Dynamic vortex evolution in a single nozzle-flapper valve under coupled effects of flow rate and flapper clearance

In this paper, the effect of seal clearance on the efficiency of a turbine with a shrouded rotor is compared with the effect of the tip clearance when the same turbine has an unshrouded rotor. The shrouded versus unshrouded comparison was undertaken for two turbine stage designs one having 50% reaction the other having 24% reaction. Measurements for a range of clearances, including very small clearances, showed three important phenomena. Firstly, as the clearance is reduced, there is a “break-even clearance” at which both the shrouded turbine and the unshrouded turbine have the same efficiency. If the clearance is reduced further, the unshrouded turbine performs better than the shrouded turbine, with the difference at zero clearance termed the “offset loss”. This is contrary to the traditional assumption that both shrouded and unshrouded turbines have the same efficiency at zero clearance. The physics of the break-even clearance and the offset loss are discussed. Secondly, the use of a lower reaction had the effect of reducing the tip leakage efficiency penalty for both the shrouded and the unshrouded turbines. In order to understand the effect of reaction on the tip leakage, an analytical model was used and it was found that the tip leakage efficiency penalty should be understood as the dissipated kinetic energy rather than either the tip leakage mass flow rate or the tip leakage loss coefficient. Thirdly, it was also observed that, at a fixed flow coefficient, the fractional change in the output power with clearance was approximately twice the fractional change in efficiency with clearance. This was explained by using an analytical model.

In this paper, the effect of seal clearance on the efficiency of a turbine with a shrouded rotor is compared with the effect of the tip clearance when the same turbine has an unshrouded rotor. The shrouded versus unshrouded comparison was undertaken for two turbine stage designs one having 50% reaction, the other having 24% reaction. Measurements for a range of clearances, including very small clearances, showed three important phenomena. Firstly, as the clearance is reduced, there is a “break-even clearance” at which both the shrouded turbine and the unshrouded turbine have the same efficiency. If the clearance is reduced further, the unshrouded turbine performs better than the shrouded turbine, with the difference at zero clearance termed the “offset loss.” This is contrary to the traditional assumption that both shrouded and unshrouded turbines have the same efficiency at zero clearance. The physics of the break-even clearance and the offset loss are discussed. Secondly, the use of a lower reaction had the effect of reducing the tip leakage efficiency penalty for both the shrouded and the unshrouded turbines. In order to understand the effect of reaction on the tip leakage, an analytical model was used and it was found that the tip leakage efficiency penalty should be understood as the dissipated kinetic energy rather than either the tip leakage mass flow rate or the tip leakage loss coefficient. Thirdly, it was also observed that, at a fixed flow coefficient, the fractional change in the output power with clearance was approximately twice the fractional change in efficiency with clearance. This was explained by using an analytical model.

The CSF shunt valve is a medical device whose main function is to regulate intracranial pressure and drain excess CSF. The authors have developed a new therapeutic method for treating hydrocephalus, namely the tandem shunt valve system, which has the potential of flexibly controlling the CSF flow rate and intracranial pressure in patients. The properties of the tandem system were verified by performing in vitro experiments. An in vitro system with a manometer was built to measure pressure and flow rates of water in open systems using the Codman Hakim Programmable Valve and the Strata adjustable pressure programmable valve. A single valve and 2 single shunt valves connected in series (the tandem shunt valve system) were connected to the manometer to check the final pressure. Conventional single shunt valve systems require valve pressures to be set higher to slow down the CSF flow rate, which inevitably results in a higher final pressure. On the other hand, the tandem shunt valve system uses the combination of 2 valves to slow the CSF flow rate without increasing the final pressure. The authors succeeded in experimentally demonstrating in vitro results of tandem systems and their effectiveness by applying a model to show that the valve with the higher pressure setting determined the final pressure of the entire system and the flow rate became slower than single shunt valve systems.

The effect of inlet and outlet blade angles on the performance of a micro regenerative pump was examined. The head of the regenerative pump was little increased by changing the blade angles compared with the original pump with the inlet and outlet blade angles of 0 degree. The effect of the axial clearance on the performance was also examined. The head was increased largely by decreasing the axial clearance. The computation of the internal flow was performed to clarify the cause of the increase of the head due to the decrease of the clearance. The local flow rate in the casing decreased as the leakage flow rate through the axial clearance decreased due to the decrease of the clearance. By offsetting the performance curve with the local flow rate, the effect of the clearance did not appear and it was found that the larger head in the smaller clearance was just caused by the smaller local flow rate in the casing. In the case of the smaller clearance, the smaller local flow rate caused the smaller circumferential velocity near the front and rear sides of the impeller, and the angular momentum in the casing and the head increased.

This study uses a numerical approach to examine the visual axial pressure gradient and friction factor characteristics of supercritical CO2 turbulent flow in a concentric annulus. The Computational Fluid Dynamics (CFD) software package (FLUENT) was applied for the investigation. The inlet temperature varied from 31 to 110 °C at two operating pressures 9 MPa and 14 MPa. The effect of mass flow rate, annulus clearance, and shaft rotational speed on the pressure gradient and friction factor are investigated. The results show that the pressure gradient is non-linear and the friction factor changes abruptly near the critical point. The effect of mass flow rate and shaft rotational speed on the friction factor is found significant whereas the effect of clearance is insignificant. The friction factor for a given condition is found in the range 0.042-0.029. A one-and-a-half times increase in the friction factor was found when there was a two-time increase in the rotational speed. A satisfactory agreement is obtained between the results predicted by CFD (fluent) when compared with the results predicted by the Darcy Weisbach equation and the Moody diagram and then with the experimental. Hence the Darcy Weisbach equation and Moody diagram can be an effective means of determining the pressure and friction factor respectively for the supercritical CO2 turbulent flow application through the concentric annulus.

A variable-flow-rate pesticide application system using six bypass centrifugal pressure nozzles was designed, built, and tested. The rate of output flow from the nozzles was regulated by a single valve. The variation in nozzle flow rate and distribution characteristics with changes in bypass and inlet pressures were studied. A nozzle output flow turndown ratio of 6 to 1 was obtained. The spray angle varied from 86 to 80 deg over the 6 to 1 turndown ratio, affecting the combined-nozzle spray distribution patterns only slightly. The system provides the capability of adjusting the pesticide application rate or of maintaining a constant rate over a range of travel speeds by means of a single control valve without signifi-cant degradation of spray characteristics.

Effects of tube-support clearance and preload on in-plane fluidelastic instability of tube arrays

This study is concerned with a stage of a radial low-flow reaction turbine, which is used in aircraft engines, propellant feed systems of rocket engines, turbocharging systems of internal combustion engines, etc. The goal of the study is to investigate the effect of the clearance between the impeller and the stationary housing of a radial-flow turbine on its power parameters. The paper shows the need to refine, supplement, and sort parametric data on the effect of the axial clearance between the free edge of a radial-flow turbine impeller blade and the stationary housing on the turbine power parameters. It is shown that clearances in the turbine setting play an important role in the working process and significantly affect the key performance characteristics. The correctness of the methodological approaches to the tests and experimental studies conducted is verified by the results of other authors. The studies were conducted in two stages. At the first stage, a turbine stage was tested as a part of a single model gas-dynamic circuit with a compressor stage and a combustion chamber. At the second stage, tests were carried out with two independent gas-dynamic ducts of the turbine and compressor, in which the working fluid was supplied to the units separately, with the possibility of flow rate control. The novelty of the study consists in obtaining new data on the effect of the axial clearance in small-sized radial low-flow turbines on the key power and performance parameters of the stage. In the study, generally accepted methods of experimentation and data processing were used. The obtained results allow one to relate the parameters of the expansion process in reaction gas turbines to the axial clearance value. The practical value of the results lies in the possibility of using the obtained experimental data in designing low-flow impeller machines for jet engines and in refining computational methods.

This paper presents a numerical investigation of the effect of tip clearance on the suction performance and flow characteristics at different flow rates in a vertical mixed-flow pump. Numerical analyses were carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations. Steady computations were performed for three different tip clearances under noncavitating and cavitating conditions at design and off-design conditions. The pump performance test was performed for the mixed-flow pump and numerical results were validated by comparing the experimental data for a system characterized by the original tip clearance. It was shown that for large tip clearance, the head breakdown occurred earlier at the design and high flow rates. However, the head breakdown was quite delayed at low flow rate. This resulted from the cavitation structure caused by the tip leakage flow at different flow rates.

A new integrated nozzle-flapper valve equipped with a piezoelectric actuator and an isothermal chamber has been developed and studied in detail. The designed single stage valve controls the pressure and flow rate simply, effectively, and separately. This idea can easily be used in the pilot stage of a two-stage valve as well. Application of isothermal condition in the valve load chamber eliminates the dynamic malfunction that may persist from temperature variation within the valve load chamber; consequently, the governing equations for the prediction of pressure dynamics in the chamber are much more accurate and simpler. The valve has been equipped with a stacked type piezoelectric actuator which has a unique behaviour. Furthermore, stiffness, in the selected actuator, is enhanced against the thrust of the discharging flow from the nozzle, thus decreasing the complexity of dynamic equations of the valve. A detail mathematical model and simulation was developed to study the dynamic performance analysis of the proposed valve. An experimental test rig was built to validate the results of simulations. The unique features and performance of the proposed valve were studied thoroughly. The valve’s governing equations are nonlinear in nature, and some variables of the equations are a source of some uncertainties; sliding mode approach was used to control the steady and unsteady pressure and output flow rate of the valve.

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.

In this article, a piezoelectrically actuated flow excitation approach is presented for producing short rise time flow rate changes. This is a crucial requirement from flowmeter dynamic calibration. A single nozzle-flapper valve (NFV) is adopted as excitation flow generator. A commercially available piezo stack drives the flapper. Time-domain comparison between pressure difference across the reference restrictor and the indicated value of tested flowmeters in the circuit is made for the current dynamic performance of the tested flowmeter. Computational fluid dynamics (CFD) simulation is implemented for the pipeline system to investigate the excitation characteristics based on the dynamic pressure distribution. The experimental device is designed, using a turbine flowmeter in a fuel pipeline. The excitation experiments are conducted, with varying voltages applied to the piezo stack and fuel supply pressure. The experimental dynamic pressure in the control chamber agrees well with that obtained by CFD simulation. And the pressure gain on null position of the single NFV is slightly smaller than the theoretical value, whose correction factor is derived. This article demonstrates that a piezoelectrically actuated NFV can be effectively used in generating short rise time flow rate changes under different operating conditions, avoiding disturbance to the upstream flow field of the tested flowmeters. The flow excitation device is applicable to flowmeter dynamic calibration.

Effects of endwall clearances of variable diffuser vane on centrifugal compressor performance

Many theoretical analyses of extrusion ignore the effect of the flight clearance when predicting the pumping capability of a screw. This might be reasonable for conventional extruder screws with “normal” clearances but leads to errors when more advanced screw designs are considered. We present new leakage-flow models that allow the effect of the flight clearance to be included in the analysis of melt-conveying zones. Rather than directly correcting the drag and pressure flows, we derived regression models to predict locally the shear-thinning flow through the flight clearance. Using a hybrid modeling approach that includes analytical, numerical, and data-based modeling techniques enabled us to construct fast and accurate regressions for calculating flow rate and dissipation rate in the leakage gap. Using the novel regression models in combination with network theory, the new approximations consider the effect of the flight clearance in the predictions of pumping capability, power consumption and temperature development without modifying the equations for the down-channel flow. Unlike other approaches, our method is not limited to any specific screw designs or processing conditions.

In the unshrouded axial turbine, the tip clearances can result in the loss of turbine efficiency and the penalty of turbine performance. Therefore, investigating the blade tip geometry of improving the turbine performance has a great significance. This paper is to study the effects of non-uniform tip clearance on the flow field in a turbine cascade. The numerical works are performed at the incidence angle of 0 degree and the exit Reynolds number of 1.7 × 105 based on the blade chord. In the investigations, the flat tip (Basic) geometry was employed as a benchmark, and three different tip geometries, including the pressure side squealer (PSQ), suction side squealer (SSQ) and grooved tip (Grooved), were studied. The tip clearances are all specified as 1.18% of the chord. The squealer height is set to 2.94% of the chord. The endwall static pressure, tip leakage loss, flow capacity and the development of tip leakage vortex are discussed. And the numerical results show that the grooved tip which can obtain the least total pressure loss, is helpful to smooth the pressure change from pressure side to suction side and suppress the intensity of tip leakage vortex. The tip clearance flow in the pre semi-passage is mainly involved in the passage vortex, and in the post semi-passage it is added to the tip leakage vortex. Compared with the Basic, PSQ and SSQ tips, the Grooved tip contributes to reducing the tip leakage flow and the tip leakage loss. And the leakage flow can be strengthened in the middle passage for the PSQ. The difference between the area averaged streamwise coefficient and mass averaged loss is almost opposite for the SSQ and Grooved tip, which is uncertain the performance of the turbine cascade with the SSQ and Grooved tip is better than the Basic tip.