Rear Rotor Research Articles

Blade rows interaction in contra-rotating axial flow pump designed with different rotational speed concept

The contra-rotating axial flow pump consisiting of counter-rotating tandem rotors has been expermentally confirmed with better performances than the conventional axial flow pump, but it is known to suffer from the significant potential interaction between the counter-rotating blade rows, which is responsible for the repetitive stresses and unfavourable to the reliable operation. Consequently, to improve the realiability of contra-rotating axial flow pump including the reduction of the blade rows interaction, a new type of rear rotor was designed in the previous study by the rotational speed optimization methodology with some additional considerations. In the present study, to understand the effectiveness of the new design method, instantaneous static pressure fluctuations on the casing wall under the design and off design conditions are investigated by means of experimental and numerical simulation methods. The Fourier analysis is employed to process the data obtained from experiments and numerical simulations, and the axial distribution of the Blade Passing Frequency (BPF) amplitude is obtained. The new rear rotor shows weakened BPF amplitude both upstream and downstream especially at the positions between the two blade rows in both CFD and EFD analyses, implying the reduced blade rows interaction with the new rear rotor.

On vortex–airfoil interaction noise including span-end effects, with application to open-rotor aeroacoustics

Abstract A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip–vortex produced by an upstream rotating blade in the rotor–rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip–vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture.

Short‐Term In Vivo Performance of the Cleveland Clinic PediPump Left Ventricular Assist Device

The PediPump was implanted in six healthy lambs (mean 25.6 ± 1.4 kg) between the left ventricular apex and the descending aorta to evaluate in vivo performance for up to 30 days. Anticoagulation was achieved by continuous heparin infusion. Three animals were euthanized prematurely, two because of respiratory dysfunction and one because of deteriorating pump performance resulting from thrombus formation inside the pump. Three lambs were electively sacrificed 30 days after implantation; all had stable hemodynamics and minimal hemolysis, as indicated by low plasma free hemoglobin (2.5 ± 3.1 mg/dL). Mean 30-day pump flow was 1.8 ± 0.1 L/min at a pump speed of 12 200 ± 400 rpm. Neither activated clotting time nor activated partial thromboplastin time followed the changes in heparin dose. At necropsy, depositions were observed at the front (n = 1) and rear rotor axial positioning stops (n = 4); improved polishing techniques on the stationary stop surfaces and the addition of a hard-carbon, thin-film coating on the rotating stop of the pumps used for the last two experiments addressed the deposition seen earlier. In conclusion, the PediPump showed excellent hydraulic performance and minimal hemolysis during support for up to 30 days. Depositions observed at the axial positioning stops in earlier experiments were addressed by design and material refinements. We continue to focus on developing effective anticoagulation management in the lamb model as well as on further evaluating and demonstrating pump biocompatibility.

Optimization of a counter-rotating wind turbine using the blade element and momentum theory

A counter-rotating wind turbine has a front rotor and a rear rotor which rotate in opposite directions on the same axis. Compared to a single rotor, the flow field of the counter-rotating wind turbine is complicated due to the interactions between the front rotor and the rear rotor. The wake induced by the front rotor works on the inflow of the rear rotor and is essentially an unsteady flow state. In order to estimate the performance of a counter-rotating wind turbine, it is necessary to consider more variables than the case of a single-rotor wind turbine and to prepare an estimation system capable of performing delicate predictions. For the optimization of a counter-rotating wind turbine, the pitch angles, radius ratios, and rotation speeds of two rotors are chosen as the design values and variations of the power coefficients and thrust coefficients can be observed in this study. The torque balance of the two rotors due to the kinematic coupling of the generator is considered. Modeling by means of the blade element and momentum theory for the optimization of a counter-rotating wind turbine is developed to predict the front rotor flow and the wake flow generated by the front rotor. The wake flow is then applied for the inflow of the rear rotor. A vehicle test is carried out to validate the prediction. The optimized solution is found using a multi-island genetic algorithm.

Experimental analysis of flow structure in contra-rotating axial flow pump designed with different rotational speed concept

As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head — flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carried out to understand the complicated internal flow structures in the rotors.

수직이착륙 무인항공기용 엇회전식 덕티드팬의 팁간극 영향에 대한 연구

The tip clearance effect on counter-rotating ducted fan of VTOL UAV in hovering condition, was investigate using computational analysis. The SST turbulence model is employed in this study. The numerical results of baseline model are validated by wind tunnel test in hovering and forward conditions. It is observed that if tip clearance of one rotor in the counter-rotating ducted fan increase then the thrust coefficient of another rotor increases. In Addition to this, when the tip clearance of the rear rotor increases, the thrust of the ducted fan is improved due to increasing of average total pressure at exit plane.

Low Speed Design of Rear Rotor in Contra-Rotating Axial Flow Pump

Abstract The application of contra-rotating rotors for higher specific speed pump has been proposed in our studies, which is in principle effective for reducing the rotational speed and/or the pump size under the same specification of conventional axial flow pump. In the previous experiments of our prototype, the cavitation inception at the tip region of the rear rotor rather than that of the front rotor and the strong potential interaction from the suction surface of the rear rotor blade to the pressure surface of the front one were observed, indicating the possibility to further improve the pump performance by optimizing rotational speed combination between the two rotors. The present research aims at the design of rear rotor with lower rotational speed. Considering the fact that the incoming flow velocity defects at the tip region of the rear rotor, an integrated inflow model of ‘forced vortex’ and ‘free vortex’ is employed. The variation of maximum camber location from hub to tip as well as other related considerations are also taken into account for further performance improvement. The ideas cited above are separately or comprehensively applied in the design of three types of rear rotor, which are subsequently simulated in ANSYS CFX to evaluate the related pump performance and therefore the whole low speed design idea. Finally, the experimental validation is carried out on one type to offer further proofs for the availability of the whole design method.

Analysis of simulated flyover Contra Rotating Open Rotors noise data by using beamforming techniques for moving sources

The relevance of beamforming techniques to analyze conventional airframe noise sources from flyover noise measurements is now well-known. With the development of Contra Rotating Open Rotors (CROR), the performance of such techniques needs to be assessed. To this aim, realistic ground CROR noise data are simulated. First, the flow is simulated by a U-Rans approach in the CROR frame. The front rotor consists of 11 blades and the rear rotor is composed of 9 blades. In addition, the incoming flow Mach number is M = 0.2. Then, the hydrodynamic blade pressure is propagated toward a ground microphone array by using the Ffowcs-Williams Hawkings' equation. The CROR follows an horizontal trajectory at constant speed (M = 0.2) and 150 m altitude. Finally, the microphone array data are analyzed by a conventional beamforming-based deconvolution technique for moving sources, DAMAS-MS. The results show that the amplitude of the harmonics of each blade passage frequency is correctly recovered. However, the amplitude of the interaction tones is badly estimated. To overcome this difficulty, the DAMAS-MS methodology, based on an acoustic source model constituted of uncorrelated monopoles, should be modified in order to introduce the correlation between the monopoles.

The nonlinear harmonic method: from single stage to multi-row effects

The nonlinear harmonic method (NLH) and its extension to the modelling of the clocking effects can simulate the unsteady flows in multistage machines at much lower CPU cost. The bladerow interactions that can be reproduced are those between adjacent rotors and stators and also between successive rotors or successive stators, including the contra-rotating open rotors (CROR). However, the simulation of the unsteady effects of the engine pylon on the flow in the rear rotor requires the modelling of the time-varying disturbance from a stator of periodicity 1 (the pylon) into a rotor that is not adjacent, requiring an extension of the current NLH method. In addition, it has been observed that in some stator1/rotor/stator2 configurations, the amplitude of the perturbation associated with a blade passing frequency (BPF) in a row is not only created by the adjacent row but is also modified in space by the interaction of the periodic disturbances coming from the other two rows. For instance, for a struts/rotor/stator machine, the spatial frequencies of the periodic disturbance in the stator could be provoked not only by the interaction with the adjacent rotor but also by an additional interaction with the periodic flow coming from the struts. The present paper introduces a method that enables the identification of these spatial frequencies for a general row1/row2/row3 configuration. Besides, any row can be a stator or a rotor and the time-varying disturbances are not only produced by the interaction with the adjacent row but also with the other rows. A more general NLH method is therefore obtained. The proposed method was validated against a three-cylinder test case, a CROR test case, a struts/rotor/stator case and an impeller/bladed diffuser/volute case.

Experimental Study of the Instationary Flow Between Two Ducted Counter-Rotating Rotors

The purpose of this work is to study experimentally the aerodynamic characteristics of a subsonic counter-rotating axial-flow fans system operating in a ducted configuration. The fans of diameter D=375 mm were designed to match the specification point using an original iterative method: the front rotor blade cascade is designed with a conventional inverse method, setting the radial distribution of the Euler work. The through-flow is then computed using an axisymmetric and radial equilibrium assumption, with empirical models of losses. The rear rotor is not conventional but is designed to straighten the radial profile of the tangential velocity. The design of the front rotor is then modified until the stage meets the requirements. The experimental setup is arranged such that the rotation rate of each fan is independently controlled and that the axial distance between the rotors can be varied from 17% to 310% of the midspan chord length. Systematic measurements of the global performances and local measurements of the velocity field and of the wall pressure fluctuations are performed, in order to first validate the design method, and to explore the effects of the two specific free parameters of the system, the axial spacing and the ratio of rotation rates. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The developed design method slightly overpredicts the pressure rise and slightly underpredicts the best ratio of rotation rates. Flow angle measurements downstream of the stage show that the outflow is not completely straightened at the design point. Finally, the system is highly efficient on a wide range of flow rates and pressure rises: this system has thus a very flexible use, with a large patch of high efficient operating points in the parameter space.

J055022 二重反転形小型軸流ファンの前後段翼列間距離が性能特性と内部流れに及ぼす影響(〔J055-02〕流体機械の研究開発におけるEFD/CFD(2))

Small-sized axial fan is used as air cooler for electric equipments. But there is strong demand for higher power of fan according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is necessary, however it causes the deterioration of efficiency and increases the noise. Contra-rotating axial fan is smaller than conventional axial fan under the same rotational speed, and is effective for lower rotational speed design under the same diameter. Then, contra-rotating rotors were proposed for the improvement of the performance of small-sized axial fans and the advantages of it on the point of view of the performance were confirmed. In the present paper, the performance curves and internal flow of the contra-rotating small-sized axial fan with 100mm diameter obtained by the experimental and numerical analysis results are shown and the pressure distribution and attack angle of rear rotor at the design flow rate are clarified. Furthermore, the influence of the blade row distance on the performance and internal flow condition is clarified and higher performance design of the contra-rotating small-sized axial fan are discussed.

0427 低速設計後段動翼を採用した二重反転形軸流ポンプの低流量特性(OS4-2 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

The contra-rotating axial flow pump with two rotors rotating reversely, had been proved with remarkable performance benefits as well as the significant interaction between blade rows in the our previous experiments. A new type of rear rotor, aiming at the reduction of blade rows interaction and the secondary flow suppression, showed the favorable performance both in EFD and CFD method at the design condition, while an unfavorable positive slope was found on the performance curve in the partial flow rate range. In the present research, to further understand the mechanism of the positive slope, internal flow fields of contra-rotating rotors at partial flow rates were fully investigated by means of experimental measurements and numerical simulations.

0428 低速設計後段動翼を採用した二重反転形軸流ポンプの動翼列間干渉(OS4-4 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

0428 低速設計後段動翼を採用した二重反転形軸流ポンプの動翼列間干渉(OS4-4 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

Influence of Blade Row Distance on Performance and Flow Condition of Contra-Rotating Small-Sized Axial Fan

Small-sized axial fans are used as air coolers for electric equipment. There is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of the efficiency and the increase of noise. Then, the adoption of contra-rotating rotors for small-sized fans is proposed for the improvement of the performance. In the case of contra-rotating rotors, blade row distance between the front and the rear rotors influences on the performance and the noise. Therefore, it is important to clarify the optimum blade row distance between front and rear rotors. The performance curves of the contra-rotating small-sized axial fan under the condition of different blade row distances are shown and the blade row interaction between the front and the rear rotors are discussed by the numerical results. Furthermore, the optimum blade row distance of the contra-rotating small-sized axial fan is considered.

On high efficiency operation of contra-rotating axial flow pump with rotational speed control toward effective energy saving

For high specific speed pump with high performance operation, a contra-rotating axial flow pump has been proposed and the effectiveness of rotational speed control of front and rear rotors has been demonstrated experimentally. In the present paper, a prediction method of pump characteristics under the condition of optimized rotational speed control is proposed, based on consideration of flow mechanism in both front and rear rotors. The accuracy of prediction is examined for two combinations of front and rear rotors. Then, the amount of energy saving by application of rotational speed control method for the contra-rotating axial flow pump is demonstrated and an advantage of usage of contra-rotating pump is discussed.

Velocity interference in the rear rotor of a counter-rotating wind turbine

A counter-rotating wind turbine having two rotors rotating in opposite directions on the same axis is proposed to improve the aerodynamic performance of a wind turbine. In order to predict the aerodynamic performance of the counter-rotating wind turbine, the inflow interference in its rear rotor by the wake of the front rotor needs to be considered because the rear rotor operates inside the wake of the front rotor. In the previous research, the rear rotor was assumed to operate inside the fully developed stream tube of the front rotor to define the inflow condition on the rear rotor. In this study, to consider simultaneously the aerodynamic interaction between the two rotors of the counter-rotating wind turbine without any assumption on the inflow velocity of the rear rotor, an aerodynamic analysis of the counter-rotating wind turbine was carried out by using a free-wake vortex lattice method. The power coefficient and the wake geometry of the counter-rotating wind turbine were compared with those of a single rotor wind turbine, and the induction factors on the rear rotor were compared with that from the BEMT, assuming that the rear rotor operated inside the fully developed stream tube of the front rotor.

J051054 二重反転形軸流ポンプ後段翼車の低回転数設計

An application of contra-rotating rotors, in which a rear rotor is in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. However, our prototype rear rotors designed with the conventional method under the same rotational speed as the front rotor have revealed several problems; the head is not satisfied even at the design flow rate, cavitation inception is observed on the rear rotor despite of the head increase of front rotor and so on. In the present study, to solve these problems, three new rear rotors are designed based on the reduced speed design with taking account of information from the previous studies. One of them, which considers the outlet flow distribution of front rotor as well as the control of secondary flow with the different maximum camber position from hub to tip and the small incidence angle for better cavitation performance, is found to show the best performance in the numerical simulations. An experimental validation is carried out for this rotor, showing that the rotor satisfies the design specifications with higher total efficiency than the existing rotor at the design flow rate. Discussions on off-design performances are also made based on the measured performance data.

J051033 二重反転形小型軸流ファンの羽根車内の非定常内部流動について

Small-sized axial fan is used as air cooler for electric equipments. But there is demand for higher power of fan according to the increase of quantity of heat from electric device. Therefore, higher rotational speed design is necessary but it causes the deterioration of efficiency and increases the noise. Contra-rotating axial fan is smaller than single axial fan under the same rotational speed, and is effective for lower rotational speed design under the same diameter. In addition, contra-rotating small-sized axial fan is higher efficiency compared with single small-sized axial fan. Then, the adoption of contra-rotating rotor for small-sized fan was proposed for the improvement of performance. In the present paper, the internal flow of contra-rotating small-sized axial fan with 100mm diameter obtained by the numerical analysis is shown. Furthermore, flow condition at inlet of rear rotor influenced by the wake of front rotor which is characteristic unsteady flow condition of contra-rotating rotors and flow condition at outlet of rear rotor is mentioned by the results.

Unsteady flow condition of contra-rotating small-sized axial fan

Small-sized axial fans are used as air cooler for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of efficiency and the increase of noise. Then, the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance. In the case of contra-rotating rotors, it is necessary to design the rotor considering the unsteady flow condition of each front and rear rotor. In the present paper, the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown, and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical results. Furthermore, the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.

Internal Flow and Limiting Streamlines Observations of Contra-Rotating Axial Flow Pump at Partial Flow Rate

An application of contra-rotating rotors, in which a rear rotor is in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. One prototype rotors, which we have designed with a conventional method, has given the positive slope of head characteristic curve especially in the rear rotor. It is necessary to understand the internal flow behavior in the rear rotor to establish the design guideline for achieving higher and more reliable performance. In the present study, we carried out the experimental investigations of the internal flow field of the rear rotor, especially at the partial flow rate, by Laser Doppler Velocimetry (LDV) for the main flow and the limiting streamlines observation on rotor surfaces for the boundary layer flows.