Special features of applying the maximal discharge principle and equation of momentum to calculate the flow coefficient for liquid centrifugal atomizers

The responses of 146 cerebellar neurons to tone stimuli were studied in 29 cats anesthetized with chloralose-urethan and in 7 decerebrate preparations. Units were classified as onset or sustained firing. Onset spikes occurred on stimulation of either ear and showed binaural facilitation, while sustained discharges were frequently only excited by monaural stimulation. The latent periods of sustained discharges appeared to be shorter than those of onset responses, and sustained discharges were also more sharply tuned than the onset units. Evidence was presented suggesting that onset responses reflected input from the inferior colliculus and sustained responses, the cochlear nucleus. The sterotyped facilitatory behavior of onset units suggested that a maximal discharge might occur if sounds were of equal intensity at each ear; 26 neurons were examined with variable interaural time or intensity differences and 10 of these exhibited maximal firing when the interaural time and intensity difference was zero--i.e., if the sound was located directly in front of the head.

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The Problem of Accounting for Heat Exchange between the Flow and the Flow Part Surfaces When Modeling a Viscous Flow in Low-Flow Stages of a Centrifugal Compressor

Applied Sciences ◽

10.3390/app10249138 ◽

2020 ◽

Vol 10 (24) ◽

pp. 9138

Author(s):

Sergey Kartashov ◽

Yuri Kozhukhov ◽

Vycheslav Ivanov ◽

Aleksei Danilishin ◽

Aleksey Yablokov ◽

...

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Centrifugal Compressor ◽

Calculation Model ◽

Flow Coefficient ◽

Low Flow ◽

Relative Width ◽

Adiabatic Wall ◽

Flow Part ◽

Computational Fluid Dynamics Cfd

In this paper, we review the problem of accounting for heat exchange between the flow and the flow part surfaces when creating a calculation model for modeling the workflow process of low-flow stages of a centrifugal compressor using computational fluid dynamics (CFD). The objective selected for this study was a low-flow intermediate type stage with the conditional flow coefficient Փ = 0.008 and the relative width at the impeller exit b2/D2 = 0.0133. We show that, in the case of modeling with widespread adiabatic wall simplification, the calculated temperature in the gaps between the impeller and the stator elements is significantly overestimated. Modeling of the working process in the flow part was carried out with a coupled heat exchanger, as well as with simplified accounting for heat transfer by setting the temperatures of the walls. The gas-dynamic characteristics of the stage were compared with the experimental data, the heat transfer influence on the disks friction coefficient was estimated, and the temperature distributions in the gaps between disks and in the flow part of the stage were analyzed. It is shown that the main principle when modeling the flow in low-flow stage is to ensure correct temperature distribution in the gaps.

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Structural Response of a Single-Stage Centrifugal Compressor to Fluid-Induced Excitations at Low-Flow Operating Condition: Experimental and Numerical Study

Energies ◽

10.3390/en14144292 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4292

Author(s):

Kirill Kabalyk ◽

Andrzej Jaeschke ◽

Grzegorz Liśkiewicz ◽

Michał Kulak ◽

Tomasz Szydłowski ◽

...

Keyword(s):

Centrifugal Compressor ◽

Numerical Study ◽

Structural Response ◽

Flow Coefficient ◽

Low Flow ◽

Dynamic Strain ◽

Duct Acoustics ◽

Numerical Noise ◽

Partial Load ◽

Compressor Impeller

The article describes an assessment of possible changes in constant fatigue life of a medium flow-coefficient centrifugal compressor impeller subject to operation at close-to-surge point. Some aspects of duct acoustics are additionally analyzed. The experimental measurements at partial load are presented and are primarily used for validation of unidirectionally coupled fluid-structural numerical model. The model is based on unsteady finite-volume fluid-flow simulations and on finite-element transient structural analysis. The validation is followed by the model implementation to replicate the industry-scale loads with reasonably higher rotational speed and suction pressure. The approach demonstrates satisfactory accuracy in prediction of stage performance and unsteady flow field in vaneless diffuser. The latter is deduced from signal analysis relying on continuous wavelet transformations. On the other hand, it is found that the aerodynamic incidence losses at close-to-surge point are underpredicted. The structural simulation generates considerable amounts of numerical noise, which has to be separated prior to evaluation of fluid-induced dynamic strain. The main source of disturbance is defined as a stationary region of static pressure drop caused by flow contraction at volute tongue and leading to first engine-order excitation in rotating frame of reference. Eventually, it is concluded that the amplitude of excitation is too low to lead to any additional fatigue.

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Periodic flow structures in a turbofan fan stage in windmilling

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020948297 ◽

2020 ◽

pp. 095441002094829

Author(s):

Nicolás García Rosa ◽

Adrien Thacker ◽

Guillaume Dufour

Keyword(s):

Mass Flow ◽

Turbulence Intensity ◽

Flow Separation ◽

Variable Mass ◽

Flow Coefficient ◽

Test Bed ◽

Ambient Conditions ◽

Low Velocity ◽

Blade Passing Frequency ◽

Flow Through

In a fan stage under windmilling conditions, the stator operates under negative incidence, leading to flow separation, which may present an unsteady behaviour due to rotor/stator interactions. An experimental study of the unsteady flow through the fan stage of a bypass turbofan in windmilling is proposed, using hot-wire anemometry. Windmilling conditions are reproduced in a ground engine test bed by blowing a variable mass flow through a bypass turbofan in ambient conditions. Time-averaged profiles of flow coefficient are independent of the mass flow, demonstrating the similarity of velocity triangle. Turbulence intensity profiles reveal that the high levels of turbulence production due to local shear are also independent of the inlet flow. A spectral analysis confirms that the flow is dominated by the blade passing frequency, and that the separated regions downstream of the stator amplify the fluctuations locked to the BPF without adding any new frequency. Phase-locked averaging is used to capture the periodic wakes of the rotor blades at the rotor/stator interface. A spanwise behaviour typical of flows through windmilling fans is evidenced. Through the inner sections of the fan, rotor wakes are thin and weakly turbulent, and the turbulence level remains constant through the stage. The rotor wakes thicken and become more turbulent towards the fan tip, where flow separation occurs. Downstream of the stator, maximum levels of turbulence intensity are measured in the separated flow. Large periodical zones of low velocity and high turbulence intensity are observed in the outer parts of the separated stator wake, confirming the pulsating motion of the stator flow separation, locked at the blade passing frequency. Space-time diagrams show that the flow is chorochronic, and a 2 D non-linear harmonic simulation is able to capture the main interaction modes, however, the stator incidence distribution could be affected by 3 D effects.

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Surge in a Low-Speed Radial Compressor

Volume 1: Turbomachinery ◽

10.1115/98-gt-426 ◽

1998 ◽

Cited By ~ 3

Author(s):

Corine Meuleman ◽

Frank Willems ◽

Rick de Lange ◽

Bram de Jager

Keyword(s):

Flow Rate ◽

Pressure Rise ◽

Flow Coefficient ◽

Lumped Parameter Model ◽

Pressure Oscillations ◽

Vaned Diffuser ◽

Flow Angle ◽

Radial Compressor ◽

Low Speed ◽

Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

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Fan Performance Scaling With Inlet Distortions

Journal of Turbomachinery ◽

10.1115/1.4039433 ◽

2018 ◽

Vol 140 (7) ◽

Cited By ~ 6

Author(s):

J. J. Defoe ◽

M. Etemadi ◽

D. K. Hall

Keyword(s):

Design Flow ◽

Flow Coefficient ◽

Axial Fan ◽

Fan Performance ◽

Physical Mechanisms ◽

Viscous Losses ◽

Performance Scaling ◽

Large Distortion ◽

Stator Blade ◽

Primary Focus

Applications such as boundary-layer-ingesting (BLI) fans and compressors in turboprop engines require continuous operation with distorted inflow. A low-speed axial fan with incompressible flow is studied in this paper. The objectives are to (1) identify the physical mechanisms which govern the fan response to inflow distortions and (2) determine how fan performance scales as the type and severity of inlet distortion varies at the design flow coefficient. A distributed source term approach to modeling the rotor and stator blade rows is used in numerical simulations in this paper. The model does not include viscous losses so that changes in diffusion factor are the primary focus. Distortions in stagnation pressure and temperature as well as swirl are considered. The key findings are that unless sharp pitchwise gradients in the diffusion response, strong radial flows, or very large distortion magnitudes are present, the response of the blade rows for strong distortions can be predicted by scaling up the response to a weaker distortion. In addition, the response to distortions which are composed of nonuniformities in several inlet quantities can be predicted by summing up the responses to the constituent distortions.

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Flow Coefficient Evaluation of Poppet Valves Used in Reciprocating Compressors for LDPE

Volume 5: High Pressure Technology; Nondestructive Evaluation Division; Student Paper Competition ◽

10.1115/pvp2008-61286 ◽

2008 ◽

Author(s):

Enzo Giacomelli ◽

Massimo Schiavone ◽

Fabio Manfrone ◽

Andrea Raggi

Keyword(s):

Pressure Drop ◽

Time Pressure ◽

Experimental Tests ◽

Operating Conditions ◽

Flow Coefficient ◽

Operating Life ◽

High Fatigue ◽

Strongly Connected ◽

And Performance ◽

Poppet Valves

Poppet valves have been used for a long time for very high pressure reciprocating compressors, as for example in the case of Low Density Polyethylene. These applications are very critical because the final pressure can reach 350 MPa and the evaluation of the performance of the machines is strongly connected to the proper operation and performance of the valve itself. The arrangement of cylinders requires generally a certain compactness of valve to withstand high fatigue stresses, but at the same time pressure drop and operating life are very important. In recent years the reliability of the machines has been improving over and over and the customers’ needs are very stringent. Therefore the use of poppet valves has been extended to other cases. In general the mentioned applications are heavy duty services and the simulation of the valves require some coefficients to be used in the differential equations, able to describe the movement of plate/disk or poppet and the flow and related pressure drop through the valves. Such coefficients are often determined in an experimental way in order to have a simulation closer to the real operating conditions. For the flow coefficients it is also possible today to use theoretical programs capable of determining the needed values in a quick and economical way. Some investigations have been carried out to determine the values for certain geometries of poppet valves. The results of the theory have been compared with some experimental tests. The good agreement between the various methods indicates the most suitable procedure to be applied in order to have reliable data. The advantage is evident as the time necessary for the theoretical procedure is faster and less expensive. This is of significant importance at the time of the design and also in case of a need to provide timely technical support for the operating behavior of the valves. Particularly for LDPE, the optimization of all the parameters is strongly necessary. The fatigue stresses of cylinder heads and valve bodies have to match in fact with gas passage turbulence and pressure drop, added to the mechanical behavior of the poppet valve components.

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Introduction of an Universal Scale-Up Method for the Efficiency of Axial and Centrifugal Fans

Volume 1A: Aircraft Engine; Fans and Blowers ◽

10.1115/gt2014-25403 ◽

2014 ◽

Cited By ~ 2

Author(s):

Peter F. Pelz ◽

Stefan S. Stonjek

Keyword(s):

Test Data ◽

Scale Up ◽

Pressure Rise ◽

Flow Coefficient ◽

Total Efficiency ◽

Scaling Method ◽

Centrifugal Fans ◽

Axial Fans ◽

Definition Of ◽

Acceptance Tests

Acceptance tests on large fans to prove the performance (efficiency and total pressure rise) to the customer are expensive and sometimes even impossible to perform. Hence there is a need for the manufacturer to reliably predict the performance of fans from measurements on down-scaled test fans. The commonly used scale-up formulas give satisfactorily results only near the design point, where inertia losses are small in comparison to frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulas used so far fail. In 2013 Pelz and Stonjek introduced a new scaling method which fullfills the demands ( [1], [2]). This method considers the influence of surface roughness and geometric variations on the performance. It consists basically of two steps: Initially, the efficiency is scaled. Efficiency scaling is derived analytically from the definition of the total efficiency. With the total derivative it can be shown that the change of friction coefficient is inversely proportional to the change of efficiency of a fan. The second step is shifting the performance characteristic to a higher value of flow coefficient. It is the task of this work to improve the scaling method which was previously introduced by Pelz and Stonjek by treating the rotor/impeller and volute/stator separately. The validation of the improved scale-up method is performed with test data from two axial fans with a diameter of 1000 mm/250mm and three centrifugal fans with 2240mm/896mm/224mm diameter. The predicted performance characteristics show a good agreement to test data.

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