A high vacuum degree high stability multi-boundary linkage's induced wheel performance test system

Abstract

The application relates to a high-vacuum high-stability multi-boundary linkage performance test system of an inducer, and relates to the field of a pump inducer performance test system. The system comprises a circulating system for realizing circulation of test medium water; a pressure control system for realizing accurate adjustment of internal pressure of the test system based on real-time reading of inlet pressure; a flow control system for realizing real-time online adjustment of flow in a manner that PID algorithm is combined with neural network algorithm; and a measurement system which is electrically connected with a measurement control terminal, is uniformly controlled and data is collected by the measurement system, and realizes multi-boundary parameter linkage adjustment functions of flow, pressure and rotating speed of the inducer test system. The application can keep the whole system stable under high-vacuum conditions, significantly reduce unnecessary cavitation, and improve the stability and precision of cavitation performance and transient characteristic test of the inducer.

Description

Technical Field

[0001] This invention relates to the field of pump inducer performance testing systems, specifically a high-vacuum, high-stability, multi-boundary linkage inducer performance testing system. Background Technology

[0002] Cavitation is an unavoidable phase change phenomenon in the operation of hydraulic machinery. When the local pressure of the fluid is lower than the saturated vapor pressure, the fluid changes from a liquid to a gaseous state, forming cavitation bubbles. When these bubbles flow to a high-pressure region, they collapse, generating instantaneous impacts. This process repeats continuously during pump operation, leading to a decline in pump performance and even component damage. To suppress cavitation and reduce its negative impacts, adding an inducer before the impeller inlet to increase the inlet pressure is a widely used and effective method to improve pump cavitation performance. The quality of the inducer directly determines the pump's cavitation performance; therefore, it is necessary to conduct systematic, controllable, and repeatable experimental research on the working mechanism and performance characteristics of the inducer under cavitation conditions. However, the inducer typically operates in a low-pressure and highly turbulent transient environment, with complex cavitation morphologies and disordered flow structures, significantly influenced by the coupling effects of multiple factors such as rotational speed, inlet pressure, flow rate, and structural parameters. Relying solely on whole-pump tests or engineering operation data makes it difficult to achieve repeatable, high-precision measurements of the initiation, development, and instability processes of cavitation in the inducer, significantly limiting related mechanism research and performance evaluation. Therefore, it is necessary to construct a dedicated experimental platform with the inducer as the research object to conduct systematic research on the cavitation performance and flow characteristics of the inducer.

[0003] Induced wheel cavitation often occurs under extremely low inlet pressure conditions, placing high demands on the vacuum capability of the test system. Simultaneously, the cavitation process itself is highly transient; insufficient stability of the test bench can easily introduce additional interference, affecting the accuracy and repeatability of the test results. Therefore, the induced wheel test bench must possess a high vacuum maintenance capability to cover the initial, development, and critical conditions of induced wheel cavitation; and a highly stable ability to control boundary conditions such as pressure, flow rate, and speed to simulate actual operating conditions under different adjustments and ensure the reliability of cavitation morphology and performance parameter measurements.

[0004] Based on the above requirements, we will develop an induced wheel test system with high vacuum, high stability and adjustable characteristics under multiple boundary conditions. This system has important engineering application value and theoretical research significance for evaluating the cavitation performance of induced wheels, optimizing structural parameters and verifying numerical simulation models. Summary of the Invention

[0005] To address at least one of the technical problems in the background art, this invention provides a high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system. This system can maintain overall system stability under high vacuum conditions, significantly reduce unnecessary cavitation, and improve the stability and accuracy of induction wheel cavitation performance and transient characteristic testing. Simultaneously, through multi-boundary parameter linkage adjustment, it enables performance testing of the induction wheel under dynamic operating conditions, providing a reliable test platform for induction wheel dynamic process performance research.

[0006] To achieve the above objectives, the present invention provides a high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system, comprising: a circulation system, a measurement system, a pressure control system, and a flow control system; The circulation system is used to circulate the test medium, water. The pressure control system, based on real-time readings of the inlet pressure, enables precise adjustment of the internal pressure of the test system. The flow control system uses a combination of PID algorithm and neural network algorithm to adjust the flow rate in real time online. The measurement system is electrically connected to the measurement control terminal and is uniformly controlled and data acquired by the measurement system, realizing the linkage adjustment function of multiple boundary parameters such as flow rate, pressure, and speed of the induced wheel test system.

[0007] Furthermore, the circulation system includes a test bench, a closed circulating water tank, and an inducer test section; the test bench has a multi-layer structure, with the closed circulating water tank placed at the bottom layer of the test bench and the inducer test section placed at the top layer of the test bench; the closed circulating water tank and the inducer test section are connected to form a circulation loop.

[0008] Furthermore, the inducer test section includes an inlet section, a transparent tube, and an outlet section connected in sequence; the inducer is installed inside the transparent tube, and the drive shaft connected to the inducer passes through the bearing housing and is connected to the output shaft of the drive motor through a coupling; Annular pressure measuring chambers are set on the inlet and outlet sections of the inducer test section for installing pressure sensors; pressure pulsation sensor interfaces are set on the pipe walls of the inlet and outlet sections for installing pressure pulsation sensors; and a cross-shaped guide plate is set inside the outlet section.

[0009] Furthermore, the pressure control system includes a vacuum pump and an air compressor. Three pipelines are provided on the top of the circulating water tank, which are respectively connected to the vacuum pump, the air compressor and the atmosphere, and are equipped with electric valves. The internal pressure of the system is regulated by the vacuum pump and the air compressor connected to the circulating water tank.

[0010] Furthermore, the flow control system includes an inlet valve and an outlet valve, which are invoked by the measurement and control terminal. Based on the flow data measured by the measurement system, the flow is controlled in real time by adjusting the outlet valve.

[0011] Furthermore, the measurement system includes: a flow meter, a pressure sensor, a pressure pulsation sensor, a torque meter, an online temperature sensor, and an online dissolved oxygen meter; the flow meter is installed on the circulation loop, the pressure sensor is installed in the annular pressure measuring chamber, and the pressure pulsation sensor is installed in the pressure pulsation sensor interface; the torque meter is installed on the output shaft of the drive motor; the online dissolved oxygen meter and the online temperature sensor are installed on the circulating water tank.

[0012] Furthermore, the measurement system also includes a high-speed camera, which is arranged outside the transparent tube to visualize the cavitation structure and flow evolution process inside the inducer wheel.

[0013] Furthermore, due to the distance difference between the flow meter and the test section of the inducer wheel, the test system needs to correct for the flow delay. The actual flow rate should be the flow rate before time Δt, where Δt is equal to the distance L between the inducer wheel and the flow meter divided by the flow velocity.

[0014] Furthermore, the multi-boundary parameter linkage adjustment function is implemented by the measurement and control terminal. Based on the test history data of single-boundary adjustment, the test software performs self-learning based on neural network, fits the mathematical model related to the boundary parameters of flow, pressure and speed, and carries out multi-boundary parameter linkage adjustment based on the mathematical model to realize the performance test of the induced wheel under the dynamic process of the specified variable working condition curve.

[0015] The beneficial effects of this invention are as follows: (1) Under the influence of height difference and gravity, the inlet of the inducer wheel obtains a stable pressure drop that is not affected by the outside world, which is conducive to the realization of high vacuum at the inlet of the experimental inducer wheel and at the same time ensures the stability of system pressure.

[0016] (2) The system pressure is relatively high in other locations except for the inducer test section, which helps to reduce unnecessary cavitation and greatly improves the stability and accuracy of the test system.

[0017] (3) The multi-boundary parameter linkage adjustment realizes the performance test of the inducer under the specified working condition change curve, and provides a test basis for the dynamic process performance test of the inducer. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the setup for the inducer test system; Figure 2 This is a schematic diagram of the induced wheel test section.

[0019] In the figure: 1-Test bench; 2-Circulating water tank; 3-Inducer wheel test section; 4-Inlet valve; 5-Outlet valve; 6-Flow meter; 7-Inlet section; 8-Transparent tube; 9-Outlet section; 10-Inducer wheel; 11-Bearing box; 12-Drive motor; 13-Torque meter; 14-Annular pressure measuring chamber; 15-Pressure pulsation sensor interface. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0023] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0024] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linking," and "socketing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0025] To achieve the above objectives, such as Figure 1 As shown, the present invention provides a high vacuum, high stability, multi-boundary linkage performance testing system for an inducer wheel 10, comprising: a circulation system, a measurement system, a pressure control system, and a flow control system; The circulation system is used to circulate the test medium, water. The pressure control system, based on real-time readings of the inlet pressure, enables precise adjustment of the internal pressure of the test system. The flow control system uses a combination of PID algorithm and neural network algorithm to adjust the flow rate in real time online. The measurement system is electrically connected to the measurement control terminal and is uniformly controlled and data acquired by the measurement system, realizing the linkage adjustment function of multiple boundary parameters such as flow rate, pressure, and speed of the inducer wheel 10 test system.

[0026] This invention provides a high-vacuum, high-stability, multi-boundary linkage performance testing system for an inducer wheel 10. It can maintain the overall stable operation of the system under high vacuum conditions, significantly reduce the generation of unnecessary cavitation, and improve the stability and accuracy of cavitation performance and transient characteristic testing of the inducer wheel 10. At the same time, through the multi-boundary parameter linkage adjustment function, the performance testing of the inducer wheel 10 under dynamic working conditions can be realized, providing a reliable test platform for the study of the dynamic process performance of the inducer wheel 10.

[0027] The circulation system includes a test bench 1, a sealed circulating water tank 2, and an inducer test section 3. The test bench 1 has a multi-layer structure, with the sealed circulating water tank 2 placed at the bottom layer and the inducer test section 3 placed at the top layer. The sealed circulating water tank 2 and the inducer test section 3 are connected to form a circulation loop. The purpose of this arrangement is to raise the inducer test section 3, providing a stable base pressure drop at the inlet of the inducer 10 based on gravity, while ensuring that the internal pressure of the test system below the top layer of the bench remains at a relatively high pressure, thus avoiding unnecessary cavitation under high vacuum conditions from affecting the stability and accuracy of the test.

[0028] The technical solution has been further optimized. The circulating water tank 2 is equipped with a "well"-shaped baffle plate to mitigate interference between the inlet and outlet fluids. Simultaneously, three sets of flanges with different diameters are evenly distributed circumferentially to accommodate varying inducer wheel 10 diameters. This example uses DN100 pipe diameter, ensuring a uniform DN100 pipe diameter throughout the circulation system. Furthermore, the inducer wheel 10 diameter is scaled down to 100mm according to similarity laws, and flow rate, inlet pressure, and rotational speed are converted to corresponding operating conditions based on similarity laws.

[0029] Specifically, the test bench 1 adopts a three-layer structure design, with the sealed circulating water tank 2 arranged on the first layer and the inducer test section 3 arranged on the third layer, with a height difference of five meters. Through this layered arrangement, a stable basic pressure drop is formed at the inlet of the inducer 10 under the action of gravity, with an actual liquid level difference of 3.5m.

[0030] like Figure 2 As shown, the inducer test section 3 includes an inlet section 7, a transparent tube 8, and an outlet section 9 connected in sequence. The inducer 10 is installed inside the transparent tube 8, which is made of pressure-resistant transparent material to facilitate direct observation of the internal flow state of the inducer 10. A high-speed camera is arranged outside the transparent tube 8 to visualize the cavitation structure and flow evolution process inside the inducer 10. The drive shaft connected to the inducer 10 passes through the bearing housing 11 and is connected to the output shaft of the drive motor 12 via a coupling. Annular pressure measuring chambers 14 are respectively set on the inlet section 7 and outlet section 9 of the inducer test section 3 for installing pressure sensors; pressure sensors are also installed on the pressure measuring chambers to measure the average pressure at the inlet and outlet of the inducer 10; pressure pulsation sensor interfaces 15 are set on the pipe walls of the inlet section 7 and outlet section 9 to avoid the formation of additional cavities, thereby reducing the impact of damping effect on the accuracy of pressure pulsation measurement; a cross-shaped guide plate is set inside the outlet section 9 to weaken fluid rotation and improve downstream flow stability and performance test accuracy.

[0031] The pressure control system includes a vacuum pump and an air compressor. Three pipelines are located at the top of the circulating water tank 2, connected to the vacuum pump, air compressor, and atmosphere respectively, and equipped with electric valves. The internal pressure of the system is regulated by the vacuum pump and air compressor connected to the circulating water tank 2. The vacuum pump and air compressor are controlled and regulated by a measurement and control terminal to achieve internal pressure adjustment of the testing system. The testing system software, based on real-time readings from imported pressure sensors, achieves precise adjustment of the internal pressure of the testing system by starting, stopping, or adjusting the vacuum pump and air compressor.

[0032] The flow control system includes an inlet valve 4 and an outlet valve 5, which are invoked by the measurement and control terminal. Based on the flow data measured by the measurement system, the flow is controlled in real time by adjusting the outlet valve 5 and the circulating pump (optional).

[0033] Furthermore, the pipes and valves are connected by flanges and fixed to the platform via support frames. A water seal device is welded at the valve screw to prevent outside air from leaking in due to negative pressure in the system under high vacuum conditions.

[0034] The measurement system includes: a flow meter 6, a pressure sensor, a pressure pulsation sensor, a torque meter 13, an online temperature sensor, and an online dissolved oxygen meter; the flow meter 6 is installed on the circulation loop, the pressure sensor is installed in the annular pressure measuring chamber 14, and the pressure pulsation sensor is installed in the pressure pulsation sensor interface 15; the torque meter 13 is installed on the output shaft of the drive motor 12; the online dissolved oxygen meter and the online temperature sensor are installed on the circulating water tank 2 for real-time monitoring of the oxygen content and temperature changes of the test medium.

[0035] The measurement system also includes a high-speed camera, which is arranged outside the transparent tube 8 to visualize the cavitation structure and flow evolution process inside the inducer wheel 10.

[0036] The high-speed photography system and the pressure pulsation sensor are synchronously controlled by a high-frequency synchronous acquisition instrument to realize the synchronous acquisition of cavitation visualization images and pressure pulsation signals inside the inducer 10, thereby carrying out coupled analysis between flow structure and pressure pulsation characteristics.

[0037] To further optimize the technical solution, due to the distance difference between the flow meter 6 and the test section 3 of the inducer wheel, the test system needs to correct the flow delay. The actual flow should be the flow before time Δt, where Δt is equal to the distance L between the inducer wheel 10 and the flow meter 6 divided by the flow velocity.

[0038] To further optimize the technical solution, the multi-boundary parameter linkage adjustment function is implemented by the measurement and control terminal. Based on the test history data of single-boundary adjustment, the test software performs self-learning based on neural network, fits the mathematical model related to boundary parameters such as flow rate, pressure, and speed, and carries out multi-boundary parameter linkage adjustment based on the mathematical model to realize the performance test of the inducer wheel 10 under the specified variable working condition curve.

[0039] This invention can provide a stable pressure drop at the inlet of the inducer wheel that is unaffected by external factors under the influence of height difference and gravity, thereby improving the system's pressure stability and high vacuum capability. Based on a neural network, the invention achieves multi-boundary parameter linkage adjustment through a pressure and flow control system, enabling inducer wheel performance testing under specified operating condition curves, and providing an experimental basis for dynamic process performance testing of the inducer wheel.

[0040] The working principle of this invention is as follows: Inject the test medium water into the circulating water tank, ensuring the liquid level covers the upper outlet pipe to create a stable liquid environment. Close the inlet and outlet water valves of the inducer test section, and replenish water to the test section pipeline through the test section water inlet to remove air from the pipeline and ensure the pipeline is full of liquid. Keep the test section static to allow dissolved oxygen in the water to fully release and avoid interference from dissolved gases on cavitation morphology observation. The static time should be no less than 30 minutes.

[0041] Start the test bench drive motor and stabilize the speed at 1000 r / min using the frequency converter. Once the motor is running stably, first open the inlet valve, then open the outlet valve to establish water circulation in the pipeline, ensuring stable fluid flow within the system. Gradually adjust the frequency converter to continuously increase the motor speed to the test set value (5000 r / min). During this process, monitor parameters such as motor current and vibration to ensure safe equipment operation.

[0042] First, a constant-condition inducer performance test is conducted. The test flow rate is set, and the test control terminal automatically adjusts the outlet valve opening to adjust the flow rate to the rated test flow rate, monitored in real-time by a flow meter. The test vacuum level is set, and the test control terminal automatically starts the vacuum pump and air compressor, adjusting the system pressure to bring the inducer inlet pressure to the set value for each test condition. During this process, the outlet valve opening position and test flow rate are continuously adjusted, and the system must be kept running stably for at least one minute after each adjustment condition. Simultaneously, pressure sensors, flow sensors, and the data acquisition system are read and recorded, capturing dynamic data on inlet and outlet pressures, flow rates, and pressure pulsations under each condition. Based on this data, inducer performance curves (such as flow-head curves, flow-efficiency curves, and flow-NPSH curves) are plotted. Under the three conditions of cavitation initiation, development, and collapse, a high-speed camera is activated, focusing on the transparent observation area of ​​the test section to observe the spatiotemporal evolution of the cavitation morphology of the inducer throughout the entire process. The dynamic data of the dangerous conditions of cavitation initiation and development are recorded, and the captured images must clearly show the gas phase distribution, cavitation morphology, and collapse characteristics of the cavitation area.

[0043] Based on this, the measurement and control terminal trains the neural network using historical single-boundary adjustment test data (a database of inducer performance and corresponding valve opening, vacuum pump, and air compressor operating status under constant operating conditions) to obtain a mathematical model relating pressure control, flow control, and inducer performance. This model enables the coordinated adjustment of multiple boundary parameters, allowing dynamic process performance tests of the inducer to be conducted under specified variable operating condition curves.

[0044] After the experiment was completed, the equipment was shut down in the order of "first increase the vacuum level, then decrease the speed, and finally stop the pump". The experimental data and high-speed photographic images were sorted and analyzed, and the numerical simulation results were compared to verify the accuracy of the cavitation evaluation model.

[0045] Through the above implementation methods, the inducer wheel performance testing system described in this embodiment can maintain the overall stable operation of the system under high vacuum conditions, significantly reduce the generation of unnecessary cavitation, and improve the stability and accuracy of cavitation performance and transient characteristic testing of the inducer wheel. At the same time, through the multi-boundary parameter linkage adjustment function, the performance testing of the inducer wheel under dynamic working conditions can be realized, providing a reliable test platform for the study of the dynamic process performance of the inducer wheel.

[0046] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system, characterized in that, include: Circulation system, measurement system, pressure control system, and flow control system; The circulation system is used to circulate the test medium, water. The pressure control system, based on real-time readings of the inlet pressure, enables precise adjustment of the internal pressure of the test system. The flow control system uses a combination of PID algorithm and neural network algorithm to adjust the flow rate in real time online. The measurement system is electrically connected to the measurement control terminal and is uniformly controlled and data acquired by the measurement system, realizing the linkage adjustment function of multiple boundary parameters such as flow rate, pressure, and speed of the induced wheel test system.

2. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 1, characterized in that, The circulation system includes a test bench, a sealed circulating water tank, and an inducer test section; the test bench has a multi-layer structure, with the sealed circulating water tank placed at the bottom layer and the inducer test section placed at the top layer; the sealed circulating water tank and the inducer test section are connected to form a circulation loop.

3. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 2, characterized in that, The induction wheel test section includes an inlet section, a transparent tube, and an outlet section connected in sequence; the induction wheel is installed inside the transparent tube, and the drive shaft connected to the induction wheel passes through the bearing housing and is connected to the output shaft of the drive motor through a coupling; Annular pressure measuring chambers are set on the inlet and outlet sections of the inducer test section for installing pressure sensors; pressure pulsation sensor interfaces are set on the pipe walls of the inlet and outlet sections for installing pressure pulsation sensors; and a cross-shaped guide plate is set inside the outlet section.

4. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 3, characterized in that, The pressure control system includes a vacuum pump and an air compressor. Three pipelines are installed at the top of the circulating water tank, which are connected to the vacuum pump, the air compressor and the atmosphere respectively, and are equipped with electric valves. The internal pressure of the system is regulated by the vacuum pump and the air compressor connected to the circulating water tank.

5. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 3, characterized in that, The flow control system includes an inlet valve and an outlet valve, which are invoked by the measurement and control terminal. Based on the flow data measured by the measurement system, the flow is controlled in real time by adjusting the outlet valve.

6. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 5, characterized in that, The measurement system includes: a flow meter, a pressure sensor, a pressure pulsation sensor, a torque meter, an online temperature sensor, and an online dissolved oxygen meter; the flow meter is installed on the circulation loop, the pressure sensor is installed in the annular pressure measuring chamber, and the pressure pulsation sensor is installed in the pressure pulsation sensor interface; the torque meter is installed on the output shaft of the drive motor; the online dissolved oxygen meter and the online temperature sensor are installed on the circulating water tank.

7. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 6, characterized in that, The measurement system also includes a high-speed camera, which is arranged outside the transparent tube to visualize the cavitation structure and flow evolution process inside the inducer wheel.

8. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 6, characterized in that, Due to the distance difference between the flow meter and the test section of the inducer wheel, the test system needs to correct for the flow delay. The actual flow rate should be the flow rate before time Δt, where Δt is equal to the distance L between the inducer wheel and the flow meter divided by the flow velocity.

9. The high-vacuum, high-stability, multi-boundary linkage induction wheel performance testing system as described in claim 5, characterized in that, The multi-boundary parameter linkage adjustment function is implemented by the measurement and control terminal. Based on the test history data of single-boundary adjustment, the test software performs self-learning based on neural network, fits the mathematical model related to the boundary parameters of flow, pressure and speed, and carries out multi-boundary parameter linkage adjustment based on the mathematical model to realize the performance test of the inducer wheel under the specified variable working condition curve.

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