Experimental and theoretical study of gravity-driven falling plates

This research investigates the fluid-structure interaction phenomenon of gravity-driven falling rigid plates through a combination of experimental and theoretical approaches. Plates of varying dimensions and densities are systematically examined to explore the influence of non-dimensional parameters, including the Reynolds number (Re) and dimensionless moment of inertia (I*), on the falling patterns. High-speed photography is employed to extract plate trajectories and posterior kinematics calculations. In the range of relatively high Reynolds numbers (Re > 800), our study identifies three distinct falling modes: periodic fluttering, periodic tumbling, and marginal chaotic motion. The falling trajectories of the plates are analyzed and compared with their corresponding kinematic behaviors. By integrating theoretical analyses with experimental findings, we develop a semi-analytical model capable of calculating the real-time hydrodynamic forces and moments acting on falling plates. This model facilitates the prediction of falling trajectories for quasi-2-dimensional plates with arbitrary material and dimension combinations. Comparisons between model predictions and experimental results demonstrate good agreement in the fluttering and tumbling modes.

Stress intensity factors for an edge interface crack in a bonded semi-infinite plate for arbitrary material combination

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with an edge interface crack in bonded finite and semi-infinite plates under tension. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by the finite element method. The stress intensity factors are indicated in charts under arbitrary material combinations. For small edge interface crack, it is found that the dimensionless stress intensity factors FI and FII are not always finite depending on Dundurs' parameters α and β. In the present study, the variations of the dimensionless stress intensity factors FI and FII are clarified under arbitrary material combination with varying the relative crack length a/W. It is found that when a/W ≤ 0.4 the value of FI increases with increasing α and when a/W ≥ 0.4 the value of FI decreases with increasing α.

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combination. This paper deals with one central interface crack and numerical interface cracks in a bonded strip. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For one central interface crack, it is found that the results of bonded strip under remote uni-axial tension are always depending on the Dunders’ parameters , and different from the well-known solution of the central interface crack under internal pressure that is only depending on . Besides, it is shown that the stress intensity factor of bonded strip can be estimated from the stress of crack tip in the bonded plate when there is no crack. It is also found that when , when , and when . For numerical interface cracks , values of and with arbitrary material combination expressed by , are obtained.

An experiment has been performed to study the aerodynamics of dynamic stall penetration at constant pitch rate and high Reynolds number, in an attempt to model more accurately conditions during aircraft poststall maneuvers and during helicopter high-speed forward flight. An airfoil was oscillated at pitch rates, A = ac/2U between 0.001 and 0.020, Mach numbers between 0.2 and 0.4, and Reynolds numbers between 2-4 x 10. Surface pressures were measured using 72 miniature transducers, and the locations of transition and separation were determined using 8 surface hot-film gages. The results demonstrate the influence of the leading-edge vorticity on the unsteady aerodynamic response during and after stall. The vortex is strengthened by increasing the pitch rate and is weakened by increasing the Mach number and by starting the motion close to the steady-state stall angle. A periodic pressure oscillation occurred after stall at high pitch angle and moderate Reynolds number; the oscillation frequency was close to that predicted for a von Karman vortex street. A small supersonic zone near the leading edge at M = 0.4 was found to reduce significantly the peak suction pressures and the unsteady increments to the airloads. These results provide the first known data base of constant-pitch-rate aerodynamic information at realistic combinations of Reynolds and Mach numbers.

Fluid flow, heat transfer and entropy generation characteristics of micro-pipes are investigated computationally by considering the simultaneous effects of pipe diameter, wall heat flux and Reynolds number in detail. Variable fluid property continuity, Navier-Stokes and energy equations are numerically handled for wide ranges of pipe diameter (d = 0.50–1.00 mm), wall heat flux (q''= 1000–2000 W/m2) and Reynolds number (Re = 1 – 2000), where the relative roughness is kept constant at e/d = 0.001 in the complete set of the scenarios considered. Computations indicated slight shifts in velocity profiles from the laminar character at Re = 500 with the corresponding shape factor (H) and intermittency values (γ) of H = 3.293→3.275 and γ = 0.041→0.051 (d = 1.00→0.50 mm). Moreover, the onset of transition was determined to move down to Retra = 1,656, 1,607, 1,491, 1,341 and 1,272 at d = 1.00, 0.90, 0.75, 0.60 and 0.50 mm, respectively. The impacts of pipe diameter on friction mechanism and heat transfer rates are evaluated to become more significant at high Reynolds numbers, resulting in the rise of energy loss data at the identical conditions as well. In cases with low pipe diameter and high Reynolds number, wall heat flux is determined to promote the magnitude of local thermal entropy generation rates. Local Bejan numbers are inspected to rise with wall heat flux at high Reynolds numbers, indicating that the elevating role of wall heat flux on local thermal entropy generation is dominant to the suppressing function of Reynolds number on local thermal entropy generation. Cross-sectional total entropy generation is computed to be most influenced by pipe diameter at high wall heat flux and low Reynolds numbers.

Heat transfer in a rotating lateral outflow trapezoidal channel with pin fins under high rotation numbers and Reynolds numbers

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with a single edge interface crack as well as a double edge interface crack in a bonded plate. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stresses at the crack tip calculated by the finite element method. Then, the stress intensity factors are indicated in charts under arbitrary material combinations. Specifically, some necessary skills as refined mesh and extrapolations of the stress intensity factors are used to improve the accuracy of the calculation. It has been proved that the values shown in this paper have at least 3-digit accuracy. For the edge interface crack, it is found that the dimensionless stress intensity factors are not always finite depending on Dunders’ parameters , . For example, they are infinite when . And they are finite when , and zero when .

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with an edge interface crack in a bonded finite plate under bending. Then, the effects of material combination on the stress intensity factors are discussed. To obtain the interface stress intensity factor very accurately, a useful method is presented on the basis of the stress values at the crack tip calculated by the finite element method. The stress intensity factors are indicated in charts and compared with the ones under tension. The maximum and minimum values of the stress intensity factors are also discussed under arbitrary material combinations.

Stress intensity factors of a central interface crack in a bonded finite plate and periodic interface cracks under arbitrary material combinations

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with an edge interface crack in a bonded finite plate and semi-infinite plate. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensety factor of interface crack is presented wirh focusing on the stresses at the crack tip calculated by the finite element method. The stress intensity factors are indicated in charts under arbitrary material combinations. For the edge interface crack, it is found that the dimensionless stress intensity factors are not always finite depending on Dunders' parameters α, β.

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with an edge interface crack in a bonded finite plate and a semi-infinite plate. Then, the effects of material combination on the stress intensity factors are discussed. To obtain the interface stress intensity factor very accurately, a useful method is presented on the basis of the stress values at the crack tip calculated by the finite element method. Then, the stress intensity factors are indicated in charts under arbitrary material combinations for the bonded structure subjected to bending loading conditions and tension. For the edge interface crack, it is found that the dimensionless stress intensity factors are not always finite depending on Dundurs' parameters α and β.

Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with periodic interface cracks in a bonded infinite plate and a central interface in a bonded infinite plate. Then, the effects of material combination and relative crack length on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For periodic interface cracks, it is found that the stress intensity factors are controlled by the bimaterial parameter e alone and increase with increasing ε and relative crack length. For a central interface crack, the relationship between the dimensionless stress intensity factors F_I, F_II and relative crack length a/W are obtained under arbitrary material combinations. It is found that F_I has the maximum value when α=0.2, β=0.3 and minimum value when α=1.0, β=0 independent of a/W. On the other hand, F_II has the maximum value when α=0.1, β=0 and minimum value when α=0.2, β=0.3.

Imai suggested a new method to estimate the pressure drag coefficients of bluff bodies at high Reynolds number. He supposed that the flow at high Reynolds number might be obtained by solving a modified Navier-Stokes equation at low Reynolds number which was determined by the assumption of the eddy viscosity in the wake region. In this paper authors discuss the details of the two-dimensional viscous fluid flows past the blunt bodies of arbitrary shape at low Reynolds number (R=40) by solving numerically Navier-Stokes equations, and investigate the validity of Imai's hypothesis above mentioned.The results obtained are that Imai's idea concerning the flow pattern can be acceptable, and that the pressure drag coefficients of bluff bodies at low Reynolds number agree approximately with those in the high but subcritical Reynolds number range. But that Imai's idea gives invalid informations as to the pressure distribution along the body surface at high Reynolds number.

Effect of tip clearance variation in the transonic axial compressor of a miniature gas turbine at different Reynolds numbers