Masayuki Anyoji

Computational and Experimental Analysis of a High-Performance Airfoil Under Low-Reynolds-Number Flow Condition

A high-performance Ishii airfoil was analyzed using both a wind-tunnel and large-eddy simulations at a low-Reynolds-number condition (Re=23,000). The design guidelines for an airfoil shape with a high lift-to-drag ratio under the aforementioned condition are described by analyses of flowfields and aerodynamic characteristics of the Ishii airfoil. Compared with conventional airfoils, such as the NACA 0012 and NACA 0002, the shape characteristic effects of the Ishii airfoil on its flowfield and aerodynamic characteristics are discussed. The shape on the suction side of the Ishii airfoil can cause delays in the flow separation at low angle of attacks. The separated flow reattaches, and a separation bubble forms even when trailing-edge separation changes to leading-edge separation. The separation bubble contributes to an increase in lift coefficient. In addition, the Ishii airfoil can gain a high positive pressure on the pressure side as compared with the other two symmetric airfoils due to the camber near th...

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

Mechanisms behind the pressure distribution and skin friction within a laminar separation bubble (LSB) are investigated by large-eddy simulations around a 5% thickness blunt flat plate at the chord length based Reynolds number 5.0 × 103, 6.1 × 103, 1.1 × 104, and 2.0 × 104. The characteristics inside the LSB change with the Reynolds number; a steady laminar separation bubble (LSB_S) at the Reynolds number 5.0 × 103 and 6.1 × 103, and a steady-fluctuating laminar separation bubble (LSB_SF) at the Reynolds number 1.1 × 104, and 2.0 × 104. Different characteristics of pressure and skin friction distributions are observed by increasing the Reynolds number, such that a gradual monotonous pressure recovery in the LSB_S and a plateau pressure distribution followed by a rapid pressure recovery region in the LSB_SF. The reasons behind the different characteristics of pressure distributions at different Reynolds numbers are discussed by deriving the Reynolds averaged pressure gradient equation. It is confirmed that the viscous stress distributions near the surface play an important role in determining the formation of different pressure distributions. Depending on the Reynolds numbers, the viscous stress distributions near the surface are affected by the development of a separated laminar shear layer or the Reynolds shear stress. In addition, we show that the same analyses can be applied to the flows around a NACA0012 airfoil.

Characteristics of the Mars Wind Tunnel at Tohoku University in CO 2 Operation Mode

The Mars Wind Tunnel at Tohoku University is a low-density tunnel that can simulate Martian atmospheric flight condition. Up to the present, this tunnel has been operated using air as the working gas. To expand the capability of this tunnel and to study the effects of compressibility on airfoil performance at low Reynolds number, a modification has been made to allow the tunnel to be operated using CO 2, that is the main constituent of the Martian atmosphere. In this study, the operational characteristics as well as the flow quality in the test section are investigated in CO2 mode and compared with the results obtained in air mode. It is found that a higher Mach number can be achieved in CO 2 mode than in air mode as the speed of sound decreases with the molecular weight. No negative effect of CO 2 such as freezing inside the ejector nozzles has been observed over the entire operational conditions of the tunnel. Mach number profile is found to be uniform over a wide range of Reynolds number except inside the boundary layers on the walls. The static pressure gradient along the test section is almost zero at the total pressure of 1kPa. These results prove that the Mars Wind Tunnel has a capability to simulate the real Martian atmospheric condition.

Low Reynolds number airfoil testing in a Mars Wind Tunnel

The aerodynamic characteristics of a 5% flat plate and NACA0012-34 airfoil in low Reynolds number (Re=0.43x10 4 ~4.1x10 4 ) and high subsonic flow (M=0.1~0.6) were investigated in the Mars Wind Tunnel (MWT) at Tohoku University. A two-component balance system and Pressure-Sensitive Paint (PSP) technique have been developed to measure the lift and drag forces and pressure profiles on the model. For the flat plate, Mach number effect does not have much effect on its aerodynamic performance while Reynolds number affects the lift slope and the drag characteristics. On the contrary, for NACA001234 airfoil, both Reynolds and Mach number effects become more prominent. The lift curves are highly nonlinear and the drag polars are affected by behaviors of a laminar separation bubble in trans-critical condition. A comparison of the results obtained at different Mach numbers has suggested that the compressibility has an effect to stabilize separated shear layer. It has been verified by this experiment that the MWT can offer a unique capability to investigate airfoil performance in low Reynolds number and high Mach number flow.

Development of low density wind tunnel to simulate atmospheric flight on Mars

A new type of wind tunnel that can simulate airfoil flow in the Mars atmosphere has been designed and constructed at Tohoku University. This wind tunnel is driven by ejector and designed to simulate low-density Martian atmosphere consisting of CO2. The preliminary performance tests were conducted using air to investigate the operating envelop of the tunnel. It was demonstrated that this wind tunnel could cover the Reynolds number range from 10 4 to 10 5 and the Mach number range up to 0.71, allowing us to simulate low Reynolds number and high subsonic flow on Mars airplanes. Calibration tests were also conducted to investigate the flow characteristics in the test section. It was confirmed that the flow was kept uniform in the test section even when the total pressure was 1 kPa. There were significant effects of the boundary layer development on static pressure gradient along the test section. It was found that these effects of boundary layers could be corrected by inclining both the upper and lower walls of the test section.

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.

Effects of mach number and specific heat ratio on low-reynolds-number airfoil flows

The effects of Reynolds number, Mach number, and gas species (air and CO2) on aerodynamic characteristics of a thin flat plate and a NACA 0012-34 airfoil were investigated under low-Reynolds-number (Re=0.43×104 to 4.1×104) and high-subsonic-flow (M=0.1 to 0.6) conditions. In addition to lift and drag measurements by a two-component balance system, the pressure-sensitive paint technique was applied to measure pressure profiles on the model surface. For the flat plate, the Reynolds number moderately affects the lift and drag characteristics because of a simple behavior of the leading-edge separation bubble; the length of the separation bubble increases as the angle of attack increases. By contrast, the Mach number and specific heat ratio contribute little to the aerodynamic performance. For the NACA 0012-34 airfoil, the lift curves are highly dependent on the Reynolds number because of the formation, shift, and burst of the separation bubble, whereas the compressibility affects only the stall characteristic...

Aerodynamic Measurements in the Mars Wind Tunnel at Tohoku University

Pressure-Sensitive Paint (PSP) technique has been applied to measure pressure distribution on airfoil models at low Reynolds number (Re = 4.1x10 4.3x10) in the Mars Wind Tunnel (MWT) at Tohoku University. In this study, the capability of PSP for pressure measurement was evaluated with a particular emphasis on its applications to thin airfoil models. The obtained results show that PSP can clearly visualize pressure distributions on the airfoils, allowing us to analyze a behavior of the separated shear layer on the airfoil including laminar-to-turbulent transition and reattachment. A comparison between the PSP and balance measurements indicates that the evolution of a laminar separation bubble over the airfoil surface has a strong effect on the lift and drag characteristics. It has been also verified by this experiment that, using the proposed method for temperature correction, pressure distribution can be obtained quantitatively even on thin airfoils.

Computer analysis of the schlieren optical setup

In order to evaluate the influence of each component of the Schlieren optical setup, this work tries to simulate the whole setup by a computer, so that one can get an immediate computer image after adjusting the component. The analysis is based on the ray tracing method. All rays are traced from the light source to the recording plane, so that all components in the light path can be investigated. In our analysis, Schlieren optical setup is decomposed to two main modules, illuminating and recording optical setups. Each module contains typical optical arrangements that are commonly used. The numerical models devised for the optical arrangements are proposed, and a few results indicating the effect of the shape and the orientation of a cutoff are shown.

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.