Numerical Simulation of Influence for Induced Pipe Geometric Parameters on Exhaust Ejector Performance

This study reports on an experimental and numerical investigation of tip leakage flow control and its effects on the endwall flow structure and stall evolution of a contra-rotating fan. The control method involves the annular injection of high-momentum fluid in the axial direction, upstream of the front rotor. Five-hole probe measurements have been performed at different blade span locations to obtain the hub-to-shroud velocity distribution and also detect stall. Half-annulus transient simulations have been further conducted and validated against experimental tests. Two injection mass flow rates, 1.6% and 3.2% of the main mass flow rate, have been evaluated. Fast Fourier Transform and wavelet transform analyses have been applied to the experimental data. These analyses show that stall disturbances are intensified near the endwall, indicating the tip-critical nature of the studied fan. Under stall conditions, a modal wave in the tip region has been identified, rotating at 40% of the rotor speed. Numerical contours confirm the presence of circumferential disturbances. Also, the results reveal that rotor-2 is responsible for stall initiation. The findings further show that a 3.2% injection has sufficient momentum to eliminate the tip leakage vortex in the endwall flow. With 3.2% tip air injection, the total pressure rise coefficient and the stable operating range increased by 21% and 59%, respectively.

The three-dimensional flow inside a mixed-flow pump system was simulated by using CFX software. The Shear Stress Transport turbulent equation which combined k-ε and k-ω turbulent model was applied. The flow field in volute and discharge passage of the pump system was obtained and the hydraulic performances of the pump system were predicted. The velocity and pressure distribution in pump system were analyzed. From the calculation results it is evident that the flow in the double helix volute passage is a spiral movement combining axial and rotary flow; the static pressure distribution in the volute is symmetric; the uniformity of axial velocity distribution and velocity-weighted average swirl angle at the outlet section are relatively low; and static pressure distribution on pump blade surface is regular with higher static pressure on pressure side and lower one on the suction side. The axial forces decrease gradually with the decrease of lifting head and the radial forces decrease first and then increase. A model test of the pump system was conducted to verify the calculation results. The pressure fluctuation at certain sections of the pump system was measured from the model test. A good agreement was found for lifting head between calculated and measured results. While the deviation of the efficiency between calculated and measured results does exist in non design points which need to be improved.

Effect of induced airflow on the surface static pressure of pleated fabric filter cartridges during pulse jet cleaning

The article is devoted to the analysis of the influence of tunneling channel height change on its aerodynamic characteristics by modeling the velocity and pressure distribution of air and furnace gases. Three variants of the tunnel geometry were considered: basic, with reduced height in the firing zone and with reduced height along the entire length of the furnace. The simulation results in the dependence of the static pressure along the length of the furnace and the velocity of the furnace gas moving along its height. The analysis of the change in the velocity of the furnace gases in the tunnel has made it possible to say that the most effective in terms of uniformity of velocity distribution is the variant with the reduction of the height of the arch along the entire length of the furnace.Keywords: tunnel kiln, tunnel kiln channel, change of kiln geometry, velocity distribution modeling, static pressure distribution.

The aim of this experimental study is to investigate the diffusion of jets, with particular attention focused on the relationship between the static pressure and the stream wise mean velocity on the development of a two-dimensional air jet. A jet with three injection velocities (11.7, 23.3 and 35.0 m/s) was generated in a two-dimensional wind tunnel. The velocity distributions were measured by an X-type hot-wire anemometer. The static pressure distributions were measured by a static pressure probe developed in our laboratory, which incorporates a hot-wire anemometer. The probe is designed to be able to measure the mean static pressure and pressure fluctuation simultaneously. The sensitivity is 92.3 mV/Pa. The frequency response is flat from 16 Hz to 2.5 kHz. As a result of the experiment, it was found that negative static pressure exists in the turbulent shear layer. It is considered that the entrainment process from the negative static pressure by the vortex structure motion of the turbulent shear layer.

The launch vehicle will experience extreme acoustic environment at lift-off, which will cause the invalidation and destruction of the aerospace equipment, and reducing noise is of great significance for improving launch safety. In this paper, the numerical simulation of gas–liquid two-phase flow and its acoustic field is carried out, and the flow field is simulated by the discrete phase model (DPM), second-order Roe format, Scale-Adaptive Simulation (SAS) and three-dimensional Navier–Stokes. Based on the analysis of the flow field, the acoustic analogy integration method (FW-H) is used to predict the jet noise at the observation position. The influence of the water different injection angles and mass flow rate ratios are studied, and the results show that water injection not only reduces the temperature, velocity and vorticity at the gas–liquid interface, and the temperature at the bottom of the jet deflector, it also significantly reduces the jet noise. The total sound pressure level can be reduced to 6.92 dB by appropriate selection of the water injection angles and water injection mass flow rates. The numerical method established in this paper provides a useful tool for the design and analysis of water injection noise reduction for high-thrust multi-nozzle launch vehicle.

Metal additives have positive effects on the flow field such as increasing the temperature and thrust, while this may decrease local gaseous velocity due to inter-phase drag forces on the other hand. An in-house computational solver was developed to study the typical multiphase flow with combustion. The solver relies on Eulerian–Lagrangian model and the two-way coupling approach. Numerical simulations were carried out on an afterburning chamber of a solid-fuel ramjet to study the impact of using aluminum particles as metal additive. For micron-scale aluminum particles, the injection area, initial temperature, diameter and mass flow rate are varied influence factors, while the afterburning chamber and inlet primary high-temperature gases are fixed for all the test cases. It was found that better particle dispersion can result in higher combustion efficiency due to increasing the gas-particle contact area as well as better heat transfer and diffusion. Injecting aluminum particles with higher initial temperature and smaller diameter tend to get ignited faster and then burn more easily, which means releasing more heat in the length-limited flow field. However, the aluminum particle massflow rate has much more complicated comprehensive influence than the changing rules of the adiabatic combustion temperature based on the NASA CEA code.

In order to analyze the influence of blade outlet angle on inner flow field and performance of low-specific-speed centrifugal pump, the flow field in the pump with different blade outlet angles 32.5°and 39° was numerically calculated. The external performance experiment was also carried out on the pump. Based on SIMPLEC algorithm, time-average N-S equation and the rectified k-e turbulent model were adopted during the process of computation. The distributions of velocity and pressure in pumps with different blade outlet angles were obtained by calculation. The numerical results show that backflow areas exist in the two impellers, while the inner flow has a little improvement in the impeller with larger blade outlet angle. Blade outlet angle has a certain influence on the static pressure near the long-blade leading edge and tongue, but it has little influence on the distribution of static pressure in the passages of impeller. The experiment results show that the low-specific-speed centrifugal pump with larger blade outlet angle has better hydraulic performance.

PurposeRadial vibration of horizontal centrifugal pump has a close association with radial exciting forces. The purpose of this paper is to analyze the unsteady radial force in multistage centrifugal pump with double volute in detail and investigate the relevance of static pressure, radial force and radial vibration.Design/methodology/approachThe unsteady numerical simulation with realizable k-ε turbulence model was carried out for a multistage centrifugal pump with double volute using computational fluid dynamics codes Fluent. The performance tests were conducted by use of a closed loop system and performance curves from numerical simulation agree with that of experiment. Vibration tests were carried out by vibration probes instrumented on the bearing cover of pump near no-driven end. Fast Fourier transform was used to obtain the frequency components of radial forces on the impellers from numerical simulation, which are compared with ones of radial vibration from experiment in Y and Z direction. And the static pressure distributions in the impeller were analyzed under different flow rates.FindingsThe symmetrical double volute can effectively balance radial forces. The maximum radial force and vibration velocity appear at 0.6 Q among the three flow rates 0.6 Q, Q and 1.2 Q. The frequencies corresponding to relatively large amplitude of vibration velocities and radial forces on the impellers in Y direction are blade passing frequency of the impellers. Blade passing frequency of first-stage impeller and shaft frequency are predominating in Z direction. It indicates that the radial vibration of centrifugal pump is closely related to the unsteady radial force.Originality/valueThe unsteady radial forces of the impeller in multistage centrifugal pump with double volute were comprehensively analyzed. The radial forces should be considered to balance during the design of multistage centrifugal pump.

Experiments were conducted to validate the building blocks of a fluidically controlled variable area turbine concept that uses injected high-pressure air to effectively reduce the choke area of the turbine inlet. Preliminary results from a simple quasi-1D converging-diverging nozzle, with an injection flow slot upstream of the throat, showed a 2.2:1 ratio between throttled mass flow rate and injected mass flow rate at a constant nozzle pressure ratio. The penetration of the injection flow and corresponding reduction in the primary flow streamtube were successfully visualized using a shadowgraph technique. Building on this success, a representative single passage nozzle guide vane transonic flowpath was constructed to demonstrate feasibility beyond the quasi-1D converging-diverging nozzle. Both secondary slot blowing from the vane pressure surface and vane suction surface just upstream of the passage throat again successfully reduced primary flow. In addition, fluidic vortex generators were used on the adjacent suction surface to reduce total pressure loss and further throttle the primary flow. Implications for application of this active flow control technology to a variable area turbine are considered.

A three-dimensional numerical model of coupled fluid flow and heat transfer in EGS system is investigated. The model considers a single uniform fracture surrounded by a three dimensional low permeable rock matrix. The flow is imposed on a fracture plane, consisting of a doublet system. The primary objectives of this paper are to analyze the effects of injection temperature and mass flow rates on heat extraction performances. The study results showed that for lower injection temperature heat extraction rates from the reservoir are higher. In case of higher injection mass flow rate, energy output increased significantly. However, after thermal breakthrough the energy output drops are seen faster in comparison of lower mass injection case. The faster energy drop with the time are result of the slower heat conduction inside the low permeable rock matrix perpendicular to the fracture. The present model neglected the fracture aperture evolution even though transmissivity reduction is observed. The transmissivity reduction is the results of flow resistance. The flow resistance inside the fracture is increased due to the non-laminar flow and cooling. The combined effect leads to rise the flow impendence of the reservoir. These effects are more for the higher mass at the lower injection temperature.

The flow characteristics of homogeneous gases in complex systems are an important issue in many areas, including underground mines. The flow in mine excavations and ventilation systems is described by known mathematical relationships that could be applied to various cases. In this paper, a flow in a duct with a local sink of mass and momentum for multiple variants of cooperation of a mechanical fan was analyzed. The relationships for the total and static pressure of air in the duct were derived. In the next stage, a calculation example of how the mass flow rate of air, and the total and static pressure of the flowing air will change in the tested sections for the duct with and without a sink, is presented. The derived formulas and calculated values for the considered calculation case allow the verification of the obtained relationships at the measurement station. Analyzing the results of the examples presented in the article, it can be concluded that the total and static pressure at the sink point differ depending on the equation of motion used. In the case of the classic equation, the value of total pressure is lower than the value calculated from the new equation of motion, and the difference between them is about 20 Pa. In the case of static pressure, this difference is about 46 Pa. Qualitative differences in the static pressure distribution at the release location were also demonstrated. Depending on the applied approach, positive or negative changes in the static pressure are noticed. The presented form of the equation of motion made it possible to determine the flow characteristics in the duct with a point mass and momentum sink in the case of the operation with and without a fan.

BackgroundPlantar pressure analysis is widely used in the study of knee osteoarthritis (KOA). The present study aimed to investigate the static and dynamic plantar pressure distribution in patients with different stages of unilateral KOA using the Footscan® platform system.Material/MethodsWe recruited 94 patients aged 61.75±7.23 years old with different stages of unilateral KOA for static and dynamic analysis using the Footscan® platform system. The static pressure (%) of the left, right, anterior, posterior, and the pelvic rotation (°) was assessed. The peak pressure (PP, kPa) was investigated in 10 areas of the foot: medial heel (MH), lateral heel (LH), midfoot (MF), first to fifth metatarsals (M1–M5), hallux (T1), and toes 2–5 (T2–5). The correlation between KOA stages and plantar pressure distributions was investigated.ResultsThe results revealed that static pressure on the unaffected side and pelvic rotation were positively correlated with KOA stages. In addition, there was a positive correlation between KOA stages and PP of M5, MF, and LH zones on the affected side and PP of M2, M3, and M4 zones on the unaffected side, and a negative correlation between KOA stages and PP of T1 and T2–5 zones on the affected side.ConclusionsWith the progression of KOA, static plantar pressure tends to distributed on the unaffected side, and the dynamic plantar pressure tends to be distributed laterally on both feet. The plantar pressure distributions in unilateral KOA patients are abnormal and are closely related to the severity of KOA.

Numerical simulations are performed to characterize the secondary injection thrust vector control. For this objective the following measurements were taken: considering the flow to be compressible and turbulent using Realizable k-ε turbulence model accompanied by enhanced wall treatment, the comparison between the CFD results and the experimental results shows a very good agreement. Then a parametric study on injection mass flow rate (changing secondary stagnation pressure) with the same injection location and injection angle is done. The results stated that increasing the injectant mass flow rate lead to shock impingement from opposite wall at secondary stagnation pressure 1.4 of the primary stagnation pressure.

For an asymmetric scroll compressor for heat pump application, a numerical simulation was carried out to investigate the effects of injection port design on the compressor's performance under gas injection. To validate the simulation, the numerical results were compared with experimental results obtained from a scroll compressor with a base injection port design. There was good agreement between simulation and experimental results, with around a 1% difference in the injection mass flow rate when the injection pressure was below <TEX>$12kgf/cm^2A$</TEX> for the heating mode. Various injection port angular positions were numerically tested to yield better injection performance. The largest improvement in heating capacity was obtained at angles of <TEX>$240^{\circ}$</TEX> and <TEX>$200^{\circ}$</TEX> inward from the scroll wrap end angle for low-temperature and standard heating conditions, respectively, while the maximum COP improvement was at <TEX>$365^{\circ}$</TEX> and <TEX>$280^{\circ}$</TEX>, respectively. A considerable improvement in cooling capacity was also found at the injection port angle of <TEX>$240^{\circ}$</TEX>.