Dimensionless Analysis Method Research Articles

Research on a New Flow Measurement for Intelligent Injection Tools

Intelligent separate injection technology can achieve continuous monitoring data of layered water Injection wells. So it can find out the inefficient water circulating formation timely. Then the water injection schemes can be adjusted in real-time to ensure the high water injection pass rate. It can also increase the working efficiency of the workers’ because of its automatic mode.But its prime cost is high, which limits its large-scale industrialization application in fine layered water injection wells. The key part is the intelligent water distributor in the intelligent separate injection technology. The cost of electromagnetic flow meter accounts for 38% in the intelligent water distributor. The paper intends to research on flow measurement without flow meter to reduce the high-cost. The pressure difference equation was established for flow rate and the opening ratio of the nozzle using the dimensionless analysis method. The empirical parameters of the equation were obtained through laboratory experiments. The pressure sensors are used to monitor the pressure of water injection wells while achieving the measurement of layered flow rate.The laboratory experiments results indicate that the calculated flow rate obtained by this method coincides well with the standard flow rate. The relative error is less than 12%. Then,it provides a new flow measurement method for intelligent injection tools. The most significant feature is that the flow meter is no longer mandatory for intelligent water distributors. Due to the cheaper cost that it provides a technical support for the large-scale industrialization application of intelligent separate injection technology in fine layered water injection wells.

Experimental investigation on diffusion and fountain behavior of bubble plumes in quiescent water

Bubble plumes are a common phenomenon, which are simultaneously hazardous and exploitable. Diffusion and fountain behavior, regarded as significant characteristics of bubble plumes, were investigated in this experiment utilizing high-speed photography and image processing techniques within a rectangular bubble column crafted from organic glass. The diffusion, coalescence, and collapse phenomena of bubble plumes were visualized during their ascent under varying gas flow rates in quiescent water. Furthermore, the influence of gas supply pressure, flow rate, and water depth on the fountain height was examined. The research findings demonstrate that an increase in gas supply pressure and flow rate leads to a subsequent rise in fountain height once the bubble plume reaches the surface. Conversely, a reduction in the fountain height is observed with an increase in the depth of gas release. Through the application of a dimensionless analysis method, the factors influencing the fountain height were correlated, resulting in the proposal of a relationship formula for predicting fountain height. The predicted outcomes exhibited good consistency with the data reported in this experiment.

Numerical study on the effects of blocking ratio and spraying angle on the smoke flow characteristics of new energy vehicle fires in tunnels

Compared with traditional fuel vehicle fires, new electric vehicle fires have a fast flame propagation rate and higher smoke toxicity. Thus, higher requirements need to be implemented when designing tunnel fire protection. In this study, a horizontal highway tunnel with a rectangular cross-section is taken as the research scenario, and the FDS numerical simulation method is used to study the effects of different blocking ratios and key parameters of the water mist system in a rectangular tunnel under longitudinal ventilation on the smoke temperature and flow state near the fire source area. The results indicate that the average velocity of smoke in the vicinity of the fire source in the tunnel is mainly related to the cross-sectional size of the obstruction, and changing the spray angle does not affect the state of the smoke flow field. The relationship between the cross-sectional size of the blocked vehicles in the tunnel and the spray angle is proposed. In addition, when the blocking ratio reaches 25%, the back-layer length of smoke corresponding to the subsequent blocking ratio remains basically unchanged. Setting a reasonable spray angle can significantly reduce the CO mass fraction in the tunnel, while the visibility of the tunnel will also decrease. Using the dimensionless analysis method, a critical velocity correction model based on the blocking ratio factors is proposed. These research results provide a theoretical reference for the design of longitudinal ventilation and smoke exhaust for new energy-electric vehicles in highway tunnels.

Mathematical Modeling Study of Pressure Loss in the Flow Channels of Additive Manufacturing Aviation Hydraulic Valves

The application of additive manufacturing in the field of aviation hydraulics greatly improves the design freedom of hydraulic valve internal flow channels. Pressure loss in hydraulic valve internal flow channels is a primary factor that designers need to consider, and the rapid prediction of pressure loss is very helpful for flow channel design. At present, most studies only focus on how much the pressure loss in an additive manufacturing (AM) hydraulic channel is reduced compared with an original hydraulic channel, and a mathematical model of pressure loss in an AM curved channel is still lacking. In this paper, the pressure loss in a curved flow channel was firstly studied, and the main parameters affecting the pressure loss were determined using the dimensionless analysis method. Using computational fluid dynamics simulation, the relationships between the flow channel diameter, the flow channel length, the flow channel curvature radius, the fluid velocity and pressure loss were studied. According to the multiple regression analysis method, the mathematical model of pressure loss in aviation hydraulic channels was developed, and the model was solved based on the orthogonal experimental results. The pressure loss in the flow channel samples fabricated using selective laser melting was tested, and the results showed that the average error between the test results and the mathematical model calculation results was 7.72%. This model can be used to quickly predict the pressure loss in curved flow channels in the aviation hydraulic field.

Modeling effective heat transfer and ventilation in deeply buried underground tunnels

Underground traffic tunnels serve as entry and exit buildings for structures underground spaces. Most ventilation and air-conditioning systems in underground spaces rely on traffic tunnels for cooling or preheating to save energy. To analyze the cooling or preheating performance of the traffic tunnel, a combination of the energy conservation law, boundary layer theory, and field measurement was used to establish a simple heat transfer model of the deeply buried underground tunnel for smooth and rough conditions. Moreover, the dimensionless analysis method was used to perform a dimensionless analysis of the results. Field tests found that the air temperature in the traffic tunnel harmonically fluctuates from 20.2 °C to 29.4 °C at the entrance with time. The fluctuation amplitude decreases along the tunnel, and the air temperature difference between the peaks and troughs is only 1.2 °C at the outlet. In summer, the air temperature decreases and increases exponentially from 29.4 °C to 23.4 °C and from 20.2 °C to 22.2 °C along the tunnel during the day and night, respectively. The convective heat transfer coefficients are 2.31 W m−2 K−1, 4.05 W m−2 K−1, and 3.32 W m−2 K−1 under smooth, rough, and test conditions, respectively. Dimensionlessizing the air temperature found that the established model is a good description of the exponential decay of air temperature. Combined with the heat transfer models, the effective heat transfer analysis showed that the effective and optimal heat transfer lengths of the underground traffic tunnel were 1545 m and 628 m, respectively. The established the heat transfer model that calculated the temperature distribution of underground traffic tunnels provides important theoretical support for underground traffic tunnels as natural air conditioners, which have important economic and environmental benefits.

Predictive modeling approach for the jet lag in multi-pass cutting of thick materials using abrasive waterjet

Machining thick materials and freeform surfaces using abrasive waterjet (AWJ) is a limited approach owing to the jet lag effect. Here, we propose a machining strategy for multi-pass cutting wherein each forward cutting pass has the same starting position and fixed cutting parameters. The strategy incorporates the following two benefits: an increase in the cutting capacity owing to a reduction in the energy loss of the upper part and an improvement in surface quality. Furthermore, we adopt a single-factor approach to experimentally analyze the changing trend of jet lag using the proposed technique. We demonstrate that the proposed multi-pass cutting reduces the jet lag and improves the surface quality. We use particle erosion theories and a dimensionless analysis method to propose a model of the predictive jet lag, along with the optimal cutting parameters and multi-pass cutting depth. This model is validated using independent cutting parameters. The predictive model is in good agreement with the experimental results, deviating by a maximum of 6 % for 304 stainless steel. Notably, this model enables the prediction of jet lag for different cutting depths and parameters; furthermore, it exhibits significant engineering value by expanding the application range of freeform surface machining using AWJ technology.

Multiscale Sensitivity Analysis of Hydraulic Fracturing Parameters Based on Dimensionless Analysis Method

Abstract The optimal design of hydraulic fracturing parameters is the key to commercial exploitation of unconventional reservoirs. Hydraulic fracturing test is one of the main methods for optimizing fracturing parameters. It is known that scale effect exists between laboratory experiments and field treatments of hydraulic fracturing. However, studies on how to eliminate the scale effect are rarely reported. In this work, we conduct sensitivity analysis on rock mechanical parameters and fracturing parameters at different scales by using the dimensionless analysis method. The initiation and propagation process of field hydraulic fracturing is reproduced through laboratory tests, and fracturing parameters are analyzed by using numerical simulation. Our results show that the fracture propagation in the laboratory is inconsistent with that in the field fracturing. The fracture initiation and propagation in the field can be reproduced in experiments by using samples with high modulus and low toughness as well as high-viscosity fracturing fluid. Microcracks are created before the breakdown pressure is reached, and hydraulic fractures extend perpendicular to the direction of the minimum principal stress. The Carter’s leak-off coefficient has little effect on breakdown pressure and propagation pressure, but the injection rate and the horizontal principal stress have significant effects on breakdown pressure. This study provides a theoretical basis and guidance for the design of fracturing parameters both in the laboratory and in the field.

Deep analysis of the transient behavior of centrifugal pumps during startup and shutdown

The transient startup and shutdown of centrifugal pumps is inevitable and its transient performance has thus attracted increasing attention in recent years. This study aims to reveal the transient characteristics of centrifugal pumps during the start-stop process by using the dimensionless analysis method and quasi-steady-state method. The research objects are three typical centrifugal pumps with an impeller structure. The startup process includes quick and slow startup, and the shutdown process includes low-speed and high-speed idle rotation. Results show that the similarity law of centrifugal pumps can be applied to transient hydraulic performance prediction under full flow conditions during slow startup and under small flow conditions during quick startup and idle shutdown. Quick or slow startup does not affect the evolution of the dimensionless power coefficients. The research result may be useful for the design of the new fluidmachinery equipment by utilizing transient hydraulic performance.

Interaction mechanism of water movement and gas desorption during spontaneous imbibition in gas-bearing coal

After a series of permeability enhancement and gas drainage measures are implemented in low permeability coal seams, the gas content still does not up to national standard. How to improve the transformation rate from adsorbed gas to free gas is very important. Coal seam water injection is a comprehensive disaster prevention measure. The flowing of water includes the processes of seepage and spontaneous imbibition during coal seam water injection. The process of seepage mainly displaces free gas, which shows the characteristics of rapid attenuation. The gas and water interact with each other during spontaneous imbibition which is an important way of water movement to the depth of coal seam. Spontaneous imbibition is the key to fully wetting, which provides guarantee for the water distribution in coal seam, and which establishes the foundation for the replacement of adsorbed gas. In this paper, a device integrated the isobaric water addition, isobaric desorption and spontaneous imbibition height measurement was developed. Isobaric desorption can ensure that the replaced gas is quantitatively tested. The change of electrical resistivity was grouped into the processes of sudden change, fast change and gradual change. The spontaneous imbibition height increases with increasing gas pressures during isobaric imbibition. Based on dimensionless analysis method, the mechanism that the greater the gas pressure around the capillary with one end opening, the more obvious the plugging effect is revealed. The lower the gas pressure, the better the wetting effect on the micropores and some mesopores. The equilibrium state of micropores and some mesopores determines whether the process of spontaneous imbibition is over. This study realizes the recognition of coal seam water injection technology.

Experimental research on locations of the average wind speed point of anemometer station in rectangular roadway based on LDA

Aiming at the characteristics of wind flow pulsation and randomness that traditional contact instantaneous wind method fails to embody, the non-contact turbulence test means of Laser Doppler Anemometer (LDA) was used to test wind speed of the wind station roadway section. Experimental results show that under the Reynolds number 2.3×104~6.5×104, even if in the steady flow of wind station, the instantaneous wind speed distribution of roadway section presents the distribution of irregular wavy lines due to random fluctuation characteristics of airflow. The wind speed distribution accords with exponential function forms, and the average wind speed location away from the edge of the wall of the vertical distance and the length ratio of about 0.17, 0.15 0.14, 0.11 and 0.08 based on statistical average of turbulence with the statistical results of regularity, and introducing the dimensionless analysis method. Research shows that the traditional principle and method for measuring wind can only meet the needs of the general engineering, but it cannot reflect underground wind turbulence pulsation characteristics. However, the experimental test results based on turbulence average test results have provided the basis to determine the location of the average wind speed point of anemometer station, and also provided basic parameters for the research and development of the underground intelligent wind instruments.

A novel defrosting initiating strategy for automotive air conditioner heat pumps based on frost thickness growth prediction

Automotive air conditioning heat pump systems draw increasing attention as an alternative to conventional electric heaters. Once the air temperature falls below the freezing point, frost begins to form on the surface of the evaporator. The accurate defrost strategies could avoid heat exchange efficiency reduction and prevent heating capacity from decaying, which are the main factors affecting the energy efficiency of electric vehicle heat pump systems. The frost characteristic on micro-channel heat exchanger of the electric vehicle heat pump system is tested, and a novel defrosting strategy which is based on the dimensionless analysis method is introduced too. Conclusions could be drawn as following: a correlation that considers the effects of ambient parameters and structural parameters has been developed to predict the frost thickness on fins with dimensionless analyses. Based on this correlation, the relative error and the RMS error between the experimental data and the predicted value are 8.44% and 12.54%, respectively; the effective blockage ratio (EBR), a parameter that accurately reflects the blockage ratio and directly linked to the system operation state, is first proposed. Through the analysis between the EBR and system heating capacity, it can be concluded that the optimal defrosting start-point is identified as the EBR reaches 30%. With this method, the defrosting start-time can be found accurately and effectively to avoid unnecessary defrost cycles, thus leading to a highly efficient operation and low energy consumption for the electric vehicle heat pump system.

Stability analysis of a parallel channel-loop system with single-phase natural circulation under asymmetric conditions

Flow instability can cause mechanical oscillations in the equipment as well as periodic changes in the thermal stress, both of which have a great impact on the safety of the reactor. In addition, flow instability can interfere with the control system, making it difficult to capture stable parameters. In this study, to examine the change in the stability of a parallel channel-loop system with natural circulation under asymmetric conditions, the single-loop natural circulation system is taken as the starting point, and the control equations are obtained by using a dimensionless analysis method. The Fourier expansion of displacement term in the control equations is carried out to obtain the Jacobian matrix representing the single-loop natural circulation system. Based on this matrix, the Jacobian matrix model of parallel channel-loop system is constructed. According to the model, the natural circulation stability of parallel channel-loop under different load and resistance difference is analyzed, and the effects of geometric characteristics, coolant and power on the stability boundary under asymmetric condition are examined. The results show that there are two critical Reynolds numbers, and the system becomes unstable when the load difference introduced by the left and right loops is greater than the critical Reynolds numbers. The area of stable region can be increased by increasing the aspect ratio and heating zone length, and reducing the pipe diameter and cooling zone length. Furthermore, the stability boundary of natural circulation is sensitive to the aspect ratio and the length of heating zone. In addition, the stability can be improved within the allowable range of the natural circulation by choosing liquid metal coolant and increasing the pressure drop, and this model cannot accurately describe the changes in the stability boundary at low power. Overall, the above results can serve as useful reference for the design of the parallel channel-loop systems and can be used to improve the stability of natural circulation. The stability boundary can be used to preliminarily judge the stability distribution and the variation trend of the parallel channel-loop system with a certain degree of reliability.

Experimental study of different typical shape falling-rocks impacting on the sand cushion and dimensionless analysis

An experimental study on the impact force and penetration of falling rocks with three typical shapes, including spherical, conical and flat shapes, against the cushion was carried out. The experimental results show that the shape of the falling rock has a significant influence on the impact results. Under the same conditions, the flat blocks have the highest impact force, the lowest penetration depth and the shortest peak impact time, and the opposite for the conical falling rocks, with spherical blocks are between the two. The dimensionless analysis method was adopted to convert the mass, velocity, shape, size of the falling rock, the strength and density of the cushion layer into the dimensionless strength impact factor I, density impact factor λ and shape impact factor ψ. The correlation analysis between the impact factors and penetration test data shows that: (1) The effects of the impact factors I and λ on the final depth of penetration zm/d are similar. (2) The analysis of the impact factors I and λ effects on penetration depth shows that I and λ are relatively independent. The pattern of the I effects on the depth of penetration is generally consistent for different λ values.

A new heat transfer correlation for supercritical water flowing in a vertical tube - an hitherto approach

This paper provides an hitherto new approach of a heat transfer correlation based on heat flux to mass flux ratio for predicting wall temperature of supercritical water flowing in a bare vertical tube. Totally 10,174 numbers of experimental data were collected, Out of which 4236 data are heat flux/mass flux ≤0.4 and 5938 data are heat flux/mass flux>0.4. These data were obtained from various experimental resources and Lookup table and it covers q/G ranges from 0.085 to 1.295, mass flux ranges from 201 to 3500 kgm−2 s−1, heat flux ranges from 129 to 1600 kWm−2, pressure ranges from 225 to 320 bar, diameter of the tube 4.4 to 38 mm and bulk fluid enthalpy ranges of 250 to 3200 kJkg−1 of vertical tube working at various supercritical working conditions based on normal, enhancement and deteriorated heat transfer regions. By using these data, a new heat transfer correlation is derived for finding the wall temperature by Levenberg-Marquardt (LM) algorithm of multi dimensionless analysis method with Nonlinear curve fitting method. A general form of forced convection heat transfer correlation was obtained by Buckingham Π theorem. The Wall temperatures predicted by various 7 existing correlations along with this new correlation are found by Visual basic program and compared with experimental data for evaluating the deviations. The rank was provided based on error band from ±0.5% to ±50% etc., and error analysis were conducted for proving the best fitting correlation.

Mechanics analysis of ultra-thin chip peeling from substrate under multi-needle-ejecting and vacuum-absorbing

Chip peeling-off, mainly accomplished through the cooperation of needle-ejecting and vacuum-absorbing, plays a critical role in chip transferring process. However, there are few studies involving the quantification of process parameters, such as optimal needle position, needle force or displacement, to access to a reliable chip peeling. In this paper, optimization criteria for a high success rate of thin chip peeling-off are presented. With the cooperation of multi-needle-ejecting and vacuum-absorbing, the chip-adhesive-substrate structure is modeled within the framework of Timoshenko’s beam theory, and the competing fracture behavior between chip cracking and peeling-off in the peeling process is analyzed. A dimensionless peeling health index Γis proposed to evaluate the health status of the chip in the peeling process, and the effects of the needle position, the chip-adhesive-substrate structure geometry and material on the peeling health index are examined. On a basis of the numerical results, the optimal conditions for high-productivity peeling are achieved, which are the optimal needle position roughly at the edges of the chip, and the optimal shift point of changing the condition from needle-ejecting to vacuum-absorbing where the crack length in the adhesive layer expands to nearly the half value of the chip length. In addition, the expressions of the optimal ejecting needle force/displacement corresponding to the optimal shift point are obtained by the dimensionless analysis and fitting method. Furthermore, the optimization criteria including the optimal needle position and the optimal shift point of changing the condition from needle-ejecting to vacuum-absorbing are verified by experiments.

Dimensionless numerical analysis method for flexible body with large deformation, displacement and time-varying length

A tethered system, which is a multibody system in which multiple rigid bodies are connected via a flexible tether, is currently used for space and deep-sea exploration. In order to perform accurate work with such tethered systems, the ability to comprehend tether dynamics behavior with large deformation/displacement and time-varying length is crucial. Numerical analyses are beneficial in that it is difficult to carry out experiments in such environment. In this paper, an efficient numerical approach is proposed for a flexible body motion with time-varying length using a dimensionless equation of motion. Generally Absolute Nodal Coordinate Formulation (ANCF), which is a nonlinear finite element method is effective for dynamic simulation of a flexible body motion. VFE-ANCF, which applies variable-domain finite element (VFE) as a method of expressing time-varying length to ANCF, was proposed to represent the motion of a flexible body with large deformation, displacement and time-varying length. However, conventional approach using VFE-ANCF has a problem that the accuracy changes depending on the length change. So in this paper, to avoid this problem, dimensionless variables are introduced using representative value that changes with time-varying length. In addition, the usefulness of this method is shown by comparing the numerical results using this method and the conventional method.

Effects of equivalent diameter on vertical PMMA combustion in natural convection environment

SummaryA series of combustion experiments of polymethyl methacrylate (PMMA) plates with two shapes, three thicknesses, and different sizes was performed to investigate the effects of equivalent diameter on combustion characteristics of vertical PMMA in a natural convection environment. Two digital video cameras were used to record the burning process. The temporal variation of mass was recorded by an electronic balance. The influence of equivalent diameter on mass loss rate and flame height was then analyzed theoretically. Convection and radiation heat transfer were calculated and modeled in the theoretical analysis and compared to experiment. The result shows that the theoretical prediction of mass loss rate for each equivalent diameter is in good agreement with the experimental measurements. In addition, the relationship between flame height and heat release rate was analyzed using dimensionless analysis method. It was found that the flame height for vertical PMMA burning in a nature convection environment is dominated by heat release rate and equivalent diameter.

Study on Flow Characteristics of a Turbulent Boundary Layer and Vortex Structure of High Pressure Guide Vanes in SCO2 Turbines

In order to further understand the aerothermodynamic performance and flow loss mechanism of SCO2 turbines, RANS equations and an SST Turbulence Model were chosen for a numerical study on the secondary flow and vortex structure of cascades using the commercial software CFX. The dimensionless vorticity analysis method was used to study the flow characteristics of the logarithmic layer and viscous sublayer in high pressure guide vane cascades. The new vortex structure and formation mechanism of the vortices were given and analyzed. Simulation results indicated that during the motion of the boundary layer in the cascades, the logarithmic layer and viscous sublayer obtain the different rotational direction vorticity, respectively. The endwall logarithmic layer and pressure side leg of the horseshoe votex gradually develop into the passage vortex, with the endwall viscous sublayer gradually developing into the corner viscous sublayer vortex II and the endwall viscous sublayer vortex I. The endwall viscous sublayer that rolled by the passage vortex is encountered with the upstream-side and radial boundary layer of the vane at the suction separation line, forming the suction separation line vortex beside the passage vortex. A pair of radial transition vortices are formed between the wake and the main stream.

Numerical investigating flow characteristic of swirling turbulent round jet

Swirling waterjet, using swirling and cutting capacity of high velocity waterjet beam, is a kind of technology widely applied in foundation processing, tunnelling, coalbed methane mining, and etc. It is extremely complicated because the existence of high velocity gradient and swirling, nevertheless, knowing unsteady interior flow characteristic and flow pattern which tremendously affects cutting capacity of waterjet is what we concern about. In this article, computational fluid dynamics is utilized to study flow characteristics of swirling turbulent waterjet, convergent nozzle structure with swirling is chosen as prototype and investigational region is selected as waterjet flow could be fully developed, structured mesh and grid number independent is obtained, Reynolds stress turbulence model is employed and standard wall functions is chosen as the near-wall treatment, pressure boundary conditions are applied on inlet and outlet boundaries, the SIMPLE algorithm is employed to couple the pressure and velocity, and time step size and number is selected reasonably. According to numerical simulation results, statistical analysis method, comparative analysis method and dimensionless analysis method is used to analyse central line velocity attenuation, velocity profile of different axial and radial position, flow pattern and vorticity characteristics, influence of different swirling velocity is also investigated, cutting capacity and influence factor of high pressure swirling water jet is evaluated. It is valuable for application of CFD in swirling waterjet field and helpful for understanding interior filed of swirling waterjet flow, meanwhile, this work could also provide reference for further investigation and application about swirling waterjet.

Influence of plasma channel impedance model on electrohydraulic shockwave simulation

The simulation of electrohydraulic shockwaves is the key technology for their application and device design. The analytical approach of underwater pulsed discharge is described using the dimensionless analysis method, which combines energy based hydrodynamic equations and the electrical differential equation describing the discharge characteristics of the circuit. A constant plasma channel impedance model based on the experimental results and an improved time-varying plasma channel impedance model based on the Braginskii equation are proposed and presented. The plasma channel impedance has a great influence on the deposited energy into the plasma channel and then affects the calculation and analysis of the shockwave propagation. The electrical characteristics and fluid physical properties are taken into consideration, and the results are compared. The application range of different impedance models is summarized, and the time-varying impedance model can provide a more accurate result in the simulation of shockwave propagation. The dimensionless analysis method, together with a time-varying impedance model, could be a useful tool for evaluation of the electrohydraulic shockwave in practical applications and applied physics research of underwater spark discharge.