Current state and future trends in boundary layer control on lifting surfaces

Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application

Simulating flow in silicon Y-bifurcated microchannels

Microfluidic devices are excessively used for various biomedical, chemical, and engineering applications. The most common microfluidic platforms are obtained from polydimethylsiloxane (PDMS). Platforms based on etched silicon wafers anodically bonded to Pyrex glass are more mechanically rigid, have better sealing and there is no gas permeability compared to those obtained from PDMS [1,2]. The aim of our work is to numerically analyze fluid flow in anisotropically etched silicon microchannels sealed with Pyrex glass. We present simulations of fluid flow in Y-bifurcated microchannels fabricated from the etched {100} silicon in 25 wt% tetramethylammonium hydroxide (TMAH) water solution at the temperature of 80°C [3]. We have explored two symmetrical Y-bifurcations that are defined with acute angles of 36.8° and 19° with the sides that are along the and crystallographic directions in the masking layer [3], respectively. The angles between obtained sidewalls and {100} silicon of two ingoing microchannels for the first and second Y-bifurcation are 72.5° and 80.7°, respectively. The sidewalls of outgoing microchannel in both cases are defined with crystallographic directions and they are orthogonal to the surface of {100} silicon wafer. The appropriate widths of ingoing and outgoing microchannels are 300 and 400 μm, respectively. The depth of microchannels is 55 μm. All simulated flows are three-dimensional (3D), steady and laminar [4], while the investigated fluid is water. Velocities and pressure values are defined at the inlet and outlet boundaries, respectively. The resulting flows are illustrated by velocity contours. The obtained conclusions from fluid flow simulations of presented simple Y-bifurcations provide guidance for future fabrication of complex microfluidic platforms by a cost-effective process with good control over microchannel dimension

Optimal airfoil design and wing analysis for solar-powered high altitude platform station

The ability of flying continuously over prolonged periods of time has become target of numerous research studies performed in recent years in both the fields of civil aviation and unmanned drones. High altitude platform stations are aircrafts that can operate for an extended period of time at altitudes 17 km above sea level and higher. The aim of this paper is to design and optimize a wing for such platforms and computationally investigate its aerodynamic performance. For that purpose, two-objective genetic algorithm, class shape transformation and panel method were combined and used to define different airfoils with the highest lift-to-drag ratio and maximal lift coefficient. Once the most suitable airfoil was chosen, polyhedral half-wing was modeled and its aerodynamic performances were estimated using the CFD approach. Flow simulations of transitional flow at various angles-of-attack were realized in ANSYS FLUENT and various quantitative and qualitative results are presented, such as aerodynamic coefficient curves and flow visualizations. In the end, daily mission of the aircraft is simulated and its energy requirement is estimated. In order to be able to cruise above Serbia in July, an aircraft weighing 150 kg must accumulate 17 kWh of solar energy per day

Two-dimensional numerical analysis of active flow control by steady blowing along foil suction side by different urans turbulence models

The effects of active separation control by steady blowing jets were investigated numerically on three different examples: subsonic flow past Aerospatiale A airfoil at 13º angle-of-attack, transonic flow past NACA 0012 airfoil at 4º angle-ofattack, and transonic flow in linear compressor/turbine cascade. Performed analyses are two-dimensional, flow is turbulent (or transitional) while fluid is viscous and compressible. Jets are positioned along the suction sides of the foils, the first one being located just upstream of the separation point, and modeled by source terms added to flow equations. Several different jet diameters and intensities are investigated. As the choice of turbulence model affects the final solution of Reynolds equations, turbulence is modeled by four different models: Spalart- Allmaras, realizable k-ε, k-ω SST, and γ-Reθ, and a comparison of obtained results is performed. Goals of the study include definition of an adequate numerical setting that enables sufficiently correct simulation of the problems in question as well as evaluation of the possible increase in aerodynamic performances. Lift coefficients, lift-to-drag ratios or relative pressure differences are improved for all controlled cases

Optimal airfoil design and wing analysis for solar-powered high altitude platform station

The ability of flying continuously over prolonged periods of time has become target of numerous research studies performed in recent years in both the fields of civil aviation and unmanned drones. High altitude platform stations are aircrafts that can operate for an extended period of time at altitudes 17 km above sea level and higher. The aim of this paper is to design and optimize a wing for such platforms and computationally investigate its aerodynamic performance. For that purpose, two-objective genetic algorithm, class shape transformation and panel method were combined and used to define different airfoils with the highest lift-to-drag ratio and maximal lift coefficient. Once the most suitable airfoil was chosen, polyhedral half-wing was modeled and its aerodynamic performances were estimated using the CFD approach. Flow simulations of transitional flow at various angles-of-attack were realized in ANSYS FLUENT and various quantitative and qualitative results are presented, such as aerodynamic coefficient curves and flow visualizations. In the end, daily mission of the aircraft is simulated and its energy requirement is estimated. In order to be able to cruise above Serbia in July, an aircraft weighing 150 kg must accumulate 17 kWh of solar energy per day

Metoda za posmatranje i analizu protoka fluida u Si-Pyrex staklo opto-mikrofluidnim platformama

Ovo tehničko rešenje predstavlja razvoj metode za posmatranje i analizu protoka fluida u silicijum-Pyrex staklo opto-mikrofluidnim platformama. Metoda se zasniva na snimanju video zapisa pomoću metalografskog mikroskopa sa digitalnom kamerom dok se špric pumpama (syringe pump) definisano zadaje protok fluida kroz izrađenu platformu. Platforma se sastoji od mikrokanala koji su izrađeni procesima mikromašinstva, odnosno vlažnog hemijskog nagrizanja, i anodnog bondovanja silicijuma i Pyrex stakla. Kroz staklo platforme se posmatraju i snimaju protoci različitih fluida sa ili bez čestica u mikrokanalima. Mikrokanali mogu biti različitog dizajna i definisani u silicijumu i/ili Pyrex staklu. Validacija funkcije izrađene platforme (mikromiksera ili separatora čestica) vrši se analizom fotografija ili frejmova video zapisa pomoću odgovarajućih softverskih paketa, na primer ImageJ

Morphometric study of uninvolved rectal mucosa 10 cm and 20 cm away from the malignant tumor

Recently, many details of the interplay between tumor cells and tumor-associated stromal elements leading to the progression of malignant disease were elucidated. In contrast, little is known about the role of uninvolved stromal tissue in the remote surrounding of the malignant tumor. Therefore, we performed a computer-aided morphometric study of rectal mucosa in samples taken 10 cm and 20 cm away from the malignant tumor during endoscopic examination of 23 patients older than 60 years. The samples of rectal mucosa from 10 healthy persons of corresponding age subjected to diagnostic rectoscopy during active screening for asymptomatic cancer were used as control. All structural elements of the rectal mucosa were studied and the number of nucleated cells in the lamina propria per 0.1 mm2 of tissue was assessed. Our study revealed a reduced number of cells in the lamina propria of the rectal mucosa 10 cm and 20 cm away from the tumor lesion in both male and female patients. The decreased mucosal height and increased crypt number were registered in female patients 10 cm away from the tumor. The connective tissue of lamina propria showed a disorderly organization: the collagen fibers were frail, loosely arranged and signs of tissue edema were present. Small blood vessels and capillaries were much more frequently seen than in healthy tissue. Our results demonstrate the complex interactions between the cancer and remote mucosal tissue of the affected organ