] Divide the surface mesh of the ducted propeller and the surface or underwater vehicle and the volume mesh of the fluid area, set the boundary conditions, initial conditions, and turbulence model.

[0010] Step 2: Solve the RANS equation to obtain the correction speed coefficient J * , correction speed coefficient J * Used to correct the lower propeller thrust, ducted thrust and mass flow rate after using body force instead of solid propeller.

[0011] By setting the velocity monitoring surfaces of the inlet surface, the duct inlet and the duct outlet, the corresponding axial average velocity V of the inlet surface can be obtained. inflow , the axial velocity at the duct inlet and the axial velocity at the duct outlet.

[0012] The correction speed coefficient J * Defined as:

[0013]

[0014] Where λ is the mass flow correction coefficient; V inflow is the average axial velocity of the inlet surface, and n is the propeller speed. The inlet surface is a circular surface with an outer diameter of D and an inner diameter of the hub diameter, and its axial position is the propeller disk surface.

[0015] V induced is the ducted propeller axial induced speed, which is the difference between the axial speed at the duct outlet and the axial speed at the duct inlet.

[0016] Preferably, the mass flow correction coefficient λ is solved according to the following process:

[0017] a. By numerically solving the Reynolds average (RANS) equation, the numerical relationship between the speed V and the mass flow rate Q0 of the solid ducted propeller at each speed n is obtained: Q0 = f(V); the mass flow rate is defined as Q = ρSV Inflow , where S is the inlet surface area and ρ is the fluid density.

[0018] b. The numerical relationship between λ, V and mass flow rate Q of the duct body force model is obtained through numerical simulation, and the formula λ = g(V,Q) is obtained through surface fitting.

[0019] c. Substituting the real-time ship speed v of the ducted propeller with the body force model, obtained by numerically solving the Reynolds-averaged (RANS) equations, into equations Q0 = f(V) and λ = g(V, Q), we can obtain the mass flow rate Q0 = f(v) of the physical ducted propeller at the real-time ship speed v. Based on the principle of flow equality, we can then calculate the mass flow rate correction factor λ = g(v, f(v)).

[0020] Preferably, in step c, the flow equality principle is that the mass flow rate Q0 of the physical ducted propeller at the real-time speed v is equal to the mass flow rate Q of the duct-coupled body force model, i.e., Q0 = Q. The physical meaning of the flow equality principle is that the macroscopic characteristics of the flow field in the duct of the duct-coupled body force model and the physical ducted propeller are the same (the mass of fluid passing through the duct per unit time is equal), thereby obtaining the same duct thrust, propeller thrust, and vehicle resistance for the two.

[0021] Step 3: Correct the speed coefficient J according to real-time * , interpolate the propeller single blade performance curve to obtain the corresponding thrust coefficient K TP =f(J * ), and then the propeller thrust T P .

[0022] The open water performance curve of a solid propeller (without duct, called a single propeller) is obtained through experiments or numerical simulations.

[0023] Step 4: Write a field function on the simulation platform to specify the volume force distribution form and spatial distribution area to obtain the specific volume force source term, and load the RANS equation to solve it to obtain the catheter thrust T D and vehicle resistance.

[0024] Preferably, in step 4, the propeller body force distribution is in the form of spatially uniformly distributed axial force.

[0025] Preferably, in step 4, the radial range of the propeller body force spatial distribution area is between the hub radius and the inner diameter of the duct, and the axial range is the range covered by the lateral projection of the blade. At this time, the specific expression of the body force source term is Where V PThe volume of space occupied by the body force source, the direction of the body force source is the propeller axis, and it is limited to the aforementioned specified area.

[0026] Preferably, the flow field around the vehicle is calculated by numerically solving the RANS equation, and the propulsion performance of the vehicle is obtained by coupling the flow field with the duct thrust and the propeller thrust.

[0027] In general, the improved body force method proposed by the present invention can achieve the following beneficial effects compared with the prior art:

[0028] 1. The number of grids and the difficulty of generation are reduced in the numerical simulation of ducted propellers, making the numerical calculation stable and fast; at the same time, the time scale span of the physical field is narrowed, significantly shortening the calculation time.

[0029] 2. When calculating the incoming flow velocity, the propeller thrust calculation based on the body force method is more accurate by correcting the induced velocity of the ducted propeller.

[0030] 3. A mass flow correction factor was introduced to modify the mass flow rate of the duct-with-body-force model to align it with the values ​​obtained from physical experiments or numerical simulations that are highly accurate but time-consuming. This resulted in the same macroscopic characteristics of the flow field within the duct of the duct-with-body-force model and the actual ducted propeller (the mass of fluid passing through the duct per unit time is equal), resulting in accurate values ​​for the duct thrust and ship / boat resistance.

[0031] 4. This invention overcomes the shortcomings of existing propeller body force methods by introducing the condition of equal mass flow rate, enabling accurate prediction of the coupled hydrodynamic forces of the ship / hull and ducted propeller, and enabling efficient and accurate dynamic simulation of underwater vehicle maneuverability. This method provides valuable assistance for predicting vessel maneuverability, optimizing ship design, and improving vessel performance, and possesses considerable theoretical and engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the simulation-experimental comparison of the traditional body force method applied to a ducted propeller.

[0033] Figure 2 The figure is a flow chart of the method for calculating the hydrodynamic force of a ducted propeller according to the present invention.

[0034] Figure 3 This is a schematic diagram of the inlet surface and inlet and outlet positions of the ducted propeller of the present invention.

[0035] Figure 4 This is an example diagram showing the numerical relationship between the mass flow correction coefficient λ, ship speed V, and mass flow rate Q for the duct body force model.

[0036] Figure 5 Schematic diagram of the spatial distribution of volume force sources of the present invention.

[0037] Figure 6 Schematic diagram of the geometric model and mesh encryption area of ​​the hull and duct of the present invention.

[0038] Figure 7 Schematic diagram of the simulation-test comparison of the rear ducted propeller of the boat according to the present invention.

[0039] Figure 8 This is a schematic diagram of the application of the ducted propeller hydrodynamic calculation method of the present invention to boat rear propulsion. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further explained in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the invention.

[0041] See also Figure 2 The present invention provides a method for calculating the hydrodynamics of a ducted propeller based on the flow equality principle and its application, the method comprising the following steps:

[0042] Step 1: Establish a viscous fluid calculation model based on the RANS equation.

[0043] The RANS equation is:

[0044]

[0045] Where: x i , x j are the coordinate components (i, j = 1, 2, 3), i > is the ensemble average of the fluid velocity component, ρ is the fluid density, is the pressure ensemble average, f i is the body force source term, υ is the fluid kinematic viscosity coefficient, <u′ i u′ j > is the Reynolds stress tensor.

[0046] Specifically, the method includes establishing a three-dimensional model of a ducted propeller and a surface or underwater vehicle (hereinafter referred to as the vehicle), and determining a propeller speed n. The propeller speed n is determined by specific maneuverability tests, such as self-propulsion tests, slewing tests, and Z-type tests.

[0047] Divide the surface mesh of the ducted propeller and the surface or underwater vehicle and the volume mesh of the fluid area, set the boundary conditions, initial conditions, and turbulence model.

[0048] Step 2: Solve the RANS equation to obtain the correction speed coefficient J *

[0049] Set the velocity monitoring surfaces at the inlet surface, the duct inlet, and the duct outlet to obtain the axial average velocity V of the inlet surface. inflow , the axial average velocity at the duct inlet and the axial average velocity at the duct outlet. The duct propeller inlet surface and inlet and outlet positions are shown as follows Figure 3 shown.

[0050] The correction speed coefficient J * Defined as:

[0051]

[0052] Where λ is the mass flow correction coefficient; V inflow is the average axial velocity of the inlet surface, and n is the propeller speed. The inlet surface is a circular surface with an outer diameter of D and an inner diameter of the hub diameter, and its axial position is the propeller disk surface.

[0053] V induced is the ducted propeller axial induced speed, which is the difference between the axial speed at the duct outlet and the axial speed at the duct inlet.

[0054] Corrected advance coefficient J * is the propeller advance coefficient after mass flow correction (λ=0 indicates the conventional advance coefficient without mass flow correction J * After replacing J, the correction of mass flow in the duct can be achieved based on the momentum theorem, that is, when the accelerating duct propeller (body force) rotates forward, the propeller disk axial velocity increment |ΔV Inflow | is less than the axial velocity increment at the duct outlet |ΔV induced It is easy to see that when λ>1, the change in the inflow surface (propeller disk) speed due to the existence of λ is |ΔV Inflow | is always less than the change in induced velocity due to the presence of λ|ΔλV induced Compared with λ=0, when λ takes a value in the interval [1, +∞], the correction speed coefficient J * The mass flow Q increases, thereby correcting the low propeller thrust, duct thrust and mass flow in the duct after using body force instead of the solid propeller. * Substitute J to solve the propeller thrust coefficient K TP This can make the propeller thrust, duct thrust, and vehicle resistance values ​​more accurate. Therefore, the mass flow rate can be corrected based on the corrected advance coefficient J*.

[0055] Preferably, the mass flow correction coefficient λ is solved according to the following process:

[0056] d. By numerically solving the Reynolds average (RANS) equation, the numerical relationship between the speed V and the mass flow rate Q0 of the solid ducted propeller at each speed n is obtained. Q0 = f(V); the mass flow rate is defined as Q = ρSV Inflow , where S is the inlet surface area and ρ is the fluid density.

[0057] e. Obtain the numerical relationship between λ, V, and mass flow rate Q for the duct body force model through numerical simulation, and use surface fitting to formulate the equation λ = g(V, Q);

[0058] The RANS equations are numerically solved to obtain the mass flow correction coefficient λ for the duct-with-body-force model, and the numerical relationship between the speed V and the mass flow rate Q, λ = g(V,Q). Specifically, numerical simulations can be performed using several values ​​of the mass flow correction coefficient λ and the speed V to obtain the mass flow rate Q corresponding to the duct-with-body-force model. The relationship λ = g(V,Q) is then obtained through surface fitting. Please refer to Figure 4 Example of calculation results.

[0059] f. Substituting the real-time ship speed v of the ducted propeller with the body force model, obtained by numerically solving the Reynolds-averaged (RANS) equations, into equations Q0 = f(V) and λ = g(V, Q), yields the mass flow rate Q0 = f(v) of the physical ducted propeller at the real-time ship speed v. Based on the principle of flow equality, the mass flow rate correction factor λ = g(v, f(v)) can be calculated.

[0060] Preferably, in step c, the flow equality principle is that the mass flow rate Q0 of the physical ducted propeller at the real-time speed v is equal to the mass flow rate Q of the duct-coupled body force model, i.e., Q0 = Q. The physical meaning of the flow equality principle is that the macroscopic characteristics of the flow field in the duct of the duct-coupled body force model and the physical ducted propeller are the same (the mass of fluid passing through the duct per unit time is equal), thereby obtaining the same duct thrust, propeller thrust, and vehicle resistance for the two.

[0061] Step 3: Correct the speed coefficient J according to real-time * , interpolate the propeller single blade performance curve to obtain the corresponding thrust coefficient K TP =f(J * ), and then the propeller thrust T P .

[0062] The open-water performance curve of a physical propeller (without a duct, known as a single propeller) is obtained through testing or numerical simulation. Taking numerical simulation as an example, the single propeller model and the flow domain are meshed, and the multi-reference system method is used to simulate the rotational motion of the physical propeller. The propeller speed is fixed, and different advance coefficients are obtained by varying the incoming flow velocity. The governing equations of the fluid domain (RANS) are solved, and the axial thrust of the single propeller is monitored. The thrust coefficient of the single propeller at each advance coefficient can be obtained.

[0063] The obtained single propeller open water performance curve is imported into the simulation platform in the form of a table or a fitting curve, and the corrected advance coefficient J is obtained by interpolation. * The corresponding propeller thrust coefficient K TP The propeller thrust T is obtained according to the propeller thrust coefficient. P , using the following calculation formula:

[0064] T P =K TP ρn 2 D 4 (3)

[0065] Where ρ is the fluid density and D is the propeller diameter.

[0066] Step 4: Write a field function on the simulation platform to specify the volume force distribution form and spatial distribution area to obtain the specific volume force source term f i , and load the RANS equation (1) to solve and obtain the catheter thrust T D and vehicle resistance.

[0067] Preferably, in step 4, the propeller body force distribution is in the form of spatially uniformly distributed axial force.

[0068] Preferably, in step 4, the radial range of the propeller body force spatial distribution area is between the hub radius and the inner diameter of the duct, and the axial range is the range covered by the lateral projection of the blade, such as Figure 5 As shown. At this time, the specific expression of the body force source term is Where V P The volume of space occupied by the body force source, the direction of the body force source is the propeller axis, and it is limited to the aforementioned specified area.

[0069] In order to verify the rationality of the above calculation method, the present invention conducts numerical simulation on the No.19A+Ka4-70 (P / D=1) ducted propeller with Myring rotor, where the propellers are respectively a solid propeller, a traditional body force source and an improved body force source, and compares the simulation results of duct thrust, propeller thrust, hull resistance, etc. with the experimental values. The geometric models of the hull and duct and the mesh encryption area are as follows: Figure 6 The hydrodynamic simulation results of the ducted propeller boat are shown in Figure 7 shown.

[0070] Depend on Figure 7 It can be seen that the ducted thrust, propeller thrust, and hull resistance of the improved body force method at various speeds closely match the corresponding physical propeller simulation results. Compared with the traditional body force method applied to ducted propeller simulation, this method overcomes the shortcomings of the existing propeller body force method by introducing the condition of equal mass flow rate, accurately predicting the coupled hydrodynamic forces of the vehicle and the ducted propeller, and achieving efficient and accurate dynamic simulation of underwater vehicle maneuverability. This method provides valuable assistance for predicting vessel maneuverability, optimizing ship design, and improving vessel performance, and has considerable theoretical and practical value.

[0071] On the other hand, the present application provides an application of the above-mentioned ducted propeller hydrodynamic calculation method, which is applied to the prediction of propulsion performance of a navigation body.

[0072] The flow field around the vehicle is calculated using a viscous flow method, and the flow field is coupled with the total thrust of the ducted propeller to obtain the propulsion performance of the vehicle.

[0073] The motion of the vehicle can be regarded as a rigid body motion, and the ducted propeller of the vehicle provides power. After the flow field is initialized during numerical calculation, the velocity information of the grid at that moment is read from the propeller inlet surface and the duct inlet and outlet, and is used to calculate the size of the propeller body force source (that is, the size of the propeller thrust); at the same time, the speed of the vehicle at that moment is read to calculate the mass flow correction coefficient, and the accurate duct thrust and vehicle resistance at that moment are obtained by correcting the mass flow in the duct. The method proposed in the present invention continuously reads the instantaneous velocity from the grid where the body force source is located when calculating the propeller thrust and the mass flow correction coefficient at each time step, and then uses the updated instantaneous velocity and vehicle speed to calculate the propeller thrust, duct thrust and vehicle resistance, and finally solves the coupled motion of the vehicle-ducted propeller. The ducted propeller body force method corrected by mass flow can accurately simulate the total thrust of the ducted propeller and the vehicle resistance, and the flow field distribution is as follows. Figure 8 shown.

[0074] In summary, this application proposes a ducted propeller body force concept and method based on the principle of mass flow equality, which enables accurate calculation of propeller thrust, duct thrust, and navigation body resistance. This overcomes the shortcomings of existing propeller body force methods in simulating the hydrodynamic performance of ducted propellers. This will play an important role in the efficient optimization design of ship types, the development of new ship types, and the improvement of ship navigation performance, and has certain theoretical significance and engineering practice value. By fully utilizing the rapidly developing modern computer simulation and analysis technology, a high-precision and rapid prediction method for ship design and navigation performance based on simulation analysis is established, providing solid technical support for further improving the navigation performance of the new generation of ships.

[0075] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. ​

Claims

1. A method for calculating the hydrodynamics of a ducted propeller, characterized in that: The following steps are involved: Step 1: Establish a viscous fluid calculation model based on the RANS equation; Step 2: Solve the RANS equation to obtain the correction speed coefficient J * , correction speed coefficient J * To correct the low propeller thrust, ducted thrust and mass flow rate after using body force instead of physical propeller; Step 3: According to the correction speed coefficient J * , interpolate the propeller single-blade open water performance curve to obtain the corresponding thrust coefficient K TP =f(J * ), and then the propeller thrust T P ; Step 4: Write a field function on the simulation platform to specify the volume force distribution form and spatial distribution area to obtain the specific volume force source term, and load the RANS equation to solve it to obtain the catheter thrust T D and resistance of surface or underwater vehicles; The step 1 comprises: establishing a three-dimensional model of the ducted propeller and the surface or underwater vehicle, and giving a propeller speed n; Divide the surface mesh of the ducted propeller and the surface or underwater vehicle and the volume mesh of the fluid area, set boundary conditions, initial conditions, and turbulence model; In step 2, the correction speed coefficient J * Calculated by the following formula: Wherein, λ is the mass flow correction coefficient, and its value range is [1, +∞]; V inflow is the average axial velocity of the inlet surface; V induced is the axial induced velocity of the ducted propeller. The inlet surface is a torus with an outer diameter of D and an inner diameter of the hub diameter. Its axial position is the propeller disk surface. The axial induced velocity of the ducted propeller is the difference between the axial velocity at the duct outlet and the axial velocity at the duct inlet.

2. A ducted propeller hydrodynamic calculation method according to claim 1, characterized in that: The mass flow correction coefficient λ is obtained based on the mass flow equality principle. The mass flow equality principle is that the mass flow Q0 of the physical ducted propeller at the real-time speed v is equal to the mass flow Q of the duct with the body force model, that is, Q0=Q.

3. A ducted propeller hydrodynamic calculation method according to claim 2, characterized in that: The mass flow correction factor λ is solved by the following process: a. Numerical simulation is used to obtain the numerical relationship between the speed V and the mass flow rate Q0 of the solid ducted propeller at each speed n. Q0 = f(V), where the mass flow rate is defined as Q = ρSV Inflow , where S is the inflow surface area; b. Using numerical simulation to obtain the numerical relationship between λ, V, and mass flow rate Q for the duct body force model, and using surface fitting to obtain the equation λ = g(V, Q); c. Substituting the real-time ship speed v of the ducted propeller body force model obtained through numerical solution into the equations Q0 = f(V) and λ = g(V, Q), we can obtain the mass flow rate Q0 = f(v) of the physical ducted propeller at the real-time ship speed v. Based on the principle of mass flow equality, we can then calculate the mass flow rate correction factor λ = g(v, f(v)).

4. The method for calculating hydrodynamics of a ducted propeller according to claim 1, characterized in that: In step 4, the propeller body force distribution form is a spatially uniformly distributed axial force; the radial range of the propeller body force spatial distribution area is between the hub radius and the inner diameter of the duct, and the axial range is the range covered by the lateral projection of the blade.

5. The method for calculating hydrodynamics of a ducted propeller according to claim 1, characterized in that: In step 3, the open water performance curve of the propeller is obtained through experiments or numerical simulations.

6. An application of the method for calculating hydrodynamics of a ducted propeller according to any one of claims 1 to 5, characterized in that: It is used to predict the propulsion performance of surface or underwater vehicles.

7. Application of the method for calculating hydrodynamics of a ducted propeller according to claim 6, characterized in that: The flow field around the surface or underwater vehicle is calculated using a viscous flow method, and the flow field is coupled with the thrust of the ducted propeller to obtain the propulsion performance of the vehicle.

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