Static Pressure Distribution Research Articles

Formation mechanism of static pressure circumferential double-peak distribution in a centrifugal compressor under the action of downstream boundary

In the centrifugal compressor applied in the automobile turbochargers, the asymmetric structure of volute causes the non-uniform flow field in the impeller and compressor stall. The non-uniformity of the flow field in the compressor can be reflected by the casing-wall static pressure distribution. In this study, by removing the volute and directly imposing different simplified static pressure boundary conditions at the diffuser outlet, the formation mechanism of casing-wall static pressure circumferential double-peak distribution of the compressor is explored. It is found that the mass flow rate is redistributed at the impeller outlet due to local high static pressure induced by the volute tongue, which results in the formation of two airflow regions with high velocity in the diffuser, ultimately leading to the static pressure circumferential double-peak distribution in the diffuser and the impeller. Noted that because of the existence of the blades, the airflow regions with high and low velocity formed in the diffuser are locked within a limited range of one or more widths of the blade passage. When the number of blades in the compressor is large, the static pressure can appear as multi-peak distribution in the circumferential direction. Moreover, the result of the mass flow rate redistribution at the impeller outlet is determined by the static pressure distribution characteristics at the diffuser outlet.

Aerodynamic performance of profiled endwalls with upstream slot purge flow in a linear turbine cascade having pressure side separation

In aeroengines, purge flow directly fed from the compressor (which bypasses the combustor) is introduced through the disk space between blade rows to prevent the hot ingress. Higher quantity of purge gas fed through the wheel space can provide additional thermal protection to the passage endwall and blade surfaces. However, the interaction of purge flow with the mainstream flow leads to higher secondary losses. Secondary losses inside a turbine blade passage can be reduced effectively by endwall contouring. This paper presents computational investigation on the influence of non-axisymmetric endwall contouring over endwall secondary flow modification in the presence of purge flow with the pressure side bubble (PSB). The experimental analysis was conducted for the base case without purge and base case with purge (BCP) configurations having flat endwalls. The total pressure loss coefficient and exit yaw angle deviation were measured with the help of a five-hole pressure probe. Static pressure distribution over the blade midspan was obtained by 16 channel Scanivalve. Aerodynamic performances of three different profiled endwalls are numerically analyzed and are compared against the BCP configuration. The effects of different contoured endwall geometries on endwall static pressure distribution and secondary kinetic energy were also discussed. Analysis shows that in the first contoured endwall configuration (EC1), the formation of stagnation zones at a contour valley close to the suction surface causes the exit total pressure loss coefficient to increase. The shifting of the contour valley near to the pressure surface (EC2 configuration) has resulted in local acceleration of the diverted pressure side leg of the horseshoe vortex over the hump toward the end of the passage. In the third configuration (EC3 configuration), reduced valley depth and optimum hump height have effectively redistributed the endwall pitchwise pressure gradient. The increased static pressure coefficient at the endwall near to the pressure surface has eliminated the PSB formation. In addition, computational results of unsteady Reynolds averaged Navier–Stokes simulations are obtained for analyzing transient behavior of PSB, with more emphasis on its migration on the pressure surface and transport across the blade passage. The additional work done by the mainstream fluid to transport the low momentum PSB fluid has caused higher aerodynamic penalty at the blade exit region. In this viewpoint, the implementation of contoured endwalls has shown beneficial effects by eliminating the PSB and related secondary vortices. At 27% of axial chord downstream of the blade trailing edge, a 4.1% reduction in the total pressure loss coefficient was achieved with endwall contouring.

Design for New Type Centrifugal Fan and Passageway of the Air Conditioner Indoor Unit

This paper introduces a design flow for the low-speed high-efficient centrifugal impeller applicable to the new type indoor hanging unit, with the matching inlet collector and non-uniform outlet diffusion passageway being also designed. Under the influence of the inlet collector, the attack angle deviation and air intake distortion occur to the centrifugal impeller. While the unsteady pressure fluctuation generated by the non-uniform diffusion passageway can also affect the flow in the passage of the upstream blades. The preliminary design and optimization of the above three parts are described in this paper based on the needs of overall design, the outlet flow rate is also increased by adjusting the static pressure distribution in the inside centrifugal impeller, consequently the flow separation generated by the guide blade in the diffusion passage is improved and the outlet uniformity of the diffuser is enhanced. Finally, the feasibility analysis for the overall design is performed in this paper, to ensure the design requirements can be met.

Simulating Turbulent Air Flow Past a Hemispherical Body

ABSTRACT The flow of air past a smooth surface-mounted hemisphere is investigated numerically using six common RANS turbulence models and seeking steady flow solutions. Where possible, the turbulence models are applied using standard wall functions, resolving the viscous sublayer, and the enhanced wall treatment option in ANSYS Fluent. Results of the simulations are compared against measurements taken in a wind tunnel experiment. The comparison shows that enhanced wall treatment and resolving the boundary layer on a low Reynolds number mesh yields superior accuracy compared to standard wall functions or resolving the boundary layer on a high Reynolds number mesh, for all the turbulence models considered. The RNG k - ε model with enhanced wall treatment applied is found to yield the most accurate prediction of the static pressure distribution across the surface of the hemisphere model. Conversely, the Reynolds Stress model and the standard k - ω model are found to give the least accurate predictions, irrespective of the near-wall modelling approach applied. It is found that good agreement with the experimental data for this case offlows can be attained using each of the near-wall modelling techniques if a well-suited turbulence model is used. Keywords: hemisphere, wind tunnel, turbulence modelling, computational fluid dynamics, steady flow

Experimental Study of Twin Connected Pipe Jets

Two parallel pipe jets of 20 mm diameter were placed 1.2 mm diameter apart and were connected by a 4 mm wide channel all along the central plane of the jets. The mean velocity flow field of the jets was investigated for three Reynolds number 16300, 34400 and 49200. The Reynolds number was based on the exit velocity of the jets and jet diameter. The experiment was performed in an air jet facility and yaw meter was used for measurement of mean velocity and its direction. Their variations along the longitudinal, transverse, and lateral directions have been analyzed. A significant change of the jet flow field is observed near the exit of the jet. The combined effect of the jets diminishes the presence of recirculation region at the immediate exit rather enhances the energy and momentum transfer between their individual flow fields. Static pressure and kinetic energy distribution are also studied and a momentous variations have been noticed with varying Reynolds number.

Experimental Study of Twin Connected Pipe Jets

Two parallel pipe jets of 20 mm diameter were placed 1.2 mm diameter apart and were connected by a 4 mm wide channel all along the central plane of the jets. The mean velocity flow field of the jets was investigated for three Reynolds number 16300, 34400 and 49200. The Reynolds number was based on the exit velocity of the jets and jet diameter. The experiment was performed in an air jet facility and yaw meter was used for measurement of mean velocity and its direction. Their variations along the longitudinal, transverse, and lateral directions have been analyzed. A significant change of the jet flow field is observed near the exit of the jet. The combined effect of the jets diminishes the presence of recirculation region at the immediate exit rather enhances the energy and momentum transfer between their individual flow fields. Static pressure and kinetic energy distribution are also studied and a momentous variations have been noticed with varying Reynolds number.

Flow physics of highly loaded tandem compressor cascade with non-axisymmetric endwall profiling

Tandem configuration is an effective methodology to reduce flow separation on compressor blade suction surface and to improve blade loading. However, in modern highly loaded cases, corner separation remains as its single blade counterpart. In this study, non-axisymmetric endwall profiling (NAEP) was utilized in a highly loaded tandem cascade (diffusion factor D = 0.69), aiming at reducing its severe corner separation and revealing the unique flow mechanism while NAEP is utilized in tandem cascade. NAEP was designed in both forward (F) blade and rare (R) blade separately, and was investigated numerically in tandem environment. Results show that, NAEP in F blade passage can effectively eliminate the corner separation and reduce loss generation, whereas NAEP in R blade passage has no positive effect on corner separation and even promotes loss production. The optimal NAEP approximately removes the corner separation completely, with loss coefficient reducing by as much as 37.8%. The optimal NAEP for the tandem cascade features optimal axial location at the origin of corner separation. There is an optimal NAEP height (0.02 of blade height), under which NAEP can achieve pretty good control effect while the peak of NAEP varies in a large axial location range. In the tandem configuration, it is found that NAEP transfers blade loading from R blade to F blade; the static pressure increases significantly for the entire cascade, but the static pressure distribution of F blade does not exhibit as the design intent of NAEP. In addition, it is interesting to find that the flow turning near endwall reduces after endwall profiling, which is unique in tandem cascade and is contrast to the view on conventional configuration. On the contrary, NAEP in R blade has no influence on the corner separation of the tandem cascade; due to the decrement of cross-passage pressure gradient for R blade, the flow overturning near endwall reduces.

Review on the aerodynamics of intermediate compressor duct

In a turbofan engine, the air is brought from the low to the high-pressure compressor through an intermediate compressor duct. Weight and design space limitations impel to its design as an S-shaped. Despite it, the intermediate duct has to guide the flow carefully to the high-pressure compressor without disturbances and flow separations hence, flow analysis within the duct has been attractive to the researchers ever since its inception. Consequently, a number of researchers and experimentalists from the aerospace industry could not keep themselves away from this research. Further demand for increasing by-pass ratio will change the shape and weight of the duct that uplift encourages them to continue research in this field. Innumerable studies related to S-shaped duct have proven that its performance depends on many factors like curvature, upstream compressor’s vortices, swirl, insertion of struts, geometrical aspects, Mach number and many more. The application of flow control devices, wall shape optimization techniques, and integrated concepts lead a better system performance and shorten the duct length. This review paper is an endeavor to encapsulate all the above aspects and finally, it can be concluded that the intermediate duct is a key component to keep the overall weight and specific fuel consumption low. The shape and curvature of the duct significantly affect the pressure distortion. The wall static pressure distribution along the inner wall significantly higher than that of the outer wall. Duct pressure loss enhances with the aggressive design of duct, incursion of struts, thick inlet boundary layer and higher swirl at the inlet. Thus, one should focus on research areas for better aerodynamic effects of the above parameters which give duct design with optimum pressure loss and non-uniformity within the duct.

Influence of the relative momentum flux ratio on the mixing of hydrogen jets in an M=4 crossflow

The paper presents the results of numerical simulation of the 3D flows in a plane channel with the abrupt expansion. Sonic hydrogen jets are supplied from two circle orifices located opposite each other on the channel walls before the backward-facing step. The numerical simulations are carried out under the conditions of experiments performed at the hot-shot wind tunnel IT-302M ITAM SB RAS for the following flow parameters: Mach number at the entrance of the channel M = 3.84, the total temperature T0 = 1715 K, and the total pressure P0 = 6.5 MPa. Calculations were performed with a change in the jet supply pressure from 0.4 to 3.6 MPa, which ensures the variation in the jet-to-crossflow momentum flux ratio in the range of J = 0.7 ÷ 6. Mathematical modeling was performed in ANSYS Fluent based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k-ω SST turbulence model. A comparison of the calculated and experimental data on the flow structure, as well as the static pressure distributions on the walls, indicates a satisfactory agreement. The calculated results made it possible to obtain a clearer understanding of the 3D flow structure in the channel and reveal the influence of the injection pressure on the level of mixing.

Experimental and numerical investigation of expansion corner effects on isolator performance

Abstract In the present study, the effect of expansion corner on suddenly expanded flow process has been studied. Experimental investigations have been carried out on a convergent-divergent (C-D) nozzle and isolator duct, where the expansion of the channel is formed through the presence of a 1, 2 and 3 expansion corners (EC) respectively. Flow from nozzle exit of the nozzle of Mach, M = 2.0 was suddenly expanded into the axi-symmetric duct having a cross sectional area of 4.84 times the nozzle exit area. The wall static pressure along the length of the duct and the Pitot pressure at the exit plane of the duct were measured for all the configurations. Computational fluid dynamics (CFD) technique was employed for visualizing the shock-train in the expanded duct. The isolator with one expansion corner was found to be more efficient in achieving a high static pressure rise. The experimental and numerical wall static pressure distribution values were compared for isolators with EC = 2 and found to be in good agreement with each other with a maximum absolute percentage deviation of 11%.

Experimental and numerical investigation of expansion corner effects on isolator performance

Abstract In the present study, the effect of expansion corner on suddenly expanded flow process has been studied. Experimental investigations have been carried out on a convergent-divergent (C-D) nozzle and isolator duct, where the expansion of the channel is formed through the presence of a 1, 2 and 3 expansion corners (EC) respectively. Flow from nozzle exit of the nozzle of Mach, M = 2.0 was suddenly expanded into the axi-symmetric duct having a cross sectional area of 4.84 times the nozzle exit area. The wall static pressure along the length of the duct and the Pitot pressure at the exit plane of the duct were measured for all the configurations. Computational fluid dynamics (CFD) technique was employed for visualizing the shock-train in the expanded duct. The isolator with one expansion corner was found to be more efficient in achieving a high static pressure rise. The experimental and numerical wall static pressure distribution values were compared for isolators with EC = 2 and found to be in good agreement with each other with a maximum absolute percentage deviation of 11%.

CFD modelling of physical velocity and anisotropic resistance components in a peaked stored grain with aeration ducting systems

Modelling airflow in large stored grain silos has been dealt with superficial velocities and with uniform airflow resistance across the bulk. However, superficial velocities are always lower than physical velocities in an isotropic medium. Besides, due to varying grain properties, there is a high potential of variation in airflow resistances along the vertical and horizontal directions.Thus, a 3D CFD model was developed considering physical velocity in an anisotropic porous media to predict airflow and static pressure distribution from a V-shaped aeration floor. Varying airflow resistances along the horizontal direction of an element were incorporated into the model to account for the variation in grain properties. Mesh independency tests were conducted for achieving numerical stability during the steady-state simulation. The model was validated using the static pressure taps and airflow data measured in an on-farm grain storage silo.A 0.35 m mesh size was optimized using the static pressure and airflow data in the silo model. Least error for static pressure and airflow predictions were observed when horizontal airflow resistance was 50% of the vertical airflow resistance. Furthermore, the model predicted that 14.3% of the total grain volume exhibited a low airflow rate below the recommended value of 2 L s−1 t−1 including a significant proportion of the top grain volume above the eave height. Due to 85% of the non-perforated section on the silo floor, 12.6% of the lower grain volume up to a maximum height of 4.4 m above the floor exhibited the low airflow regime. As physical experimentations are tedious, the proposed physical velocity based model could be extended for simulating different options for minimizing dead zone proportions for better grain storage management.

Numerical analysis of the effects of gas-phase properties on the internal characteristics and wear in a centrifugal pump

Centrifugal pumps are indispensable in aquaculture engineering. The existence of bubbles is inevitable in a centrifugal pump and may affect the performance of the pump which delivers solid-liquid two-phase flow. Thus, this study aims to analyze the effects of gas-phase properties on the internal characteristics of a centrifugal pump by using a computational fluid dynamic code based on Eulerian multiphase mode and a standard k–ε two-equation turbulence model. Results show that gas-phase properties, such as concentration and diameter, affect the absolute pressure and the phase distribution in the centrifugal pump. The gas-phase distribution on the working faces of blades is greater than forces on the back face of the blades. The larger the diameter of the gas-phase is, the easier it is to be concentrated; Thus, the working face of the blades is prone to cavitation and corrosion, and with the increase of the bubble size, the cavitation corrosion of the back surface of the impeller becomes more serious. The solid-phase velocity and static pressure distribution increase with increasing concentration or diameter of gas-phase. The solid-phase is more easily leave the impeller area and enter the volute because of the existence of gas-phase, which may lead to abrasion of volute. The existence of gas makes the solid velocity distribution in the centrifugal pump more uneven, which may cause uneven wear of the centrifugal pump. The obtained results by this method can reveal the effects of gas-phase properties and wear on the internal characteristics in centrifugal pumps and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.

Investigation of combustion modes and pressure of reflective shuttling detonation combustor

Detonation combustors are considered promising alternatives to conventional combustors because they offer high thermal efficiency and fast combustion. However, especially for the rotating detonation combustor, the theoretical propulsive performance has not been confirmed in experimental studies because the highly unsteady flow field hinders the measurements process. To understand the involved phenomena in more detail, a reflective shuttling detonation combustor (RSDC) with a rectangular combustion chamber was developed. The interior of the chamber can easily be visualized owing to its two-dimensional quality. Utilizing the RSDC, several combustion tests with gaseous ethylene and oxygen were conducted for different values of mass flow rates and equivalence ratios. Combustion modes from the tests were classified into four types based on the fast Fourier transform (FFT) analysis of the luminous intensity of the CH* self-luminescence images captured by a high-speed camera and a band pass filter. Simultaneously, the theoretical total pressure of a conventional isobaric combustor was compared to the static pressure measured at the bottom of the RSDC chamber. For the detonation modes, the ratio between experimentally measured static pressure and the theoretical pressure varied depending on the location in the chamber owing to the distribution of the time-averaged static pressure. Furthermore, the pressure ratio of the detonation modes was up to 18% lower than that of the deflagration mode potentially owing to the flow velocity induced by the detonation waves.

Numerical and analytical predictions of nuclear steam generator secondary side flow field during blowdown due to a feedwater line break

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

Numerical investigation of wet inflow in steam turbine cascades using NURBS-based mesh generation method

In this paper, the impact of existence of wetness in the inflow of stationary cascades of steam turbine blades has been numerically investigated. A new mesh generation method based on non-uniform rational B-splines (NURBS) has been adopted to reduce the numerical error of the wet inflow simulation. Moreover, two common meshing scenarios namely blade-to-blade (BB) and periodic-to-periodic boundary (PP) are studied and different angle of the grid at the trailing edge have been considered. The classical nucleation theory corrected by Courtney–Kantrowitz model and the Young's droplet growth model are employed to simulate the condensation phenomenon. By validating against experimental data, the results showed that implementing the proposed NURBS-based meshing technique decreased the prediction errors of static pressure distribution and droplet average radius by 35.64% and 78.44%, respectively, in comparison to typical grid generation methods. In addition, it was observed that existence of wetness at inlet significantly decreased the supercooling degree and postponed the nucleation process. Thus, the nucleation rate could be ameliorated in the case when we have a specific amount of wetness fraction in the inflow.

Avaliação do sistema operacional de uma unidade armazenadora de silos secadores e a qualidade de grãos de arroz

A garantia da padronização e qualidade dos grãos de arroz se devem às boas práticas de pós-colheita. Assim, o objetivo do trabalho foi avaliar o desempenho operacional e a qualidade de grãos de arroz armazenados em silos secadores. O trabalho foi realizado numa unidade armazenadora composta por cinco silos secadores. Na primeira etapa, foram armazenados grãos de arroz em casca, com diferentes massas e alturas, analisando a movimentação de ar e a temperatura. Na sequência, avaliou-se a movimentação do ar no interior da massa de grãos para diferentes processos de peneiramento. Logo, realizou-se a coleta das amostras de arroz em onze diferentes pontos, para análise física dos grãos. Assim, as variações das alturas e a forma de processamento da massa de grãos influenciaram na pressão estática e no desempenho silos secador, reduzindo a capacidade de trabalho e interferindo na qualidade dos grãos. A eficiência da secagem dos grãos de arroz foi inversamente proporcional ao aumento da pressão estática, evidenciando secagem incompleta nas camadas superiores. A operação de peneiramento contribuiu na redução de impurezas e melhorou a distribuição da pressão estática das camadas de grãos, favorecendo a movimentação do ar. Os lotes de grãos de arroz não repeneirados apresentaram a formação de corredores de passagem de ar, prejudicando a secagem e a qualidade dos grãos. Concluiu-se, para que o sistema silo secador tenha eficiência operacional é fundamental homogeneizar os teores de água dos grãos, eliminar totalmente as impurezas e matérias estranhas através de rotinas de peneiramento.

Numerical simulation on structural dynamics of 5 MW wind turbine

Considering the rigid-flexible coupling system of 5 MW wind turbine, the static pressure, fluid temperature, Mach number, vorticity, shear stress and velocity distribution of tower flange are obtained under the combined action of wind shear and fluctuating wind. The dynamic response of rigid-flexible coupling structure is studied by the combined action of the whole vibration and local vibration of 5 MW wind turbine. Through the analysis of dynamic parameter change curve, the improvement measures of tower structure are put forward, and the dynamic response of the structure before and after improvement is compared. The superiority of the improved structure is expounded, so as to provide reference basis for engineering application.

Experimental study on the effects of diversion device on pulse-jet cleaning of horizontal filter cartridge

In recent years, horizontal cartridge filters have developed rapidly and been gradually used in the industrial production. However, most existing studies are focused on the vertical dust collectors, and there are few studies on the effect of diversion device type on the cleaning performance of horizontal filter cartridge. Therefore, in order to investigate the influence of this important factor on the peak static pressure of this filter cartridge, three typical diversion nozzles were used to the experiment. This study examined the peak static pressure distribution along the surface of the filter cartridge during the pulse-jet cleaning process. The results showed as follows: among these three types of diversion nozzles, the rotating nozzle has the smallest size and the best uniformity of peak static pressure, but the peak static pressure was too low due to the energy consumption by rotation. For venturi, although the cleaning requirements can be guaranteed, the excessive pressure of the filter cartridge bottom can easily cause partial damage. Compared with these two, the diffuser nozzle can ensure excellent cleaning performance and make a smaller space occupation of horizontal cartridge filters. In general, it is suggested to select the diffuser nozzle for horizontal cartridge filter.

Supersonic flow in the rectangular duct of an air inlet with the separation-induced interaction of the boundary layer with shock waves

Results of a numerical study of the flow structure in the rectangular duct of a model air inlet with the interaction of the shock wave generated by the inlet cowl with the turbulent boundary layer on the inner duct surfaces are reported. A configuration involving a convergent entrance section and a constant-cross-section throat was analyzed. The numerical simulation of the three-dimensional flow with free-stream Mach number M = 4 was performed on the basis of the Reynolds-averaged Navier-Stokes equations and the k-ω SST model of turbulence. As a result of the calculations, the limit streamlines and the distributions of static pressure on the duct surfaces, as well as the distributions of total pressure and the fields of Mach number in duct cross sections were obtained. The structure of the flow is analyzed and the possibility of occurrence of longitudinal vortex structures in the corner region of the intake-duct throat is shown.