Bump Configurations Research Articles

A Numerical Investigation of the Geometric Parametrisation of Shock Control Bumps for Transonic Shock Oscillation Control

At transonic flight conditions, shock oscillations on wing surfaces are known to occur and result in degraded aerodynamic performance and handling qualities. This is a purely flow-driven phenomenon, known as transonic buffet, that causes limit cycle oscillations and may present itself within the operational flight envelope. Hence, there is significant research interest in the development of shock control techniques to either stabilise the unsteady flow or raise the boundary onset. This paper explores the efficacy of dynamically activated contour-based shock control bumps within the buffet envelope of the OAT15A aerofoil on transonic flow control numerically through unsteady Reynolds-averaged Navier–Stokes modelling. A parametric evaluation of the geometric variables that define the Hicks–Henne-derived shock control bump will show that bumps of this type lead to a large design space of applicable shapes for buffet suppression. Assessment of the flow field, local to the deployed shock control bump geometries, reveals that control is achieved through a weakening of the rear shock leg, combined with the formation of dual re-circulatory cells within the separated shear-layer. Within this design space, favourable aerodynamic performance can also be achieved. The off-design performance of two optimal shock control bump configurations is explored over the buffet region for M = 0.73, where the designs demonstrate the ability to suppress shock oscillations deep into the buffet envelope.

A chip-level electrothermal-coupled design model for high-power light-emitting diodes

An advanced three-dimensional electrothermal-coupled simulation model basing on finite-element method numerical simulation is developed to study the electrical and thermal properties of chip-level high-power GaN-based light-emitting diodes (LEDs). The current spreading, heat generation, and transfer in the device are comprehensively considered in this model. The current-spreading effect of the transparent current-spreading layer and the thermal performance of LEDs with interdigitated-electrodes are investigated. The simulation results prove that the temperature distribution in the active layer is strongly affected by the electrode pattern. The obvious heat accumulation in LEDs with conventional interdigitated-electrode patterns can be seen both in the simulated results and the infrared measured results. The heat transfer efficiency can be improved by using a symmetry electrode pattern design. The thermal management of the bump configurations in flip-chip LEDs is also studied. A more reasonable and thermal effective bump configuration is presented, and the simulated results show that a lower average temperature and more uniform heat distribution in the chips can be obtained.

Shock-Wave/Boundary-Layer Interaction Control Using Three-Dimensional Bumps for Transonic Wings

Three-dimensional bumps have been developed and investigated on transonic wings, aiming to fulfill two major objectives of shock-wave/boundary-layer interaction control, that is, drag reduction and buffet delay. An experimental investigation has been conducted for a rounded bump in channel flow at the University of Cambridge and a computational study has been performed for a spanwise series of rounded bumps mounted on a transonic aerofoil at the University of Stuttgart. In both cases wave drag reduction and mild control effects on the boundary layer have been observed. Control effectiveness has been assessed for various bump configurations. A double configuration of narrow rounded bumps has been found to perform best, considerably reducing wave drag by means of a well-established X-shock structure with little viscous penalty and thus achieving a maximum overall drag reduction of about 30%, especially when significant wave drag is present. Counter-rotating streamwise vortex pairs have been produced by some configurations as a result of local flow separation. On the whole a large potential of three-dimensional control with discrete rounded bumps has been demonstrated both experimentally and numerically.

Characterization of bump arrays at RF/microwave frequencies

A systematic procedure for the characterization of complex bump configurations at RF and microwave frequencies, is presented. Beginning with simple arrangements—single- and two-coupled bumps—full-wave electromagnetic (EM) field analysis, circuit simulations and RF measurements were used for the development and validation of their respective equivalent circuit models. These models were then extended to characterize three-coupled bumps, both in linear and triangular configurations. Finally, a combination of all the electrical parameters obtained from these simple bump configurations was used to characterize a complete bump array, taking into consideration that for pitches used in most high-speed packages, EM coupling between a bump and its “next but one” neighbor can be neglected.

The structural instability of transonic flow associated with amalgamation/splitting of supersonic regions

We study inviscid transonic flow in a channel with a bump modeling an airfoil at zero incidence. A few simple bump configurations are considered. Numerical simulations show the existence of singular free-stream Mach numbers, which trigger the splitting/amalgamation of local supersonic regions. An analysis of this phenomenon contributes to the understanding of the nonuniqueness of transonic solutions at certain free-stream conditions.

Formation of selective epitaxially grown silicon with a flat edge by ultra-high vacuum chemical vapor deposition

We studied the dependence of selective epitaxially grown silicon (SEG-Si) shape on the conditions of ultra-high vacuum chemical vapor deposition using disilane (Si 2H 6) gas, which grew on Si (1 0 0) substrates patterned with SiO 2 stripes. SEG-Si edges typically formed two types of configurations: facets and bumps. It was confirmed that the shape of SEG-Si edge is strongly dependent on the growth mode of the (1 0 0) plane: facet configurations are formed in the mass transfer limited region, and bump configurations are formed in the kinetically limited region. Therefore, it was concluded that the surface migration length of adatoms resulting from the decomposition of Si 2H 6 molecules is related to the formation of the shape of the SEG-Si. Moreover, it was confirmed that the flat shape of the SEG-Si is obtained by adjusting both the Si 2H 6 flow rates and the growth temperature.

Wideband scalable electrical model for microwave/millimeter wave flip chip interconnects

We present a method for developing fully scalable lumped element models for flip chip interconnects. Measurements of test structures and full wave simulations are used to generate circuit models for various single bump configurations. Furthermore, regression models are developed for scaling the values of the elements with the physical attributes of the circuit. First, the method is validated using only two factors, then the model is extended to more inputs related to the bump geometry and placement. The values of L and C in a simple /spl pi/ model have been scaled with the conductor overlap, the distance from the ground bump to the edge of the ground plane, the width of the CPW launch, the bump height and diameter. Explicit formulas are obtained for L and C as a function of those variables. It has been found that the value of the inductance varies with the conductor overlap, bump height and diameter, while the capacitance is mostly affected by conductor overlap. This paper presents the first fully scalable model for microwave flip chip technology.

Dynamic Structural Properties of Compliant Foil Thrust Bearings—Comparison Between Experimental and Theoretical Results

This paper describes an experimental investigation into the dynamic characteristics of corrugated foil (bump foil) strips used in compliant surface foil thrust bearings. This study provided the first opportunity to quantify the dynamic structural stiffness and equivalent damping coefficients of bump foil strips for a wide range of operating conditions. The experimental data were compared to results obtained by a theoretical model developed earlier. The effects of bearing design parameters, such as static loads, dynamic displacement amplitudes, bump configurations, pivot locations, surface coatings, and lubricant were also evaluated. An understanding of the dynamic characteristics of bump foil strips resulting from this work offers designers a means for enhancing the design of high-performance compliant foil bearings.

Compliant Foil Bearing Structural Stiffness Analysis—Part II: Experimental Investigation

This paper describes the second part of an investigation into the mechanism of deformation of the corrugated foil (bump foil) strips used in compliant surface foil bearings. In the earlier work, a theoretical model was developed to predict the structural characteristics of bump foil strips under various loads, including the effects of the friction forces between the compliant elements, local interaction forces, load distribution profiles, and bump configurations. In the experiments described here in, two-dimensional deflections of bump foils were recorded via an optical tracking system for a wide range of operating conditions to verify the feasibility of the theoretical model. Test results corroborate the theoretical model for the linear regions of load and the deflection parameters. The effects of the bearing design parameters, such as bump configuration, load profile, and surface coating and lubricant, on the structural characteristics of the bump foil strip were investigated. In addition, the source and mechanism of nonlinear behavior of the bump foil strips under light load conditions were examined, and more effective methods of achieving both Coulomb damping and optimum structural compliance were investigated. An understanding of the analytical and semi-empirical relations resulting from this work offers designers the potential for enhancing the design of high-performance compliant foil bearings.