Daiju Numata

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.

Unsteady PSP Measurement of Transonic Buffet on a Wing

In this study, unsteady pressure field caused by transonic buffeting phenomena on a generic transport model was analyzed using unsteady PSP. The tests were conducted in the JAXA 2-m Transonic Wind Tunnel at M=0.85 and the model angle of attack was varied between 2.5 and 6.8 degrees. From the obtained unsteady PSP data, the RMS of pressure fluctuation was calculated to detect the areas with strong shock oscillation. Spectral analysis was also conducted in order to find frequencies of shock oscillation and their correlation with pressure fluctuation. As the angle of attack increases, the shock position moves upstream and shock oscillation becomes stronger. At 6.8 degrees, two distinct areas with strong shock oscillation were observed. The spectral analysis shows that, under buffeting conditions, shock oscillation frequencies are distributed around either of 490 Hz or 365 Hz. Noticeable effects from the PSP coating on the measured aerodynamic forces were noticed, indicating that even the small roughness of the unsteady PSP coating has an influence on the transonic buffeting phenomena.

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...

Development of Ultrafast-Response Anodized-Aluminum Pressure-Sensitive Paints

In order to apply Pressure-Sensitive Paint (PSP) to unsteady shock-wave phenomena, Anodized-Aluminum PSP (AA-PSP) with ultrafast response was fabricated and its response time to a step pressure change was evaluated by using a shock tube. Phosphoric acid was used as electrolyte in anodization and the anodic alumina with pore diameter as large as 160 nm was successfully fabricated. The improved AA-PSP achieved a response with the time constant of 0.35 s. This is the fastest PSP ever reported. We applied this AA-PSP to interactions of a moving shock wave with a circular cylinder. The results show that the improved AA-PSP can visualize the shock reflections and the shock diffractions with the ever-highest spatial and temporal resolution. Nomenclature Ai = Stern-Volmer coefficients d = pore diameter, nm Deff = effective diffusion coefficient, m 2 s -1

Compressibility Effects on Airfoil Aerodynamics at Low Reynolds Number

The objective of this study is to clarify the Mach number effect on the aerodynamic characteristics of airfoils at low Reynolds number. In this study, we conducted airfoil tests using a flat plate and a triangular airfoil in the Mars Wind Tunnel at Tohoku University. Reynolds number was set at 3,000 and 10,000 and Mach number at 0.15, 0.5 and 0.7. Aerodynamic force and pressure distributions on the models were measured using a force balance and Pressure-Sensitive Paint (PSP). The results show that the compressibility effect has an effect to move the flow separation point backward and to delay a reattachment of separated shear layer on the airfoil. These effects reduce the lift and the maximum lift-drag ratio.

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.

Nonlinear Lift on a Triangular Airfoil in Low-Reynolds-Number Compressible Flow

Numerical and experimental analyses of the aerodynamic performance of a triangular airfoil in low-Reynolds-number compressible flow are performed. This airfoil is one of the candidates for propeller blades on a possible future Martian air vehicle design. Based on past experimental studies conducted in the Mars Wind Tunnel at Tohoku University, this airfoil is known to exhibit nonlinear lift behavior. In the present study, direct numerical simulations of low-Reynolds-number compressible flow over a spanwise periodic triangular airfoil are conducted to identify the source of nonlinear lift. The numerical results reveal that the source of the nonlinear aerodynamic behavior is the lift enhancement provided by the large leading-edge vortex generated. For compressible low-Reynolds-number flow, the wake structure becomes elongated, causing the nonlinear lift enhancement to appear at higher angles of attack compared to the case of incompressible flow.

Influence of Turbulence Intensity on Aerodynamic Characteristics of an NACA 0012 at Low Reynolds Numbers

.Experiments were conducted by using a low-density testing capability of the Mars Wind Tunnel at Tohoku University. For Reynolds number below 50,000, aerodynamic force and pressure distribution on the model were measured using a force balance and pressure sensitive paint (PSP) for various turbulence intensities. Turbulence intensity in the wind tunnel was changed by using wire-mesh grids having different wire diameters. The results obtained in this study indicated that an increase of turbulence intensity had an effect to improve lift and drag characteristics of the airfoil. With an increasing turbulence intensity, the lift coefficient increased at low angles of attack and near the stall angle. The drag coefficient decreased in all conditions. Also, improvements of the stall angle and the maximum lift coefficient were observed. The characteristics of an NACA 0012 airfoil was dependent both on Reynolds number and turbulence intensity. The overall effects of increasing turbulence intensity were similar to those of increasing Reynolds number.

Experiment study of ejecta composition in impact phenomenon

Impact tests were held to clarify the relationship between the composition of ejecta and these of the projectile and the target plate under different impact kinetic energy and impact velocity. Two sets of impact experiments were held, one using high carbon chromium bearing steel (SUJ-2) projectile and Al2017-T4 plate (Fe/Al impact), and the other using Al2017-T4 projectile and SUJ-2 plate (Al/Fe impact). The spherical projectile is of 7.94 mm in diameter, made of Al2017-T4 or SUJ-2. The impact velocity considered is from 2.5 to 4.2km/s. By recovering and analyzing the injected SUJ-2 and the Al2017-T4 fragments separately, we can quantitatively measure the composition of the injected fragments, and clarify how it depends upon the material of the projectile and the target plane. We further investigate the effects of velocity and kinetic energy of the projectile on the ejecta composition.

Polymer/Ceramic PSP with Reduced Surface Roughness for Unsteady Pressure Measurement in Transonic Flow

Polymer/ceramic pressure-sensitive paints (PC-PSPs) with reduced surface roughness were developed for measuring unsteady pressure fields in transonic flow. Four types of PC-PSPs, each having different particle size, mass content, solvent, and so on, were formulated and applied to transonic wind-tunnel tests of a Common Research Model airfoil. The effects of surface roughness on unsteady transonic flow on the airfoil were evaluated at Mach 0.74 and Reynolds number of 5.0 x 10 6 . It was found that all four PC-PSPs had capabilities to measure time-series pressure distributions, but the location of a shock wave and the root-mean-square pressure fluctuations differed depending on types of PC-PSP. Among all tested PC-PSPs, the PC-PSP having arithmetic surface roughness of 0.5 μm and cutoff frequency of 3 kHz yielded data practically the same as that of a clean airfoil. Using this PC-PSP, propagation of pressure waves and oscillation of shock waves on the airfoil were clearly captured. A spectral analysis showed that the fundamental frequency of shock-wave oscillation agreed very well with that calculated based on the mechanism proposed by Lee. These results show that the selected PC-PSP can offer a powerful means to study transonic buffeting on airfoils and 3D wings.