Eisuke Outa

Early Stall Warning Technique for Axial-Flow Compressors

This paper proposes a unique stall risk index based on pressure signals by high-response transducers on the casing wall at the rotor leading-edge location. The aim of the research is to explore the possibility of reducing current excessive stall margin requirement for compressor design based on the worst-case scenario. The index is generated by computing correlation degradation of pressure time histories of current and one revolution before over each blade pitch. Tests conducted on a single-stage low-speed compressor exhibits that the correlation diminishes significantly with proximity to stall, and the proposed technique might have the capability of generating a stall warning signal sufficiently in advance of spike inception. Extensive experiments on a research compressor show that the degree of the index degradation depends on various factors, such as flow coefficient, tip clearance, and rotor blade incidence. In order to obtain a reliable stall warning signal in practical use, these effects must be carefully examined.

Long term animal experiments with an intraventricular axial flow blood pump

A miniature intraventricular axial flow blood pump (IVAP) is undergoing in vivo evaluation in calves. The IVAP system consists of a miniature (13.9 mm) axial flow pump that resides within the left ventricular (LV) chamber and a brushless DC motor. The pump is fabricated from titanium alloy, and the pump weight is 170 g. It produces a flow rate of over 5 L/min against 100 mmHg pressure at 9,000 rpm with an 8 W total power consumption. The maximum total efficiency exceeds 17%. A purged lip seal system is used in prototype no. 8, and a newly developed “Cool-Seal” (a low temperature mechanical seal) is used in prototype no. 9. In the Cool-Seal system, a large amount of purge flow is introduced behind the seal faces to augment convective heat transfer, keeping the seal face temperature at a low level for prevention of heat denaturation of blood proteins. The Cool-Seal system consumes <10 cc purge fluid per day and has greatly extended seal life. The pumps were implanted in three calves (26, 30, and 168 days of support). The pump was inserted through a left thoracotomy at the fifth intercostal space. Two pursestring sutures were placed on the LV apex, and the apex was cored with a myocardial punch. The pump was inserted into the LV with the outlet cannula smoothly passing through the aortic valve without any difficulty. Only 5 min elapsed between the time of chest opening and initiation of pumping. Pump function remained stable throughout in all experiments. No cardiac arrhythmias were detected, even at treadmill exercise tests. The plasma free hemoglobin level remained in the acceptable range. Post mortem examination did not reveal any interference between the pump and the mitral apparatus. No major thromboembolism was detected in the vital organs in Cases 1 or 2, but a few small renal infarcts were detected in Case 3.

Evaluation and prediction of blade-passing frequency noise generated by a centrifugal blower

The blade-passing frequency noise, abbreviated to BPF noise, of a low-specific-speed centrifugal blower is analyzed by separating the frequency response of the transmission passage and the intensity of the noise source. Frequency response has previously been evaluated by the authors using a one-dimensional linear wave model, and the results have agreed well with the experimental response in a practical range of the blower speed. In the present study, the intensity of the noise source is estimated by introducing the quasi-steady model of the blade wake impingement on the scroll surface. The effective location of the noise source is determined by analyzing the cross-correlation between measured data of the blower suction noise and pressure fluctuation on the scroll surface. Then, the surface density distribution of a dipole noise source is determined from pressure fluctuation expressed in terms of quasi-steady dynamic pressure of the traveling blade wake. Finally, the free-field noise level is predicted by integrating the density spectrum of the noise source over the effective source area. The sound pressure level of the blower suction noise is easily predicted by multiplying the free-field noise level by the frequency-response characteristics of the noise transmission passage.

Detailed Measurements of Three-Dimensional Flows and Losses Inside an Axial Flow Turbine Rotor

Detailed traverse measurements of three dimensional flows and the associated losses inside a turbine rotor passage were carried out in the rotating frame of reference by using small five hole Pitot tubes. Strong secondary flows including passage vortices, a leakage vortex and various separation vortices were found to occur in the passage, and they are significantly influenced by the rotor speed, variation of which con t...sponds to different test incidences and blade loadings. Loss generation process in the rotor . is described in relation to the migration of low energy fluids which are driven by the various vortices and their interaction at different rotor incidences.

Noise and vibration related to the patterns of supersonic annular flow in a pressure reducing gas valve

Cause of intense aerodynamic noise and vibration from a contoured type valve is revealed in close relation to the supersonic flow patterns. Simple conical plugs are used in the experiments, and the valve pressure ratio is up to twenty. Four typical patterns of the flow are observed by schlieren photography. In one of these patterns, the jet flow along the plug separates from the wall to form an annular jet impinging on the inner wall of the valve chest. Such flow oscillates significantly in resonance with the acoustic modes of the chest cavity. The radiated noise and the dynamic force acting on the valve stem reach intense levels, dominated by some discrete components of the corresponding frequencies. The mechanisms to generate or to suppress the flow oscillation, leading to the intense noise and vibration, are discussed.

Effect of operating methods of wind turbine generator system on net power extraction under wind velocity fluctuations in fields

The effect of how a wind turbine generator system is operated is discussed from the viewpoint of net power extraction with wind velocity fluctuations in relation to the scale and the dynamic behavior of the system. On a wind turbine generator system consisting of a Darrieus-Savonius hybrid wind turbine, a load generator and a battery, we took up two operating methods: constant tip speed ratio operation for a stand-alone system(Scheme1) and synchronous operation by connecting a grid(Scheme2). With our simulation model, using the result of the net extracting power, we clarified that Scheme1 is more effective than Scheme2 for small-scale systems. Furthermore, in Scheme1, the appropriate rated power output of the system under each wind condition can be confirmed.

High‐Resolution Fluorescent Particle‐Tracking Flow Visualization within an Intraventricular Axial Flow Left Ventricular Assist Device

Flow visualization is typically applied in blood pump development to both confirm the design expectations and identify regions that may be predisposed to blood element deposition and trauma. Rotary pumps, in particular, place high demands on the technique chosen to visualize the flow given the limited visual accessibility of the flow path and the high impeller speeds. Fluorescent image-tracking velocimetry currently is used at the University of Pittsburgh Medical Center to visualize flow accurately inside of these pumps both qualitatively and quantitatively. Flow patterns under steady conditions within an intraventricular axial flow, left ventricular assist pump (prototype No. 7, SUN Medical Technology Research Corporation, Nagano, Japan) were investigated using this technique. The flow fields at the impeller-stator interface and at the pump outlet were given specific attention. This allowed the assessment of the fluid dynamics throughout the hydrodynamic design limits of the pump.

AN N-S SIMULATION OF STALL CELL BEHAVIOR IN A 2-D COMPRESSOR ROTOR - STATOR SYSTEM AT VARIOUS LOADS

Stall characteristics and stall cell behavior in a linear cascades system of a single stage axial compressor are presented by applying a numerical analysis of compressible N-S equations. The system consists of a rotor and a stator, where flow is assumed to be periodic over six blades and ten vanes respectively. Although the number of blades and vanes per period is much less than that in the real-rig, and the analysis is conducted in a laminar viscosity mode, computed stage performance from normal operation to deep stall agrees fairly well with experimental data. In deep stall, rotor cell propagates in linkage with stator cell at a computed speed of 65 % of the rotor speed. This speed is considerably close to the measured value of 55 %. Stall cell propagation is discussed on flow patterns showing stall development, stall induction in the follower blade and interaction between the rotor and stator.

Unsteady Behavior and Control of Diffuser Leading-Edge Vortex in a Centrifugal Compressor

The unsteady behavior of a vortex generated on the diffuser leading-edge, which is called the leading-edge vortex (LEV), is discussed through experiments and numerical simulation. The LEV is different from the separating vortex of the diffuser leading-edge and passage vortex of the diffuser, develops rapidly with a decrease in the compressor mass flow rate, and forms a flow blockage in diffuser passages. Therefore, the evolution of the LEV may become a cause of diffuser stall. Additionally, in one attempt to control the LEV, two types of tapered diffuser vanes, which are shroud- or hub-side tapered diffuser vanes, were adopted. Though the shroud-side tapered diffuser vane can effectively reduce the compressor noise level, the compressor performance deteriorates remarkably. On the other hand, the hub-side tapered diffuser vane not only reduces the compressor noise level but also improves the compressor performance. According to the visualization results of the oil-film methods and numerical simulations, the hub-side tapered diffuser vane can suppress the evolution of the LEV in the compressor low-flow-rate operation.Copyright

Effects of the Inlet Endwall Boundary Layer on 3-D Flows and Loss Evolution in a Linear Turbine Cascade

A three-dimensional Navier-Stokes computation was made for investigating internal flow phenomena of a linear turbine cascade, and the results were compared with the test data obtained inside the cascade passage. The present code was found to fairly well simulate the experimental data, as well as various vortices being generated in the cascade passage. In this paper, detailed mechanisms of the loss generation are discussed mainly from the computational point of view.Copyright