Throttle Characteristics Research Articles

Study of vortex throttle characteristics with adjustable resistance by rotation of the vortex chamber inlet channel

Abstract The study is aimed at obtaining and analyzing the flow and cavitation characteristics of the proposed control devices, which are in demand in control systems for aircraft and rocket engines, chemical and other technological processes that require a wide range of flow control at high pressure drops. The characteristics of vortex throttling devices with cylindrical and spherical chambers were obtained, providing flow control in the range of 0.1–25 kg/s. A change in flow rate in the range of 3.5–3.8 can be achieved by changing the flow swirl intensity without throttling the flow sections. When vortex devices operate, the threshold for the occurrence of cavitation shifts to the region of small values of P out /P in, and, starting from the values of the geometric characteristic A > 4.5, cavitation is absent throughout the entire range of flow control. The pressure drop at the inlet channel of the vortex chamber does not exceed 10–30 % of the total resistance of the device. The torque on the control roller is small, 1.8–2.8 Nm, regardless of the flow rate.

Multi-fidelity simulation of aeroengine for far-off-design conditions using iterative coupled method based on auxiliary maps

Iterative coupled methods are widely used in multi-fidelity simulation of rotating components due to the simple implementation, which iteratively eliminates the errors between the computational fluid dynamics models and approximate characteristic maps. However, the convergence and accuracy of the iterative coupled method are trapped in characteristic maps. In particular, iterative steps increase sharply as the operation point moves away from the design point. To address these problems, this paper developed an auxiliary iterative coupled method that introduces the static-pressure-auxiliary characteristic maps and modification factor of mass flow into the component-level model. The developed auxiliary method realized the direct transfer of static pressure between the high-fidelity models and the component-level model. Multi-fidelity simulations of the throttle characteristics were carried out using both the auxiliary and traditional iterative coupled methods, and the simulation results were verified using the experimental data. Additionally, the consistency between the auxiliary and traditional iterative coupled methods was confirmed. Subsequently, multi-fidelity simulations of the speed and altitude characteristics were also conducted. The auxiliary and traditional iterative coupled methods were evaluated in terms of convergence speed and accuracy. The evaluation indicated that the auxiliary iterative coupled method significantly reduces iterative steps by approximately 50% at the near-choked state. In general, the auxiliary iterative coupled method is preferred as a development of the traditional iterative coupled method in the near-choked state, and the combined auxiliary-traditional iterative coupled method provides support for successful multi-fidelity simulation in far-off-design conditions.

Direct multi-fidelity integration of 3D CFD models in a gas turbine with numerical zooming method

Multi-fidelity simulation improves the simulation accuracy and captures more detailed information about aero engines under limited computing resources, which is implemented by coupling different levels of models using numerical zooming methods. However, there is an obvious problem in traditional zooming methods such as the iterative coupled zooming method or mini-map method: both the convergence and accuracy depend highly on the component general characteristic maps. Based on the investigation of a micro gas turbine, a direct zooming method (Cycle with CFD in it, CWCFD) is developed. It directly embeds the 3D CFD compressor and turbine model into a 0D component-level model without component general characteristic maps. Then, the CWCFD zooming method is compared with the traditional 0D component-level model in terms of the throttle characteristics of the micro gas turbine, and the experimental data of the ground test is performed to verify the effectiveness of the CWCFD zooming methods. The results indicate that the CWCFD zooming method matches well with the test data better than the traditional 0D component-level model.

Numerical study on throttling characteristics of RBCC engines in ejector mode

Investigating the throttling characteristics of Rocket-Based Combined Cycle (RBCC) engines in ejector mode is crucial for adapting to varied flight mission demands. This study employs validated RANS numerical methods to investigate throttling effects on an experimental kerosene-fueled RBCC engine under two representative flight conditions: ground take-off (Mach 0) and supersonic flight (Mach 2.0). Results indicate that, at Mach 0, throttling reduces the entrained secondary stream and increases mixing efficiency, but exacerbates mixing losses, which cannot be offset by the thrust produced by the secondary stream due to its weak working capacity. Therefore, specific impulse performance deteriorates during throttling. Moreover, the optimum mixture ratio remains at 2.4, consistent with conventional rockets. Conversely, at Mach 2.0, throttling mitigates the primary stream’s squeezing effect to augment the entrained secondary stream. Simultaneously, throttling enhances mixing efficiency to improve the utilization of residual fuel. Consequently, the optimum mixture ratio shifts from 2.4 to below 1.4, which contributes to harnessing the work capacity of the secondary stream generated by ram effects, and significantly improves specific impulse performance. This study emphasizes the distinct throttling characteristics at different Mach numbers and provides pivotal insights for developing more efficient RBCC engines in ejector mode.

A Performance Simulation Methodology for a Whole Turboshaft Engine Based on Throughflow Modelling

To accurately predict the matching relationships between the various components and the engine performance in the whole aero-engine environment, this study introduces a two-dimensional throughflow simulation method for the whole aero-engine. This method is based on individual throughflow solvers for the turbo-machinery and the combustor. It establishes a throughflow simulation model for the whole engine by integrating with the compressor-turbine co-operating equations and boundary conditions. The turbo-machinery throughflow solver employs a circumferentially averaged form of the time-dependent Navier–Stokes equations (N-S) as the governing equation. The combustor solver uses the Reynolds Average Navier–Stokes (RANS) method to solve flow and chemical reaction processes by constructing turbulence, combustion, and radiation models. The accuracy of the component solver is validated using Pratt and Whitney’s three-stage axial compressor (P&W3S1) and General Electric’s high-pressure turbine (GE-EEE HPT), and the predicted results are consistent with the experimental data. Finally, the developed throughflow method is applied to simulate the throttling characteristics of the WZ-X turboshaft engine. The results predicted by the throughflow program are consistent with the GasTurb calculations, including the trends of shaft power delivered, specific fuel consumption (SFC), inlet airflow, and total pressure ratio of the compressor. The developed method to perform throughflow simulation of the whole aero-engine eliminates the dependence on a general component map. It can quickly obtain the meridian flow field parameters and overall engine characteristics, which is expected to guide the design and modification of the engine in the future.

The throttling characteristics of supercritical carbon dioxide in the flowback process of CO2 fracturing

Carbon dioxide fracturing is used to develop oil and gas resources with low permeability and also achieve partly carbon sequestration. Nevertheless, during the process of fracturing flowback, supercritical CO2 easily undergoes a throttling phenomenon within narrow channels, leading to a rapid temperature decrease. This causes the formation of dry ice, which subsequently blocks the flowback channel. In this paper, combined with the experiment verification, the numerical simulation is primarily used to analyze the underlying causes of dry ice formation. We investigate the effect of key operational parameters, including initial pressure, initial temperature, pore diameter, and outlet pressure. The results reveal that the temperature drop is primarily caused by the shock waves during the high-speed CO2 expansion. Specifically, under the conditions of inlet pressure of 10 MPa, outlet pressure of 5.1 MPa, inlet temperature of 393 K, and pore throat diameter of 10 mm, the maximum temperature decreases by 155 K. Continuous reduction in the outlet pressure can further lead to temperature drop and its value will be below the temperature of CO2 triple point. These investigations are conducted through multi-factor simulations under representative conditions. Among these factors, the initial pressure has the most significant influence on the temperature variation. The numerical simulations provide the minimum outlet pressures at which CO2 does not form dry ice under conditions of various pressures, temperatures, and pore throat diameters. Further, a specific fitting relationship among these parameters is established to obtain the minimum outlet pressures, and the corresponding fitting error is within 10%.

Throttling characteristics prediction methodology for combined grooves in directional spool valves under variable flow rates

There is a contradiction between the calculation accuracy and cost when computing the pressure and flow rate. A throttling characteristics prediction methodology for directional spool valve was proposed to balance the contradiction. The throttling characteristics were represented by the flow-number, defined as the product of the flow coefficient and the orifice area, to reveal simultaneously the mapping relationships of the two versus the spool geometry, stroke and flow rate. The pressure and flow rate characteristics at different strokes were obtained through the computational fluid dynamic (CFD) simulations that were validated through bench testing. The concept of saturated flow-number theory was introduced to describe the effects of the flow rate on the flow-number. Models for the saturated flow-number and critical flow rate were established using the U-shape groove, a typical throttling structure, as an example to illustrate the effects of groove structure and opening. The throttling characteristics of the directional spool valve could be predicted by the flow-numbers of the combined grooves. The simulated and experimental results demonstrate that the prediction methodology achieves high calculation accuracy while incurring minimal costs. This methodology holds significant implications for the forward design of valve spool throttling structures.

Research on Downhole Throttling Characteristics of Gas Wells Based on Multi-Field and Multi-Phase

The formation of natural gas hydrates seriously affects the production efficiency of gas wells. Obtaining the correct temperature and pressure profile along the wellbore of gas wells is a prerequisite for accurately predicting the location of hydrate formation and using downhole throttling technology. According to the numerical iterative transfer law of wellbore microelement state parameters, a multi-field and multi-phase coupling method is proposed. Based on the analysis of typical temperature and pressure models, considering the gas well velocity field and density field, a gas well multi-phase correction coefficient is introduced. Based on the judgment method of multi-phase flow pattern, the friction gradient equation of multi-phase flow is obtained, and the respective theoretical prediction equations are created for the temperature field, pressure field, density field, and velocity field. Thereby, a wellbore temperature and pressure field model with multi-field and multi-phase coupling is established. The model was applied to K1 and K2 gas wells, and the calculation results of the research model were compared with the PIPESIM simulation results and measured values. At the same time, the mean μ, variance σ, and the coefficient of variation Cm were evaluated, and the results show that the coefficient of variation of the calculation results of this research model is less than 15%, which indicates greater accuracy than the PIPESIM simulation results. These findings provide a theoretical basis for the design of wellbore structures and the use of downhole tools.

Особенности математического моделирования ГТД непрямой реакции

The article presents the developed mathematical model for calculating the parameters and characteristics of an indirect reaction gas turbine engine, which is implemented in asoftware environment and embedded in the general algorithm of the pro-gram "Calculation of traction-economic and mass-specific characteristics of a power plant and aircraft motion parameters". At the same time, special attention is paid to the features ofmathematical modeling of indirect reaction gas turbine engines with respect to turbojet engines. A description of a mathematical procedure for solving systems of nonlinear algebraic equations in determining the parameters and characteristics of a power plant in off-design modes of operation using a modified Newton's method is presented. The results of verification of the modified program are also shown by comparing the parameters and char-acteristics of the power plant based on the AI-24VT turboprop engine calculated with its help, with the characteristics taken from the technical description, with a detailed analysis of the qualitative and quantitative flow of throttle characteristics in accordance with the generally accepted theory of aviation engines

Characteristics Analysis of the Pilot-Operated Proportional Directional Valve by Experimental and Numerical Investigation

The main valve spool structure of the pilot-operated proportional directional valve is diverse and has a direct impact on the flow field. To improve the valve’s performance, this work studied the characteristics of four types of spool structures with the following throttling groove arrangements: no throttling groove, a U-shaped groove, a triangle groove, and a combined groove. This study analyzed the flow field simulation of four spool structures under the same opening degree and different pressures to study the flow field cavitation characteristics and pressure distribution in the valve. According to the simulation results, the necessity of opening throttling grooves for the pilot proportional directional valve and the advantages of combined grooves over U-shaped and triangular grooves were verified. Then, the proportional valve with a combined groove structure was simulated and analyzed to study its throttling characteristics, steady flow characteristics, and flow and load differential pressure characteristics, and further explore the advantages of a combined groove. Finally, the experimental results are compared with the simulation results, which can provide a theoretical reference for the selection of the throttle groove of the proportional valve and the structural design of the slide valve.

Multiphase throttling characteristic analysis and structure optimization design of throttling valve in managed pressure drilling

As the key equipment to achieve accurate control of wellhead pressure during managed pressure drilling, the throttle valve can ensure the bottom hole pressure accurately controllable during the migration of invading gas in the annulus. At present, most of the research focuses on the throttling characteristics of single-phase fluid, and the research on the pressure regulation characteristics of throttle valve under the condition of multiphase flow is still relatively weak. In this paper, the mathematical model and CFD model of multiphase flow in the throttle valve are established, and the multiphase throttling characteristics under different hydraulic parameters are studied. The rationality of the proposed model is verified by field full-scale experiments. The results show that throttling pressure drop shows a nonlinear trend with the opening, which is not conducive to field application. Furthermore, through the sensitivity analysis of the throttle characteristic curve under multiphase flow conditions, the geometric structure of the throttle valve core is optimized to realize the fine adjustment of the wellhead back pressure under multiphase flow conditions, which is of guiding significance for wellbore pressure control under gas invasion condition.

Численное моделирование процессов дросселирования прямоточного воздушно-реактивного двигателя

Aimed at determining the maximum allowable pressure in the combustion chamber causing no flow separation in the air intake device, numerical simulation of the throttling process in a ramjet engine was carried out. Calculations were made in two formulations: with local and global time steps. When comparing results obtained using these approaches, the possibility was found to determine the air intake device throttling characteristics without losing the accuracy at the initial stages of designing the ramjet engines with introduction of the local time step. The non-stationary model created the basis for selecting the optimal integration step to minimize computational resources. The flow pulsations period was evaluated for the event of a surge. These pulsations frequencies were registered in the extremely low frequency range.

Theoretical and experimental research on damping characteristics of CDC shock absorber

CDC (Continuous Damping Control) shock absorber is the typical representative of the stepless valve-controlled type, which has the advantages of low cost and stable performance. Based on the throttling characteristics of the CDC valve, the damping force mathematical model of the CDC shock absorber is established. Through simulation analysis, the indicator characteristics and speed characteristics of the CDC shock absorber under different input currents and speeds are obtained. A CDC shock absorber testbed is built to study damping characteristics, and the results are compared with the simulation results. The results show that the indicator diagram obtained by simulation and experiment is smooth without distortion, and the speed characteristic diagram is smooth without a large mutation point. The experimental values of damping force are slightly larger than the simulation values. The relative error between the simulation data and the experimental data is basically less than 10% and the model has high accuracy. When the input current is the same, the damping force increases with the increase of piston rod speed. When the speed of the piston rod is the same, the damping force of the rebound and compression stroke decreases with the increase of input current.

Throttling Characteristics of a Supersonic Variable Inlet at Different Internal Contraction Ratios

Supersonic inlets with a wide operating Mach number range can regulate the internal contraction ratio (defined as the area ratio of the duct entrance and throat, denoted as ICR) to improve the critical total pressure recovery performance and flight condition adaptability. To elucidate the association between the downstream throttling characteristics and the ICR, a rectangular supersonic inlet with a variable ICR (ranging from 1.21 to 2.04) was designed. Using a high-speed schlieren and dynamic pressure acquisition system, a series of experimental studies was carried out in a supersonic wind tunnel at a freestream Mach number of 2.9. The results indicate that the downstream-throttling unstart modes of the inlet at different ICRs can be divided into two classes, namely, a “steadily changing” mode and an “abruptly changing” mode. As the ICR increases, the inlet substantially improves its compression and throttling performances by sacrificing a small amount of mass flow. Moreover, the inlet’s throttling characteristics at different ICRs are dominated by the flow loss of the terminal shock train. Then, the influence mechanism of the ICR on the inlet’s downstream throttling characteristics is revealed, and a throttling characteristic prediction model for rectangular supersonic variable inlets is established.

A method for numerical simulation of mode transition process of compression system of variable cycle engine based on throttle valve model

In order to study the aerodynamic characteristics of the compression system of a variable-cycle engine during its mode transition, a low-order model was established based on the throttle valve theory to describe the throttle characteristics of the mode selection valve at its different opening degrees. The model was applied to the outlet of a double-bypass variable-cycle fan in the form of characteristic boundary. A 3D low-order hybrid computational model was established for the numerical simulation of flow fields in the mode transition process of the compression system. The calculation accuracy and effectiveness of the throttle valve model were verified by comparing its calculation results with those of the 3D valve model. The simulation method was further applied to the prediction and analysis of the fan performance variation during the single and double bypass mode transitions of the variable-cycle fan. The simulation results show that: the throttle coefficient, which represents the throttle intensity, has something to do only with the flow area ratio of the valve but has nothing to do with its angle. Therefore, the throttle valve model is universal for valves with different motion angles; the throttle valve model can accurately predict the variation trend of the aerodynamic characteristics of the fan in all stages of the mode transition process. Compared with the 3D valve model, the prediction error of the pressure ratio of the fan in all stages is less than 1.93%, and the efficiency error is less than 1.05%. In the valve closing process, the second-stage rotor performance changes more dramatically, and the first-stage rotor performance changes with lag.

Study on Downhole Throttling Characteristics of High Water Content Gas

In order not to hinder gas production, we usually hope that the bottom hole effusion can be discharged to the surface with high-pressure natural gas. For the production data of high water content gas wells, the problems of insufficient water content and liquid-carrying capacity affecting gas well production should be considered. Based on the wellbore gas-liquid two-phase pipe flow theory and heat transfer theory, the temperature and pressure coupling prediction model of a high water-bearing gas well is established. Combined with the downhole throttling mechanism and gas-liquid two-phase homogeneous flow theory, the temperature and pressure field distribution model is established. The results show that compared with the Ramey model and Hassan and Kabir model, the temperature and pressure coupling prediction model of high water-bearing gas wells established in this study has the smallest coefficient of variation in the four groups of data tests. Based on this, the effects of different working conditions and choke diameter on downhole throttling characteristics of high water-bearing gas wells are analyzed. The findings of this study are helpful to better predict the wellbore temperature and pressure coupling of high water-bearing gas wells and provide more effective help for the smooth production of gas wells.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ РЕЗУЛЬТАТОВ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ И ЭКСПЕРИМЕНТАЛЬНОГО ИССЛЕДОВАНИЯ ДРОССЕЛЬНЫХ ХАРАКТЕРИСТИК ВОЗДУХОЗАБОРНЫХ УСТРОЙСТВ

Now, without exaggeration, it is possible to assert the existence of a new powerful alternative that has come to replace the physical experiment. Methods of computational fluid dynamics allow you to solve a large list of practical problems. However, an important issue of any numerical study is the assessment of the adequacy of the numerical forecasts obtained. When conducting a numerical study, you need to start with solving a test problem, the solution of which is already well known from earlier and reliable studies (in-situ or analytical). When solving a test problem, the mathematical model is configured and verified. In this connection, this paper presents the results of numerical simulation of the flow of configurations of annular air intake device located in the inter-caliber space with various geometric parameters of the central body, which determine the main parameters characterizing their gas-dynamic perfection. The method of conducting a computational experiment to determine throttle characteristics is shown. Based on a comparison of calculations with experimental data, a conclusion is made about the possibility of using the ANSYS Fluent software package for further use in solving similar problems.

Transport category airplane flight range calculation accounting center-of-gravity position shift and engine throttling characteristics

A problem facing world commercial aviation is a provision of the flight range and an increase in the fuel efficiency of transport category airplanes using fuel trim transfer application, which allows for decreasing airplane trim drag at cruise flight. In the existing mathematical models, center-of-gravity position is usually assumed fixed, but with fuel usage, center-of-gravity shifts within the definite range of center-of-gravity positions. Until the fuel trim transfer was not used in airplanes, the center-of-gravity shift range was rather short, that allowed to use the specified assumption without any considerable mistakes. In case of fuel trim transfer use, center-of-gravity shifts can reach 15…20 % of mean aerodynamic chord, that requires considering the center-of-gravity actual position during the flight range calculation. Early made estimated calculations showed the necessity of following mathematical model improvement using accounting the real engine throttling characteristics. The goal of this publication is to develop a method of flight range calculation taking transport category airplane into account actual center-of-gravity position with fuel using and variation in engine-specific fuel consumption according to their throttling characteristics. On the basis of real data from engine maintenance manuals, formulas are obtained for approximation throttling characteristics of turbofan engines in the form of dimensionless specific fuel consumption (related to the specific fuel consumption at full thrust) dependence on the engine throttling coefficient. A mathematical model (algorithm and its program implementation using С language in Power Unit 11.7 R03 system) has been developed to calculate the airplane flight range accounting its actual center-of-gravity position shift with fuel usage and variation in specific fuel consumption according to engine throttling characteristics. Using comparison with known payload-range diagram, adequacy of developed mathematical model is shown. Recommendations to improve the mathematical model are also given.

Devising a method for calculating the turboshaft gas turbine engine performance involving a blade-by-blade description of the multi-stage compressor in a two-dimensional setting

The design and adjustment of modern gas turbine engines significantly rely on the use of numerical research methods. This paper reports a method devised for calculating the thermogasdynamic parameters and characteristics of a turboshaft gas turbine engine. The special feature of a given method is a two-dimensional blade-by-blade description of the compressor in the engine system. Underlying the calculation method is a nonlinear mathematical model that makes it possible to describe the established processes occurring in individual nodes and in the engine in general. To build a mathematical model, a modular principle was chosen, involving the construction of a system of interrelated and coordinated models of nodes and their elements. The approach used in modeling a two-dimensional flow in the compressor makes it possible to estimate by calculation a significant number of parameters that characterize its operation. With the help of the reported method, it is possible to estimate the effect of changing the geometric parameters of the compressor height on the characteristics of the engine. To take into consideration the influence of variable modes of air intake or overflow in various cross-sections along the compressor tract, to determine the effect of the input radial unevenness on the parameters of the compressor and engine in general. To verify the method described, the calculation of thermogasdynamic parameters and throttle characteristics of a single-stage turboshaft gas turbine engine with a 12-stage axial compressor was performed. Comparison of the calculation results with experimental data showed satisfactory convergence. Thus, the standard deviation of the calculation results from the experimental data is 0.45 % for the compressor characteristics, 0.4 % for power, and 0.15 % for specific fuel consumption. Development and improvement of methods for calculating the parameters and characteristics of gas turbine engines make it possible to improve the quality of design and competitiveness of locally-made aircraft engines.

Dynamic Performance of Partially Orifice Porous Aerostatic Thrust Bearing.

The aerostatic thrust bearing’s performance under vibration brings certain changes in stiffness and stability, especially in the range of 100 to 10,000 Hz, and it is accompanied by significant increase in fluctuations due to the changes in frequency, and the size of the gas film damping. In this research work, an analysis is carried out to evaluate the impact of throttling characteristics of small size orifice on stiffness and stability optimization of aerostatic thrust bearings. There are two types of thrust bearing orifices such as: partial porous multiple orifice and porous thrust bearings and their effects on variations in damping and dynamic stiffness are evaluated. A simulation based analysis is carried out with the help of the perturbation analysis model of an aerostatic thrust bearing simulation by using FLUENT software (CFD). Therefore, two models of aerostatic thrust bearings—one with the porous and other with partial porous orifice are developed—are simulated to evaluate the effects of perturbation frequencies on the damping and dynamic stiffness. The results reveal a decrease in the amplitude of dynamics capacity with an increase in its frequency, as well as a decrease in the damping of partial porous aerostatic thrust bearings with an increase in the number of orifices. It also reveals an increase in the radius of an orifice with an increment of damping of bearing at the same perturbation frequency and, with an increase in orifice height, a corresponding decrease in the damping characteristics of bearings and in the dynamic stiffness and coefficient of damping of bearing film in the frequency range less than 100 Hz.