CN112108278A - Pulse oscillation device based on mathematical model construction design - Google Patents
Pulse oscillation device based on mathematical model construction design Download PDFInfo
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- CN112108278A CN112108278A CN202010970419.5A CN202010970419A CN112108278A CN 112108278 A CN112108278 A CN 112108278A CN 202010970419 A CN202010970419 A CN 202010970419A CN 112108278 A CN112108278 A CN 112108278A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
- B05B1/34—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl
- B05B1/3405—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl
- B05B1/341—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl before discharging the liquid or other fluent material, e.g. in a swirl chamber upstream the spray outlet
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Abstract
The invention discloses a pulse oscillation device based on mathematical model construction design, and relates to the technical field of pulse oscillators. Including shell, efflux entry, first discrete vortex, efflux export, the discrete vortex of second, first air steam pocket, first air bubble and second air bubble, the fixed efflux entry that is provided with in top of shell, this pulse oscillation device based on mathematical model founds the design, jet impact performance is strong, the enhancement of pulse signal mutability, amplitude variation is more stable, be favorable to improving jet impact performance, possess the characteristics of comparatively stable impulse effect, internal system is comparatively stable, the excitation is swung the formation that the large-scale swirl and the pulse pressure oscillation effect that exist in the cavity will lead to vortex cavitation and oscillation cavitation in the self-excited oscillation cavity, thereby strengthen the cavitation of efflux export, effectively promote the cavitation effect of efflux, do benefit to water pressure signal's transmission and stack simultaneously, difficult the fracturing problem that appears.
Description
Technical Field
The invention relates to the technical field of pulse oscillators, in particular to a pulse oscillation device based on mathematical model construction design.
Background
The oscillating pulse jet is formed by modulating transient flow and a water acoustics principle, has the characteristics of pulse jet and cavitation jet, is a novel pulse jet which has a simple structure, no additional external driving structure, no dynamic seal, larger pressure transformation characteristic and strong cavitation, the impact effect is obviously better than that of continuous jet, especially in a submerged state, the oscillation pulse jet has stronger destructive power than the common jet, and is a jet with great development prospect, the pulse oscillation device has wide application prospect in the fields of mining rock breaking, oil drilling, ship cleaning and the like, the oscillation pulse oscillator in the current market has the problems of general jet impact performance, unstable signal fluctuation, inconvenience for transmission and superposition of water pressure signals and easiness in cracking, and further the service effect is general.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a pulse oscillation device constructed and designed based on a mathematical model, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: a pulse oscillation device based on a mathematical model construction meter comprises a shell, a jet flow inlet, a first discrete vortex, a jet flow outlet, a second discrete vortex, a first air sac, a first air bubble and a second air bubble, the top of the shell is fixedly provided with a jet inlet, the bottom of the jet inlet extends into the shell and is connected with a jet outlet, the top of the two sides of the jet flow outlet is provided with a first discrete vortex, one side of the inner cavity of the shell is provided with a first air sac, the other side of the inner cavity of the shell is provided with a second air steam pocket, second discrete vortexes are arranged among the first air steam pocket, the second air steam pocket and the jet flow outlet, a second air bubble is arranged at the bottom of the inner cavity of the jet flow outlet, and a first air bubble is arranged on the outer side of the bottom of the jet flow outlet.
Further optimizing the technical scheme, when unstable disturbance waves such as vorticity pulsation in a high-speed jet flow beam in an upstream nozzle of the jet flow inlet penetrate through an intracavity shear layer, a large-scale vortex ring structure is formed through the selective amplification effect of the unstable shear layer, a vortex ring in shear flow collides with a downstream collision wall to generate pressure disturbance waves and reflects the pressure disturbance waves upstream, new disturbance is induced at the separation position of the upstream shear layer, and when the new disturbance is matched with the original disturbance frequency and has a proper phase relation, resonance occurs to cause periodic change of fluid impedance in the cavity, so that modulation processes of complete blocking, partial blocking and non-blocking of the jet flow are completed, and pulse jet flow is formed.
The technical scheme is further optimized, when stable liquid flows through the outlet of the resonant cavity to shrink the section, self-excitation pressure excitation is generated, the pressure excitation is fed back to the resonant cavity to form feedback pressure oscillation, the size of the resonant cavity and the Stouhal number of the fluid are properly controlled, the frequency of the feedback pressure oscillation is equal to the inherent frequency of the resonant cavity, and therefore acoustic resonance is formed in the resonant cavity, jet flow at the outlet of the nozzle is changed into intermittent vortex flow, and the jet flow effect is far higher than that of common jet flow due to the structure of the intermittent vortex flow.
The technical scheme is further optimized, discrete vortexes in the high-speed jet flow of the oscillation pulse oscillator are selectively amplified in a shearing layer to form a large-scale vortex structure, cavitation steam sacs which are symmetrically distributed along the axis of the chamber are finally formed, the steam sacs generate periodic energy gathering and releasing on incoming flow of the jet flow inlet, continuous jet flow is converted into pulse jet flow, and therefore the oscillation cavity is arranged in the shell, and simultaneously the large-scale vortex existing in the oscillation cavity and the pulse pressure oscillation effect can cause vortex cavitation and oscillation cavitation in the self-excitation oscillation cavity.
Further optimizing the technical scheme, the factors influencing cavitation include: flow boundary conditions, absolute pressure, flow velocity, viscosity, surface tension, gas core content in water, and inflow conditions, but the main influencing factors are pressure and flow velocity, usually defining the cavitation number.
In the formula, P∞And PVPressure and velocity at a steady flow state point in the flow system; ρ is the liquid density.
Further optimizing the technical scheme, when the flow rate is unchanged and the environmental pressure is reduced or the environmental pressure is unchanged and the flow rate is increased, the critical state that tiny cavities happen to occur for the first time in a very small area in a flow field is called cavitation inception, the cavitation number corresponding to the critical state is called incipient cavitation number, when the cavitation number is reduced to be below the incipient cavitation number, cavitation bubbles begin to appear in large quantity, so the cavitation degree is generally measured by the size of the cavitation number, and in order to enhance the cavitation effect of a jet flow outlet channel, the cavitation effect can be realized by reducing the cavitation number, namely: increasing the incoming flow velocity, decreasing the ambient pressure or increasing the cavitation bubble pressure, and therefore, in order to enhance the cavitation effect of the jet outlet channel, increasing the incoming flow velocity or decreasing the ambient pressure is generally implemented.
Further optimizing the technical scheme, the impact effect of the oscillation pulse jet of the oscillation pulse oscillator mainly depends on the size of the kinetic energy of the jet and the strength of the cavitation effect, and the frequency characteristic of the device has decisive influence on the impact effect of the pulse jet.
Further optimizing the technical scheme, the static pressure of the effluent water of the oscillation cavity is obviously increased, the pulsating pressure is periodically enhanced, on the basis, the outlet water pressure characteristics under the conditions of installing the oscillator and not having the oscillator are actually measured on site, and the numerical simulation result is compared with the actual condition to find that the numerical simulation result has better consistency.
Compared with the prior art, the invention provides a pulse oscillation device constructed and designed based on a mathematical model, which has the following beneficial effects:
this pulse oscillation device based on design is found to mathematical model, jet impact performance is strong, the pulsed signal mutability reinforcing, amplitude variation is more stable, be favorable to improving jet impact performance, possess the characteristics of comparatively stable impulse effect, the internal system is comparatively stable, the excitation is swung the formation that the large scale swirl and the pulse pressure oscillation effect that exist will lead to vortex cavitation and oscillation cavitation in the self-excited oscillation cavity in the cavity, thereby strengthen the cavitation of jet export, effectively promote the cavitation effect of fluidic, do benefit to hydraulic signal's transmission and stack simultaneously, the difficult problem that splits that appears.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic diagram of the oscillating pulsed jet generation principle of the present invention;
FIG. 3 is a schematic diagram of an exemplary oscillating pulsed jet generating structure according to the present invention;
FIG. 4 is a schematic structural diagram of an oscillation pulse generator according to the present invention;
FIG. 5 is a schematic diagram of an oscillation pulse generation lumped parameter equivalent model according to the present invention;
FIG. 6 is a graphical representation of Strouhal number versus operating pressure for certain operating conditions of the present invention;
FIG. 7 shows a schematic view of the present invention DcThe damping ratio is shown in the figure corresponding to different cavity lengths of the lower system when the diameter of the upper nozzle and the lower nozzle which are different from 90mm is larger than that of the lower system;
FIG. 8 is a graphical representation of different cavity lengths versus amplitude frequency for the system of the present invention;
FIG. 9 is a schematic diagram of the damping ratios corresponding to different chamber diameters of the system when the diameter ratio of the upper and lower nozzles is 1.5 chambers and 50mm long according to the present invention;
FIG. 10 is a cloud view of the internal flow field of the oscillator under the condition of 5.0MP of inlet water pressure;
FIG. 11 is a cloud view of the internal flow field of the oscillator under the condition of 20.0MP inlet water pressure;
FIG. 12 shows the water flow distribution inside the oscillator under the condition of 5.0MPa inlet water pressure according to the present invention;
FIG. 13 is a schematic view of the internal monitoring cross-sectional position of the oscillation chamber of the present invention;
FIG. 14 is a schematic view of the average static pressure fluctuation at the inlet and outlet cross-section of the chamber of the present invention;
in the figure: 1. a housing; 2. a jet inlet; 3. a first discrete vortex; 4. a jet outlet; 5. a second discrete vortex; 6. a first air bladder; 7. a second air bladder; 8. a first air bubble; 9. a second air bubble.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example (b):
referring to fig. 1 to 14, a pulse oscillation device constructed and designed based on a mathematical model includes a housing 1, a jet inlet 2, a first discrete vortex 3, a jet outlet 4, a second discrete vortex 5, a first air bladder 6, a first air bladder 7, a first air bubble 8 and a second air bubble 9, the jet inlet 2 is fixedly disposed on the top of the housing 1, the bottom of the jet inlet 2 extends into the housing 1 and is connected with the jet outlet 4, the first discrete vortex 3 is disposed on the top of each of two sides of the jet outlet 4, the first air bladder 6 is disposed on one side of an inner cavity of the housing 1, the second air bladder 7 is disposed on the other side of the inner cavity of the housing 1, the second discrete vortex 5 is disposed between the first air bladder 6 and the jet outlet 4, and the second air bubble 9 is disposed on the bottom of the inner cavity of the jet outlet 4, the outer side of the bottom of the jet outlet 4 is provided with a first air bubble 8.
As a specific optimization scheme of this embodiment, please refer to fig. 2, when an unstable disturbance wave, such as a vorticity pulsation, in a high-speed jet flow in an upstream nozzle of the jet flow inlet 2 passes through an intra-cavity shear layer, a large-scale vortex ring structure is formed through selective amplification of the unstable shear layer, a vortex ring in shear flow collides with a downstream collision wall to generate a pressure disturbance wave and reflects upstream, a new disturbance is induced at a separation position of the upstream shear layer, when the new disturbance is matched with an original disturbance frequency and has a proper phase relationship, resonance occurs to cause a periodic change in impedance of a fluid in a cavity, a modulation process of "complete blocking", "partial blocking", and "non-blocking" of the jet flow is completed to form a pulsed jet flow, please refer to fig. 3, when a stable fluid flows through an outlet of a resonant cavity and contracts in a cross section, a self-excited pressure excitation is generated, this pressure excitation is fed back into the resonant cavity to create feedback pressure oscillations, and fig. 3 is a nozzle of two typical configurations of an oscillating pulsed waterjet: the size of a resonance cavity and the Strouhal number of fluid are properly controlled, so that the frequency of feedback pressure oscillation is equal to the natural frequency of the resonance cavity, acoustic resonance is formed in the resonance cavity, jet flow at an outlet of the nozzle is changed into an interrupted vortex circulation flow, and the jet flow effect is far higher than that of common jet flow due to the structure of the interrupted vortex circulation flow.
As a specific optimization scheme of the embodiment, a strong cavitation effect can be formed by a self-excited oscillation pulse effect, the jet forming and cavitation processes are shown in FIG. 1, discrete vortexes in high-speed jet of the oscillation pulse oscillator are selectively amplified in a shear layer to form a large-scale vortex structure, finally cavitation balloons which are symmetrically distributed along the axis of a chamber are formed, the balloons generate periodic energy gathering and releasing on incoming flow of a jet inlet 1, continuous jet is changed into pulse jet, and therefore the oscillation effect and the certain cavitation effect are achieved, an oscillation cavity is arranged in the shell 1, and simultaneously the large-scale vortex and the pulse pressure oscillation effect existing in the excitation oscillation cavity cause the formation of vortex cavitation and oscillation cavitation in the self-excited oscillation cavity, so that the cavitation effect of a jet outlet is enhanced, and the cavitation effect of jet is effectively promoted, factors that affect cavitation include: flow boundary conditions, absolute pressure, flow velocity, viscosity, surface tension, gas core content in water (microbubbles, solid particles, etc.) and inflow conditions, etc., but the main influencing factors are pressure and flow velocity, usually defining the cavitation number.
In the formula, P∞And PVPressure and velocity at a steady flow state point in the flow system; ρ is the liquid density.
When the flow velocity is unchanged and the environmental pressure is reduced or the environmental pressure is unchanged and the flow velocity is increased, the critical state that tiny cavities happen to occur for the first time in a very small area in a flow field is called cavitation inception, the cavitation number corresponding to the cavitation inception is called the inception cavitation number, when the cavitation number is reduced to be below the inception cavitation number, cavitation bubbles begin to appear in large quantity, so the cavitation degree is generally measured by the cavitation number, and in order to enhance the cavitation effect of a jet flow outlet channel, the cavitation effect can be realized by reducing the cavitation number, namely: increasing the incoming flow velocity, decreasing the ambient pressure, or increasing the cavitation bubble pressure, and therefore, in order to enhance the cavitation effect of the jet outlet channel, increasing the incoming flow velocity or decreasing the ambient pressure is generally implemented.
Pulse cavity frequency mathematical model, the impulse jet impact effect of oscillation mainly depends on the size of efflux kinetic energy and the power of cavitation effect, and the frequency characteristic of device has decisive influence to impulse jet impact effect, and according to classical self-excited oscillation pulse generation structure model, the simplification can obtain the impulse generator of oscillation and can show as figure 4, and the factor that influences the self-excited pulse effect mainly includes two aspects: structural parameters and operating parameters of the self-excited pulse generator, wherein the structural parameters mainly comprise the diameters d of the upper nozzle and the lower nozzle1、d2Lower nozzle taper alpha, oscillation cavity diameter DcAnd a cavity length L; the operating parameters of the oscillating pulse essentially include the upper nozzle inlet pressure P1And a flow velocity V1。
According to the fluid network theory, a parameter equivalent model in the set of laser nozzles can be derived from a steady-state assumed model as shown in fig. 5:
the flow resistance is:
the flow volume is as follows:
the influenza is:
wherein the content of the first and second substances,
wherein v is the average nozzle velocity, m/s;
is the local resistance coefficient of the nozzle, CfIs the nozzle flow coefficient, /)0The length of the straight pipe section in front of the inlet of the upper nozzle is mm; a. the0The diameter of the straight pipe section in front of the inlet of the upper nozzle is mm; a. the1、A2The cross-sectional area before and after the change was mm 2.
In combination with the initial conditions, P1(t)＝0，P2(t)＝0，P2′(t)＝0，P2The pressure transfer function of the system can be found, and the natural circular frequency of the nozzle can be found as follows:
by substituting expressions (2-3) to (2-5) for expression (2-6), the natural frequency of the oscillation generating apparatus can be obtained:
in the formula, a is the wave speed of the fluid in the oscillation cavity.
The fluid wave velocity in the cavity can be expressed as:
in the formula, K1Is the fluid bulk modulus, Pa; α' is the voidage; rhomKg/m3 for mixed fluid density; dmThe boundary expansion modulus, Pa, of the mixed fluid in the oscillation cavity.
It can be seen that, with constant operating parameters, only the chamber diameter D is increasedcOr chamber length LcThe natural frequency of the oscillation generating device is reduced; increasing the diameter ratio d of upper and lower nozzles2/d1The natural frequency of the oscillation generating device increases.
Since the instability of the free shear layer is independent of the amplitude, mach number and reynolds number of the disturbance amplification and the initial disturbance, it depends only on the Strouhal number defined by:
where f is the perturbation frequency and L is the chamber length.
Because the initial disturbance frequency f is consistent with the self-oscillation pulse frequency in the development of the fluid, when the self-oscillation pulse frequency of the fluid is the same as or in integral multiple relation with the natural frequency of the system, the jet flow and the nozzle form resonance, and the jet flow pulse energy value reaches the maximum.
According to the information found in literature, the trend of the change curve of the Strouhal number under different working pressures is very similar to the trend of the invariant curve of the self-excitation frequency under different working pressures, the change curve of the Strouhal number along with the pressure is fitted, and the change rule of the Strouhal number along with the pressure can be approximately determined by the following power function empirical formula:
St＝aPb (2-10)
in the formula, a and b are constants determined by structural parameters under specific working conditions, and according to a change curve of the Strouhal number along with the working pressure under the specific working conditions shown in FIG. 6, the Strouhal number is gradually reduced to a gentle 0.1 accessory along with the increase of the pressure, and the influence on the Strouhal number is smaller when the pressure is larger.
According to the orifice outflow formula, there are
Then by
It can be deduced that:
by fixing structural parameters other than the length of the cavity, the method can obtain
The above formula can thus be found:
cst is a constant related to the structure only, from which it can be seen that the self-excited pulse frequency f is inversely proportional to the inlet flow velocity v and the cavity length, given the structural parameters. Under the condition of fixed cavity length, the self-excitation pulse frequency is in a decreasing trend along with the increase of working pressure and the increase of inlet flow speed; under the condition of stable inlet flow rate, the self-excited pulse frequency tends to increase along with the reduction of the length of the cavity.
The parameter proportion of the oscillation pulse generator is calculated according to results of literature data and theories, the structural parameters of the oscillation pulse generator are proportioned, and based on the formula (2-9), the structural parameters influencing the inherent frequency of the oscillation pulse generator mainly comprise the ratio of the diameters of an upper nozzle and a lower nozzle (d)2/d1) Length L of the oscillation chambercDiameter of the oscillation chamber Dc. For an oscillating system, when the damping ratio is 0 < xi < 1, the system is under-dampedIn the state, the system performs constant amplitude oscillation at the natural frequency; the larger the damping ratio is, the smaller the oscillation amplitude of the system is, the smaller the damping ratio is, the slow system attenuation is realized, and the system is relatively stable. When the damping ratio xi is more than 1, the system is in an ultra-damping state, the response speed of the system is low, no oscillation exists, the attenuation speed of the system is high, and the system is unstable. Therefore, through the structural analysis of the system, the optimal damping ratio is determined to ensure that the system is in a stable state.
1. Lower nozzle diameter ratio d2/d1The impact on the pulse frequency:
as can be seen from fig. 7, when the self-excited chamber cavity diameter of the self-excited oscillation pulse nozzle is fixed, the system damping ratio and the pulse natural frequency are correspondingly improved along with the increase of the area ratio of the upper nozzle and the lower nozzle; when d is2/d1When the damping ratio is less than or equal to 1.5, the damping ratio of the system is more than 0 and less than xi and 1, and the diameter ratio M corresponding to the optimal resonance peak value of the system is 1.25, which shows that the performance characteristic of the system pulse jet is better under the small diameter ratio.
2. Length L of oscillation chambercInfluence on pulse frequency
When the cavity diameter of the oscillation cavity of the self-excited oscillation pulse nozzle is fixed, the damping ratio and the pulse natural frequency of the system are reduced along with the increase of the cavity length, as can be seen from fig. 7, the cavity length is within the range of 40-60 mm, the damping ratio of the system is more than 0 and less than xi, the stability of the system is good, as can be seen from fig. 8, the smaller the cavity length is, the larger the system peak value is, but the smaller the cavity length is, the larger the damping ratio is, the system is unstable, the system is stable, and when the cavity length is 50mm, the system obtains a good resonance peak value.
According to the conclusion of literature data of previous research, the size range of the oscillation cavity which can generate better pulse effect under the condition of large flow and low pressure mainly meets the following conditions: diameter ratio D of cavity diameter to lower nozzlec/d26-9, the diameter ratio of the upper nozzle and the lower nozzle2/d11.2-2.3, length-diameter ratio L of the oscillation cavityc/DcThe research conclusion is in a satisfied condition range, and the consistency is better.
3. The structure design of the oscillation pulse generating device is as follows:
according to the parameter proportion analysis of the oscillation pulse generating device, the reasonable parameter proportion of the oscillation pulse generating device is as follows: the diameter ratio of the upper nozzle and the lower nozzle is 1.5, the length of the oscillation cavity is 50mm, the diameter of the oscillation cavity is 100m, the optimum cone angle of the oscillation cavity is 120 degrees according to the research conclusion of relevant literature data, and the design conditions meet the research requirements. Therefore, the reasonable diameter of the upper nozzle is selected according to the flow value of the actual pump station.
Simulation analysis of oscillation pulse flow field characteristics:
FLUENT is one of the CFD software currently in the world's leading position, and is widely used to simulate various fluid flow, heat transfer, combustion, and pollutant transport problems. FLUENT is specialized software for simulating and analyzing fluid flow and heat transfer with complex profiles.
Before using FLUENT to solve, a more detailed solution scheme should be made for the physical problem to be solved, and the factors to be considered include: determining CFD model targets, selecting calculation types, selecting physical models and determining a solving process. When the above problem is clear, CFD modeling and solving can begin. The solving steps are as follows: creating a grid, operating a proper solver, inputting the grid, checking the grid, selecting a format of a solution, selecting a basic equation needing to be solved, determining a needed additional model, specifying boundary conditions, adjusting control parameters of the solution, initializing a flow field, counting the solution and checking a stored result.
What model and grid division: in order to improve the precision of a simulation result, an unstructured grid division mode is adopted to divide a calculation area into about eighty thousand triangular grid units, and grid division is dense.
Model selection and boundary conditions were calculated: the model selects an unsteady implicit pressure solver to solve an N-S equation set and selects a SIMPLE method, namely a semi-implicit method for solving a pressure coupling equation, a PRESTO mode is selected as a pressure field discrete mode, and a QUICK mode is selected as a density field, a momentum field, a turbulent flow energy field, a water vapor component field, a turbulent flow dissipation rate field and an energy field discrete mode.
According to the cavitation generation theory, when the pressure of the water flow is lower than the saturated vapor pressure in the state, the water flow starts to generate cavitation. In the process that high-speed high-pressure water flows in the oscillator, due to sudden change of the shape of the flow channel, the pressure of the water flow is changed sharply, the boundary layer of the wall surface is separated, so that jet flow forms a Cavitation zone in the oscillator, and a large number of Cavitation bubbles appear in water jet flowing through the Cavitation zone, so that a Cavitation Model (Cavitation Model) is required to be added on the premise of selecting a Mixtue Model two-phase flow Model.
The boundary conditions of the oscillator mainly include parameters for setting the inlet boundary, and three conditions of 5.0MPa, 10.0MPa and 15.0MPa of inlet pressure are set respectively.
Analyzing the characteristics of the oscillation flow field:
water pressure distribution in the cavity: when the inlet water pressure is 5.0MPa and 20.0MPa respectively, the cloud pictures of the flow field characteristics in the oscillator are shown in fig. 11 and 12, the water flow speed and pressure in the axial lead area of the inlet and the outlet of the oscillator are high, the pressure in the cavity is reduced along with the approach of the outlet hole, and the general pressure trend is increased and distributed along the approach of the outlet hole; the flow velocity in the cavity is obvious in vortex outlet at a cone angle close to the outflow port, the vortex intensity is increased along with the increase of the water pressure at the inlet, the range is small, and the change of a velocity field is not obvious except in a boundary area; the strong cavitation effect is formed in the cavity and mainly distributed in the cone angle area of the outflow hole, the cavitation range and the intensity are increased along with the increase of the water pressure of the inlet, the characteristic of coexistence of water and air also obviously appears in the water distribution of the outflow hole influenced by the cavitation effect, and the stable pulse effect is formed.
Analyzing the cavitation effect: when the inlet water pressure is 5.0MPa, a central water flow acceleration area is generated at the inlet of the oscillator, the turbulence degree at the boundary of the water flow acceleration area is intensified, discrete vortexes are generated at the boundary of the jet flow acceleration area, the water flow acceleration area can promote the formation of low-pressure vortex rings axially symmetric to the periphery of the jet flow center, and cavitation air bags can be formed due to the low-pressure vortex rings.
When the inlet water pressure is 5.0MPa, large vortex rings symmetrical about the central axis of the water jet can be formed in the cavity of the oscillator according to the distribution of the internal streamline of the oscillator, as shown in fig. 12; according to the volume fraction distribution diagram of water vapor inside the oscillator, huge cavitation air bags symmetrical about the axis of the water jet can be formed in the cavity of the oscillator, the outlet of the oscillator is a gas-liquid mixture in a cavitation bubble form, cavitation is generated in the center of a large vortex ring inside the oscillator to form the cavitation air bags, and the intermittent vortex ring flow structure generated by the oscillator can enable the jet effect to be far higher than that of ordinary jet.
Analysis of pulse hydrostatic pressure characteristics: the average hydrostatic pressure of the inlet and outlet sections of the oscillation chamber is monitored in real time, a schematic monitoring position is shown in fig. 13, the first internal section and the second internal section are respectively the inlet section and the outlet section of the chamber, and the water pressure of the inlet and the outlet of the chamber under different inlet water pressure conditions is analyzed.
The static pressure characteristics of the inlet and the outlet when the inlet water pressure is 5.0 MPa: fig. 14(a) is a chamber inlet cross-section average static pressure curve when the inlet water pressure is 5.0MPa, the inlet static pressure waveform is disordered, the oscillation signal is unstable, the amplitude change is large, and the spike pulse signal is significant. Under the simulated condition, the average inlet static pressure amplitude is about 0.7kPa, the pressure amplitude is small, fig. 14(b) is a curve of the average static pressure of the cross section of the outlet of the chamber when the inlet water pressure is 5.0MPa, the outlet of the chamber has a regular periodic pressure pulsation effect, the pulse signal is stable and smooth, the peak pulse is gentle, and the pulse abnormal signal is few. Under the simulated conditions, the outlet static pressure amplitude is about 5.0kPa on average, and the pressure amplitude is larger. Compared with the inlet static pressure characteristic, after water flows are processed by the oscillator, the amplitude of the oscillation pulse signal is obviously increased, the fluctuation periodicity and regularity are enhanced, and the pulse abnormal signal is obviously weakened, so that the pulse effect and the static pressure energy of the water flow are enhanced under the oscillation effect of the oscillation cavity.
The static pressure characteristics of the inlet and the outlet when the inlet water pressure is 10.0 MPa: after the inlet water pressure is increased, the mutation of an inlet static pressure pulse signal is enhanced, and the amplitude change is more stable; the outlet water pressure pulse amplitude is increased, the pulse signal is relatively smooth relative to the inlet static pressure, and the frequency of the pulse signal is basically unchanged.
As analyzed above, as the inlet water pressure increases, the pulsation frequency of the average static pressure at the inlet and the outlet of the oscillation chamber increases, and the sharp impulse property of the water pressure is enhanced; the static pressure at the outlet is higher than the static pressure at the inlet, and the increase of the water pressure at the outlet is reduced along with the increase of the water pressure at the inlet. Therefore, after the treatment of the oscillator, the hydrostatic pressure pulsation is enhanced, the pulsation energy is increased, and the improvement of the jet impact performance is facilitated.
Through the parameter design and characteristic analysis of the pulse oscillator of key equipment in the coal seam grooving fracturing technology, theoretical analysis based on the pulse water jet characteristic and the natural frequency of the oscillation pulse generator is mainly developed, the oscillation pulse generator suitable for coal mine underground water jet impact and hydraulic fracturing is designed on the basis of the existing research result analysis, the structural parameters of an oscillation cavity are optimized, the effluent process of water flowing through the oscillator is numerically simulated by FLUENT software, the flow field characteristic and the cavitation effect in the oscillation cavity are analyzed, and the average static pressure of the inlet and outlet sections in the oscillation cavity is contrastively analyzed; simulation results show that the static pressure of the effluent water of the oscillation cavity is obviously increased, and the pulsating pressure is periodically enhanced. On the basis, outlet water pressure characteristics under the conditions that the oscillator is installed and the oscillator is not installed are actually measured on site, the numerical simulation result is compared with the actual condition to find that the numerical simulation result has better consistency, and the effect that the oscillator improves water pressure impact and fracturing is verified.
It should be noted that the foregoing is only a preferred embodiment of the invention and the technical principles employed, and it will be understood by those skilled in the art that the invention is not limited to the specific embodiments described herein, and that various obvious changes, rearrangements and substitutions can be made by those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in more detail by the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (8)
1. The utility model provides a pulse oscillation device based on mathematical model construction design, includes shell (1), efflux entry (2), first discrete vortex (3), efflux export (4), second discrete vortex (5), first air steam pocket (6), second air steam pocket (7), first air bubble (8) and second air bubble (9), its characterized in that, the fixed efflux entry (2) that is provided with in top of shell (1), the bottom of efflux entry (2) extends to shell (1) inside and connects and is provided with efflux export (4), the top of efflux export (4) both sides is provided with first discrete vortex (3), one side of shell (1) inner chamber is provided with first air steam pocket (6), the opposite side of shell (1) inner chamber is provided with second air steam pocket (7), all be provided with second vortex (5) between first air steam pocket (6) and second air steam pocket (7) and efflux export (4) The bottom of the inner cavity of the jet flow outlet (4) is provided with a second air bubble (9), and the outer side of the bottom of the jet flow outlet (4) is provided with a first air bubble (8).
2. The pulse oscillation device constructed and designed based on the mathematical model according to claim 1 is characterized in that when an unstable disturbance wave such as vorticity pulsation in a high-speed jet flow in an upstream nozzle of the jet flow inlet (2) passes through an intracavity shear layer, a large-scale vortex ring structure is formed through the selective amplification effect of the unstable shear layer, a vortex ring in the shear flow collides with a downstream collision wall to generate a pressure disturbance wave and is reflected upstream, a new disturbance is induced at the separation position of the upstream shear layer, and when the new disturbance is matched with the original disturbance frequency and has a proper phase relationship, resonance occurs to cause the periodic change of the fluid impedance in the cavity, so that the modulation processes of complete blocking, partial blocking and non-blocking of the jet flow are completed, and a pulse jet flow is formed.
3. The pulse oscillation device constructed and designed based on the mathematical model as claimed in claim 2, wherein when the stable liquid flows through the outlet of the resonant cavity and contracts the cross section, a self-excited pressure excitation is generated, the pressure excitation is fed back to the resonant cavity to form a feedback pressure oscillation, the size of the resonant cavity and the Stewart-Harr number of the fluid are properly controlled, the frequency of the feedback pressure oscillation is equal to the natural frequency of the resonant cavity, so that an acoustic resonance is formed in the resonant cavity, the jet flow at the outlet of the nozzle becomes an interrupted vortex flow, and the structure of the interrupted vortex flow enables the jet flow effect to be far higher than that of the common jet flow.
4. The pulse oscillation device constructed and designed based on the mathematical model as claimed in claim 1, wherein the discrete vortexes in the high-speed jet of the oscillation pulse oscillator are selectively amplified in the shear layer to form a large-scale vortex structure, and finally cavitation balloons symmetrically distributed along the axis of the chamber are formed, the balloons generate periodic energy accumulation and release to the incoming flow of the inflow port (1), so that the continuous jet is changed into the pulse jet, and therefore the pulse jet has pressure fluctuation and certain cavitation effect, the oscillation cavity is arranged inside the shell (1), and simultaneously the large-scale vortex existing in the excitation oscillation cavity and the pulse pressure oscillation effect cause the formation of vortex cavitation and oscillation cavitation in the self-excited oscillation cavity.
5. The pulse oscillation device of claim 4 wherein the factors that influence cavitation include: flow boundary conditions, absolute pressure, flow rate, viscosity, surface tension, gas core content in water, and inflow conditions, but the main influencing factors are pressure and flow rate, usually defining the cavitation number.
In the formula, P∞And PVPressure and velocity at a steady flow state point in the flow system; ρ is the liquid density.
6. The pulse oscillation device constructed and designed based on the mathematical model according to claim 5, wherein when the flow rate is unchanged and the environmental pressure is reduced or the environmental pressure is unchanged and the flow rate is increased, a critical state in which the tiny cavities happen to occur for the first time in the extremely small area in the flow field is called cavitation inception, a corresponding cavitation number is called inception cavitation number, when the cavitation number is reduced to be below the inception cavitation number, cavitation bubbles begin to appear in a large number, so that the cavitation degree is generally measured by the cavitation number, and in order to enhance the cavitation effect of the jet outlet channel, the cavitation effect can be achieved by reducing the cavitation number, that is: increasing the incoming flow velocity, decreasing the ambient pressure or increasing the cavitation bubble pressure, and therefore, in order to enhance the cavitation effect of the jet outlet channel, increasing the incoming flow velocity or decreasing the ambient pressure is generally implemented.
7. The pulse oscillation device constructed and designed based on the mathematical model as claimed in claim 1, wherein the impact effect of the oscillation pulse oscillator oscillation pulse jet is mainly determined by the magnitude of the kinetic energy of the jet and the strength of the cavitation effect, and the frequency characteristic of the device has a decisive influence on the impact effect of the pulse jet.
8. The pulse oscillation device constructed and designed based on the mathematical model as claimed in claim 4, wherein the outlet water pressure of the oscillation cavity is significantly increased, the pulsation pressure is periodically increased, and on the basis, the outlet water pressure characteristics under the conditions of installing the oscillator and not having the oscillator are actually measured on site, and the numerical simulation result is compared with the actual condition to find that the numerical simulation result has better consistency.
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| CN114459073A (en) * | 2022-02-28 | 2022-05-10 | 海信（山东）空调有限公司 | Air conditioner and control method thereof |
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| CN116593126B (en) * | 2023-07-11 | 2023-09-15 | 中国石油大学(华东) | Cavitation performance evaluation method of cavitation nozzle |
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