Velocity Decay Research Articles

Mechanism evaluations of conventional and suspended HVOF thermal spraying based on EDC and EDM combustion models

Suspended high-velocity oxygen fuel (SHVOF) thermal spraying technology can spray solid particles with nano or sub-micron scale, and effectively prepare high quality coatings by wrapping solid particles into suspension with solvent. The HVOF and SHVOF processes are numerically simulated in this study. The gas phase and discrete phase were simulated by the bidirectional coupling Euler-Lagrange method. The state equation of ideal gas and realizable k-ε turbulence model were used to simulate gas phase flow. The effect of eddy dissipation model (EDM) and eddy dissipation concept (EDC) model on turbulent combustion reaction was discussed. Due to that EDM model simplifies the Arrhenius rate of different reactions, there are errors in the prediction of spraying combustion process. To solve the problem, the chemical kinetic mechanism of multi-component combustion reaction for the propylene, ethanol and oxygen was introduced in EDC model for the first time in this study. This method has not yet been used in the modeling of thermal spraying. The suspended droplets are a mixture of ethanol and WC-12Co powder. Results show that the atomization and evaporation of suspension significantly disturb the flow field and reduce the internal pressure and temperature of spray gun. Compared with the EDM model, the EDC model can well predict the peak temperature in the combustion chamber, the prediction of particle temperature and velocity is higher, and the temperature and velocity decay are slower during flight. Compared with the median particle size d50 in actual, two combustion models can effectively predict the median particle size after drying, which is the premise of accurately predicting the flight characteristics of particles.

Myoelectric fatigue and motor-unit firing patterns during sinusoidal vibration superimposed on low-intensity isometric contraction.

Vibration exercise (VE) has shown promising results for improving muscle strength and power performance when superimposed on high-level muscle contraction. However, lowlevel contraction may be more preferable in many rehabilitation programs due to the weakness of the patients. Unfortunately, the effects and underlying physiological mechanisms of VE superimposed on low-level contraction are unclear. This study aims to investigate the fatiguing effects and motor unit (MU) firing patterns during VE with low-level muscle contraction. Twenty-one healthy participants performed 60-s isometric contraction of the upper limb under a baseline force at 30% maximum voluntary contraction and superimposed vibration with an amplitude of 50% baseline and different frequencies at 0 Hz (control), 15, 25, 35, and 45 Hz. High-density surface electromyography (EMG) was recorded on the biceps brachii. The decay in muscle fiber conduction velocity, calculated in 3-s sliding windows, was employed as an indicator of myoelectric fatigue. MU firing patterns were obtained by decomposing the high-density EMG into MU spike trains. VE, particularly at 25 Hz, produces increased myoelectric fatigue as compared to the control condition. Besides, synchronized MU discharges are observed at the vibration frequency for 15- and 25-Hz VE and the sub-harmonics for 35- and 45-Hz VE. Furthermore, VE-induced increase in MU synchronization (as compared to control) seems to decrease with myoelectric fatigue. Significance: Our findings suggest that VE may be a suitable modality for rehabilitation programs, providing useful insights for subscribing appropriate VE training protocols.

NUMERICAL INVESTIGATION OF TURBULENCE CHARACTERISTICS AND SELF-SIMILARITY IN A HIGHLY AERATED STABLE HYDRAULIC JUMP USING LARGE EDDY SIMULATION

This work presents a numerical study of a stable hydraulic jump at Froude number 4.25 and Reynolds number 1.15×105 inside a horizontal and rectangular channel with a length of 3.2 m, a width of 0.5 m and a height of 0.4 m using large eddy simulation (LES). Classical hydraulic jump characteristics are obtained, such as conjugate depths, jump length, void fraction and velocity profiles. The hydraulic jump maximum streamwise velocity decay and shear layer spreading rate are simulated and compared with experimental data. For these parameters, numerical results demonstrate that is possible to stablish an analogy with other shear flows, such as the horizontal plane wall jet. Profiles of streamwise and vertical components of mean velocity are simulated, and self-similarity is observed for cross-sections located at the recirculation region of the jump. Self-similarity is also observed in terms of turbulent fluctuations, insofar as LES simulations indicate a high level of turbulence in the recirculation region. The simulated root mean square of streamwise velocity fluctuations, , ranges from 0.5 to 0.7 of the maximum cross-sections velocity, whereas the root mean square of vertical component of velocity fluctuations, , stays around 0.5 of the maximum cross-sections velocitiy. All validation comparisons show good agreement with the selected experimental data of Kramer and Valero (2020) and Wang (2014), presenting average deviations always lesser than 5%.

Effect of aspect ratio on mean flow characteristics of cruciform orifice jet

PurposeThe purpose of this study reports the effects of aspect ratio (AR) on mean flow characteristics of the cruciform orifice jet.Design/methodology/approachThe aspect ratio is the height-to-width ratio of the lobe of the cruciform shape. The aspect ratios considered are 0.25, 0.5, 0.75, 1, 2, 3 and 4. The turbulent jet flow is issued through an orifice being fitted to the jet tunnel facility. The velocity measurements are recorded with the help of pitot-static tube connected to a digital manometer setup. The Reynolds number calculated using the equivalent diameter 50.46 × 10–3 m and exit velocity 51.23 m/s was 1.75 × 105. Based on the experimental data, the streamline velocity decay plots, the potential core length (PCL), mean velocity profiles and velocity half widths were plotted, and discussions were made based on the measured data. A smoke-based flow visualization was carried out at moderate Reynolds number 5396.FindingsThe PCL remains almost constant for the aspect ratio 0.25:1 and then starts decreasing for the aspect ratio 1:4. The decrease in PCL indicates improved mixing. The off-center peaks are found along the major axis in mean velocity profiles for almost all cruciform jets. More than one axis switching occurs and can be identified by the crossover points. The location of the first crossover point shifts forward, and the second crossover point shows an oscillating trend. The flow visualization exhibits the jet evolution, and the distance up to which the jet maintains the cruciform shape is increased with the aspect ratio.Research limitations/implicationsThe experiments are limited to air in air jet under isothermal conditions.Social implicationsThe cruciform orifices can be used as fuel injectors and in air-conditioning systems, thereby improving efficiency and energy usage.Originality/valueThe aspect ratio effects on PCL and axis switching are used to explain the mixing characteristics. Flow visualization was also used to support the discussion.

Analysis of confined cavity evolution and related pressure created by hydrodynamic ram

The impact of high-velocity projectiles on fluid-filled containers can induce the hydrodynamic ram (HRAM) effect, leading to the creation of a cavity within the fluid. The evolution of this cavity is subject to the constraints imposed by the container. This study aims to investigate the decay of projectile velocity and the development of confined HRAM cavities using a combined approach involving experimental and analytical methods. In contrast to existing research, this study accounts for the varying projectile velocities during different HRAM phases. Furthermore, enhancements have been introduced to the established cavity model, encompassing refinements in pressure differentials both inside and outside the cavity, alongside adjustments to the radial extent of liquid disturbance. The effectiveness of these refinements has been substantiated through experimental evidence. The findings illuminate two prominent constraint effects exerted by the container on the dynamics of HRAM cavities. Primarily, it accentuates the disparity in HRAM cavity pressures between the interior and exterior environments, and this pressure differential follows an exponential decay with distance. Secondly, it profoundly influences the flow of liquid near the wall, resulting in a considerably slower contraction of the cavity near the wall compared to its expansion phase. The evolution of the HRAM cavity is observed to manifest across three distinct stages: the unconfined cavity expansion stage, the partial cavity confinement stage, and the full cavity confinement stage.

Modelling of annular flow and sand erosion in bends using a thin liquid film method

Sand erosion in annular flow is a significant concern in offshore oil and gas industry. A thin liquid film method is proposed to construct annular flow and evaluate sand erosion in bends. The method analyses the liquid film and gas core separately. The direct interaction between the liquid film and gas core is studied based on the equivalent roughness of the liquid film, and the indirect interaction is presented through the entrainment and deposition of droplets. A new relation of the entrainment rate is proposed to describe the microscopic process of droplet entrainment. Sand erosion is calculated using the thin liquid film method, which considers the effects of the liquid entrainment and velocity decay of the particles passing through the liquid film. The thin liquid film method is fully verified by comparing with experimental data.

Numerical investigation of the velocity and spreading characteristics of non-circular turbulent jets at different Reynolds numbers

The flow field characteristics of non-circular turbulent jets are investigated numerically. A steady numerical simulation is conducted using the k–ε turbulence model in Ansys Fluent software. A hotwire anemometer is utilized to collect velocity data along the jet centerline for velocity validation. The jet exit Reynolds numbers vary from 200 to 5000, covering both laminar and turbulent regimes. The mean flow field characteristics, such as mean velocity, turbulent intensity, velocity decay, and half-jet spread width, are examined. The simulated results depict that mean velocity profile decay reveals a universal decay pattern, and the lateral velocity distribution shows a top-hat-like velocity profile in the near field. It significantly changed into peak-shaped and parabolic-shaped at a far downstream distance. The turbulent intensity profile reveals that shear layer growth begins near the jet exits, and entrainment becomes strong with the Reynold number. The potential core region increases with Reynolds numbers. The jet spread width shows a linear increment with the jet exit Reynolds number. The presented numerical results agree well with the measured experimental results and are consistent with published data.

Physics Application in Traditional Archery: Sight-lines Method for Aiming Using a Traditional Bow

<p lang="en-AU" align="justify">The absence of bow sight in a traditional bow can be replaced by introducing sight lines as a reference for accurate elevation angles in archery. Assuming a quadratic drag force acting on the arrow, a sight line can be calculated by using the values of target distances, initial arrow speed, arrow velocity decay, and the stance of the archer. This method can improve shooting accuracy for various target distances.</p>

Study on impact of gap difference on plasma distribution of direct current vacuum circuit breaker with double-break

During the fault current breaking process of a mechanical direct current vacuum circuit breaker (DC VCB) with double-break (DB), the mechanism’s dispersion can result in a gap difference between the two breaks. A DB DC VCB breaking experiment platform is constructed in order to investigate the impact of gap difference on plasma distribution during the DB DC VCB breaking process. During the experiment, a high-speed camera is used to capture the vacuum arcing process at the two breaks under varying gap difference conditions. Then, the arc feature parameters and their variations during the zero-zone process are extracted using image processing techniques, and the distribution patterns of plasma and arc energy at the two breaks are analyzed and compared. When there is no gap difference between the two breaks of the experimental DB DC VCB, there are no significant differences in arc energy and the sizes of high-, medium-, and low-temperature plasma zones between the two breaks. When there is a gap difference between two breaks, the break with the smaller gap has larger high and medium-temperature plasma zones, more concentrated arc energy, higher particle concentration, lower arc diffusion velocity and arc energy decay velocity, and a greater amount of residual plasma after the extinguishing of the arc. When the gap difference exceeds a certain threshold, energy spots appear on the contact surfaces, and a high concentration corridor of residual particles remains between the contacts after the current crosses zero, forming a breakdown weak point that eventually leads to arc re-ignition (hence interruption failure) under the action of transient recovery voltage.

Dynamic response of chain mail fabrics with variable stiffness

Variable stiffness fabrics have gained considerable attention due to their advantages in repeatability, deformability, and controllability of stiffness. However, existing variable stiffness fabrics are limited in fitting complex geometrical surfaces and understanding their dynamic mechanical response. This study aims to address these gaps through experimental testing and numerical simulations. Three fabric samples with different single-cell particles were fabricated to investigate the low-velocity impact response of variable stiffness chain mail fabrics. Impact tests were conducted on the fabrics using small balls at three velocities (2.5 m/s, 3.8 m/s, and 4.8 m/s) to analyze the influence of confining pressure variation on the mechanical properties. The results demonstrate that the impact resistance of chain mail fabric significantly improves as the confining pressure increases from 0 kPa to 60 kPa. That fabric consisting of traditional rings velocity decay value increased from 19.3% to 50.2 % at an impact velocity of approximately 4.8 m/s. Notably, the fabric composed of octahedral particles exhibited limited resistance to ball impact without applying confining pressure. However, when a pressure of 60 kPa was applied, the fabric effectively resisted ball impact and caused upward ball velocity. Multiple impact tests on single-layer fabrics and single impact tests on double-layer fabrics confirmed that fabrics consisting of square ring particles demonstrated better resistance to multiple impacts. The degree of interlocking within the topological interlocking structure, influenced by confining pressure, emerged as a crucial factor contributing to enhanced impact resistance. Numerical simulations revealed that the application of confining pressure promoted the formation of new contacts between interlocking particles. The number and quality of these contacts directly affected the overall mechanical properties, resulting in a solid-like structure. This research provides novel insights for developing structural fabrics with fast, reversible, and controllable stiffness adjustment characteristics.

Enhancement of heat transfer by flowing turbulent jet on a linearly decaying (LD) wavy wall

The influence of a partial linearly decaying (LD) wavy wall on different fluid flow and thermal parameters has been investigated for the turbulent jet. For the present study, a segment of wall from the leading edge is made with a constant amplitude 0.8a (a = nozzle height), followed by a segment of LD wavy wall. In the region of LD wavy wall, the amp (amplitude) of wavy wall is linearly reduced from 0.8a amplitude to 0a in the downstream direction. The LD wavy wall segment varies from 100% to 0%. For 100% LD wavy wall, the whole wall is made of linearly decaying amplitude, whereas for, 0% LD wavy wall, the whole wall is made wavy with a constant amplitude. The Reynolds number at the inlet is same for all the cases, i.e. 15,000 to maintain the fully turbulent condition at the exit of nozzle. The problem is solved numerically using k−ε RNG model. The results obtained from this study show that for 100% LD wavy wall the velocity decay is minimum and as the % of LD wavy wall decreases, the velocity decay increases. Whereas the thermal decay of jet is maximum in the case of 100% LD wavy wall. Similarly, Ymax, YTmax, and the velocity and thermal jet spread are found to be minimum for the 100% LD wavy wall and all these parameters increase as the % of LD wavy wall decreases. The maximum increment in the heat transfer rate is 27.9% for 100% LD wavy wall in regards to the baseline case (plane wall). However, the maximum increment in thermal hydraulic performance (THP) is noticed for the wavy wall with 50% LD wavy wall, which is equal to 6.7%. In a previous study (ArchanaKumari, 2021 [1]), the increment of 19.0% and 5.3% is observed for the heat transfer and THP respectively. In the present study by introducing LD wavy wall, the increment in the heat transfer and THP are quite significant.

Numerical investigation of mixing process of high-pressure jet-cutting clay by water–air coaxial nozzle considering soil rheological properties

Simulation and accurate modeling of the mixing process of the high-pressure jet-cutting clay by the water–air coaxial nozzle is significantly important for the performance optimization of the triple fluid jet grouting. In this paper, a numerical model considering the soil rheological properties is proposed to investigate the mixing process of the high-pressure jet-cutting clay. The cohesive force model of clay is obtained based on the solution of the power law index and consistency factor by coupling the Herschel-Bulkley and soil logarithmic models. The interaction model among the gas phase, the liquid phase, and the clay medium is further established through use of the drag force model. A laboratory device of high-pressure jet-cutting transparent clay is developed to prove the feasibility of the proposed model for the mixing process of the high-pressure jet-cutting clay. Finally, using the validated numerical model, the mixing process of the high-pressure jet-cutting clay by the water–air coaxial nozzle with varying radial spacings between the air nozzle and water nozzle is numerically investigated, and the axial stability of the jet, the width of the cross-sectional profile, and the variation of the central axis velocity field of the mixing process are analyzed. Results demonstrated that the variation trend of the jet in both simulations and experiments is consistent, and the maximum error in jet depth is better than 3.3%, validating the accuracy of the numerical model of the mixing process of the high-pressure jet-cutting clay. The optimal radial spacing size for a water–air coaxial nozzle in high-pressure jetting of clay medium is 1.4 mm, which provides the best axial stability, the narrower jet cross-section, and the slowest decay of jet velocity along the central axis.

In‐flight force estimation by flight mill calibration

AbstractThe study of insect flight is important for conservation and sustainability efforts, as predicting insect dispersal can aid management programmes in tackling economic and ecological harm from, for example, invasive species. Flight mills are invaluable tools for measuring the factors of insect flight under laboratory conditions, as they lower several technical and financial barriers to conduct experiments. It is especially difficult, however, to make assumptions about the energetic cost of tethered flights conducted using different tethers, or even on different flight mills, due to the mechanical variability of the bearing friction and air resistance of the rotating assembly. This additional uncertainty necessitates a larger number of replicates for any given standard of statistical confidence. By characterising flight mill friction, this uncertainty can both be reduced in magnitude and assigned a specific, well‐defined numerical value. We present a simple methodology to characterise this friction through dynamic calibration of the flight mill, at a high statistical confidence. This study uses videography of a flight mill undergoing free velocity decay due to friction, using an in‐house developed software to extract angular velocity from video data. However, the technique is readily adaptable to other measurement techniques. Using the velocity, alongside the mass moment of inertia of the flight mill, allows us to determine the rotational friction coefficient. This friction coefficient provides precise measurements of thrust production, and therefore the energy expenditure of flight, by the tethered insect.

Flow structure and impinging interactions of two confined turbulent converging jets in crossflow

In this work, time-resolved particle image velocimetry (TR-PIV) measurements are carried out to study the flow structure and impinging interactions of two confined turbulent converging jets in crossflow, with the upstream and downstream jets inclined at 20° and 170° with respect to the oncoming crossflow direction. Experiments are conducted for fixed dimensionless nozzle separation distance of s=L/D=3, fixed dimensionless nozzle-to-target surface distance of H/D=6.73, fixed duct Reynolds number of Re=3500 and two jets' Reynolds numbers of Rej=3000 and 6000 that correspond to jets'-to-crossflow velocity ratios of rj=3.45 and 6.91, respectively. Flow visualization images showing ensemble-averaged and instantaneous flow distributions and turbulent characteristics including Reynolds stresses and turbulence intensities for equal and non-equal discharge velocities of the jets are presented on several orthogonal planes of the test section. The swirling strength criterion has been employed to identify coherent structures, and cross spectral analysis of the fluctuating velocity signals detecting subharmonic and harmonic sideband frequencies identify the merging and breakup interactions of the evolving coherent structures. The snapshot proper orthogonal decomposition technique (POD) has been applied to extract the dominant vortical structures and to quantify their relative and cumulative energy contributions to the total kinetic energy fluctuation. The spatial structure of the main four POD modes and the temporal projections of these POD coefficients have been explored to understand the spatio-temporal characteristics of the dominant turbulent fluctuations and their spectral characteristics. Our results show the effect of the velocity ratios on the jets' trajectories, penetration, spreading characteristics, crossflow entrainment through the inner and outer shear layers, transverse velocity decay, size of the converging region and location of the combining point. In addition, the dimensionless shedding frequencies of the oscillating combined jet, the developing wall jets and wake vortices have been obtained. Furthermore, it has been shown that for all values of the jets' velocity ratios employed in this study, a recirculation region does not develop in the converging region.

Acute isolated vertigo with vertical up-beating nystagmus: A rare case of nucleus intercalatus of Staderini ischemia

The role of intercalatus nucleus of Staderini (INS), the most caudal of the perihypoglossal nuclei, is much debated. Last research seems to suggest that this nucleus plays a role as a vertical eyes movements integrator. The few clinical reports present in the literature that describe isolated lesions of the INS have described patients presenting in acute with up-beating vertical spontaneous nystagmus. Isolated acute lesion of INS is, in fact, much rare, and, without other neurological signs, is exceptional. We present a case of acute isolated vertigo with no other neurological signs or symptoms, due to INS ischemia provoked by vertebral artery stenosis. The patient presented with spontaneous vertical up-beating nystagmus that showed at videonystagmographic recording, a clear exponential decay of angular slow-phase velocity, that is considered a typical sign of neural integrator impairment. This case seems to represent a further confirm that INS is part, as a vertical-to-position neural integrator, of the neural circuit controlling the vertical eyes movements.

Research on explosive damage effects of tungsten fiber-reinforced Zr-based bulk metallic glass matrix composite shell

To expand the application range of explosive fragmentation projectiles, tungsten fiber-reinforced bulk metallic glass matrix composite (WF/Zr-MG) is used as the warhead shell in static explosion experiments, and is compared with 40CrMnSiB steel shells. The experimental results showed that, compared with 40CrMnSiB steel shells, the fragments produced by the WF/Zr-MG shell exhibit a larger aspect ratio, smaller average size, and a greater number of fragments at distances of 3 m and 5 m, with an equal number of fragments at a distance of 8 m. Theoretical calculations showed that the initial velocity of the fragments produced by the WF/Zr-MG shell is lower, but their velocity decay is slower, resulting in a greater determined damage range. The research results showed that WF/Zr-MG can be used as a shell material for explosive fragmentation projectiles, which can enhance their destructive power.

Gangue Source Reduction Technology and Process Optimization Based on Underground Coal Gangue Photoelectric Separation

The precise identification of damp, sticky coal gangue; efficient jet nozzle separation; and process layout in a narrow, restricted space are essential technologies for gangue source reduction based on underground gangue photoelectric separation, which is critical for the long-term growth of coal mines. In this paper, the X-ray absorption fine structure (XAFS) method was used to identify the X-ray absorption law of different atoms in coal-based minerals and explore the differences in the microscopic crystal properties of coal gangue; the numerical simulation calculation of four commonly used nozzles—namely, flat, convergent, flat–convergent, and streamline—was carried out using Fluent software for coal gangue jet separation to optimize the nozzle morphology and parameters. The technical characteristics of the underground layout of the photoelectric separation system for coal gangue were expounded, and the technological layout of the separation system was explored. The results showed that the absorption coefficients μ(E) of Al and Si atoms in minerals to X-rays are significantly different, and the XAFS method has the ability to identify coal, gangue, and other minerals. The streamlined nozzle has a long jet core area, slow decay of jet velocity, low gas consumption per unit time, and better performance than the other three types of nozzles. Based on the development and mining system of the Renjiazhuang Coal Mine, three kinds of photoelectric separation system layout schemes of coal gangue were designed, namely centralized layout, distributed layout, and mobile layout. The advantages and disadvantages of each scheme were compared, which enriched the technical means of gangue source reduction.

Computation of Turbulent Jet in a Confined Counterflow

The mean flow field of a turbulent jet issuing into a confined, uniform counterflow is studied. Computations are performed for a range of jet-to-counterflow velocity ratio ranging from 2 to 20 and jet exit-to-confining duct diameter ratio from 5 to 100. The flow field is dominated by a large recirculation region due to the interaction between the jet and the counterflow. The velocity profiles in a limited region of the jet are found to be self-similar. The jet penetration length varies linearly with velocity ratio for large values of diameter ratio. The presence of the external bounding walls cause departure from this linear relationship. A model for velocity decay along the jet centreline available for the unconfined case is shown to be useful for the confined cases also. An interesting double-peak in turbulence intensity along the jet centreline is observed.

Research on the influences of motion characteristics of jetting projectile charge under water

Shaped charge warhead is important for enhancing the damage performance of underwater weapons. This paper used finite element analysis software and based on JPC water penetration experiments to examine the influence of liner parameters (wall thickness, material), charge aspect ratio, and stand-off distance on the movement characteristics of JPC in water. The findings reveal that the head diameter of the JPC increases and experiences significant erosion after entering the water, the effective length of the JPC in water undergoes two distinct phases: a growth phase and a decrease phase, with the velocity of the JPC decaying exponentially. Increasing the liner thickness, stand-off distance and the charge aspect ratio can improve the erosion resistance and the velocity retention capacity of the JPC. The optimal ranges for liner thickness and stand-off distance are 0.0363Dk to 0.0545Dk (Dk is the charge diameter), the stand-off distance should be within 1.0Dk. After the charge aspect ratio higher than 1.25, the charge structure exerts minimal influence the movement characteristics of the JPC in water. Material density plays a crucial role in the velocity decay pattern of the JPC during penetration. JPC with higher densities exhibit superior velocity retention capabilities in water, with the velocity decay pattern converging if the densities are similar. Consequently, copper, tantalum and tungsten liners are deemed appropriate for underwater shaped charge warhead. Finally, the results will provide an important reference for the design of underwater shaped charge warhead.

Structural design and flow field characteristics analysis of a new spin-on multi-hole jet drill bit for radial horizontal wells

In order to improve the rock breaking and drilling capacity of the jet bit in radial drilling, a new spin-type multi-hole jet bit was designed. The RNG K-ε turbulence model is used to analyze the flow characteristics of the internal and external flow fields of the designed jet bit, and the influence of the rotational speed and nozzle distribution on the flow field characteristics of the jet bit is analyzed to provide a basis for the design and structural parameter optimisation of the jet bit in radial horizontal wells. The results show that the internal flow field of the jet bit can be divided into four zones: the forward jet zone, the bottomhole overflow zone, the reverse overflow zone and the low-speed reverse flow zone. The reverse jet consists of six straight jets uniformly distributed along the circumferential direction and arranged at equal angles around the axis of the rotating body in the flow field. The reverse jet also impinges on the well wall to form an overflow zone, which provides self-propulsion and acts as a reaming agent. As the injection distance increases, the axial velocity rapidly decreases to zero and the decay velocity of the three groups of jets gradually approaches at the impact wall. Rotational speed has an effect on the decay of the flow velocity at the centre of the forward jet axis. When the angle of inclination is very small, the rotational speed has almost no effect on the decay of the axial velocity of the jet. The greater the angle of inclination, the greater the linear angular velocity at the jet exit, the more the jet mixes with the surrounding crossflow, the faster the dissipation of jet energy and the faster the jet decays along the axis. Controlling the magnitude of the rotational speed has to be taken into account in the design. Initially, the optimum values of the different structural parameters were determined as the central nozzle coinciding with the drill axis, the central forward nozzle deflection angle of 20°, the external nozzle deflection angle of 20° and the external nozzle tension angle of 15°.