Tangential Velocity Gradient Research Articles

The influence of the guide vane positioning on the flow field of a turbo air classifier

AbstractAs the important component to guide the airflow in the classifier, installation position of the guide vane determines the width of the classification annular region and influences the flow field distribution. The influence of the guide vane positioning on the flow field in the annular region is analyzed through numerical simulation. The simulation results show the tangential velocities near the inner edge of the guide vanes increase, and the tangential velocity gradient decreases with decrease of the width of the annular region. The increases of turbulent dissipation rate near the guide vanes are beneficial to powder dispersion. However, the increases of turbulent dissipation rate near the rotor cage aren′t conducive to uniformity of the flow field. In case of the narrow annular region, the cut size gradually increases when the width of the annular region increases. However, when the width of the annular region continues to increase, the particle′s residence time become long, and the solid concentration increases significantly to increase the probability of particle aggregation. The reasonable range of the installation diameter of the guide vane in the classifier is between 504 mm and 524 mm.

Analysis of stability and internal flow mechanisms in spiral annular flow with different swirlers

Spiral annular flow within ducts is widely utilized in modern industry, with the swirler serving as a critical component in generating such flow patterns. The structure of the swirler significantly influences the generation and stability of the spiral annular flow. This study selected four different swirler structures with outstanding performance from previous research and analyzed their characteristics through visual image processing combined with numerical simulations. By analyzing the amplitude information of the wave fluctuations in the annular swirling flow liquid film under different operating conditions using probability density functions, it was found that the swirler A(Flat-vane swirler) and swirler B(Flat-vane swirler with hub) produced smaller fluctuations in the annular swirling flow liquid film, indicating better stability compared to the swirler C(Arc-vane swirler) and swirler D(Spiral-vane swirler), which exhibited poor performance. Combining the numerical simulation results with the analysis of the internal mechanism of the swirlers, it was discovered that within the swirler A and swirler B, the fluid between the swirler vanes experienced a larger pressure gradient, resulting in phenomena such as “jump” and “pull” under this pressure gradient. This, in turn, contributed to the generation of greater tangential velocity and radial pressure gradient after the fluid exited the swirler. Due to the influence of the swirler structure, the swirler A and swirler B did not completely separate the fluid region into four independent spaces. Instead, in the central connection area of the rear section of the swirler, the gas phase components aggregated earlier, greatly promoting the downstream generation of spiral annular flow. This study analyzed the two-phase flow process and mechanism inside the swirler, filling a gap in previous research and providing important references for the optimization and selection of swirlers.

Numerical Study of the Purge Flow’s Effect on the Loss Mechanism of the Blocking and Shear Effects

The loss mechanism of shear and upstream blockage caused by the interaction of the purged flow and ingested gas needs to be systematically studied to optimize the flow near the rim. In order to study the causes and influence factors of blocking and shearing effects and quantify their losses reasonably, the three-dimensional unsteady numerical method validated by the experiment data was adopted to study the turbine with three kinds of sealing structures. The block and shear loss are quantified by integrating the dissipation coefficient in the volume where the specific aerodynamic loss occurs. The result indicated that there was a larger radial velocity and smaller tangential velocity of the purged flow relative to the main flow caused the blocking effect. Therefore, its loss is affected by the seal flow and seal structure. The shear effect is mainly affected by the tangential velocity gradient and the axial velocity gradient near the cavity exit. The contribution of the tangential velocity gradient to shear loss is increased with the enlarged sealing efficiency. Through research, it is clear that increasing the purge flow’s tangential velocity is beneficial to reducing the shear loss and has a positive significance for weakening the blocking effect in the main flow channel. Furthermore, the influence of sealing structure on blocking and shear effect must be particularly considered since both are related to sealing efficiency.

Aerodynamic and thermo-acoustic stability analysis in a super-steady reactive flow

Aerodynamic and thermo-acoustic stability were systematically analyzed to reveal the underlying cause of the super-steady performance found in a strong rotating reactive flow, which is achieved using a stratified vortex-tube combustor (SVC) employing methanol as fuel. Results show that the SVC possesses a wide stability limit and weak pressure fluctuation with a uniform flame. The lean stability limit is always smaller than 0.2 and the amplitude of pressure fluctuation is generally within 2 kPa, indicating a super-steady combustion process. The large tangential velocity produces a large centrifugal force that suppresses the turbulent motion to promote aero-dynamic stability, yielding a small Froude number. The delay in the mixing process is the crucial reason for the generation of the stratified distribution of species and the triple-flame structure. The large transport fluxes of the species and enthalpy promote the reaction and ignition processes to intensify the combustion, which produces a large density gradient to promote thermo-acoustic stability. The large tangential velocity and density gradient result in a large Richardson number, suggesting the laminarization of the fluid. The momentum flux and its fluctuation decrease distinctly downstream of the vortex-flow because of the strong momentum exchange and transfer in the vortex flow, which weakens the pressure fluctuation in the post-flame zone. The intensified combustion can also increase the burning velocity, and promotes its matching with the flow field. The reduced momentum flux and the increased burning velocity are responsible for good thermo-acoustic stability.

Time-Resolved Wall Shear Rate Mapping Using High-Frame-Rate Ultrasound Imaging.

In atherosclerosis, low wall shear stress (WSS) is known to favor plaque development, while high WSS increases plaque rupture risk. To improve plaque diagnostics, WSS monitoring is crucial. Here, we propose wall shear imaging (WASHI), a noninvasive contrast-free framework that leverages high-frame-rate ultrasound (HiFRUS) to map the wall shear rate (WSR) that relates to WSS by the blood viscosity coefficient. Our method measures WSR as the tangential flow velocity gradient along the arterial wall from the flow vector field derived using a multi-angle vector Doppler technique. To improve the WSR estimation performance, WASHI semiautomatically tracks the wall position throughout the cardiac cycle. WASHI was first evaluated with an in vitro linear WSR gradient model; the estimated WSR was consistent with theoretical values (an average error of 4.6% ± 12.4 %). The framework was then tested on healthy and diseased carotid bifurcation models. In both scenarios, key spatiotemporal dynamics of WSR were noted: 1) oscillating shear patterns were present in the carotid bulb and downstream to the internal carotid artery (ICA) where retrograde flow occurs; and 2) high WSR was observed particularly in the diseased model where the measured WSR peaked at 810 [Formula: see text] due to flow jetting. We also showed that WASHI could consistently track arterial wall motion to map its WSR. Overall, WASHI enables high temporal resolution mapping of WSR that could facilitate investigations on causal effects between WSS and atherosclerosis.

Multi-fuel combustion performance analysis and operating characteristics of a vortex-tube combustor

In this work, an ultra-steady combustion technique was attempted to achieve fuel adaptability combustion. The combustion performances of five representative gaseous fuels in a stratified vortex-tube combustor were investigated in terms of the stability limit, pressure fluctuation, and flame topology. Results show that the lean stability limit of the global equivalence ratio for the five fuels can always be less than 0.15 with a uniform flame front, whilst the amplitude of pressure fluctuations is always below 2300 Pa, indicating a super-steady combustion process. The non-premixed flame structure guarantees a high mass concentration near the reaction zone, whilst the vortex flow also decreases the local flow velocity, inhibiting flame blow-out, and suggesting good self-adjusting capacity under various global equivalence ratios. The synergistic action of the flow and flame structures transports the interior high-enthalpy burnt gas and exterior unburnt gas to the exterior unburnt gas and reaction zones to promote the ignition and reaction procedures, resulting in an intensified combustion. The large tangential velocity and density gradient result in the large values of Richardson number, which indicates that laminarization of the flow arises and results in good aero-dynamic and thermo-dynamic stabilities. The resultant good self-adjusting capacity and three types of dynamic stabilities are the intrinsic causes of the ultra-steady combustion process in this combustor. Ultimately, the generalized criterion of stabilization can be defined by the combination of Richardson and Rayleigh numbers, for which large Richardson and small Rayleigh numbers are required for a highly steady combustion process.

Stagnation heat flux estimation in spherically blunt axisymmetric hypersonic models

Hypersonic flows have high heat transfer rates, and their management is essential to avoid detrimental effects. Since accurate prediction and measurement of heat flux in hypersonic test facilities are complicated, heat flux at the stagnation point is mostly estimated using Fay and Riddell formulation with Newtonian tangential velocity gradient approximation. Although it is relatively accurate and reliable, some errors creep in due to incompetent modelling of the tangential velocity gradient. This article studies the applicability of Olivier's tangential velocity gradient formulation for a sphere in the estimation of stagnation heat flux for spherically blunt axisymmetric hypersonic models. Oliver’s estimation accurately models the tangential velocity gradient of spherically blunt axisymmetric hypersonic models as the heat flux estimates deviated only by approx. 2%–4% from the measured heat flux. A simplified model for tangential velocity gradient using Shock Standoff Distance and density ratio is also derived and tested for accuracy.

Stabilization mechanism revelation of a novel vortex-tube combustion technique: LES with sgs-pdf approach

The paper revealed the in-depth stabilization mechanisms of a novel vortex-tube combustion technique by using ethanol as fuel, which is implemented by a stratified vortex-tube combustor (SVC). The stability properties of the SVC are investigated, showing that the SVC has a wide stability limit and low-pressure fluctuation amplitudes with a uniform flame front. The equivalence ratio at the lean flammability limit is always below 0.2, and the amplitude of pressure fluctuation is less than 2000 Pa, indicating a highly steady combustion process. The non-premixed flame structure guarantees high mass concentrations near the reaction zone, while the vortex flow also decreases the local flow velocity, inhibiting flame blow-out, thus providing good self-adjusting capacity under various global equivalence ratios. The vortex–flame interaction transports the interior high-enthalpy burnt gas to the exterior unburnt gas region, thereby promoting ignition. The exterior unburnt gas is also transported to the flame front where it promotes reaction and yields an intensified combustion. The large tangential velocity and density gradient result in the large values of Richardson number, which suggests that laminarization of the flow occurs and results in good aero-dynamic and thermo-dynamic stabilities. The small values of the Rayleigh number indicate good flame-dynamic stability. Therefore, the resultant good self-adjusting capacity and three types of dynamic stabilities are the intrinsic causes of the ultra-steady combustion process in this combustor.

Effects of high-speed spin on the reacting flow of drag reduction equipment under rapid depressurization

• The coupled combustion of two gases under dual environmental stress was simulated. • The effects of spin on the reaction flow under depressurization were analyzed. • A vortex core forms with a high tangential velocity gradient in the spin case. • Mass addition is a primary factor for the spin to improve the device performance. The drag reduction equipment (DRE) suffers dual environmental stress of high-speed spin and rapid depressurization during the launching process, disturbing the projectile intensely. To research the effect of this extreme process on heat and mass transfer, flow field development, as well as drag reduction performance of the DRE, a numerical model was established based on the MT-based pyrotechnics combustion mechanism and the H 2 -CO combustion mechanism. Simulation on the unsteady reacting flow was conducted to investigate the effect of high-speed spin on the performance of the DRE under depressurization. The results indicate that the wake flow field of the DRE transforms from a supersonic under-expanded jet into a subsonic swirling flow, and two recirculation zones with low-pressure appear at the base of the DRE. The transition region between propellant gas and igniter gas in the combustion chamber displays the Kelvin-Helmholtz instability, in which a vortex core forms with a high tangential velocity gradient. The igniter gas burns in the combustion chamber, resulting in an axial high-temperature region. And then the combustion products of igniter gas are mixed with propellant gas and inject outwards, reacting with the air near the jet boundary to be an intense post-combustion. High-speed spin improves the nozzle mass flow rate, enhancing the post-combustion. Eventually, compared with the non-spin case, the mass flow rate and base temperature in the case of 20,000 rpm are improved by 67.6% and 21.56%, respectively. And the base drag is reduced by 10.14%.

Geometrical configuration of hydrocyclone for improving the separation performance

The inherent defect of particle misplacement in traditional hydrocyclones is the main reason for the deterioration of separation accuracy and has obtained wide attentions. This paper presents three novel hydrocyclones based on the traditional cylindrical-conical type and cylindrical type. The effect of the hydrocyclone structure on the flow field characteristics and separation performance is investigated by a validated two fluid model. The numerical results show that a higher turbulence intensity deteriorates the separation performance of CCB type (cylindrical-conical-flat bottom type) and C type (cylindrical type), while a greater tangential velocity and velocity gradient improve the separation accuracy of MS type (multi-stage cylindrical type). Hydrocyclones with a flat-bottom structure reduces the misplaced fine particles due to the effect of the internal swirling flow and the axial circulation flow in the spigot. The MS type has the lowest imperfection value and the cut size of 76.5 μm implying a sharpness separation sharpness and an appropriate separation result. CC type has the minimum cut size of 62.21 μm, while the maximum cut size of 120.68 μm for C type.

Breakup process of liquid jet in gas film

In order to study the breakup process of liquid jet in gas film, the backlit photography technique and the VOF TO DPM method are used for experimental and simulation research respectively. Water and air are used as simulant media. Grid adaptive technology is used to refine the gas-liquid interface grid and improve the capture accuracy of the gas-liquid interface. The results show that there are two main breakup processes of liquid jet in gas film: column breakup and surface breakup. The local high-pressure zone in front of the liquid jet makes the jet have a large normal velocity gradient, which causes R-T instability. The surface wave that is generated by the R-T instability is mainly responsible for the liquid column breakup. When the thin liquid film reaches a column breakup point, the airflow penetrating the trough of the surface wave causes the jet column to break. The tangential velocity gradient is generated when the gas film bypasses the liquid jet surface, which causes K-H instability. The K-H surface waves cause ligaments and droplets to strip from the surface of the liquid jet. The local momentum ratio has an important influence on the breakup process of the liquid jet in gas film. When the local momentum ratio is low, the breakup of liquid jet is dominated by the K-H instability. As the local momentum ratio increases, the breakup of liquid jet is gradually dominated by R-T instability. The local momentum ratio plays an important role in the distribution range of the liquid jet in gas film. When the local momentum ratio is low, the ligaments and droplets caused by the liquid jet are mainly distributed within the range of gas film. As the local momentum ratio increases, part of the ligaments and droplets escape from the range of the gas film. The liquid jet penetrates the gas film when the local momentum ratio is greater than 0.74. The breakup length and the penetration depth are both affected by the local momentum ratio. The breakup length increases with the local momentum ratio increasing. The penetration depth also increases with the local momentum ratio, and the penetration depth increases significantly when the liquid jet penetrates the gas film.

Iterative PIV interrogation for complex wall-bounded flows

The strategy of the iterative PIV algorithm is discussed with the aim of investigating transitional wall-bounded flows. It is proposed to start the algorithm with a coarse prediction of the large-scale tangential velocity gradient to eliminate its negative effect. A window correlation with image deformation technique is then iteratively conducted to capture the fluctuating flow structures. Synthetic particles are created based on the DNS result of a typical hypersonic transitional boundary layers to evaluate the performance of the algorithm. Effects of several parameters, including the mean tangential displacement gradient, particle diameter, particle density and background noise on the level on the evaluation, are systematically investigated. Four methods to initially predict the near-wall flow are compared, including the directly-used window correlation with image deformation (WC) (Scarano 2002 Meas. Sci. Technol. 13 R1–19), the WC method with static particles added in the solid region (Zhu et al 2013 Meas. Sci. Technol. 24 125302), the image gradiometry method (Nguyen et al 2009 Proc. 6th Int. Symp. on Turbulence and Shear Flow Phenomena (Seoul, Korea, 2009)) and the newly-proposed joint-translation-shear correlation method method. The results show that, compared with the other three approaches, the performance of the new method is greatly enhanced for evaluating the dynamical flow properties, even if the displacement gradient is very high. Finally, experimental data on artificially disturbed boundary layers from a low-speed and a high-Mach-number wind tunnel are used to evaluate the new method, which is able to evaluate the mean and instantaneous velocity fields in both cases.

Influence of Disc Tip Geometry on the Aerodynamic Performance and Flow Characteristics of Multichannel Tesla Turbines

As a competitive small-scale turbomachinery option, Tesla turbines have wide potential in various fields, such as renewable energy generation systems and small power equipment. This paper investigates the influence of disc tip geometry, including its profile and relative height, on the aerodynamic performance and flow characteristics of one-to-one and one-to-many multichannel Tesla turbines. The results indicate that compared to the turbine with blunt tips, the isentropic efficiency of the one-to-one turbine with sharp tips has a little decrease, which is because the relative tangential velocity gradient near the rotational disc walls decreases a little and additional vortices are generated at the rotor inlet, while that of the one-to-many turbine with sharp tips increases significantly, resulting from an increase in the relative tangential velocity in the disc channels and a decrease in the low Mach number and vortex area; for instance the turbine efficiency for the former relatively decreases by 3.6% and that for the latter increases by 13.5% at 30,000 r/min. In addition, the isentropic efficiency of the one-to-many turbine with sharp tips goes up with increasing relative height due to increasing improvement of flow status, and its increment rate slows down. A circular or elliptic tip performs better with lower relative height and a triangular tip behaves better with higher relative height. To sum up, a blunt disc tip is recommended for the one-to-one turbine, and a sharp disc tip is for the one-to-many turbine. The relative height and tip profile of the one-to-many turbine should be determined according to their effects on turbine performance, manufacturing difficulty and mechanical deformation.

Nonlinear thermal effects in unsteady shear flows of a rarefied gas

We study the response of a rarefied gas in a slab to the motion of its boundaries in the tangential direction. Different from previous investigations, we consider boundaries displacements at nonsmall Mach ($\mathrm{Ma}$) numbers, coupling the dynamic and thermodynamic gas states, and deviating the system from its low-velocity isothermal condition. The problem is studied in the entire range of gas rarefaction rates, combining limited case ballistic- and continuum-flow analyses with direct simulation Monte Carlo computations. A nonlinear solution is derived in the ballistic regime for arbitrary velocity profiles and amplitudes. At near-continuum conditions, a slip-flow time-periodic solution is obtained for the case of oscillatory boundary motion, by expanding the flow field in an asymptotic Mach power series. The effect of replacing between isothermal and adiabatic surfaces is examined. The results indicate that, at all Knudsen ($\mathrm{Kn}$) numbers, the thermodynamic fields and normal velocity component are dominated by double-frequency (and descending higher-order even-frequency harmonic) time dependence, different from the fundamental-frequency time dependence dominating the tangential gas velocity. At continuum-limit conditions, this stems from the quadratic viscous dissipation term (negligible at low-Mach conditions), coupling the square of the tangential velocity gradient as a forcing term. System nonlinearity also results in an unsteady normal force acting on the boundaries, overcoming the tangential force with increasing $\mathrm{Ma}$. A marked difference from the latter is that the normal force either decreases with $\mathrm{Kn}$ or, at sufficiently small actuation frequencies, varies nonmonotonically with $\mathrm{Kn}$, reaching a maximum at some intermediate rarefaction conditions.

Experimental Investigation of Flow Distortion in an Auxiliary-Power-Unit-Style Inlet System

The flowfield inside a rectangular-sectioned 90 deg bend was studied using laser Doppler velocimetry. The bend used in the present study was part of an auxiliary power unit for helicopter engines. The results showed strong tangential velocity gradients near the inlet of the 90 deg bend and reverse flow at the inlet corner near the top wall and the outer wall. Rapid mixing was observed as the flow traveled through the bend. Additionally, measurements were acquired at constant-theta planes with a high spatial resolution to better resolve the secondary flow structures. The geometric asymmetry in the circular-to-rectangular transition duct was measured, and the effect of this asymmetry on the downstream flowfield was characterized. Results showed that the asymmetry of the transition duct led to asymmetric flow through the bend. This was one of the few studies that showed how a small change in the upstream geometry yielded very different flow patterns, which were eventually mixed out by the exit of the bend, and thus provided some guidance on acceptable manufacturing tolerances.

정상유동 장치에서 유동 특성 평가 방법에 대한 연구(4) - 유속분포(2)

This paper is the forth investigation on the evaluation methods of flow characteristics in a steady flow bench. In the previous works, it was concluded that the assumption of the solid rotation might cause serious problems and both of the eccentricity and the velocity profile distort the flow characteristics when using the ISM at 1.75B plane. Also particle image velocimetry (PIV) measurement at this position showed that the real velocity profile was far from the assumption of ISM evaluation. In this paper, the planar velocity profiles were measure from 1.75B to 6.00B position by PIV and the characteristics were examined according to the valve angles and lifts for further investigations about the effect of the position on the velocity profile. The results show that <TEX>$26^{\circ}$</TEX> valve angle is always an unique exceptional case in all aspects. If the valve angle is <TEX>$21^{\circ}$</TEX> and below, the planar velocity profiles according to the lift and the position are similar to each other, however, the tangential velocity curves along with the radial direction have common tendencies up to <TEX>$16^{\circ}$</TEX> angle. Also the well arranged swirl behaviors are generally observed at the position above 3.00B and the velocity contour lines come closer to the concentric circle as the valve lift increases. In addition, the gradient of tangential velocity along with the radial direction from the swirl center becomes stable and constant as the position goes downstream. Concurrently the velocity gradient is larger to the eccentric direction of the center. In the meantime the tangential velocity curves along with the radial direction are irregular and various at 1.75B, however, they become regular and reach higher level as the evaluation position goes downstream. At this time the curves of 4.50B are the best fitted to the ideal one. On the other hand in an exceptional case, <TEX>$26^{\circ}$</TEX>, the velocity contours are very complicated over 6mm valve lift regardless the position and the gradient increases to the opposite direction of the eccentric center. Also, 6.00B is a best fitting position in the geometrical cylinder center base. With respect to the swirl center, the distribution range of centers for 1.75B is different to that for the other positions and the eccentricities of this plane are larger regardless the valve angle. After 1.75B, there is no certain tendency in the center position change according to the valve angle and lift. Additionally, the eccentricities are not sufficiently small to neglecting the effect on ISM measurement.

The Three-Dimensional Velocity Distribution of Wide Gap Taylor-Couette Flow Modelled by CFD

A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisablek-εmodel. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.

Mass Transfer around Axisymmetric Particles of Revolution in Variable Diffusion Coefficient Liquids

Mass transfer around axisymmetric solid particles of revolution at high Peclet numbers has been theoretically studied. The liquid is a constant density binary system, having a variable diffusion coefficient, which depends on the solute concentration. Asymptotic solutions for very short and very long times are presented, and the only requirements are the shape of the particle, the tangential velocity gradient at the surface of the particle, and an expression for the variable diffusion coefficient liquid.

Exact solution and CFD simulation of magnetorheological fluid purely tangential flow within an eccentric annulus

In this paper, hydrodynamic characteristics of Magnetorheological (MR) fluid flow within an eccentric annulus have been investigated analytically and numerically. The MR fluid obeys the Herschel–Bulkley constitutive relation with a magnetic field dependent on yield stress. While the eccentric ratio or the gap between two cylinders is very small, local flow can be assumed between two parallel plates. With this simplification of motion equation, the effects of the magnetic field, eccentricity ratio and power-law exponent (n=0.25, 0.5 and 1) on the tangential velocity, torque and pressure gradient are analyzed analytically. Then, the results were compared with two-dimensional (2D) simulations for a system of two eccentric cylinders filled with a MR fluid. The Computational Fluid Dynamics (CFD) simulation results show good agreement with analytical solution. A wider range of the various parameters has been studied by the 2-D simulations. The influences of MR effects on flow field are significant and not negligible. The viscosity increases by increasing the magnetic field and eccentricity ratio, consequently providing an enhancement in the yield stresses and total torque required to rotate the inner cylinder.

Numerical investigation of cone angle effect on the flow field and separation efficiency of deoiling hydrocyclones

In this study, the effect of cone angle on the flow field and separation efficiency of deoiling hydrocyclones is investigated taking advantage of large eddy simulation. The dynamic Smagorinsky is employed to determine the residual stress tensor of the continuous phase. The method of Lagrangian particle tracking with an optimized search algorithm (closest cell) is applied to evaluate the separation efficiency of deoiling hydrocyclone. Simulations are performed on a 35-mm deoiling hydrocyclone with the three different cone angles of 6, 10 and 20 degree. The numerical results revealed that the changes in the cone angle would affect the velocity and pressure distribution inside hydrocyclone, and lead to changes in the separation efficiency. However, the large cone angle increases the tangential velocity and pressure gradient inside the hydrocyclone, but reduces the separation efficiency. The reasons behind the decrease in the separation efficiency are the flow structure and reduction of oil droplets residence time in hydrocyclones with large cone angles.