Amplitude Of Pressure Fluctuations Research Articles

Reduction of noise generated by cylinder-airfoil interaction using grooved structures on the upstream cylinder

The cylinder-airfoil interaction noise can be reduced by changing the shape of the leading edge of the downstream airfoil. Generally, this way not only can reduce the interaction noise at middle and high frequency, but also can change the peak noise at the low frequency. This study attempts to affect the cylinder-airfoil interaction noise from the perspective of reducing the intensity of the upstream wake shedding vortex. In order to achieve this target, the equally spaced grooves were cut into the upstream cylinder, and the acoustic wind tunnel tests at various incoming velocities (20–60m·s−1) were conducted to compare the interaction noise of cylinder-airfoil (NACA0012) models. It is found that the grooved structure can effectively reduce the peak noise at characteristic frequencies bellow 1000 Hz and the broadband noise in the mid-frequency ranging from 1000 Hz to 3000 Hz, especially for the higher incoming velocity. Thereinto, the peak noise and overall sound pressure level (OASPL) with the grooved cylinder are reduced by 13 dB and 7.2 dB, respectively at the incoming velocity of 60 m·s−1. The numerical simulations based on the large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) acoustic analogy were performed to further reveal the mechanisms of noise reduction when the velocity is 60 m·s−1. The results show that the vortex shedding from cylinder wake is suppressed by the grooved cylinder and the vortex structure at the leading edge of the airfoil is also cut into the small-scale vortex structures by the grooved structure. The pressure fluctuation amplitude and the peak value turbulent kinetic energy in the wake of the grooved cylinder are significantly reduced. In addition, the further spectrum analysis reveals that the weak correlation of the vortex shedding on the grooved cylinder could lead to the suppression of the pressure fluctuation in the cylinder wake, and thereby the interaction noise is significantly reduced.

Experimental study on flow evolution and pressure fluctuation characteristics of the underwater suction vortex of water jet propulsion pump unit in shallow water

The occurrence of the underwater suction vortex will cause the ship to vibrate violently and even lose thrust. The evolution process of the underwater suction vortex was obtained by high-speed photography. According to the characteristics of vortex in different phases, its diachronic process can be divided into five phases: premonitory, nascent, developing, weakening, and disappearing. The underwater suction vortex is a vertical axis vortex below the intake, and its shape is similar to a tornado, showing a form of thick at the top and thin at the bottom. The pressure fluctuation test studied the time-frequency characteristics of pressure fluctuation induced by the underwater suction vortex. The results show that the underwater suction vortex can cause the pressure fluctuation amplitude to recover after a sudden drop. The frequency of characteristic low frequency induced by the underwater suction vortex is 0.28 Hz, which is easy to be ignored. The corresponding amplitude of this frequency is much larger than that of other frequencies, and the low-frequency pressure fluctuation induced by the underwater suction vortex is dominant. The results can provide a theoretical basis for the mechanism and prevention of suction vortex of water jet propulsion pump unit.

Numerical investigation of the effect of axial clearance on the last stage of marine turbine

The axial clearance between the stationary and moving blade rows has a significant impact on the weight and volume of marine turbines, while excessively small clearance can lead to collisions between stator and rotor or even threaten the ship. To investigate the effects caused by axial clearance in marine turbines, a numerical simulation is performed on the last stage of a subsonic low-pressure turbine. The results show a significant effect of the axial clearance on the flow field. When the axial clearance increases, the pressure fluctuation amplitude on the blade surface decreases significantly, but the instability strengthens. There are many vortex structures at the blade root identified by the Q criterion. Vortex structures become smaller with the expanding axial gap, separating into multiple small vortex structures, which is the critical cause of instability. By FFT analysis, the change of axial gap mainly affects the blade passing frequency. Excessive axial clearance results in instability components in the spectrum because of the interaction of rotor-stator interaction and vortex structures in the flow field. The efficiency decreases slightly as the axial gap increases. This study provides a reference for the design of the axial clearance of the last stage of the marine turbine.

Gas lifted well performance evaluation based on operational parameters’ fluctuations

The paper describes the gas lifted well performance evaluation ability based on operational parameters’ fluctuations analysis. Experimental laboratory research showed that the optimum gas-liquid lift performance correlates with minimal fluctuation of flowrate and pressures. Also, trials in the «Neft Dashlary» oilfield were conducted. Gas lifted well’s flowing tubing head pressure fluctuations were evaluated at different lift gas injection rates – below, above, and at the optimum gas injection rates. The results of field trials show that at optimum gas lifter well performance, the tubing head pressure fluctuation amplitude reduction and frequency increase is observed. This is in line with theoretical prediction and lab experiments conducted. It is shown that gas lifted and naturally flowing wells’ performance quick evaluation is doable during normal operation. The introduced method allows timely detection of well performance deviation from optimal. Necessary measures can be taken to optimize the wells without conducting additional surveillance. Keywords: well; gas lift; flow rate; operational parameters; well performance.

Study on the Influence of Overflow Well Shut-In Mode on Wellbore Pressure Distribution in Ultradeep Wells

Summary With the deepening of exploration and development of oil and gas resources, more complex oil and gas reservoirs have been found, and oil and gas well drilling has gradually developed to ultradeep (>8000 m). In the oil and gas exploration and development of deep and ultradeep wells, a small-size borehole is usually used to uncover the target layer. In the drilling stage, the annular space gap of slimhole construction is small, the pressure difference is large, and the tripping fluctuation pressure is large; therefore, overflow is easy to occur. Because the upward channeling speed after overflow is fast, the pressure fluctuation caused by shut-in is large, and the requirements for well control are high, making it very important to study the shut-in mode after drilling overflow and the fluctuation of annulus pressure to ensure the safety of ultradeep well drilling. However, the current research on shut-in mode only focuses on changing the length of shut-in time and does not consider the operation steps of closing different components. It is obviously not rigorous to simplify semisoft shut-in and soft shut-in into a hard shut-in process with a long time. In this paper, the pressure wave velocity model and transient flow model of multiphase flow in the annulus are established. The shut-in process of different wellhead components is considered for the first time, the corresponding wellhead opening function is constructed, and the effects of different well shut-in methods on annulus pressure distribution and water hammer effect are studied. Some conclusions can be drawn: The annulus pressure wave velocity aam decreases rapidly with the increase of void fraction and decreases gradually with the increase of solid particle concentration. After hard shut-in, the wellhead pressure increases rapidly and fluctuates periodically. The shorter the shut-in time, the greater is the wellhead pressure. The displacement of drilling fluid has little influence on the pressure peak but has a great influence on the amplitude of pressure fluctuation. When the annulus pressure rises, the casing bulges outward to produce additional tension, while the drillpipe shrinks inward to produce additional pressure. When the annulus pressure drops, the casing shrinks inward to produce additional pressure, while the drillpipe bulges outward to produce additional tension. During soft shut-in, the closing time of the blowout preventer (BOP) has a great impact on the annulus pressure of the wellhead. When the shut-in time is short, the pressure rises instantaneously and fluctuates violently and the cycle is short; during semisoft shut-in, the larger the opening of the throttle valve, the smaller is the fluctuating pressure of the wellhead when the BOP is closed. When the throttle valve is closed after the BOP is closed, then the larger the opening of the throttle valve, the greater will be the fluctuating pressure. With the calculation and discussion of wellbore stress distribution during shut-in of an overflow well in this paper, we hope to provide reference for two groups of people mainly. For one thing, it can offer a new idea, calculation method, and meaningful conclusion to other researchers who are studying in this area. For another, it will help engineers making decisions when overflow occurs.

Experimental investigation on pressure fluctuation characteristics of a mixed-flow pump as turbine at turbine and runaway conditions

The pump as turbine (PAT) converts water energy into electricity energy, which greatly accelerates the construction of new power system. However, in the actual use of pump as turbine, its complex internal flow usually causes high-amplitude pressure pulsation, which seriously affects the operation efficiency of the PAT. The investigation on pressure-pulsation characteristics of a mixed-flow pump at turbine and runaway conditions is carried out in an open test rig, and the frequency domain characteristics of the pressure pulsation are analyzed based on FFT (Fourier Frequency Transform). The results show that, at the turbine mode, when the flow rate is greater than 0.8Q, the pressure fluctuation amplitude is almost three times that under small flow condition. Furthermore, when the flow rate is greater than 0.9Q, the shaft frequency and blade passing frequency occupy the dominant and secondary frequency positions in terms of the pressure fluctuation at the inlet of the volute, respectively. Moreover, when the flow rate is greater than 0.9Q, the pressure amplitude of the high-frequency component in the second section of the volute is very high, and the pulsation amplitude under a high flow rate condition is almost three to four times that under a low flow rate condition. The above phenomena show that the mixed-flow PAT is more suitable for operation under the flow rate conditions of 0.7Q and 0.8Q. In addition, at the runaway condition, when the head increases to 5.8 m, the pulsation amplitude at 7 times the shaft frequency increases significantly, which is almost 3.7 times that at the first two head conditions. The pressure pulsation which ranges from the double blade passing frequency to the triple blade passing frequency is significantly intensified, and the amplitude of the pressure pulsation at 7 times the shaft frequency is almost 3.7 times that at 3.75 m and 4.9 m.

Numerical study on knock characteristics and mechanism of a heavy duty natural gas/diesel RCCI engine

In this paper, the knock phenomenon of reactivity controlled compression ignition (RCCI) engine fueled with natural gas/diesel was numerically studied. The knock mechanism of the RCCI engine is explained and the strategy of suppressing knock is put forward. The knock characteristics were studied by setting monitoring points in different spaces positions of the cylinder. The results show that the pressure oscillation amplitude at the center and edge of the cylinder is large under the high load condition of RCCI engine. In addition, the knock mechanism was studied by using pressure difference method, maximum amplitude of pressure oscillation, important components, temperature isosurface, pressure fluctuation and heat release rate. The results show that the knock of RCCI engine is mainly caused by the end-gas auto-ignition. The pressure difference results show that the characteristic frequency is consistent with the natural resonance mode (0,1) of the cylindrical combustion chamber. On this basis, the effects of pilot oil injection timing and compression ratio on engine knock are further studied. It is confirmed that diesel knock and end-gas knock may exist simultaneously in the same cycle when RCCI engine knock occurs. And diesel knock occurs before top dead center, and end-gas knock occurs after top dead center. Proper adjustment of pilot oil injection timing and reduction of compression ratio can effectively suppress engine knock.

Numerical Simulation of Axial-Flow Pump Cavitation Based on Variable Frequency Speed Regulation

In order to investigate the influence of variable voltage and variable frequency (VVVF) regulation on the cavitation performance of the axial-flow pump, numerical simulation and experiments were used to analyze the cavitation performance of an axial-flow pump under different VVVF modes. The VVVF modes were uniform acceleration with constant acceleration, variable acceleration with increasing acceleration, variable acceleration with decreasing acceleration, and its corresponding deceleration scheme. Furthermore, a comprehensive performance test rig was built for the pump to carry out cavitation visualization tests which verified the accuracy of numerical simulation. For the uniform acceleration scheme with constant acceleration, the change of flow field inside the impeller was stable, the expansion rate of cavitation was slow, and the growth rate of the cavitation volume was the slowest. For the variable acceleration scheme with decreasing acceleration, the cavitation extended rapidly due to the large initial velocity. For the variable acceleration scheme with increasing acceleration, cavitation extension was the slowest. The growth rate of the cavity volume of the two variable acceleration schemes was faster than that of the uniform acceleration scheme, and the changing trend was consistent. This feature indicates that the impeller rotation speed has a significant impact on cavitation, and excessive rotation speed will rapidly extend the cavitation. By monitoring the influence of cavitation on pressure distribution under VVVF, it was shown that the three acceleration schemes all produce large pressure fluctuation. For the uniform acceleration scheme with constant acceleration, the fluctuation range of pressure was more balanced, and the pressure dropped slowly. For the acceleration scheme with higher acceleration, the pressure fluctuation amplitude increased in the late stage of acceleration and the pressure decline speed accelerated. For the acceleration scheme with decreasing acceleration, the pressure showed a downward trend with violent fluctuations in the early stage and gradually tended to be flat in the late stage.

Experimental and numerical validation of a Francis turbine draft tube designed for mitigation of pressure fluctuations

This paper presents an experimental and numerical investigation of the internal flow in a Francis turbine draft tube previously designed for minimizing pressure fluctuations and energy losses in off-design conditions. The design of the draft tube geometry is based on an original approach combining Design of Experiments and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The proposed method provides new insight on the influence of the draft tube geometry on the flow dynamic behaviour on one hand and enables the determination of a geometry promoting flow stability and hydraulic performance on another hand. CFD simulations of the internal flow in the final geometry showed promising results in terms of flow stability compared with the initial geometry designed by conventional CFD-aided methods. A reduced-scale model of the prototype machine featuring the final draft tube geometry is finally installed and tested in laboratory. Tests include performance and pressure fluctuations measurements over the complete operating range. The analysis of the results shows that the draft tube flow remains globally stable over the complete part-load range with pressure fluctuations amplitude lower than 1% of the net head. It is also shown that the dominant pressure component at the runner outlet in the draft tube cone is of synchronous nature. The physical mechanisms of excitation are finally highlighted by analysis of unsteady CFD simulation results.

Pressure fluctuation characteristics of a pump turbine in a draft tube: New insight into water column separation

The pumped-storage hydropower station is the most reliable, economic, long-term, large capacity, and mature energy storage technology in the power system, and it is an important component of renewable energy. Cavitation and water column separation of a pumped storage unit are important and widely researched factors in the safe and stable operation of a unit. This study focused on the evolution of water column separation of a pump turbine and its relationship with the pressure distribution of the cross section of a draft tube as well as the pressure pulsation characteristics of different measuring points in the cross section of the draft tube. A pumped storage experimental platform that can realize water column separation is established, and experiments with different opening angles are carried out. The results show that there are three factors that impact water column separation and cavitation: gas nucleus, vaporization pressure, and duration of vaporization pressure. Water column separation is the development and continuation of cavitation. The difference between the center pressure of the vortex rope and the wall pressure is large, reaching 2.23 m at a large opening. The pressure fluctuation amplitude of the wall measuring point is greater than that of the other measuring points in the same cross section, but the frequency characteristics are the same. In the transition process, the pressure pulsation amplitude of the liquid column bridging is the largest, and the largest pressure pulsation amplitude can reach 4.18 m at a small opening.

Numerical Study of Unsteady Pressure Fluctuation at Impeller Outlet of a Centrifugal Pump

Intense fluid-dynamic interaction at the impeller outlet strongly affects the unsteady flow and pressure stability within the centrifugal pump. In order to have a better understanding of the pressure fluctuation of centrifugal pumps, a numerical calculation is carried out by using the RNG k-epsilon turbulence model under various flow rates. The numerical calculation results are compared with the experimental results in order to verify the reliability of the calculation model. The amplitude and frequency distribution of pressure fluctuation at the impeller outlet is obtained and analyzed in the time and frequency domain. The research results show that the blade passing frequency is the dominant frequency of the pressure fluctuation. And the pressure fluctuation is a periodic fluctuation. As the flow rate decreases, the periodicity of the pressure fluctuation decreases. Besides, the amplitude and intensity of pressure fluctuation are closely related to flow rate and spatial location. At the low flow rate, the amplitude of pressure fluctuation in the time domain and frequency domain is enlarged greatly, especially near the tongue region. The pressure difference distribution on both sides of the blade surface is extremely uneven, and the pressure changes significantly.

Inverse transfer function identification for high-frequency pressure probes using M-sequence pressure generators

Accurate unsteady pressure measurement is important for the development and improvement of turbomachinery. The miniature pressure probe can adapt to the accurate measurement of pressure in a tight space under harsh working conditions, but the presence of the pressure transmission line makes the probe frequency response characteristics poor, and even causes the pressure signal to be distorted. In this paper, a novel Maximum-length sequence (M-sequence) pressure generator was developed, which generated pulsating pressure signals with wide frequency range and large amplitude pressure fluctuations at a fixed speed, and a time-domain parametric probe inverse transfer function identification method based on finite impulse response (FIR) adaptive filter using the generator was proposed. Four probes with different geometric parameters were fabricated. The probe inverse transfer function obtained by the FIR adaptive filter was compared with that obtained by the traditional non-parametric method to verify the accuracy of the identification method. The pressure at the pressure tap of the probes were reconstructed from the pressure measured by the probe and the inverse transfer function, which was in good agreement with the pressure measured by the reference sensor.

Development and fluid fluctuation analysis of a novel valve-controlled energy recovery device for small-scale reverse osmosis desalination systems

Energy recovery devices (ERD) are vital for improving the energy efficiency of reverse osmosis (RO). Nevertheless, small-scale seawater RO systems are rarely equipped with ERDs, mainly because of the associated high capital and maintenance costs. Herein, we propose a new type of reciprocating switcher (RS)-ERD with dual self-boost hydraulic cylinders that can pre-pressurize the low-pressure hydraulic cylinder during stroke switching. The structure and working process of the pre-pressurization reciprocating switcher (PPRS)-ERD are presented, and mathematical models of the entire system are established. Based on these models, a detailed performance analysis is performed. Compared to the conventional RS-ERD, both the high pressure (HP) check valve cores and hydraulic cylinders move smoothly, which suggests that the vibrations of the check valves and cylinders can be neglected. The maximum pressure fluctuation amplitudes of HP seawater (HPS) at the outlet and HP brine (HPB) at the inlet are 0.015 MPa and 0.016 MPa, which represent decreases of 98.91 % and 98.87 %, respectively. The flow fluctuation amplitudes of HPS and HPB do not exceed 0.17 m3/h and 0.07 m3/h, which represent improvements of 95.34 % and 96.59 %, respectively.

Experimental and Numerical Investigation of Rotor–Stator Interaction in a Large Prototype Pump–Turbine in Turbine Mode

In recent years, large-capacity, high-head pump–turbine units have been developed for pumped storage power plants to effectively utilise water energy and store large amounts of electricity. Compared with the traditional Francis turbine unit, the radial distance between the trailing edge of the guide vanes and the leading edge of runner blades of high-head pump–turbine unit is smaller, so the rotor–stator interaction and the corresponding pressure fluctuations in the vaneless space of pumped storage units are more intense. The pressure fluctuations with high amplitudes and high frequencies induced by rotor–stator interaction (RSI) become the main hydraulic excitation source for the structures of the unit and may cause violent vibration and fatigue damage to structural components, and seriously affect the safe operation of the units. In this paper, the RSI of a high-head pump–turbine in turbine mode of operation is studied in detail by means of site measurement and full three-dimensional unsteady simulations. The results of RSI-induced pressure fluctuations in turbine mode are analysed experimentally and numerically. The accuracy of the numerical calculations is verified by comparing with the measured results, and the variation law of RSI is deeply analysed. The results show that the pressure fluctuations in the vaneless space are affected by the wake of the guide vane, the rotating excitation of the runner, the low-frequency excitation of the draft tube, and the asymmetric characteristics of the incoming flow of the spiral case, and shows significant differences in spatial position. The findings of the investigation are an important and valuable reference for the design and safe operation of the pumped storage power station. It is recommended to design the runner with inclined inlets to reduce the amplitudes of RSI-induced pressure fluctuations and to avoid operating the pump–turbine units under partial load for long periods of time to reduce the risk of pressure fluctuation induced severe vibration on the structures.

Experimental investigation of temperature distribution and hydrodynamics characterization in a high-temperature gas–solid fluidized bed with sidewall liquid injection

Liquid injected into the fluidized bed greatly influences the heat and mass transfer ability and fluidization behavior of the particles. This paper systematically investigated the effects of liquid mass flow rate and superficial gas velocity on temperature distribution, bubble behavior, and pressure fluctuations in a bubbling bed contained liquid injection at the sidewall. The results reveal that an obvious low-temperature zone is observed near the liquid injected nozzle, in which, the superheated vapor is generated and then induces the heat transfer rate in fluidized bed with liquid injection more excellent than that of the conventional fluidized bed. The area of liquid injection zone expands with the injecting liquid flow rate while narrows with superficial gas velocity. Besides, liquid evaporation promotes bubble generation. The increasing liquid amount induces the flow pattern converts to bubbling bed from fixed bed at Ug < Umf. The bubble frequency and size increase with the liquid flow rate and superficial gas velocity. Furthermore, the amplitude of pressure fluctuation is also enhanced with the liquid flow rate. After liquid injecting, a distinct multi-modal distribution is plotted in the power spectral density curve and the low-frequency of peak less than 1 Hz increases with the mass of liquid. The intensity of the peak is enhanced and the bandwidth is broader in incoherent-output power spectral density, indicating more disorder fluidization.

Investigation of 3D Transient Flow and Discharge Pressure Pulsation of Helical Roots Air Compressor for Hydrogen Fuel Cell Vehicle

The Roots air compressor has a great potential for air supply in a hydrogen fuel cell vehicle (HFCV) because of its high efficiency, reliable operation, and wide range of flow rates. However, pressure pulsation of the Roots compressor could causes early failure of components of a fuel cell system. In this paper, numerical and experimental investigation on the discharge pressure pulsation of a helical Roots compressor was presented. First, a three-dimensional transient computational fluid dynamics model was built to examine and evaluate the pressure fluctuation amplitude. Then, the influences of angle steps and rotating speed on the fluctuation amplitude of discharge pressure were explored based on the numerical model. Meanwhile, a test rig was carried out to investigate the performance of the air compressor. The maximal discrepancy between experiment and simulation was within 8%. Finally, the effect of the opening angle of the discharge port profile on pressure pulsation was studied. The results showed that the fluctuation amplitude decreased from 6.48% to 1.87% with the opening angle increasing from 77° to 90°. The distribution of velocity showed that the dominating vortexes gradually dissipated with the increase of opening angle, and consequently contributed to the attenuation of the pressure pulsation. It provides new guidance for the structural optimization design of Roots air compressor.

Acoustic-Fluid-Structure Interaction (AFSI) in the Car Underbody

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The turbulent flow around vehicles causes high amplitude pressure fluctuations at the underbody, consisting of both hydromechanic and acoustic contributions. This induces vibrations in the underbody structures, which in turn may lead to sound transmission into the passenger compartment, especially at low frequencies. To study these phenomena we present a run time fully coupled acoustic-fluid-structure interaction framework expanding a validated hybrid CFD-CAA solver. The excited and vibrating underbody is resembled by an aluminium plate in the underbody of the SAE body which allows for sound transmission into the interior.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;Different excitation situations are generated by placing obstacles at the underbody upstream of the aluminium plate. For this setup we carry out a fully coupled simulation of flow, acoustics and vibration of the plate. The simulation results are compared and validated with experimental results of surface microphones, acceleration measurements and sound spectra of the interior. The analysis of the results focuses on the ratio of hydromechanic and acoustic excitation in frequency space and on possible back coupling effects of the structural vibration on the results. In the outlook, one example of an application of this method in the vehicle development is given.&lt;/div&gt;&lt;/div&gt;

Anti-phase oscillations of an elliptical cavitation vortex in Francis turbine draft tube

In this paper, the dynamic behavior of a precessing cavitation vortex featuring an elliptical cross section in Francis turbine draft tube is investigated. This phenomenon may occur for values of discharge coefficient within 70%–85% of the discharge coefficient at the best efficiency point, for which Francis turbines can experience the onset of the so-called upper-part load (UPL) instability. The latter is characterized by the propagation of high-amplitude synchronous pressure fluctuations through the complete hydraulic circuit. High-speed visualizations of the cavitation vortex are performed on a Francis turbine model by means of two cameras synchronized with pressure sensors arranged along the draft tube for different Thoma numbers at a given discharge coefficient. A simplified analytical model of the cavitation vortex is proposed. It enables the interpretation of the video post-processing results in the frequency domain and the estimation of both the vortex cross section dimensions and their oscillations with time. It is first demonstrated that both the vortex cross section ellipticity (given by the ratio between its semi-major and semi-minor axes) and the amplitude of its oscillations are directly correlated with the amplitude of UPL pressure fluctuations during intermittent UPL instability. Furthermore, the evolution along the draft tube of the dimensions of the elliptical vortex cross section and their oscillations during fully developed UPL instability is highlighted. The ellipticity of the vortex cross section increases as the vortex center position gets closer to the draft tube wall away from the turbine outlet. In addition, the vortex cross section dimensions oscillate with opposite phase from either side of a pressure node located along the draft tube. This results in low oscillations of the total void fraction in the draft tube, compared with results obtained locally. This effect should be considered in the one-dimensional modeling of the cavitation flow during UPL instability for further stability analysis. The new insights on UPL instability presented in this paper may potentially lead to a better theoretical understanding and modeling of this phenomenon in Francis turbines draft tube.

Influence of shock-vibration loads of drilling equipment on the drilling indicators of oil and gas wells

When drilling oil and gas wells, downhole and drilling wellhead equipment is subject to the influence of significant vibration processes of different directions with different amplitude-frequency characteristics. The paper describes the main sources of vibration of drilling equipment, which have a downhole origin. In this paper an amplitude-frequency characteristic of oscillatory processes of a drill string and their influence on drilling performance are given. In addition to the sources of fluctuations of the bottomhole nature of origin, sources of the wellhead nature can also be distinguished. Thus drilling mud pump is a generator of pulsations and beats of the pressure of drilling fluid, which in turn leads to the increase in the dynamics of the drilling tool, the appearance of torsional vibrations of downhole motors and bits. We established the negative influence of vibrations of the bottomhole assembly and drilling mud on the stability of the operation of hydraulic downhole motors, penetration on the bit, durability of the elements of the string and energy indicators of drilling. The proposed device allows reducing the amplitude of pressure fluctuations of the drilling fluid and drilling tool.

Combustion and Thermal Decomposition Research on 1,2‐Dicyclopropyl‐1‐Methyl Cyclopropane (DMCP) as High Energy Fuel for Liquid Rocket Propellants

Abstract1,2‐Dicyclopropyl‐1‐methyl cyclopropane (DMCP) was found a high‐energy liquid hydrocarbon propellant. A model combustion chamber was designed and manufactured to investigate the combustion performance of DMCP and Chinese rocket kerosene (RK) in comparison. Due to the higher density of DMCP, its orifice flow coefficient was 3.4 % larger than that of RK. The chamber pressure fluctuation amplitude of DMCP was within 10 % of the average pressure value. Under typical conditions, the flame intensity of DMCP combustion flame was more intense than that of RK. When the mixture ratios varied from 2.0–2.8, the characteristic velocity changes of DMCP were between 1626 m/s and 1636 m/s. It was not apparent that the characteristic velocity of DMCP was affected by the change of mixture ratio. The combustion efficiency of DMCP increased with the rise of its mixture ratio (varying between 0.902 and 0.921), higher than that of RK in a low mixture ratio. The apparent activation energy values (E) of DMCP were 202.0 kJ ⋅ mol−1 and 202.9 kJ ⋅ mol−1, respectively, according to Kissinger and Flynn‐Wall‐Ozawa (FWO) equations.