Satoshi Sekimoto

An Effective Three-Dimensional Layout of Actuation Body Force for Separation Control

We conducted large eddy simulations of the control of separated flow over an airfoil using body forces and discuss the role of a three-dimensional vortex structure in separation control. Two types of cases are examined: (1) the body force is distributed in a spanwise uniform layout and (2) the body force is distributed in a spanwise intermittent layout, with three-dimensional vortices being expected to be generated in the latter cases. The flow fields in the latter cases have a shorter separation bubble than those in the former cases although the total momentum of the body force in the latter cases is the same as or half of the former cases. In the flow fields of the latter type, the three-dimensional vortices, which are not observed in the former cases, are generated by the body force downstream of the body force distributed. Thus, three-dimensional vortices are considered to be effective in controlling the separated flow.

Comparative study of co-flow and counter blowing DBD plasma actuators for separated flow over an airfoil

A comparative study of co-flow and counter-blowing dielectric barrier discharge plasma actuator for separation control is conducted. These actuators are applied with normal mode and burst mode, where normal mode represents the actuation with continuous alternative current (AC) input and burst mode represents the actuation with the AC input switched on and off periodically. They are used for controlling the separated flow around NACA0015 airfoil at low Reynolds number Rec = 6.3 × 10. Pressure measurement and particle image velocimetry are conducted. In this study, four cases are conducted changing blowing direction, co-flow or counter-blowing, and actuation mode, normal or burst. Comparison among four cases shows that the dominant factor for suppressing separation with burst actuation is promoting transition, regardless of blowing direction. It also shows that the dominant factor of co-flow normal actuation is direct momentum addition. Counter-blowing normal actuation cannot suppress separation with any input voltage. Focusing on the minimum input voltage for suppressing separation, effectiveness for each attached case is compared and it is revealed that burst actuation more or less includes the effect of direct momentum addition.

Burst-Mode Frequency Effects of Dielectric Barrier Discharge Plasma Actuator for Separation Control

The various separation control mechanisms of burst-mode actuation with a dielectric barrier discharge plasma actuator were experimentally investigated in this study. The control of the separated fl...

Experimental study of a nano-second pulse plasma actuator for low reynolds number flow control

This paper presents basic characteristics of flow control with a nano-second pulse plasma actuator in low Reynolds number flow. Schlieren visualization in quiescent air verifies that nano-second pulse (NSDBD) actuation can generate compression waves and near-wall flow, whereas burst wave (ACDBD) actuation generates only near-wall flow. The results indicate that strength of a compression wave is independent of pulse repetition frequency. Strength of a compression wave gets stronger with increasing pulse peak voltage because rate of voltage dV0p/dt increase and localized heating is strengthened. Nano-second pulse actuation is applied to leading edge separation control of Re = 63, 000 (free stream flow velocity 10m/s). To understand flow-control characteristics of nano-second pulse actuation, two types of discharge, NSDBD and ACDBD, two types of actuator position, x/c = 0.05 and 0.1, and two types of actuator direction, co-flow blowing and counter-flow blowing, are examined. Generally, flow-control characteristics of NSDBD actuation is very similar to that of ACDBD actuation. With the same voltage amplitude, NSDBD actuation has better control capability than ACDBD actuation. Note that consumption power of NSDBD is 10 to 1000 times larger than that of ACDBD. With an actuator at more downstream position (x/c = 0.1), control capability significantly decreases and separation cannot be suppressed at all. Also results show that NSDBD actuations in counter-flow blowing are worse than those in co-flow blowing for separation suppressing. This indicates that near-wall flow of small momentum from nano-second pulse discharge affects flow-control capability in this Reynolds number condition.

Experimental Study of Effects of Frequency for Burst Wave on a DBD Plasma Actuator for Separation

Appropriate frequencies for burst wave of a dielectric barrier discharge plasma actuator at a reference voltage are investigated by the low speed wind tunnel experiment for the airfoil separation control. Here, a reference voltage is defined as the minimum voltage for controlling a reference condition, and the reference voltage is adopted for each experimental conditions to eliminate errors caused by the degradation effect of the plasma actuator and individual variability. All the experiments are conducted with the flow condition Rec = 6.3 × 10 4 and α=12. Time-averaged pressure around the surface of the actuatorapplied NACA0015 is measured. The results show that F + of higher than 1 is more effective for separation control and appropriate F + region considerably changes when BR and n are changed.

DBD Plasma Actuator Multi-Objective Design Optimization at Reynolds Number 63,000: Baseline Case

The working parameters of the dielectric barrier discharge (DBD) plasma actuator were optimized to gain an understanding of the flow control mechanism. Experiments were conducted at a Reynolds number of 63,000 using a NACA 0015 airfoil which was fixed to the stall angle of 12 degrees. The two objective functions are: 1) power consumption (P) and 2) lift coefficient (Cl). The goal of the optimization is to decrease P while maximizing Cl. The design variables consist of input power parameters. The algorithm was run for 10 generations with a total population of 260 solutions. Although the number of generations and population size was limited due to experimental constraints, the algorithm was able to converge and the approximate Pareto-front was obtained. From the objective function space, we observe a relatively linear trend where Cl increases with P and after a certain threshold, the value of Cl seems to saturate. We discuss the results obtained in the objective space in addition to scatter plot matrix and color maps. This article, with its experiment-based approach, demonstrates the robustness of a Multi-Objective Design Optimization method and its feasibility for wind tunnel experiments.Copyright

Experimental Study of Blowing Direction Effects of DBD Plasma Actuator on Separation Control of Flow Around an Airfoil

An experimental study of plasma actuator on separation control is conducted. The plasma actuator is used for control of separated flow around NACA0015 airfoil. The Reynolds number based on chord length is set to 60,000 and the angle of attack is set to 12[deg]. The plasma actuator is applied with normal mode and burst mode, where normal mode denotes continuous actuation and burst mode denotes temporary intermittent actuation. Also, actuations for co-flow blowing and counter blowing are conducted. The averaged pressure coefficients of wing surface and velocity fields are measured. For velocity fields, PIV measurement is adopted. Comparing counter and co-flow blowings of plasma actuator, the effects of counter blowing is investigated. Also, for both co-flow and counter blowing cases, we investigate the effects of burst mode. Through the series of experiments, following two types of mechanism for separation control will be discussed. One type is considered to be directly giving momentum in the boundary layer which seems to be more active in co-flow blowing with normal mode. The other type is considered to be enhancement of the mixing, leading to increase in momentum thickness of the boundary layer. The latter mechanism seems to be active in the burst mode with both co-flow and counter blowing.© 2011 ASME