Koichi Nishibe

Study on Flow Characteristics Downstream of Annular Inlet Guide Vanes

The main objectives of the present study are to identify the dominant parameters responsible for the generation of unsteady flow, determine the conditions under which flow oscillations are produced and the relation between the flow characteristics and the number of vanes with identical solidity. The flow instabilities downstream of inlet guide vanes (IGV) are clarified experimentally and by numerical simulation. The conditions for the onset of flow instability, including the number of cells and the oscillation characteristics of the unsteady flow, are discussed based on measured pressure fluctuations and the propagating angular velocity ratio of the instability for various radius ratios (r3/r2). The effectiveness of adjusting the number of vanes to control the flow instabilities is also discussed.Copyright

Vector Control of Synthetic Jets Using an Asymmetric Slot

This is a fundamental study on the jet vectoring control by means of adjusting the synthetic jet Strouhal number (frequency) without slot shape change with time in actuators. This work involved introduction of asymmetric slots with various beak lengths in free synthetic jets for various frequencies, experimentally and numerically. Furthermore, the behavior of synthetic jets was compared with that of the continuous jets. In our experiment, velocity measurements for both types of jets were performed using a hot-wire anemometer with an I-type probe and a traverser, and flow visualization for observing the behavior of the jets was performed using the smoke wire method. Through the experiment, typical flow patterns and time-averaged velocity distributions of synthetic jets for various beak lengths and Strouhal number were demonstrated. The time-averaged velocity was measured at a reference point on the slot centerline to evaluate the degree of the bend of the jets and the obtained data was used in the Strouhal number-beak length map.Copyright

The Influence of an Asymmetric Slot on the Flow Characteristics of Synthetic Jets

The purpose of this paper is to elucidate the influence of an asymmetric slot on the flow characteristics of synthetic jets. In this study, the relation between flow characteristics of two-dimensional synthetic jets and beak-shaped asymmetric slots is investigated experimentally and numerically. Results clarify that the vortex pair with different x-direction locations induced by the asymmetric slot produces a large-scale circulation region on the opposite side of the beak in the case of long beaks. It is also demonstrated that flow fields for synthetic jets depend on asymmetric slot beak length; in contrast, continuous jets are independent of asymmetric slot beak length.

Performance Characteristics of a Fan Using Synthetic Jets

Studies of synthetic jets generated by compact actuators have been conducted for various applications such as drag reduction, boundary layer separation control, and multi-flow mixing. In this paper, a jet fan that utilizes synthetic jets is proposed. The flow patterns inside the jet fan are revealed, and performance curves are drawn. Static pressure distributions in the fan duct are also analyzed to discuss the process of static pressure recovery.

Flow Characteristics Downstream of Swirl Flow Generators

An attempt was made, through experiments and numerical simulations, to clarify the mechanisms associated with the flow characteristics downstream of both inlet guide vanes (IGVs) with different vane geometries and circulation control wings (CCWs) with different jet sheet momentum coefficients. The novelty of the present study lies in the proposal of a swirl flow generator which can control the flow angle without changing geometrically. The main objectives were: (1) to revalidate the numerical analysis method employed in the present study, which was used to assess the flow characteristics downstream of the IGVs and (2) to suppress flow oscillations through tangential blowing. Characteristic flow patterns downstream of flat-plate vanes and circular cylinders with tangential blowing, with identical exit flow angles, are presented, and the unsteady flow characteristics downstream of the IGVs are compared with those of the CCWs. Furthermore, the influence of the radius ratio of the device outlet to the vane exit on the unsteady flow characteristics downstream of the IGVs and CCWs is discussed based on the measured pressure and velocity fluctuations.Copyright

A Study on the Coanda Effect and the Thrust Characteristics of Synthetic Jets

Although there have recently been various studies on synthetic jets, many issues remain to be clarified, including details of the structure, Coanda effect and thrust characteristics. The present study clarifies some fundamental flow characteristics of synthetic jets near a rigid boundary by experiments and numerical simulations. In addition, a thruster model using the Coanda effect of synthetic jets is proposed and thrust characteristics are evaluated. As the main results, the flow of a synthetic jet near a rigid boundary is visualized and the trajectory of a vortex pair is demonstrated. It is confirmed that the flow patterns of the synthetic jets near a rigid boundary depend on H/b0 (offset ratio, normalized step height). The behavior of the asymmetric synthetic jets caused by the presence of the rigid wall was observed experimentally and the results were compared with numerical data. Furthermore, typical flow patterns around the proposed synthetic jet thruster and its thrust characteristics curves are shown.Copyright

Study on the Flow Characteristics of Synthetic Jets Near a Rigid Plane Boundary

The jet flows have been applied to various fields to control the flow separation. Over the last decade, several studies have investigated synthetic jets. However, there are still many clarifications needed, including details of the structure and Coanda effect of synthetic jets. The present study clarifies some fundamental flow characteristics of free synthetic jets and synthetic jets near a rigid boundary by conducting an experiment and numerical simulations. As the main results, it is found that the velocity distribution of free synthetic jets depends on K = Re/S2 (the ratio of the Reynolds number to the square of the Stokes number) and can be identified by the maximum velocity at the centerline and the jet half-width. Flow visualization is carried out applying the smoke wire method. In addition, it is confirmed that the flow characteristics of the synthetic jet near a rigid boundary and re-attachment length of the synthetic jet are determined not only by H1 /b0 (normalized step heights) but also K.Copyright