Structured Porous Material Design for Passive Flow and Noise Control of Cylinders in Uniform Flow

Abstract

Cylindrical bodies in uniform flows can be coated with a porous medium as a passive flow and noise control method in an effort to reduce the acoustic effects of vortex shedding. To date, the employed open-cell porous materials typically possess a randomized internal structure. This paper presents the design and validation of a novel 3-D printed structured porous coated cylinder that has significant flexibility, in that the porosity and pores per inch of the porous coating can be modified independently and relatively easily. The performance of the structured porous coating design is compared against porous polyurethane and metal foam with the same coating dimensions and similar pores per inch and porosity via an experimental acoustic investigation, revealing strong similarity in the passive noise control performance of each material type. A numerical comparison illustrates the similarities of the wake structure of the 3-D printed porous coated cylinder to an equivalent Darcy–Forchheimer model simulation that represents a randomized internal porous structure. The performance similarities of these different porous material types indicate that a structured porous geometry can be used to understand the internal flow behavior of the porous medium responsible for reducing the cylinder vortex shedding tone that is otherwise extremely difficult or impossible with typical randomized porous structures. Moreover, significant potential exists for the porous structure to be further optimized or smartly tailored by architectural design for different control purposes, coating geometries and dimensions, and working conditions.

Internal and Near-Wall Flow Fields of a Structured Porous Coated Cylinder and Their Role in Passive Flow and Noise Control

“…The important properties of porous media include the numbers of Pores Per Inch (PPI) [1,9] and the porosity, , as a percentage of the porous media volume with respect to a solid equivalent [4,5,10]. The typical experimentally investigated PPI range, using an MFPCC and PPCC for porous coated cylinders is from 10 PPI to 30 PPI [1,9,11,12], with significant vortex shedding tone reduction observed using 10 PPI materials [11,12].…”

“…The typical experimentally investigated PPI range, using an MFPCC and PPCC for porous coated cylinders is from 10 PPI to 30 PPI [1,9,11,12], with significant vortex shedding tone reduction observed using 10 PPI materials [11,12]. Arcondoulis et al [10] designed a Structured Porous Coated Cylinder (SPCC) that has a clear line of sight along the cylinder span, and also from the outer SPCC surface into the internal solid cylinder thus allowing the use of tomographic PIV to obtain some insight on the internal flow fields within the porous layers [13]. They showed that the tone suppression and frequency shift were very similar to PPCCs and MFPCCs with similar porosity and PPI.…”

“…While this is not desirable, it is of secondary importance relative to the study of the reduction of the fundamental bare cylinder vortex shedding flow mechanisms. It is hypothesized that the internal and near-wall flow fields of SPCC should be similar to those of the MFPCC or PPCC, due to their similar acoustic behavior when placed in uniform flow [10]. The near-wall flow field is relatively simple to compare for different cylinder types; the internal flow field and its interaction with the outside one, however, is not as simple to measure and therefore difficult to compare.…”

3D Printed Structured Porous Treatments for Flow Control around a Circular Cylinder

“…When the cylinder is covered with a porous coating the air flow not only goes around the cylinder but also through the porous coating. Flow analysis of a porous coated cylinder by [14] revealed that for a circumferential angle of up to 90 • , streamlines follow an internal path, and each pore in the medium generates a small wake, resulting in turbulent kinetic energy within each pore. The flow travels amongst adjacent pores from 90 • to 135 • .…”

Improved Energy Absorption Characteristics Based on Elastic Polymer-Modified Porous Material for Multiple Extreme Mechanical Impacts

“…High energy absorption characteristics are critically important for the protective effects, and many researchers have devoted a lot of efforts to improve them. Currently, the most widely applied materials with high energy absorption characteristics were the porous materials [5][6][7][8], which could absorb a great amount of energy by plastic deformation, resulting from the compressibility of the pore structures [9,10]. Numerous theoretical and experimental studies proved that porous materials not only had excellent energy absorption characteristics under the mechanical impact with huge energy, but also had a low density and good flexibility [11][12][13][14].…”