Chien-Chang Lin

Nonuniform motion of leading-edge vortex breakdown on ramp pitching delta wings

Vortex flow characteristics on ramp pitching delta wings of sweep angles from 59 to 70 deg were studied by flow visualization and LDA measurement. Experimental observations indicate that the movement of the breakdown point is strongly dependent on the sweep angles and the pitching rates. The moving behavior of the breakdown point can be characterized by the occurrence of two delays. The first delay is due to the fact that the flow initially takes a length of time comparable to C/U» to respond to the pitching motion. The second delay exists only for specific sweep angles and occurs in the course of pitching-up motion. It is characterized by the phenomenon that the breakdown point is moving slowly or even standing still above the wing surface for a certain length of time. The chordwise location corresponding to this occurrence shifts upstream as the pitching rate increases. This delay diminishes as the sweep angle increases. The LDA data obtained further reveal that both delays are associated with the underdevelopment of the primary vortex.

Flow distortion in a circular-to-rectangular transition duct

Experiments were made for three circular-to-rectangular transition ducts with different transition lengths at Reynolds numbers which ranged from 4 × 10 3 to 2 × 10 4 . The Reynolds number is based on the inlet boundary-layer thickness and a reference freestream velocity measured upstream of the transition duct. The secondary flow pattern developed at the exit cross-sectional plane was mapped out in detail by a three-dimensional velocity measurement technique

Local buckling of delaminated sandwich beams using continuous analysis

The paper presents a method of continuous analysis for predicting the local delamination buckling load of the face sheet of sandwich beams. The discontinuous system of a face sheet delaminated from the elastic core is treated as a continuous system of the face sheet without debond but subjected to an added force system that causes the net interfacial tractions at the separated region to vanish. The effect of transverse normal and shear resistance from the core is accounted for. The procedure allowing direct determination of the buckling load by considering the entire region without separating it into regions with and without delaminations is effective for this class of problems. Fourier series in conjunction with the Stokes transformation is used which provides a unified solution for problems with different end conditions. The concept of analysis can foreseeably be extended to two-dimensional plate problems with delamination regions of arbitrary shapes. Some numerical results are presented to illustrate the applicability of the analysis procedure and effects of various parameters to the buckling load.

Engineering analysis of buckling of delaminated beam plates

An engineering analysis procedure is presented for assessing the buckling load of beam plates having single and multiple delaminations, and with various supporting conditions. Free and constrained mode models are considered. Results based on these two models are complementing each other in estimating the buckling load of delaminated beam plates. Some numerical results for a clamped-clamped beam are presented for illustrative purposes.

Buckling of Beam-Plates Having Multiple Delaminations

An analysis procedure for determining the buckling load of beam-plates having multiple single delaminations is presented. Free and constrained models based on the usual beam-column theory are used for perfect and separated parts of delaminated segments. Successive corrections of buckled delaminated segments are made by inserting constrained models in the portions where overlapping of the upper and lower parts occurred in the segments of assumed free mode deformations. It appears to be the first time such analysis leading to buckling load with physically realistic mode of deformation has been considered. Recurrence equations relating integration constants of adjacent segments are established which lead to a 2 by 2 buckling determinant and allow direct determination of buckling mode along the entire beam-plate. Some numerical examples are presented for illustrative purposes. The procedure established appears to be simple, systematic and effective which should be useful for engineering applications.

Stresses around pin-loaded hole in composite laminates using direct boundary element method

This study is concerned with stresses around a pin-loaded hole in symmetrically stacked composite laminates of finite size using a two-dimensional direct boundary element method. Effects of friction and clearance between the pin and hole edge on the stresses are accounted for. Also geometric compatibility and force constraint between the pin and the plate are enforced. A new relation for geometric compatibility is proposed. Stress distributions and the contact angle with slip and no-slip regions around the pin-loaded hole corresponding to various parameters are investigated. Some interesting results are obtained. The present method is effective and simple to use which can be implemented with a personal computer.

Local buckling of delaminated composite sandwich plates

A two-dimensional model of the delaminated face sheet of sandwich plates for predicting local huckling using continuous analysis is presented. The analysis procedure can handle without difficulty sandwich plates having single or multiple embedded delaminations of various shapes and sizes at any locations. The continuous analysis treats the delamination between a face sheet and the core as a continuous system of a perfectly bonded laminate on the core but with an added fictitious force system to make interfacial tractions to vanish over the delaminated region. The method presented in the study is straightforward, simple, and accurate for determining the buckling load of delaminated sandwich plates. A number of numerical results accounting for the effects of transverse normal and shear stiffnesses of the core on the buckling load of sandwich plates having delaminations of various shapes and sizes at different locations are presented. The illustrative examples indicate that the present method is effective and useful for practical applications.

Studying Three-Dimensionality of Vortex Shedding Behind a Circular Cylinder with Mems Sensors

Experiments were made with 14 MEMS sensors situated along the span of a circular cylinder whose aspect ratio was 5. The signals of the MEMS sensors were sampled simultaneously as flow over the cylinder at Reynolds numbers of 10 4 . The results of Wavelet analysis of the signals indicate that the percentage of time during which strong three-dimensionality of vortex shedding was detected is about 10%.As noted, strong three-dimensionality took place when the fluctuating amplitude of the signals was severely modulated and the vortex shedding frequency reduced appeared abnormally high or low. Further noted was that the addition of a splitter plate of 0.5 or one diameter in length behind the circular cylinder was not able to suppress the three-dimensionality of the flow.

On some aspects of pin-loaded laminates

Some aspects of pin loaded laminates, including basic kinematics related to the contact angle and moving boundary, validity and applicability of cosine distribution of contact stress, effects of stiffness ratios as well as clearance and friction are presented. Numerical results on the basis of a previously developed direct boundary element procedure, with a refined and improved computational algorithm with additional capabilities are given and used for discussing various aspects of pin-loaded orthotropic laminates. Empirical formulas based on generated computer results are suggested.

Flow Visualization in a Circular-to-Rectangular Transition Duct

This work repor t s on flow behaviors nea r the wall and secondary flow structures in a c i rcularto-rectangular transition duct a t Reynolds n u m b e r s of 10*. Flow visualization exper iments were conduc ted under the condit ions of uni form and swirling inlet flows. As found, flow s t ructures observed at the rectangular exit under the swirling inlet condit ion a p p e a r very differently f rom those observed unde r the uni form inlet condition. In the fo rmer case the secondary flows a re deve loped d u e to the d e t a c h m e n t s of the swirling flow f rom the contoured wall, while in the latter case the secondary flows a re known d u e to the mechan i sm of m e a n flow straining in the corner regions.