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Three-dimensional Reynolds-averaged Navier--Stokes solutions are employed to investigate the discharge and total temperature increase characteristics of the stepped labyrinth seal with honeycomb land. First, the relations between the windage heating number and the circumferential Mach number at different Reynolds numbers for different honeycomb seals are calculated and compared with the experimental data. The obtained numerical results show that the present three-dimensional periodic model can properly predict the total temperature increase in honeycomb seals. Then, a range of pressure ratios, three inlet preswirl ratios, four sizes of honeycomb cell diameter, and nine sizes of cell depth are selected to investigate the influence of inlet preswirl ratios and honeycomb geometry sizes on the discharge and total temperature increase characteristics of the stepped labyrinth seal. It shows that the leakage rate increases with the increase in cell diameter, and the cell depth has a strong influence on the discharge behavior However, the influence of the inlet preswirl on the leakage rate is found to be little in the present study. For the total temperature increase characteristic, the inlet preswirl ratio and pressure ratio have more pronounced influence than those of cell depth and diameter Furthermore, the relations between the leakage rate and cell depth and diameter, as well as the relations between the windage heating power and cell depth and diameter, are not monotonic functions if the pressure ratio is kept constant. [DOI: 10.1115/1.4001296] Keywords: honeycomb seal leakage flow, windage heating, total temperature increase

Three-dimensional Reynolds-averaged Navier-Stokes (RANS) solutions from CFX were utilized to investigate the leakage flow characteristics in the labyrinth honeycomb seal of steam turbines. At first, the accuracy and reliability of the utilized RANS approach was demonstrated using the published experimental data of the honeycomb seal. It showed that the utilized numerical method has sufficient precision to predict the leakage performance in seals. Then a range of sealing clearances, cell diameters, cell depths, rotation speeds, and pressure ratios were investigated to determine how these factors affect the leakage flow rate of the labyrinth honeycomb seal. The computed leakage flow rate increased with increasing sealing clearance and pressure ratios. Furthermore, the results show that the studied labyrinth honeycomb seal has the optimum sealing performance in the case of honeycomb cell diameter equals labyrinth step width, and the ratio of the honeycomb cell depth to honeycomb cell diameter is 0.93 under the designed condition. The flow pattern of each case is also illustrated to describe the leakage flow characteristics in labyrinth honeycomb seals. [DOI: 10.1115/1.4000091] Keywords: labyrinth honeycomb seal, leakage flow, numerical simulation

This paper describes a numerical and experimental investigation on the flexural wave propagation properties of a novel class of negative Poisson's ratio honeycombs with tetrachiral topology. Tetrachiral honeycombs are structures defined by cylinders connected by four tangent ligaments, leading to a negative Poisson's ratio (auxetic) behavior in the plane due to combined cylinder rotation and bending of the ribs. A Bloch wave approach is applied to the representative unit cell of the honeycomb to calculate the dispersion characteristics and phase constant surfaces varying the geometric parameters of the unit cell. The modal density of the tetrachiral lattice and of a sandwich panel having the tetrachiral as core is extracted from the integration of the phase constant surfaces, and compared with the experimental ones obtained from measurements using scanning laser vibrometers. [DOI: 10.1115/1.4000785]

Sandwich panels with aluminum alloy face sheets and a hierarchical composite square honeycomb core have been manufactured and tested in out-of-plane compression. The prismatic direction of the square honeycomb is aligned with the normal of the overall sandwich panel. The cell walls of the honeycomb comprise sandwich plates made from glass fiber/epoxy composite faces and a polymethacrylimide foam core. Analytical models are presented for the compressive strength based on three possible collapse mechanisms: elastic buckling of the sandwich walls of the honeycomb, elastic wrinkling, and plastic microbuckling of the faces of the honeycomb. Finite element calculations confirm the validity of the analytical expressions for the perfect structure, but in order for the finite element simulations to achieve close agreement with the measured strengths it is necessary to include geometric imperfections in the simulations. Comparison of the compressive strength of the hierarchical honeycombs with that of monolithic composite cores shows a substantial increase in performance by using the hierarchical topology. [DOI: 10.1115/1.3086436] Keywords: honeycombs, composite, strength, sandwich panels

This paper proposes novel honeycomb tessellation and material-mask overlay methods to obtain optimal single-material compliant topologies free from checkerboard and point-flexure pathologies. The presence of strain-free rotation regions in rectangular cell based discretization is identified to be a cardinal cause for appearance of such singularities. With each hexagonal cell sharing an edge with its neighboring cells, strain-free displacements are not permitted anywhere in the continuum. The new material assignment approach manipulates material within a subregion of cells as opposed to a single cell thereby reducing the number of variables making optimization efficient. Cells are allowed to get filled with only the chosen material or they can remain void. Optimal solutions obtained are free from intermediate material states and can be manufactured requiring no material interpretation and less postprocessing. Though the hexagonal cells do not allow strain-free rotations, some subregions undergoing large strain deformations can still be present within the design. The proposed procedure is illustrated using three classical examples in compliant mechanisms solved using genetic algorithm. [DOI: 10.1115/1.2936891]