Pipe Diffuser Research Articles

Passive flow control at impeller radial bend for stall delay in centrifugal compressors with fishtail pipe diffusers

This paper proposes a new strategy for extending centrifugal compressor stall margin through shroud passive flow control placed at the impeller radial bend. Relative to the usual leading-edge location, the radial bend presents fewer geometrical constraints for flow control devices and allows them to have potentially more impact on low-momentum flow structures that lead to stall. Two centrifugal compressors with fishtail pipe diffusers are chosen for study: a high-speed transonic design exhibiting diffuser stall and a low-subsonic design with exducer stall. Four passive flow control techniques placed on the impeller shroud at the radial bend are evaluated for each compressor, in terms of stall margin improvement and efficiency penalty at design mass flow, using unsteady RANS CFD simulations. These are circumferential groove, slots, impeller recirculation pipe and diffuser-impeller recirculation pipe. The results indicate that passive flow control at the impeller shroud radial bend can be significantly more effective than at the impeller leading edge. For each compressor, the flow mechanisms associated with stall initiation and its delay by the most effective studied flow control technique as well as the associated efficiency penalty are elucidated. The findings indicate that techniques having flow injection with high spanwise penetration and low relative streamwise momentum are most effective for delaying diffuser stall, while the opposite applies to exducer stall. The design point efficiency penalty is due to mixing/shear losses from the jet-in-cross flow phenomenon in the impeller and shear losses from flow redistribution in the diffuser.

The investigation of mechanisms on pipe diffuser leading edge vortex generation and development in centrifugal compressor

Pipe diffuser can adapt the high Mach number distorted flow in high pressure ratio centrifugal compressors because of its special scallop leading edge. However, the special leading edge could generate pair vortices and it is not clear if the pair vortices have positive or negative effect on pipe diffuser performance. Besides, the generation and development of pair vortices are also need to be investigated. This work is aimed at uncovering the influence of vortices on aerodynamic loss in pipe diffuser. Pipe diffusers with several different geometries are designed for a high pressure ratio centrifugal compressor used in a small gas turbine. The generation and evolution of pair vortices in pipe diffuser passages are studied by validated state-of-the-art CFD method. Detailed understandings of the influence of different geometries on pair vortices and pipe diffuser performance are provided. Through these works, it is found that the pair vortices could enhance the flow mixing of high and low energy flow in pipe diffuser passage near throat, thus the boundary layer becomes thin, and the flow separation is suppressed near pipe diffuser throat under large negative incidence. However, pair vortices also move low momentum flow to the pressure side and induced separation in pipe diffuser cone after throat, eventually. The diffuser inlet-to-impeller exit radius ratio and diffuser cross section shape could affect the compressor performance by changing the intensity of pair vortices. The diffuser with inlet-to-impeller exit radius ratio 1.02 and the pipe diffuser with the cross section with big fillets such as 3.37 mm are recommended for their good performance. The diffuser throat area and passage count can also have impact on pair vortices, but the compressor performance is not only influenced by pair vortices when these two parameters are changed.

Numerical investigation of the diffuser throat length effect on a transonic centrifugal compressor

Vaned diffuser inlet flow uniform is challenging when the impeller is throttled to stall. In this study, we extend the stable operating range of the compressor by improving the uniform flow of the diffuser inlet. First, a numerical investigation of a transonic centrifugal compressor with a vaned diffuser is presented and compared against test data. Then, a new diffuser parameterization method is pro- posed, and the throat feature of a pipe diffuser is successfully applied to parameterized vane diffusers. The influence of the throat length and divergence angle of the diffuser on the performance of the centrifugal compressor is studied via steady and non-linear harmonic simulations. Throat length delays the time of fluid pressurization and accommodates large flow instabilities from upstream—this widens the stall margin but increases mixing loss. Divergence angle affects compressor performance. Stage peak efficiency increases by about 0.58% as the divergence angle increases from 3.79° to 5.79° but drops to about 2.46% as the divergence angle further increases from 5.79° to 11.79°. This is because the boundary layers in the diffuser channel thicken with increasing divergence angle; additionally, the fluid near the hub-pressure side first becomes unstable, then flow separation occurs along the flow direction, which results in a large flow loss. Detailed performance maps of centrifugal compressors with different throat lengths and divergence angles are given to provide a reference for designing transonic centrifugal compressors.

Impacts of the Marine Hatchery Built Environment, Water and Feed on Mucosal Microbiome Colonization Across Ontogeny in Yellowtail Kingfish, Seriola lalandi.

The fish gut microbiome is impacted by a number of biological and environmental factors including fish feed formulations. Unlike mammals, vertical microbiome transmission is largely absent in fish and thus little is known about how the gut microbiome is initially colonized during hatchery rearing nor the stability throughout growout stages. Here we investigate how various microbial-rich surfaces from the built environment “BE” and feed influence the development of the mucosal microbiome (gill, skin, and digesta) of an economically important marine fish, yellowtail kingfish, Seriola lalandi, over time. For the first experiment, we sampled gill and skin microbiomes from 36 fish reared in three tank conditions, and demonstrate that the gill is more influenced by the surrounding environment than the skin. In a second experiment, fish mucous (gill, skin, and digesta), the BE (tank side, water, inlet pipe, airstones, and air diffusers) and feed were sampled from indoor reared fish at three ages (43, 137, and 430 dph; n = 12 per age). At 430 dph, 20 additional fish were sampled from an outdoor ocean net pen. A total of 304 samples were processed for 16S rRNA gene sequencing. Gill and skin alpha diversity increased while gut diversity decreased with age. Diversity was much lower in fish from the ocean net pen compared to indoor fish. The gill and skin are most influenced by the BE early in development, with aeration equipment having more impact in later ages, while the gut “allochthonous” microbiome becomes increasingly differentiated from the environment over time. Feed had a relatively low impact on driving microbial communities. Our findings suggest that S. lalandi mucosal microbiomes are differentially influenced by the BE with a high turnover and rapid succession occurring in the gill and skin while the gut microbiome is more stable. We demonstrate how individual components of a hatchery system, especially aeration equipment, may contribute directly to microbiome development in a marine fish. In addition, results demonstrate how early life (larval) exposure to biofouling in the rearing environment may influence fish microbiome development which is important for animal health and aquaculture production.

Advances in Centrifugal Compressors

In the case where flow passes through a straight pipe to enter a centrifugal compressor the flow is straight, uniform and has no vorticity, ie swirling motion, so the swirl angle α1 = 0° as illustrated. As the flow passes through the centrifugal impeller, the impeller forces the flow to spin faster as it gets further from the rotational axis. According to a form of Euler's fluid dynamics equation, known as the pump and turbine equation, the energy input to the fluid is proportional to the flow's local spinning velocity multiplied by the local impeller tangential velocity. In many cases, the flow leaving the centrifugal impeller is travelling near the speed of sound. It then flows through a stationary compressor causing it to decelerate. The stationary compressor is ducting with increasing flow-area where energy transformation takes place. If the flow has to be turned in a rearward direction to enter the next part of the machine, e.g. another impeller or a combustor, flow losses can be reduced by directing the flow with stationary turning vanes or individual turning pipes (pipe diffusers). As described in Bernoulli's principle, the reduction in velocity causes the pressure to rise.

High-pressure ratio centrifugal compressor with two different fishtail pipe diffuser configurations

To improve fishtail pipe diffuser outflow uniformity, deswirlers and splitters are added inside and after fishtail pipe diffuser passages for a compact centrifugal compressor. The influence of clocking effects between the deswirler and fishtail pipe diffuser passage is first studied to find the optimum clocking position. The performances of these two configurations are then compared, and their loss mechanisms are determined. Finally, the compressor exit flow conditions are estimated. Either adding the deswirler after the fishtail passages or adding splitters inside the fishtail passages tends to degrade the compressor performance. The intensity of the vortices in the fishtail passages is increased; therefore, losses are induced when a deswirler is added after the fishtail passage. As splitters are added inside the fishtail passages, flow separation is observed at the splitter suction side near the hub as a result of the large incidence angle near the splitter hub and results in large losses. Adding a deswirler after fishtail passages has a negative effect on the compressor outlet flow uniformity but can eliminate the residual swirl angle. Adding splitters in fishtail diffuser passages is recommended to decrease the compressor outlet non-uniformity and residual swirl angle. Through this work, physical insight into complex flows in these two configurations is obtained to provide guidelines on a diffusing system design with a fishtail pipe diffuser.

Improving energy efficiency and fouling mitigation for membrane bioreactor in Al-Rustamiyah sewage treatment plant based on hydrodynamics

In Al-Rustamiyah sewage treatment plant in the east of Baghdad city, capital of Iraq, the membrane bioreactor suffering from a severe biofouling problem. The main reason for this problem is inefficient and inadequate aeration process. The objective of this work is to control fouling and to improve the energy efficiency of the submerged membrane bioreactor. Fouling control is achieved by optimizing the two-phase hydrodynamic parameters (air bubble diameter and shear stress), while energy efficiency improved through analysis of flow field. An experimental rig similar to real plant was built, and several operating and design parameters were experimentally tested. The parameters were air flow rate (1–9 L/min), membrane sheets spacing (3, 5, and 7 mm), and air diffuser design (pipe diffuser and disk diffuser). The bubble sizes were measured experimentally using high-speed camera. It was found that larger bubbles were produced at narrow channels between the membrane sheets. Optimization using computational fluid dynamic with ANSYS FLUENT was employed; the results showed that a bubble diameter of 2.5 mm had a slug flow pattern, resulting in better energy saving for a 3 mm space between membrane sheets with a 5 L/min air flow, while maximum shear stress obtained was (4 Pa). Nutrients removal results from synthetic sewage were 97.32, 79.68, and 13% for COD, NH3–N, and PO 4 −3 , respectively, at 6 days retention time. The results obtained are quite significant in practice because it contributes to improve the efficiency of membrane bioreactor in Al-Rustamiyah sewage treatment plant.

Investigation of a High Pressure Ratio Centrifugal Compressor with Wedge Diffuser and Pipe Diffuser

Abstract This present work is aimed at providing detailed understanding of the flow mechanisms in a highly loaded centrifugal compressor with different diffusers. Performance comparison between compressor stages with pipe diffuser and wedge diffuser was conducted by a validated flow solver. Stage with pipe diffuser achieved a better performance above 80 % rotating speed but a worse performance at lower rotating speeds near surge. Four operating points including the design point were analyzed in detail. The inherent diffuser leading edge of pipe diffuser could create a better operating condition for the downstream diffusion, which reduced the possibility of flow separation in discrete passages at design rotating speed. At 60 % rotating speed operating point, there was a large negative incidence angle. The sharp leading edge of pipe diffuser could largely accommodate this negative incidence as comparison of the round leading edge of wedge diffuser. As a result, a better performance was achieved in the pipe diffuser. At 60 % rotating speed near surge, performance of the pipe diffuser dropped below wedge diffuser. Total pressure loss of pipe diffuser exceeded that of the wedge diffuser due to the larger friction loss near wall at throat and ineffective static pressure recovery.

The Effects of Inflow Uncertainties on the Characteristics of Developing Turbulent Flow in Rectangular Pipe and Asymmetric Diffuser

In the current paper nondeterministic computational fluid dynamics (CFD) computations of three-dimensional (3D), developing, and statistically steady turbulent flow through an asymmetric diffuser with moderate adverse pressure gradient are presented. The inflow condition is assumed to be uncertain. The inlet streamwise velocity is supposed to be a stochastic process and described by the Karhunen–Loève (KL) expansion. In addition, the inlet turbulence intensity and turbulent length scale are assumed to be uncertain. The nonintrusive polynomial chaos (NIPC) expansion is used to propagate the inflow uncertainties in the flow field. The developed code is verified using a Monte Carlo (MC) simulation with 1000 Latin Hypercube samples on a planar asymmetric diffuser. A very good agreement is observed between the results of MC and polynomial chaos expansion methods. The verified uncertainty quantification method is then applied to stochastic developing turbulent flow through a 3D asymmetric diffuser. It was observed that the eigenvalues of covariance kernel rapidly decay due to the large correlation lengths and thus a few terms in the truncated KL expansion are used to describe the stochastic inlet velocity. For the KL expansion, the mean and the standard deviation are set to those measured experimentally. The uncertain inlet condition has a significant influence on the numerical results of velocity and turbulence fields specially in the developing region before the shear layers meet. It is concluded that one of the reasons for discrepancies between experimental and deterministic CFD results is the uncertainty in inflow condition. A sensitivity analysis is also performed using the Sobol’ indices and contribution of each uncertain parameter on outputs variance is presented.

Investigation of two pipe diffuser configurations for a compact centrifugal compressor

Diffusers are one of the most important factors determining the centrifugal compressor performance. The present work is aimed at providing a detailed understanding of the underlying flow and loss mechanisms in three different diffusers in a compact centrifugal compressor stage. Experimental and computational studies were conducted for various diffuser configurations, e.g. two pipe diffusers and one wedge diffuser, while keeping the throat in all the three geometries. It was found that both the pipe diffuser configurations had better aerodynamic performance than the original wedge diffuser. Furthermore, the pipe diffuser with a fishtail arrangement exhibited greater performance improvement, but had more distortion outflow than the wedge diffuser and the radial pipe diffuser because of the strong jet and wake structure caused by the fishtail turn. Nevertheless, the fishtail configuration has a smaller discharge swirl angle, which would have a positive impact on the performance of the combustor. As a result, the fishtail pipe diffuser configuration was recommended in compact centrifugal compressors.

Exhaust System for Radial and Axial-Centrifugal Compressor with Pipe Diffuser

Abstract The application of radial and axial-centrifugal compressors in turboprop, turboshaft and turbofan engines may require the construction of small diameters diffuser in order to obtain lower weight and smaller frontal area. Conventional exhaust diffusers typically have large outlet diameters for exit Mach numbers lower than 0,2 and low swirl flow to the combustor, hence the design of channel of the low-diameter diffusers called controlled-contour, fishtail-shaped diffuser or diffusing trumpet is complex. The cross-sectional shape of these channels is varied from circular to oval to elliptic and to rectangular. The paper presents an original method for determining the flow parameters in the channel and at the outlet section of the downstream diffusing trumpet for a pipe diffuser, which constitutes the downstream duct of the radial or axial-centrifugal compressor with the pipe diffuser. It also illustrates a new method for determining the geometrical parameters of the diffuser. Mentioned methods (for conceptual design of a compressor with pipe diffuser) are based on Pythagorean theorem, properties of ellipse, equation of continuity, energy equation, first law of thermodynamics, Euler’s moment of momentum equation, gasdynamics functions and definitions used in theory of turbo-machines.

Pengaruh Aerasi Injeksi Udara terhadap Beberapa Parameter Kualitas Air di Lokasi Budidaya Ikan Waduk Ir. H. Djuanda

Waste of fish farming in floating net are fish feces, urine and undigested feed which is one source of organic matter inputs in Ir. H. Djuanda. Waste organic materials can cause eutrophication of waters. Air injection is one way aeration to increase oxygen to help the process of organic matter decomposition. The purpose of this study was to assess the effect of air injection on some parameters of water quality in fish farming side. This research was conducted at the location of fish farming Ir. H. Djuanda in June-September 2013. Injection of air using a compressor with a pressure of 3 atm as a source of air and perforated pipe at a depth of 3.6 m. Air injection carried out for 8 hours. Observation point vertically at a depth of 3.6 m and horizontally at a distance of -1.5 m (behind the diffuser pipe); 0 (the diffuser pipe); 1.5 m (right and left pipe); +1.5; +3 And +6 m (in front of the pipe diffuser) and a distance of 17 m of pipe which is control. After eight hours of aeration showed that the concentration of organic matter, free carbondioxide, N-NO2 tend to belower in cages aerated but N-NO3 concentration was higher in locations aeration cage than controls cageKeywords: air injection aeration, water quality, fish cage culture, Ir. H. Djuanda Reservoir

Lightweight High-Pressure Ratio Centrifugal Compressor for Vehicles-Investigation of Pipe Diffuser Designs by Means of CFD

Lightweight High-Pressure Ratio Centrifugal Compressor for Vehicles-Investigation of Pipe Diffuser Designs by Means of CFD

Effect of bio-carrier filling rate on oxygen transfer coefficient of different diffusers in MBBR process

This paper mainly discussed the effect of bio-carrier filling rate on the oxygen transfer coefficient of different diffusers in the MBBR process. The results show that bio-carriers could increase the oxygen transfer coefficients of the microporous diffusers both in clean water and in mixed liquor because of the shearing effect that created microbubbles and enhanced microscopic hydrodynamic flow regime of the reactor. Compared to the test without bio-carriers, dosing bio-carriers could increase the oxygen transfer coefficient of microporous membrane diffuser by 10.78% in clean water and 10.17% in mixed liquor. Dosing bio-carriers could increase the oxygen transfer coefficient of the campanulate corundum aerator and perforated pipe more than the microporous membrane diffuser. Compared to the control, dosing bio-carriers could increase the KLa of campanulate corundum aerator and perforated pipe diffuser by almost 13.40 and 17.74% in clean water, and 10.97 and 20.14% in mixed liquor, respectively.

Parametric Studies of Pipe Diffuser on Performance of a Highly Loaded Centrifugal Compressor

Pipe diffusers with several different geometries were designed for a highly loaded centrifugal compressor originally using a wedge diffuser. Parametric studies on the effect of pipe diffuser performance of a highly loaded centrifugal compressor by varying pipe diffuser inlet-to-impeller exit radius ratio, throat length, divergence angle, and throat area on centrifugal compressor performance were performed using a state-of-the-art multiblock flow solver. An optimum design of pipe diffuser was obtained from the parametric study, and the numerical results indicate that this pipe diffuser has remarkable advantageous effects on the compressor performance. Furthermore, a detailed comparison of flow visualization between the pipe diffuser and the wedge diffuser was conducted to identify the physical mechanism that account for the beneficial effects of the pipe diffuser on the performance and stability of the compressor. It was found that the performance enhancement afforded by the pipe diffuser is a result of the unique diffuse inlet flow pattern. Alleviating flow distortion in the diffuser inlet and reducing the possibility of a flow separation in discrete passages are the physical mechanisms responsible for improving the highly loaded centrifugal compressor performance.

Pipe Diffuser for Radial and Axial-centrifugal Compressor

This paper presents an original method for calculation of geometric parameters of the pipe diffuser and the proposition of a method for determination of flow parameters at the outlet of the diffuser. Proposed methods may be applied for calculations at compressor conceptual design stage. Results of few experimental tests of the pipe diffuser are also presented.

Numerical Investigation of the Unsteady Flow Inside a Centrifugal Compressor Stage With Pipe Diffuser

The subject of this paper is the investigation of unsteady flow inside a transonic centrifugal compressor stage with a pipe-diffuser by utilizing unsteady 3D Reynolds-averaged Navier–Stokes simulations (unsteady 3D URANS). The computational fluid dynamics (CFD) results obtained are compared with detailed experimental data gathered using various steady and unsteady measurement techniques. The basic phenomena and mechanisms of the complex and highly unsteady flow inside the compressor with a pipe-diffuser are presented and analyzed in detail.

Experimental Investigation of a Truncated Pipe Diffuser With a Tandem Deswirler in a Centrifugal Compressor Stage

The subject of this paper is the experimental investigation of three different geometric configurations of the diffusing system in a high pressure centrifugal compressor stage for a jet engine application. The objective of this study is twofold. On the one hand, it seeks to explain the impact of truncating a diffuser and a redesigned tandem deswirler on the global stage performance; on the other hand, it aims to correlate the performance differences with local flow phenomena. For this purpose, a state-of-the-art centrifugal compressor test rig was used. Particle image velocimetry measurements visualize the separation behavior in the pipe diffuser passage. Thereby it is shown that the truncation of the diffuser changed the boundary conditions for the downstream deswirler including a high incidence. Thus, a new tandem deswirler design was implemented and measured. Moreover, the relative position of the two tandem rows is investigated. An optimal relative circumferential position for the stage efficiency and static pressure rise was found. This paper gives fundamental insight into the physical mechanisms of the influence of three geometric configurations in a centrifugal compressor stage, especially in the pipe diffuser and the deswirler. Hence, this study contributes in furthering knowledge of the fundamental principles of flow phenomena in the diffusing system of a centrifugal compressor.

Effect of friction conditions on change of sheet surface roughness during deep drawing

The application of radial and axial-centrifugal compressors in turboprop, turboshaft and turbofan engines may require the construction of small diameters diffuser in order to obtain lower weight and smaller frontal area. Conventional exhaust diffusers typically have large outlet diameters for exit Mach numbers lower than 0.2 and low swirl flow to the combustor, hence the design of channel of the low-diameter diffusers called controlled-contour, fishtail-shaped diffuser or diffusing trumpet is complex. The cross-sectional shape of these channels is varied from circular to oval to elliptic and to rectangular. The paper presents an original method for determining the flow parameters in the channel and at the outlet section of the downstream diffusing trumpet for a pipe diffuser, which constitutes the downstream duct of the radial or axial-centrifugal compressor with the pipe diffuser. It also illustrates a new method for determining the geometrical parameters of the diffuser. Mentioned methods (for conceptual design of a compressor with pipe diffuser) are based on Pythagorean theorem, properties of ellipse, equation of continuity, energy equation, first law of thermodynamics, Euler’s moment of momentum equation, gasodynamic functions and definitions used in theory of turbo-machines. The final part of the article includes principles of selection of the computational value pressure ratio for the compressor with the pipe diffuser.

Artificial upwelling to stimulate growth of non-toxic algae in a habitat for mussel farming

Large-scale artificial upwelling was tested as a method to enhance the environmental conditions for the growth of non-toxic algae in a Norwegian fjord (61°0′N, 6°22′E). The experiment was designed to evaluate if nutrient-rich seawater, brought up from below the mixed zone of a stratified fjord to the euphotic zone by air bubbling, would stimulate the growth of non-toxic relative to toxic algae. Pumping 44 m3 min−1 of air at 1 atm through a pipe diffuser submerged at 40 m depth formed a buoyancy flux that lifted 60 m3 s−1 of deep water to the upper 17 m over a period of 21 days. The supply of silicate, inorganic nitrogen and phosphate to the upper 10 m in the fjord increased, and a significant increase in the biomass of non-toxic algae was observed. The upwelling gave an increased growth of the non-toxic dinoflagellates Ceratium furca and C. tripos. After termination of the experiment, the phytoplankton biomass decreased significantly, whereas a distinct increase occurred in the relative biomass of the potentially toxic Dinophysis spp. The result is considered promising when it comes to creating controlled geographical areas with non-toxic food for mussel production.