A method for predicting suction cavitation erosion in dynamically loaded sliding bearings

Abstract

The present invention relates to a method for predicting cavitation erosion in a dynamically loaded sliding bearing, comprising the following steps: Step 1: Using a displacement sensor to measure the X(t) and Y(t) signals of the axis trajectory of the rotor within the sliding bearing; Step 2: Preprocessing the axis trajectory signals to obtain the oil film thickness h and the dynamic load perturbation coefficient K2 at time t; Step 3: Establishing the boundary conditions of the sliding bearing and, based on the oil film thickness h, the dynamic load perturbation coefficient K2, and the boundary conditions of the sliding bearing, obtaining the oil film pressure field #imgabs0# at time t, where #imgabs1# is the circumferential angular coordinate of the sliding bearing oil film and z is the axial coordinate of the sliding bearing oil film. The present invention provides a real-time, effective online detection method for monitoring the cavitation erosion area and cavitation damage intensity in sliding bearings. By measuring the axis trajectory of the rotor within the sliding bearing in real time, the current cavitation erosion level of the dynamically loaded sliding bearing can be determined.

Description

Technical Field

[0001] The invention relates to the field of mechanical engineering, in particular to a method for predicting suction cavitation erosion of a dynamic load sliding bearing. Background Art

[0002] Cavitation often occurs in oil-lubricated journal bearings in engines, reducing their service life. Periodic fluctuations in radial force from the crankshaft cause variations in oil film pressure, leading to cavitation in the upper half of the bearing, where pressure is lower. Two symmetrical cavitation zones, each elliptical in shape, form in the center of the oil supply groove on either side of the upper sliding bearing. Microjets and shock waves are the primary causes of cavitation damage to the material surface. Continuous microjets or wave impacts accumulate sufficient cavitation pits, weakening the sliding bearing surface and causing material in the cavitation zone to separate and break off.

[0003] With the increasing demand for higher speeds and heavier loads in rotating machinery, cavitation damage is increasingly occurring in dynamically loaded sliding bearings. Currently, there is a lack of effective methods for predicting cavitation damage in dynamically loaded sliding bearings during operation, making it difficult to schedule maintenance tasks based on the severity of cavitation damage. Summary of the Invention

[0004] The object of the present invention is to provide a method for predicting suction cavitation erosion of a dynamically loaded sliding bearing, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for predicting suction cavitation erosion of a dynamically loaded sliding bearing comprises the following steps:

[0007] Step 1: Use a displacement sensor to measure the X(t) and Y(t) signals of the axis trajectory of the rotor in the sliding bearing, where X(t) and Y(t) are functions of time t, and X(t) and Y(t) represent the rotor center O, respectively. R In XO J The X and Y coordinate values that change with time t in the Y coordinate system, O R is the rotor center, O J It is the center of the sliding bearing;

[0008] Step 2: Preprocess the axis trajectory signal to obtain the oil film thickness h and dynamic load perturbation coefficient K2 at time t;

[0009] Step 3: Establish the boundary conditions of the sliding bearing and obtain the oil film pressure field at time t based on the oil film thickness h, dynamic load perturbation coefficient K2 and the boundary conditions of the sliding bearing. in, is the circumferential angular coordinate of the sliding bearing oil film, and z is the axial coordinate of the sliding bearing oil film;

[0010] Step 4: According to the oil film pressure field Get time t and oil film position The fluid microjet velocity at Then obtain the time t and the oil film position Suction cavitation intensity at ;

[0011] Step 5: As time passes from t=0 to t=t n Repeat steps 1 to 4 to obtain the field distribution of suction cavitation intensity at different times, and use the integral algorithm to obtain the suction cavitation degree of the dynamic load sliding bearing

[0012] As a further solution of the present invention, the method of obtaining the oil film thickness h at time t through the axis trajectory X(t) and Y(t) signals is as follows:

[0013] Substitute the axis trajectory X(t) and Y(t) signals into formula (1) for data processing to obtain the oil film thickness h at time t;

[0014]

[0015] Where c0 is the radial clearance of the sliding bearing.

[0016] As a further solution of the present invention, the method of obtaining the dynamic load perturbation coefficient K2 at time t through the axis trajectory X(t) and Y(t) signals is as follows:

[0017] Substitute the axis trajectory X(t) and Y(t) signals into formula (1) for data processing to obtain the dynamic load perturbation coefficient K2 at time t;

[0018]

[0019] Where dX(t) / dt and dY(t) / dt are the derivatives of X(t) and Y(t) with respect to time t, respectively.

[0020] As a further solution of the present invention: in step 3, for a sliding bearing with an axial width of L, the boundary conditions of the sliding bearing are established:

[0021] (1) At the oil outlet of the sliding bearing z = ± L / 2 or at the oil inlet of the sliding bearing The oil film pressure p is equal to atmospheric pressure, the fluid volume percentage α = 1 and the cavitation slip coefficient K1 = 1;

[0022] (2) In the lubricating oil film of the sliding bearing, three regions are formed: the oil film region, the stable cavitation region and the suction cavitation region. In these three regions, at a certain time t, the oil film pressure p changes with The change of z and t is The function of z and t is expressed as

[0023] ①Oil film area:

[0024] ②Stable cavitation area:

[0025] ③Suction cavitation area:

[0026] As a further solution of the present invention: in step 3, the generalized Reynolds equation is solved by the finite difference method according to the oil film thickness h, the dynamic load perturbation coefficient K2 and the boundary conditions of the sliding bearing to obtain the oil film pressure field at time t

[0027] As a further solution of the present invention: the specific expression of the generalized Reynolds equation (3) is:

[0028]

[0029] Where R is the rotor radius, z is the axial coordinate of the sliding bearing oil film, μ l is the viscosity of the liquid, p is the oil film pressure, α is the volume percentage of the fluid, h is the oil film thickness, and the cavitation slip coefficient K1 is the slip coefficient of the interface between the fluid and the cavity.

[0030] As a further solution of the present invention: the expression of the cavitation slip coefficient K1 in the generalized Reynolds equation (3) is

[0031] Where μ a is the viscosity of the gas.

[0032] As a further solution of the present invention: the oil film pressure field Substitute into equation (5) and calculate the oil film position at time t The fluid microjet velocity at

[0033]

[0034] Where p v is the saturated vapor pressure of the liquid, R m is the statistical mean radius of the cavitation bubbles in the oil film, and ρ is the density of the liquid.

[0035] As a further solution of the present invention: Substitute into equation (6) and calculate the oil film position at time t Suction cavitation intensity at ;

[0036]

[0037] Where, v crit is the critical value of microjet velocity.

[0038] As a further solution of the present invention: the critical value v of the microjet velocity crit The expression is:

[0039]

[0040] Where p y is the yield strength of the sliding bearing material, B is a constant, and ρ is the density of the liquid.

[0041] Compared with the prior art, the present invention has the beneficial effect of providing a real-time and effective online detection means for monitoring the suction cavitation area and cavitation damage intensity in the sliding bearing.

[0042] By measuring the axis center trajectory of the rotor in the sliding bearing in real time, the current suction cavitation degree of the dynamic load sliding bearing is obtained.

[0043] Maintenance tasks can be arranged based on the current suction and cavitation erosion level of dynamically loaded sliding bearings. The suction and cavitation erosion level of dynamically loaded sliding bearings can be monitored in real time while the equipment is running, without the need to shut down or disassemble the equipment.

[0044] Other features and advantages of the present invention will be disclosed in detail in the following specific embodiments and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a schematic diagram of a sliding bearing;

[0046] Figure 2 It is a flow chart of the method for predicting suction cavitation erosion of dynamically loaded sliding bearings. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] refer to Figure 1, shows a cylindrical plain bearing rotating at a speed of Ω (surface speed U) under a dynamic load force W. Ignoring axial rotor deflection, the bearing consists of a rotor with a radius of R and a plain bearing with an inner radius of R + c0. c0 is the radial clearance of the plain bearing. In the convergent region of the oil film, the hydrodynamic pressure of the oil film rises to a peak, forming the primary load-bearing capacity. When the oil film locally increases its thickness in the divergent region, the oil film pressure may drop to its vapor pressure, causing cavitation of the lubricant. The perturbation of the rotor's center displacement under dynamic load conditions leads to suction cavitation in the plain bearing. The fluid refers to the lubricant.

[0049] like Figure 2 As shown, a method for predicting suction cavitation erosion of a dynamically loaded sliding bearing comprises the following steps:

[0050] Step 1: Detect the axis trajectory signal to obtain the axis trajectory position of the rotor;

[0051] The displacement sensor is used to measure the axis trajectory X(t) and Y(t) signals of the rotor in the sliding bearing, where X(t) and Y(t) are functions of time t and represent the rotor center O, R In XO J The X and Y coordinate values that change with time t in the Y coordinate system, O R is the rotor center, O J Is the center of the sliding bearing; among them, XO J The Y coordinate system refers to the sliding bearing center O J The coordinate system is constructed with the X-axis and Y-axis perpendicular to each other as the origin. The coordinate system is perpendicular to the axis of the sliding bearing. That is, the X-axis and Y-axis are two radial directions perpendicular to each other (refer to Figure 1 ).

[0052] Step 2: Pre-process the axis trajectory signal to obtain the oil film thickness h and dynamic load perturbation coefficient K2 at time t;

[0053] Substitute the axis trajectory X(t) and Y(t) signals into formula (1) and formula (2) for data processing to obtain the oil film thickness h and dynamic load perturbation coefficient K2 at time t respectively;

[0054]

[0055]

[0056] in, is the circumferential angular coordinate of the oil film of the sliding bearing, dX(t) / dt and dY(t) / dt are the derivatives of X(t) and Y(t) with respect to time t, respectively, and c0 is the radial clearance of the sliding bearing; the radial clearance c0 of the sliding bearing is determined based on the aperture of the sliding bearing and the diameter of the rotor, and is a fixed constant for the current system. is around the center of the sliding bearing O J The circumferential angle coordinates can be used to set the oil inlet of the sliding bearing The X-axis direction is defined at the oil inlet, and the circumferential angle coordinate is is the angle with the X-axis. X(t) and Y(t) can be converted into the oil film thickness h through trigonometric functions.

[0057] Step 3: Establish the boundary conditions of the sliding bearing;

[0058] For a sliding bearing with an axial width of L, the boundary conditions of the sliding bearing are established;

[0059] (1) At the oil outlet of the sliding bearing z = ± L / 2 or at the oil inlet of the sliding bearing The oil film pressure p is equal to atmospheric pressure, the fluid volume percentage α = 1 and the cavitation slip coefficient K1 = 1, z is the axial coordinate of the oil film of the sliding bearing;

[0060] (2) In the lubricating oil film of the sliding bearing, three regions are formed: the oil film region, the stable cavitation region and the suction cavitation region. In these three regions, at a certain time t, the oil film pressure p changes with The change of z and t is The function of z and t is expressed as

[0061] ① Oil film area: There are no cavitation bubbles, it is full of oil film, and the minimum value of the oil film pressure p is greater than zero, that is,

[0062]

[0063] ② Stable cavitation region: There is a two-phase fluid film (oil and cavitation cavity), and the oil film pressure p is always equal to zero, that is,

[0064] ③ Suction cavitation area: There is not only two-phase flow, but also high-frequency collapse of cavitation bubbles. Therefore, the minimum value of the oil film pressure p is always equal to zero, while the maximum value of the oil film pressure p is always greater than zero in this area, that is,

[0065] Step 4: Obtain the oil film pressure field at time t based on the oil film thickness h, dynamic load perturbation coefficient K2 and the boundary conditions of the sliding bearing

[0066] Substitute the oil film thickness h and the dynamic load perturbation coefficient K2 into the generalized Reynolds equation (3) of the mass conservation law;

[0067]

[0068] Where R is the rotor radius, z is the axial coordinate of the sliding bearing oil film, μ l is the viscosity of the liquid, that is, the lubricating fluid, p is the oil film pressure, α is the fluid volume percentage, h is the oil film thickness, K1 is the cavitation slip coefficient, specifically refers to the slip coefficient of the fluid and cavity interface, K2 is the dynamic load perturbation coefficient, specifically refers to the perturbation coefficient of the rotor under dynamic load; the expression of K1 is

[0069]

[0070] Where μ a is the viscosity of the gas; specifically, the value range of K1 in step 3 is calculated using formula (4) to obtain K1.

[0071] According to the boundary conditions of the sliding bearing established in step 3, the finite difference method is used to solve the generalized Reynolds equation (3) to obtain the oil film pressure field at time t

[0072] Step 5: According to the oil film pressure field Get time t and oil film position The fluid microjet velocity at Then obtain the time t and the oil film position Suction cavitation intensity at ;

[0073] The oil film pressure field Substitute into equation (5) and calculate the oil film position at time t The fluid microjet velocity at

[0074]

[0075] Where p v is the saturated vapor pressure of the liquid, R m is the statistical average radius of cavitation bubbles in the oil film;

[0076] Will Substitute into equation (6) and calculate the oil film position at time t Suction cavitation intensity at ;

[0077]

[0078] Where, v crit is the critical value of the microjet velocity, and the expression is:

[0079]

[0080] Where p y is the yield strength of the sliding bearing material, B = 300 MPa, ρ is the density of the liquid;

[0081] Step 6: As time passes from t=0 to t=t n Repeat steps 1 to 5 to obtain the field distribution of suction cavitation intensity at different times Then, the integral algorithm of formula (8) is used to obtain the suction cavitation degree of the dynamic load sliding bearing:

[0082] The formula for the degree of suction cavitation is:

[0083] The data mentioned above, except for the axis trajectory X(t) and Y(t) signals monitored in real time, the time signal t generated by synchronous measurement of the axis trajectory signal, and the data obtained by formula calculation, are all known data based on system characteristics and can be obtained through pre-testing or table lookup. For example, the rotor radius R, the density ρ of the liquid, the viscosity μ of the gas a , liquid viscosity μ l wait.

[0084] A suction cavitation erosion prediction method for dynamically loaded sliding bearings provides a real-time and effective online detection means for monitoring the suction cavitation erosion area and cavitation damage intensity in sliding bearings.

[0085] By measuring the axis center trajectory of the rotor in the sliding bearing in real time, the current suction cavitation degree of the dynamic load sliding bearing is obtained.

[0086] By measuring the X(t) and Y(t) signals of the axis trajectory of the rotor in the sliding bearing through the displacement sensor, the oil film position at time t can be obtained. The suction cavitation intensity at the position of the oil film can be obtained by accumulating the suction cavitation intensity at different times through integral calculation. The current suction cavitation level of the dynamically loaded sliding bearing can be used to schedule maintenance tasks. The suction cavitation level of the dynamically loaded sliding bearing can be monitored in real time while the equipment is running, without requiring downtime or disassembly.

[0087] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0088] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for predicting suction cavitation erosion of a dynamically loaded sliding bearing, characterized in that: The following steps are involved: Step 1: Use a displacement sensor to measure the axis trajectory of the rotor inside the sliding bearing X ( t )and Y ( t ) signal, where X ( t )and Y ( t ) is time t function, X ( t )and Y ( t ) represent the rotor center O R exist XO J Y The coordinate system changes with time t X and Y Coordinate values, O R is the rotor center, O J It is the center of the sliding bearing; Step 2: Preprocess the axis trajectory signal to obtain t Oil film thickness at time h and dynamic load perturbation coefficient K 2; Step 3: Establish the boundary conditions of the sliding bearing and adjust the oil film thickness according to the h , dynamic load perturbation coefficient K 2 and the boundary conditions of the sliding bearing t Oil film pressure field at time p ( t , φ , z ),in, is the circumferential angle coordinate of the sliding bearing oil film, z is the axial coordinate of the oil film in the sliding bearing ； Step 4: According to the oil film pressure field p ( t , φ , z ), get t Time and oil film position ( φ , z ) of the fluid microjet velocity at v jet ( t , φ , z ), and then obtain t Time and oil film position ( φ , the suction cavitation intensity at z) will be p ( t , φ , z ) into equation (5), and we can get t Time and oil film position ( φ , z ) of the fluid microjet velocity at v jet ( t , φ , z ): (5) Where, p v is the saturated vapor pressure of the liquid, R m is the statistical average radius of cavitation bubbles in the oil film, ρ is the density of the liquid; Step 5: As time goes by t =0Move to t = t n Repeat steps 1 to 4 to obtain the field distribution of suction cavitation intensity at different times, and use the integral algorithm to obtain the suction cavitation degree of the dynamic load sliding bearing C deg ( φ , z ); Will v jet ( t , φ , z ) into equation (6), and calculate t Time and oil film position ( φ , z ) at the suction cavitation intensity; (6) Where, L is the axial width, z is the axial coordinate of the oil film in the sliding bearing, v crit is the critical value of microjet velocity.

2. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 1, characterized in that: Through the axis track X ( t )and Y ( t )Signal acquisition t Oil film thickness at time h The way is: The axis trajectory X ( t )and Y ( t ) signal into formula (1) for data processing, and obtain t Oil film thickness at time h ; (1) in, c 0 is the radial clearance of the sliding bearing.

3. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 2, wherein: Through the axis track X ( t )and Y ( t )Signal acquisition t Dynamic load perturbation coefficient at time K Method 2 is: The axis trajectory X ( t )and Y ( t ) signal into formula (1) for data processing, and obtain t Dynamic load perturbation coefficient at time K 2; (2) in, dX ( t ) / dt and dY ( t ) / dt They are X ( t ), Y ( t ) for time t The derivative of .

4. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 1, wherein: In step 3, for the axial width L The boundary conditions of the sliding bearing are established: (1) At the oil outlet of the sliding bearing z =± L / 2 or at the oil inlet of the sliding bearing φ =0°, oil film pressure p Equal to atmospheric pressure, fluid volume percentage α = 1 and cavitation slip coefficient K 1=1; (2) In the lubricating oil film of the sliding bearing, three regions are formed: the oil film region, the stable cavitation region and the suction cavitation region; in these three regions, at a certain moment t , oil film pressure p along with φ , z and t changes with the changes, φ , z and t The function is expressed as p ( t , φ , z ); ①Oil film area: min{ p ( t , φ , z )} > 0, α =1, K 1=1; ②Stable cavitation area: p ( t , φ , z ) = 0 ,0< α <1,1< K 1<2; ③Suction cavitation area: min{ p ( t , φ , z )} = 0, max{ p ( t , φ , z )} > 0, 0< α ≤1, 1≤ K 1<2.

5. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 4, characterized in that: In step 3, according to the oil film thickness h , dynamic load perturbation coefficient K 2 and the boundary conditions of the sliding bearing are solved by the finite difference method to obtain the time t Oil film pressure field p ( t , φ , z ).

6. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 5, characterized in that: The specific expression of the generalized Reynolds equation (3) is: (3) Where, R is the rotor radius, z is the axial coordinate of the oil film in the sliding bearing, μ l is the viscosity of the liquid, p is the oil film pressure, α is the fluid volume percentage, h is the oil film thickness, where the cavitation slip coefficient K 1 is the slip coefficient of the fluid-cavity interface.

7. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 6, characterized in that: Cavitation slip coefficient in the generalized Reynolds equation (3) K The expression for 1 is (4) Where, μ a is the viscosity of the gas.

8. The method for predicting suction cavitation erosion of a dynamically loaded sliding bearing according to claim 1, wherein: Critical value of microjet velocity v crit The expression is: (7) Where, p y is the yield strength of the sliding bearing material, B is a constant, ρ is the density of the liquid.

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