Boundary Layer Removal Research Articles

The Ford Rolling Road Wind Tunnel Facility

<div class="section abstract"><div class="htmlview paragraph">The Ford Motor Company Rolling Road Wind Tunnel (RRWT) is a state-of-the-art aerodynamic wind tunnel test facility in Allen Park, Michigan. The RRWT has operated since January 2022 and is designed for passenger and motorsport vehicle development. The test facility includes an office area, three secure customer vehicle preparation bays, a garage area, a vehicle frontal area measurement system, and a full-scale ¾ open jet wind tunnel. The wind tunnel features an interchangeable single belt and 5-belt Moving Ground Plane (MGP) system with an integrated 6-component balance, a two-position nozzle, boundary layer removal systems, and two independent flow traverse systems. Each flow traverse has a large horizontal box beam and vertical Z-strut that can position the flow traverse accurately within the test volume. The individual traverse systems can also operate in tandem and have the capability to perform stereo PIV measurements and scale model vehicle testing, including vehicle passing or drafting simulations. The MGP can be quickly changed between single belt and 5-belt operations, requiring only a single eight-hour shift to transition between the two configurations. The efficient wind tunnel airline is capable of airspeeds up to 250 km/h in the large 26.4 m<sup>2</sup> nozzle configuration and 322 km/h in the small 18.6 m<sup>2</sup> nozzle configuration using a 12-blade, 8 m diameter fan with a 5.4 MW motor. The wind tunnel’s flow quality and aerodynamic performance compare well with similar facilities in the automotive industry. Ford Motor Company is currently correlating aerodynamic measurement data from the RRWT with other similar facilities, using 60 vehicles across multiple product lines.</div></div>

A pressure-controllable bump based on the pressure-ridge concept

An innovative type of pressure distribution for the hypersonic aircraft forebody (bump) is presented, and this design is based on the newly established known as pressure ridge (PR) flow mechanism. Studies on the low-kinetic-energy fluid over the aircraft surface are summarized. Then, the challenges of the inlet–airframe integration at high speeds are discussed. The flow structure around the bump is analyzed in detail to eliminate the side-embedded shock (SES) effect at the inlet entrance. The concept of PR is proposed to improve the overall aerodynamic characteristics of the bump, namely, the boundary layer removal, the reduction of external drag, and the streamline direction at bump end-section. On the basis of the developed inverse method to generate the bump surface by the prescribed pressure distribution, the improved PR-derived bump is designed and numerically compared with the typical pressure-controllable bump (PCB) while the identical leading edge profile is imposed. Results demonstrate that the PR creates outward and inward pressure gradients. The removed amount of boundary layer increases with the increase in outward pressure gradient. Meanwhile, the inward pressure gradient determines the streamline pattern after the bump. The PR-derived bump is 29.2% lower in height than the typical one by using a proper outward pressure gradient. The uniform area of the new bump is 30% wider than that of the typical PCB. The near-wall streamlines of the new bump are adjusted from expanding to the parallel, thereby relieving the side-compression. Changing the location, width, and peak value of the PR can lead to great flexibility in the design and optimization of aircraft forebody subjected to hypersonic flow.

Inverse design and Mach 6 experimental investigation of a pressure controllable bump

The low kinetic flow starting from the airframe leading edge is a neglected aspect in designing hypersonic air-breathing flight vehicles. Compared with other boundary layer treating technologies, the bump concept can obtain a good balance of boundary layer removal, external drag control, shock system simplification, and integration design flexibility capabilities. On the basis of conventional conical-flow theory and the new 3D inverse design method, this study proposes a pressure controllable bump concept that can generate the bump configuration inversely by the prescribed pressure distribution. The bump/inlet integration pattern is analyzed, and the basic design methodology is presented. To validate whether the pressure distribution can be used in diverting the boundary layer, experimental study of the bump and numerical simulation are conducted. Results show that the bump has generated identical pressure distribution to the design. The bump can also divert approximately 50% of the boundary layer from the incoming low kinetic flow in Mach 6. Compared with the conventional cone-derived bump in Mach 6, the new bump is 25.8% shorter in height. The flow structure is adjusted nearly parallel to the x-direction, thereby promoting the flow quality of the inlet entrance. Hence, the new inverse design method of pressure distribution expands the applicable Mach range of the hypersonic airframe forebody.

Towards a better understanding of 2D thermal-flow processes in a scraped surface heat exchanger

To optimise and to improve heat transfer in heat exchangers, a special construction with rotational blades, called scraped surface heat exchanger (SSHE), can be applied. Despite SSHE are widely used, thermal-flow processes in these devices are still not well understood. The paper presents and describes a method allowing for precise determination of heat transfer coefficient value in case of periodic heat transfer with mechanical removal of thermal boundary layer. In order to get a better insight into these phenomena, we present numerical study on laminar forced convection in a two-dimensional SSHE model. Transport equations of mass, momentum and energy are solved in a non-inertial coordinate system using finite volume method framework. Numerical model was compared both with available analytical models based on the penetration theory and experimental data available in literature. The main goal is to investigate impact of a wide range of non-dimensional parameters on heat transfer rate. Rotational Reynolds and Prandtl numbers and a non-dimensional gap varied in range 10–1000, 0.71–56.00 and 0.005–0.15, respectively. It was found that the heat transfer rate increases with increasing both Reynolds and Prandtl numbers, and decreases with increasing the non-dimensional gap. The major conclusion resulting from numerical calculations is that the non-dimensional gap plays an important role in the laminar flow regime.

The Numerical Analysis and Experimental Research of an Aspirated Counter-Rotating Compressor

Domain scaling method was used in the unsteady numerical simulation of a dual-stage counter-rotating compressor. Numerical simulation results show that there exist much high entropy low energy fluids in the tip region on the near stall condition. In order to remove the high entropy flows near the shroud casing and improve the performance of the counter-rotating compressor, the boundary layer removal was conducted on the shroud casing over front rotor (R1) and rear rotor (R2) blade tip region. By shroud casing boundary layer suction, the flow field in the tip area improves greatly and the efficiency of the compressor increases by 0.58%. Based on the numerical results, the boundary layer suction system and measurement platform were established afterwards. The experiment was carried out with 0.9% relative suction rate in R1 and R2 tip region shroud casing respectively at 70% corrected rotating speed. Experimental results also show that shroud casing boundary layer suction can improve the compressor's performance effectively on the small flow rate conditions and has a positive role to enlarge the stable operating range.

Channel Wing as a Potential VTOL/STOL Aero-Vehicle Concept

Low-cost, high efficiency, multi-purpose and compact aircraft capable of Vertical Takeoff and Landing (VTOL) or Short Takeoff and Landing (STOL) flight have long been desired by the aerospace community. The channel wing concept, first proposed by Willard Custer in the late 1940s, is a promising candidate for efficient V/STOL performance. A channel wing has an upwardly opening semi-cylindrical channel placed near the aircraft fuselage. A propulsion unit is mounted in the channel; usually a propeller located towards the rear. When the propeller is operated at static or low speed conditions, the speed of the air flowing through the channel is much higher than that of the air flowing below the wing. As a result, high lift is generated. The concept was brought to life in prototype airplanes manufactured by the Custer Channel Wing Corporation in the 1950s and the 1960s, but these designs had a number of problems. The improvements in aerospace technology since then and recent developments in circulation control technology may facilitate the realization of a superior channel wing configuration. This paper presents a comprehensive review of the most significant patents on this subject and concludes with comments on possible future developments. Keywords: Channel wing, circulation control, boundary layer removal, tilting channel, &, curved wing

Measurement of gas-phase total peroxides at the summit of Mount Tai in China

Measurement of ambient gas-phase total peroxides was performed at the summit of Mount Tai (Mt. Tai, 1534 m above sea level) in central-eastern China during March 22–April 24 and June 16–July 20, 2007. The hourly averaged concentration of peroxides was 0.17 ppbv (± 0.16 ppbv, maximum: 1.28 ppbv) and 0.55 ppbv (± 0.67 ppbv, maximum: 3.55 ppbv) in the spring and summer campaigns, respectively. The average concentration of peroxides at Mt. Tai, which is in a heavily polluted region, was much lower than hydrogen peroxide measurements made at some rural mountain sites, suggesting that significant removal processes took place in this region. An examination of diurnal variation and a correlation analysis suggest that these removal processes could include chemical suppression of peroxide production due to the scavenging of peroxy and hydroxy radicals by high NO x, wet removal by clouds/fogs rich in dissolved sulfur dioxide which reacts quickly with peroxides, and photolysis. These sinks competed with photochemical sources of peroxides, resulting in different mean concentrations and diurnal pattern of peroxides in the spring and summer. A principal component analysis was conducted to quantify the major processes that influenced the variation of peroxide concentrations. This analysis shows that in the spring photochemical production was an important source of peroxides, and the major sink was scavenging during upslope transport of polluted and humid air from the lower part of the planetary boundary layer (PBL) and wet removal by synoptic scale clouds. During the summer, highly polluted PBL air (with high NO x) was often associated with very low peroxides due to the chemical suppression of HO 2 by high NO x and wet-removal by clouds/fogs in this sulfur-rich atmosphere, especially during the daytime. Higher concentrations of peroxides, which often appeared at mid-nighttime, were mainly associated with subsidence of air masses containing relatively lower concentrations of NO y.

Numerical Investigation of End Wall Boundary Layer Removal on Highly Loaded Axial Compressor Blade Rows

This paper presents results of numerical investigations carried out to explore the benefit of end wall boundary layer removal from critical regions of highly loaded axial compressor blade rows. At the loading level of modern aero engine compressors, the performance is primarily determined by three-dimensional (3D) flow phenomena occurring in the end wall regions. Three-dimensional Navier–Stokes simulations were conducted on both a rotor and a stator test case in order to evaluate the basic effects and the practical value of bleeding air from specific locations at the casing end wall. The results of the numerical survey demonstrated substantial benefits of relatively small bleed rates to the local flow field and to the performance of the two blade rows. On the rotor, the boundary layer fluid was removed from the main flow path through an axisymmetric slot in the casing over the rotor tip. This proved to give some control over the tip leakage vortex flow and the associated loss generation. On the stator, the boundary layer fluid was taken from the flow path through a single bleed hole within the passage. Two alternative off-take configurations were evaluated, revealing a large impact of the bleed hole shape and the location on the cross-passage flow and the suction side corner separation. On both blade rows investigated, rotor and stator, the boundary layer removal resulted in a reduction of the local reverse flow, blockage, and losses in the respective near-casing region. This paper gives insight into changes occurring in the 3D passage flow field near the casing and summarizes the effects on the radial matching and pitchwise-averaged performance parameters, namely loss and deviation of the rotor and stator when suction is active. Primary focus is put on the aerodynamics in the blade rows in the main flow path; details of the internal flow structure within the bleed off-take cavities/ports are not discussed here.

Air Pollution Processing by Radiation Fogs

Several fog episodes occurred in California’s San Joaquin Valley during winter 2000/2001. Measurements revealed the fogs to generally be less than 50 m deep, but to contain high liquid water contents (frequently exceeding 200 mg/m3) and large droplets. The composition of the fog water was dominated by ammonium (median concentration = 608 μN), nitrate (304 μN), and organic carbon (6.9 ppmC), with significant contributions also from nitrite (18 μN) and sulfate (56 μN). Principal organic species included formate (median concentration = 32 μN), acetate (31 μN), and formaldehyde (21 μM). High concentrations of ammonia resulted in high fog pH values, ranging between 5.8 and 8.0 at the core measurement site. At this high pH aqueous phase oxidation of dissolved sulfur dioxide and reaction of S(IV) with formaldehyde to form hydroxymethanesulfonate are both important processes. The fogs are also effective at scavenging and removal of airborne particulate matter. Deposition velocities for key solutes in the fog are typically of the order of 1–2 cm/s, much higher than deposition velocities of precursor accumulation mode aerosol particles. Variations were observed in deposition velocities for individual constituents in the order NO2− > fogwater > NH4+ > TOC ∼ SO42− > NO3−. Nitrite, observed to be enriched in large fog drops, had a deposition velocity higher than the average fogwater deposition velocity, due to the increase in drop settling velocity with size. Species enriched in small fog drops (NH4+, TOC, SO42−, and NO3−) all had deposition velocities smaller than observed for fogwater. Typical boundary layer removal rates for major fog solute species were estimated to be approximately 0.5–1 μg m−3 h−1, indicating the important role regional fogs can play in reducing airborne pollutant concentrations.

Emissions lifetimes and ozone formation in power plant plumes

The concept of ozone production efficiency (OPE) per unit NOx is based on photochemical models and provides a tool with which to assess potential regional tropospheric ozone control strategies involving NOx emissions reductions. An aircraft study provided data from which power plant emissions removal rates and measurement‐based estimates of OPE are estimated. This study was performed as part of the Southern Oxidants Study‐1995 Nashville intensive and focuses on the evolution of NOx, SO2, and ozone concentrations in power plant plumes during transport. Two approaches are examined. A mass balance approach accounts for mixing effects within the boundary layer and is used to calculate effective boundary layer removal rates for NOx and SO2 and to estimate net OPE. Net OPE is more directly comparable to photochemical model results than previous measurement‐based estimates. Derived net production efficiencies from mass balance range from 1 to 3 molecules of ozone produced per molecule of NOx emitted. A concentration ratio approach provides an estimate of removal rates of primary emissions relative to a tracer species. This approach can be combined with emissions ratio information to provide upper limit estimates of OPE that range from 2 to 7. Both approaches illustrate the dependence of ozone production on NOx source strength in these large point source plumes. The dependence of total ozone production, ozone production efficiency, and the rate of ozone production on NOx source strength is examined. These results are interpreted in light of potential ozone control strategies for the region.

Parallel Down Flow Rinsl : Water Saving Technology in Wafer Rinse

AbstractWe had proposed parallel downflow rinse which was capable of draining out chemical carried over to rinsing bath together with wafer about twice as fast as overflow rinse. In an attempt to further improve rinsing efficiency of PDR, we have investigated (1) the effect of wafer carrier shape, and (2) removal of boundary layer on wafer surface. Boat‐type wafer holder is preferable to conventional cassette. Three stirring techniques adequate for PDR, namely, megasonic irradiation. N2 bubbling, liquid level shifting, are found effective to remove chemical ion remaining boundary layer in measuring conductivity and resistivity.

Convective removal of thermal boundary layer of thickened continental lithosphere: A brief summary of causes and consequences with special reference to the Cenozoic tectonics of the Tibetan Plateau and surrounding regions

England, P., 1993. Convective removal of thermal boundary layer of thickened continental lithosphere: a brief summary of causes and consequences with special reference to the Cenozoic tectonics of the Tibetan Plateau and surrounding regions. In: M.J.R. Wortel, U. Hansen and R. Sabadini (Editors), Relationships between Mantle Processes and Geological Processes at or near the Earth's Surface. Tectonophysics, 223: 67–73. The tectonics of Tibet and its surroundings underwent marked changes at about 8 Ma. Normal faulting of the plateau appears to have initiated at about this time. Widespread highly potassic volcanism, interpreted as the result of rapid heating of the mechanical boundary layer, began about 12-8 Ma. Such rapid heating could be the consequence of convective removal of the lower lithosphere and its replacement by asthenosphere. This process would have raised the surface height of the plateau and could have provided the driving force for extension. The diffuse deformation in the Indian Ocean probably began at about 8 Ma; analysis of the buckling of a plastic lithosphere implies that the horizontal force per unit length required to drive this deformation is consistent with uplift of the Tibetan plateau by 1–3 km. The Indian monsoon intensified at about 8 Ma. This intensification is consistent with the rapid passage of the surface height of the plateau across a threshold required to disrupt the pre-existing atmospheric circulation of the region. Taken together, these observations imply that the surface height of the Tibetan plateau rose by between 1 and 3 km in a few million years around 8 Ma. Such a rapid increase in surface height affecting an area the size of the Tibetan plateau could not be achieved by crustal thickness changes, but could have been caused by the convective removal of a substantial thickness of lower continental lithosphere of the region.

Adhesion Studies of Fluoropolymers

Abstract A comparative study of the treatment of polytetrafluoroethylene (PTFE) and poly(vinyl fluoride) (PVF) with “Tetra-Etch” has been carried out. The treatment of PTFE resulted in extensive changes in surface chemistry and topography, whereas with PVF there was no significant change in topography and the chemical changes were much less marked. However, treatment of both polymers resulted in large increases in bond strength. Multiple bonding experiments in which samples are repeatedly fractured and re-bonded were carried out with untreated PTFE and PVF. These resulted in moderate increases in bond strength with PTFE and large increases with PVF. The results indicate that weak boundary layer (WBL) removal is a key element in adhesion improvement by “Tetra-Etch” on PVF. With PTFE, WBL removal also improves adhesion, but the chemical and/or topographical changes introduced by the “Tetra-Etch” are required for optimum performance.

Wake mixing and performance of a compressor cascade with crenulated trailing edges

Trailing-edge crenulations have been shown to enhance velocity recovery (wake dissipation) and to decrease total pressure losses in the blade wakes downstream of a low-aspect ratio linear compressor cascade. A new study was performed to determine the influence of trailing-edge crenulations on outlet flow in the presence of varied inlet flow conditions. Two levels of inlet flow turbulence intensity (about 0.15 and 3%) were combined with sidewall boundary-layer removal at the cascade inlet (on or off) to provide four test conditions. Results from blades with large and small crenulations were compared with unmodified blades. For each test condition, a reduction of 10-20% in both velocity variance (enhanced wake mixing) and total pressure loss was observed in the outlet flow with the crenulated blades, while a slight decrease in turning angle was also observed.

Relationship between surface properties and adhesion for etched ultra-high-molecular-weight polyethylene fibers

Chemical etching is an established and popular method of increasing the adhesion to such materials as polyethylene. Ultra-high-molecular-weight polyethylene (UHMWPE) fibers are exceptional candidates for composite materials except for their poor adhesion. In this research, the bulk, surface and adhesive properties of as-received and chromic acid etched UHMWPE fibers have been examined. The fiber tensile properties, surface chemistry and wettability have been characterized. The adhesion of epoxy has been characterized by the interfacial shear strength of a droplet microbond. The more than six-fold increase in interfacial shear strength observed in this work is related to the etching process. The removal of an oxygen-rich weak boundary layer, surface roughening and oxidation of the UHMWPE contribute to the enhanced adhesion.

Controlling the spacing of streamwise vortices on concave walls

The wavelength of Gortler streamwise vortices changed by a factor of three by varying the amount of tunnel side wall boundary-layer removal just upstream of the concave wall test section's leading edge. Nondimensional wavelengths were achieved with the larger wavelengths resulting from increased suction. The minimum wavelength compares well with the maximum amplification curve based on past theoretical studies. Low-speed streaks appeared to merge with other low-speed streaks or were weakened to the point of disappearing as the suction level was increased. The downstream location of secondary instability onset changed with variation in suction level and/or wavelength. The Gortler number and amplification factor for secondary instability onset, however, was approximately independent of suction level and/or wavelength.

Sidewall boundary-layer removal and wall adaptation studies

This paper describes the NASA Langley Research Center 0.3m transonic cryogenic tunnel sidewall boundary-layer removal system and its integrated operation with the adaptive wall adjustment. Empty test-section measurements show that the sidewall boundary-layer displacement thickness at the model station is reduced from about 1.0 to 0.6% of the test section width when the maximum boundary-layer removal conditions are applied. Test with a supercritical airfoil model show that the iterative top and bottom wall adaptation process performs satisfactorily with sidewall boundary-layer removal. The top and bottom walls move together to correct for the freestream Mach number changes associated with the boundary-layer removal. The airfoil test showed that the boundary-layer removal does not significantly influence the midspan measurements for thin sidewall boundary layers. With successful operation of iterative wall adaptation and sidewall boundary layer removal the tunnel provides the potential for airfoil testing at flight-equivalent Reynolds numbers and low wall interference.

Computer simulation of the boundary layer oxidation and removal of atmospheric pollutants over the western Atlantic Ocean

A computer model for simulating the atmospheric chemistry and removal of polluted air parcels, within the marine boundary layer, was developed. The model was applied to the case of eastward transport of anthropogenic pollution across the western Atlantic Ocean. The model includes over 100 chemical reactions describing the gas phase processes that occur in polluted atmospheres, as well as features describing the daily photochemical cycle, changes in mixing height, air mass exchange between the boundary layer and the free troposphere and deposition. The initial concentrations for the model calculations were set to be equal to those observed during the Western Atlantic Ocean Experiment (WATOX), and the results of the computation are compared with observations in Bermuda during the same project.

Laser Doppler Velocimeter Development

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. II is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to psoition the laser beams in the channel flow. Techniques used to seed the flow with 0.5-μ-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.

Heat and mass transfer in combustion: Fundamental concepts and analytical techniques

Fundamental combustion phenomena and the associated flame structures in laminar gaseous flows are discussed on physical bases within the framework of the three nondimensional parameters of interest to heat and mass transfer in chemically-reacting flows, namely the Damköhler number, the Lewis number, and the Arrhenius number which is the ratio of the reaction activation energy to the characteristic thermal energy. The model problems selected for illustration are droplet combustion, boundary layer combustion, and the propagation, flammability, and stability of premixed flames. Fundamental concepts discussed include the flame structures for large activation energy reactions, S-curve interpretation of the ignition and extinction states, reaction-induced local-similarity and non-similarity in boundary layer flows, the origin and removal of the cold boundary difficulty in modeling flame propagation, and effects of flame stretch and preferential diffusion on flame extinction and stability. Analytical techniques introduced include the Shvab-Zeldovich formulation, the local Shvad-Zeldovich formulation, flame-sheet approximation and the associated jump formulation, and large activation energy matched asymptotic analysis. Potentially promising research areas are suggested.