Abstract Adiabatic effectiveness (η) of film cooling is strongly affected by the geometry of the film-cooling hole. This study presents and assesses a new shape-hole geometry, referred to as the Y-shaped hole, that increases η by splitting the cooling flow into three streams to improve lateral spreading and by decreasing the hole's cross-sectional area to improve downstream penetration. The Y-shaped hole was assessed computationally and experimentally by examining its usefulness in film cooling a flat plate with the cooling flow issuing from a plenum. The computations with and without conjugate heat transfer were based on the Reynolds-averaged continuity, Navier–Stokes (RANS), energy equations closed by the shear-stress transport (SST) turbulence model for the gas phase (steady RANS), and the thermal-energy equation for the solid phase. The experimental component used infrared thermography to measure surface temperature, which agreed reasonably well with computations that accounted for conjugate heat transfer. Computations with adiabatic walls show laterally averaged η produced by the Y-shaped hole to be nearly twice that obtained by the 777 and the W-shaped hole under comparable blowing and temperature ratios.

Abstract A numerical study based on steady RANS with the SST turbulence model was performed to investigate the flow and heat transfer in a ribbed U-duct with a rectangular cross section that converges linearly in the radially outward direction and diverges linearly in the radially inward direction under rotating and non-rotating conditions. Parameters examined include rotation number (Roi = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Rei = 46,000, 100,000, and 154,000), and the duct's taper angle (α = 0° and 1.41°) under conditions relevant to gas turbines used for electric power generation. Results obtained show that increasing the taper angle from 0° to 1.41°, which appears negligibly small, significantly increases both the friction coefficient and the Nusselt number whether there is rotation or not. With rotation at Roi = 0.0336 and Rei = 100,000, the maximum increase in the average friction coefficient and Nusselt number was found to be 41.7% and 36.6% respectively. Without rotation at Rei = 46,000, those are 11.5% and 14.7% respectively.

This study examines outflow boundary conditions (BCs) in computational fluid dynamics (CFD) simulations of a transition duct with and without guide vanes that converts supersonic flow exiting a rotating detonation combustor (RDC) to subsonic flow to drive a turbine. Since the flow exiting the transition duct has swirling shock waves with significant spatial and temporal variations in pressure, temperature, and Mach number, imposing proper BCs poses a challenge. To ensure all swirling shock waves exit the transition duct without creating non-physical reflected waves at its outlet, this study examined three outflow BCs: (1) the average pressure imposed at the duct’s outlet, (2) a nonreflecting BC (NRBC) with a specified average pressure imposed at the duct’s outlet, (3) the average pressure imposed at the outlet of an extension duct made up of a buffer layer and a sponge layer. This study is based on the three-dimensional, unsteady density-weighted-ensemble-averaged continuity, Navier–Stokes, and energy equations for a thermally perfect gas closed by the realizable k–ε model and “enhanced” wall functions. The results obtained show that imposing an average pressure at the transition duct’s outlet produces spurious waves that degrade the physical meaningfulness of the solution. When the NRBC was applied, swirling shock waves exited the duct’s outlet without creating spurious waves. However, its usage requires the gas to be thermally, as well as calorically, perfect, which this study shows could be a concern. By imposing the average pressure at the outlet of an extension duct, the gas does not need to be calorically perfect. The results obtained show the effects of the sponge layer’s length and coarsening ratio on damping nonuniformities in non-physical reflected waves to ensure the flow exiting the transition duct’s outlet can do so as if there are no boundaries present and has the desired average pressure—even though the BC is applied at the extension duct’s outlet.

The adiabatic effectiveness of film cooling (eta) has been characterized by the density (DRh) and blowing (BRh) ratios. In this study, dimensional analysis and computations based on Reynolds-averaged Navier-Stokes (RANS) were performed to identify and examine parameters needed to quantify eta, where film cooling is crossflow-fed instead of plenum-fed. The test problem studied is film cooling of a flat plate, where the cooling air, issuing through 30-deg inclined circular holes, is fed from a cooling channel whose flow direction is perpendicular to the direction of the hot-gas flow. For this test problem, dimensional analysis shows an additional blowing ratio is needed, denoted as BRc, to quantify eta, where BRc is the ratio of the mass flux through the film-cooling hole to the mass flux in the cooling channel upstream of the film-cooling hole. RANS results with and without conjugate heat transfer obtained by varying the mass flowrate in the cooling channel, while keeping DRh and BRh constant (DRh = 1.9 and BRh was either 0.75 or 1.0), show reducing mass flowrate in the cooling channel by one-half, which doubles BRc (from 2.6 to 5.2) to slightly affect the discharge coefficient through the film-cooling holes (<5%) but up to 85% on laterally averaged eta and up to 25% on overall cooling effectiveness. RANS results also show the flow mechanisms induced by BRc that affect eta. The RANS results of this study were validated by comparing with experimental data.

In gas turbines, tip-leakage flow (TLF) could account for up to one-third of the total stage loss in the turbine component. This study used hybrid LES-RANS (IDDES) to examine the flow in a 1.5-stage high-pressure turbine under geometric, pressure (P), temperature (T), rotational speed, mass-flow rate, Mach number, and Reynolds number conditions that are relevant to land-based, electric-power-generation gas turbines. Though IDDES was used, 95% of the flow field from the trailing edge of the first-stage stator vane to the inlet of the second-stage stator and up to 80% of the tip gap was simulated by LES. Results are presented that show details of the unsteady vortex shedding from the first-stage vane, effects of stator-rotor interactions on secondary flows in the blade passage, and the tip-leakage flow structures about the tip-gap region. The unsteadiness in the flow was found to cause the adiabatic-wall temperature and the pressure on the blade surface to vary by as much as 150 K and 0.5 MPa. In addition, the dominant frequency produced by vortex shedding at the trailing edge of the first-stage stator vane was found to be an order of magnitude higher than the frequency from blade passing. Based on the results obtained for the mean flow structures in the tip-gap region, two designs were proposed. One is where transpiration cooling should be implemented. The other is an appendage on the blade tip's pressure side to reduce the amount of TLF.

Newton’s law of cooling requires a reference temperature (Tref) to define the heat-transfer coefficient (h). For external flows with multiple temperatures in the freestream, obtaining Tref is a challenge. One widely used method, referred to as the adiabatic-wall (AW) method, obtains Tref by requiring the surface of the solid exposed to convective heat transfer to be adiabatic. Another widely used method, referred to as the linear-extrapolation (LE) method, obtains Tref by measuring/computing the heat flux (qs′′) on the solid surface at two different surface temperatures (Ts) and then linearly extrapolating to qs′′=0. A third recently developed method, referred to as the state-space (SS) method, obtains Tref by probing the temperature space between the highest and lowest in the flow to account for the effects of Ts or qs′′ on Tref. This study examines the foundation and accuracy of these methods via a test problem involving film cooling of a flat plate where qs′′ switches signs on the plate’s surface. Results obtained show that only the SS method could guarantee a unique and physically meaningful Tref where Ts=Tref on a nonadiabatic surface qs′′=0. The AW and LE methods both assume Tref to be independent of Ts, which the SS method shows to be incorrect. Though this study also showed the adiabatic-wall temperature, TAW, to be a good approximation of Tref (<10% relative error), huge errors can occur in h about the solid surface where |Ts−TAW| is near zero because where Ts=TAW, qs′′≠0.

Adiabatic effectiveness (eta) of film cooling is strongly affected by the geometry of the film-cooling hole. This study presents a new shaped-hole design, referred to as the Y-shaped hole, that seeks to increase eta by splitting the cooling flow into three streams for increased lateral spreading and by decreasing the flow's cross-sectional area for increased momentum and hence streamwise penetration. To assess the Y-shaped hole, a combined computational and experimental study was performed to examine film-cooling of a flat plate with the film-cooling flow issuing from one row of Y-shaped holes fed by a plenum. The parameters studied were the blowing ratio (BR = 0.75, 1.0, 1.3) and the temperature ratio (TR = 1.5, 1.6, 1.9). Since the Y-shaped hole has variable cross sections along the hole, the blowing ratio is defined by the mass flux at the hole's minimum cross section. The computational part of the study is based on the steady Reynolds-Averaged Navier-Stokes (RANS) equations for compressible flows that account for temperature-dependent viscosity and thermal conductivity with turbulence modelled by the Shear-Stress Transport (SST) model. Computations were performed with and without conjugate heat transfer. Results from the conjugate study were compared with experimental data, and reasonable agreement was obtained. Results with the adiabatic wall show laterally-averaged.. produced by the Yshaped hole to be nearly twice that obtained by the 777 and the W-shaped hole with BR = 1 at several TRs.

Blades in gas turbines have cross sections at the root that are larger than those at the tip so that internal cooling passages in blades are tapered. In this study, a reduced-order model (ROM) based on the integral continuity, momentum, and energy equations for a thermally and calorically perfect gas was developed to enable rapid assessments of radially outward flow in a tapered duct subjected to constant heat flux with and without rotation. The following parameters were investigated by using the ROM developed: taper angle (alpha = 0 degrees, 1.5 degrees, 3.0 degrees), ratio of mean radius to hydraulic diameter (R-m/D-h = 45, 150), rotation number (Ro = 0, 0.025, 0.25), Reynolds number (Re = 37,000, 154,000), and thermal loading (q" = 5x10(4), 10(5) W/m(2)). Results obtained show the density and pressure variation along the duct to be most affected by rotation number; velocity to be more affected by duct's taper angle; and temperature by rotation number and taper angle. Results obtained also show the temperature along the duct could decrease if the taper is sufficiently large even with high heat flux into the duct because taper increases velocity, which converts thermal energy to mechanical energy. Within the range of parameters studied, the mass flow of the cooling flow could be reduced by as much as 44% for a tapered duct to achieve bulk temperature variation similar to that of a duct without a taper. The ROM developed was validated by comparing its predictions with grid-converged CFD results obtained by steady RANS with the SST turbulence model. The maximum relative errors for density, velocity, temperature, and pressure distributions along the duct were found to be 0.6%, 3.3%, 0.4%, 0.3% for the smooth section of the duct and 3.2%, 5.6%, 0.9%, 3.0% for the ribbed section of the duct. Thus, the ROM developed performs nearly as well as CFD based on RANS but orders of magnitude more efficient computationally.

This is an in-memoriam honoring Professor Darrell W. Pepper as an exceptional researcher, educator, and engineer.

Large-eddy simulation (LES) and Reynolds-Averaged Navier–Stokes (RANS) equations were used to study incompressible flow and heat transfer in a U-duct with a high-aspect-ratio trapezoidal cross section. For the LES, the WALE subgrid-scale model was employed, and its inflow boundary condition was provided by a concurrent LES of incompressible fully-developed flow in a straight duct with the same cross section and flow conditions as the U-duct. LES results are presented for turbulent kinetic energy, Reynolds stresses, pressure–strain rate, turbulent diffusion, turbulent transport, and velocity–temperature correlations, with a focus on how they are affected by the U-turn region of the U-duct. The LES results were also used to assess three commonly used RANS models: the realizable k-ε with the two-layer model in the near-wall region, the two-equation shear-stress transport model, and the seven-equation stress-omega Reynolds stress model. Results obtained show steady and unsteady RANS to incorrectly predict the effects of unsteady flow separation. The results obtained also identified the terms in the RANS models that need to be modified and suggested how turbulent diffusion should be modeled when there is unsteady flow separation.

Large-eddy simulations (LES) were performed to study the turbulent flow in a channel of height H with a staggered array of pin fins with diameter D = H/2 as a function of heating loads that are relevant to the cooling of turbine blades and vanes. The following three heating loads were investigated—wall-to-coolant temperatures of Tw/Tc = 1.01, 2.0, and 4.0—where the Reynolds number at the channel inlet was 10,000 and the back pressure at the channel outlet was 1 bar. For the LES, two different subgrid-scale models—the dynamic kinetic energy model (DKEM) and the wall-adapting local eddy-viscosity model (WALE)—were examined and compared. This study was validated by comparing with data from direct numerical simulation and experimental measurements. The results obtained show high heating loads to create wall jets next to all heated surfaces that significantly alter the structure of the turbulent flow. Results generated on effects of heat loads on the mean and fluctuating components of velocity and temperature, turbulent kinetic energy, the anisotropy of the Reynolds stresses, and velocity-temperature correlations can be used to improve existing RANS models.

Turbine inlet temperatures in advanced gas turbines could be as high as 2000 °C. To prevent ingress of this hot gas into the wheelspace between the stator and rotor disks, whose metals can only handle temperatures up to 850 °C, rim seals and sealing flows are used. This study examines the abilities of large eddy simulation (LES) based on the WALE subgrid model and Reynolds-averaged Navier–Stokes (RANS) based on the SST model in predicting ingress in a rotor–stator configuration with vanes but no blades, a configuration with experimental data for validation. Results were obtained for an operating condition, where the ratio of the external Reynolds number to the rotational Reynolds number is 0.538. At this operating condition, both LES and RANS were found to correctly predict the coefficient of pressure, Cp, located downstream of the vanes and upstream of the seal, but only LES was able to correctly predict the sealing effectiveness. This shows Cp by itself is inadequate in quantifying externally induced ingress. RANS was unable to predict the sealing effectiveness because it significantly under predicted the pressure drop in the hot gas path along the axial direction, especially about the seal region. This affected the pressure difference across the seal in the radial direction, which ultimately drives ingress.

Counter-rotating vortices, formed by the interaction of film cooling jets and the hot gas flow, adversely affect performance of conventional film cooling designs. In two previous papers (GT2020-14317 and GT2022-82675), downstream vortex generators consisting of rectangular plates arranged in a V-shaped pattern were shown to improve cooling effectiveness by mitigating effects of the counter-rotating vortices and by deflecting the cooling jet laterally. In this study, computational and experimental methods were used to examine how cylindrical film cooling holes (D = 3.2mm, L/D = 6, p/D = 3, α = 30°) with and without downstream vortex generators perform when the flow in the coolant supply channel is perpendicular to the direction of the hot gas. For this study, the hot gas had a temperature of 650K, and an average Mach number of 0.23. The hot-gas-to-coolant temperature ratio was 1.9, and two blowing ratios (0.75 and 1.0) were studied. Results from the CFD study show how crossflow affects the interaction between the film cooling jet and hot gas flow with and without downstream vortex generators. The experimental measurements were based on infrared thermography in a conjugate heat transfer environment. Results were obtained for film cooling performance in terms of overall effectiveness, film effectiveness, and local heat transfer coefficients. The downstream vortex generators can increase the laterally averaged effectiveness by a factor of 1.5 relative to cylindrical holes, but this higher performance is restricted to low crossflow velocities and higher blowing ratios.

No AccessIntroductionsIntroduction to the Directed Energy for Aerospace Applications Virtual CollectionDonald J. Wittich, Nicholas J. Morley, Steve Griffin, Bryan Kelchner and Tom I-P. ShihDonald J. WittichAir Force Research LaboratorySearch for more papers by this author, Nicholas J. MorleyAir Force Research LaboratorySearch for more papers by this author, Steve GriffinThe Boeing CompanySearch for more papers by this author, Bryan KelchnerTeknicare, Inc.Search for more papers by this author and Tom I-P. ShihPurdue University Search for more papers by this authorPublished Online:29 Aug 2023https://doi.org/10.2514/1.J063303SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Duffner R. W., Airborne Laser: Bullets of Light, Plenum Press, New York, 1997. Google Scholar[2] Perram G. P., Cusumano S. J., Hengehold R. L. and Fiorino S. T., Introduction to Laser Weapon Systems, Directed Energy Professional Soc., Albuquerque, NM, 2010, Chap. 11.4. Google Scholar[3] Patel V. P., Koerner M. and Loeffelholz D., “Thermal Management and Power Generation for Directed Energy Weapons: Aircraft Thermal Management,” Systems Architectures, Vol. 177, May 2016, p. 61. Google Scholar[4] Wells H. G., The War of the Worlds, William Heinemann Publ., London, 1898, Chap. V. Google Scholar[5] Schawlow A. L. and Townes C. H., “Infrared and Optical Masers,” Physical Review, Vol. 112, No. 6, 1958, p. 1940. https://doi.org/10.1103/PhysRev.112.1940 CrossrefGoogle Scholar[6] Day D. A., “Hubble in the Crosshairs,” The Space Review, 2011, https://www.thespacereview.com/article/1865/1.https://www.thespacereview.com/article/1865/1. Google Scholar[7] Kopp C., “High Energy Laser Directed Energy Weapons,” Air Power Australia APA-TR-2008-0501, 2012. Google Scholar[8] Jumper E. J. and Fitzgerald E. J., “Recent Advances in Aero-Optics,” Progress in Aerospace Sciences, Vol. 37, No. 6, 2001, pp. 299–339. Google Scholar[9] Lamberson S., Schall H. B. and Alvarado O. L., “Overview of Airborne Laser’s Test Program,” AIAA Paper 2005-7650, 2005. Google Scholar[10] Griffin S. F. and Kelchner B. L., “Line-of-Sight Jitter for Advanced Tactical Laser,” AIAA Journal, Vol. 61, No. 7, 2023, pp. 3204–3209. LinkGoogle Scholar[11] De Lucca N., Gordeyev S. and Jumper E., “In-Flight Aero-Optics of Turrets,” Optical Engineering, Vol. 52, No. 7, July 2013, Paper 071405. CrossrefGoogle Scholar[12] Duffner R. W., The Adaptive Optics Revolution: A History, Univ. of New Mexico Press, Albuquerque, NM, 2009. Google Scholar[13] Gilbert K. G. and Otten L. J. (eds.), Aero-Optical Phenomena, Progress in Astronautics and Aeronautics, Vol. 80, AIAA, Washington, D.C., 1982. Google Scholar[14] Jumper E. J. and Gordeyev S., “Physics and Measurement of Aero-Optical Effects: Past and Present,” Annual Review of Fluid Mechanics, Vol. 49, Jan. 2017, pp. 419–441. CrossrefGoogle Scholar[15] De Lucca N., Gordeyev S. and Jumper E., “Global Unsteady Pressure Fields over Turrets In-Flight,” AIAA Paper 2015-0677, 2015. Google Scholar[16] Kalensky M., Jumper E., Whiteley M., Diskin Y., Gordeyev S., Drye R., Archibald A. and Grose M., “Turbulence Profiling Using AAOL-BC,” AIAA Paper 2020-0682, 2020. LinkGoogle Scholar[17] Malkus M. J., Frede M. T., Sherer S. E. and Garmann D. J., “Effect of Submergence on Transonic Flow Around a Hemisphere,” AIAA Journal, Vol. 60, No. 11, 2022, pp. 6082–6096. LinkGoogle Scholar[18] Sontag J. and Gordeyev S., “Optical Diagnostics of Spanwise-Uniform Flows,” AIAA Journal, Vol. 60, No. 9, 2022, pp. 5031–5045. LinkGoogle Scholar[19] Lynch K. P., Miller N. E., Guildenbecher D. R., Butler L. and Gordeyev S., “Aero-Optical Measurements of a Mach 8 Boundary Layer,” AIAA Journal, Vol. 61, No. 3, 2023, pp. 991–1001. LinkGoogle Scholar[20] Kelchner B. L., “Modeling and Design Methodology for the Development of Electro-Optical and Laser Systems,” AIAA Journal, Vol. 60, No. 11, 2022, pp. 6066–6075. LinkGoogle Scholar[21] Holmes R. B., “Adaptive Optics for Directed Energy: Fundamentals and Methodology,” AIAA Journal, Vol. 60, No. 10, 2022, pp. 5633–5644. LinkGoogle Scholar[22] Li C., Lu Y. and Zhang S., “Application of the General Extended-Object Wavefront Sensor into Aberration Correction of Lasers,” AIAA Journal, Vol. 60, No. 11, 2022, pp. 6076–6081. LinkGoogle Scholar[23] Negro J., Griffin S., Beazel V. and Kelchner B., “Inertial Stable Platforms for Precision Pointing of Optical Systems in Aerospace Applications,” AIAA Journal, Vol. 61, No. 8, 2023, pp. 3234–3246. LinkGoogle Scholar Next article FiguresReferencesRelatedDetailsRelated articlesIntroduction to the Directed Energy for Aerospace Applications Virtual Collection29 Aug 2023AIAA Journal What's Popular Volume 61, Number 9September 2023 CrossmarkInformationCopyright © 2023 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the eISSN 1533-385X to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp. TopicsAerodynamicsAerospace SciencesAircraft Operations and TechnologyAircraftsDefense AgenciesFlow RegimesFluid DynamicsInterdisciplinary TopicsMilitary ScienceMilitary TechnologyMissile DefenseMissile Systems, Dynamics and Technology KeywordsAerospace SciencesAdvanced Tactical LaserAircraft Operations and TechnologyCompressible FlowChemical Oxygen Iodine LasersMissile Defense AgenciesAerospace EnvironmentsFlight TestingBoeing 707Air ForcesPDF Received21 June 2023Accepted21 June 2023Published online29 August 2023

Professor Essam E. KhalilProfessor Essam E. Khalil On Wednesday, September 7, 2022, we were deeply saddened to hear that Professor Essam E. Khalil passed away at the age of 74. Professor Khalil was born on July 12, 1948, in Scotland, United Kingdom, and through his extensive career, he became one of the most respected educators/researchers in Egypt in the field of mechanical engineering. He received his B.Sc. and M.S. degrees in July 1971 and December 1973, respectively, from the Department of Mechanical Power Engineering of Cairo University. He then joined the Imperial College of Science and Technology where he received his Ph.D. in February 1977 under the supervision of Professor James Hunter Whitelaw. His dissertation is titled “Flow, Combustion and Heat Transfer in Axisymmetric Furnaces.” After finishing his Ph.D., Professor Khalil obtained a postdoctoral fellowship with the United Kingdom Atomic Energy Research Establishment in Harwell, UK. After his fellowship, he returned to Egypt as an assistant professor in the Department of Mechanical Power Engineering at Cairo University. He was promoted to Associate Professor and Professor in 1982 and 1988, respectively. During his academic career, Professor Khalil supervised many master’s and Ph.D. students in the areas of heat transfer, turbulent combustion, air distribution in buildings, and sustainability. Several of his past Ph.D. students became professors at different universities. Professor Khalil published over 950 papers in journals, conference proceedings, book chapters, and books. Some of his publications are listed in Refs [1–5]. His 1983 paper with Professors D. Brian Spalding and James H. Whitelaw titled “The Calculation of Local Flow Properties in Two-Dimensional Furnaces” was his most cited paper [6].During his academic career, Professor Khalil served as an editorial board member for Advances in Mechanical Engineering and the International Journal of Thermal and Environmental Engineering. He was a Fellow of the American Society of Mechanical Engineers (ASME); the American Institute of Aeronautics and Astronautics (AIAA); and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). He was the Regional Director for ASHRAE in the Middle East and North Africa and served on the ASHRAE Board of Directors as Director-at-Large from 2016 to 2019. He served as a Convener for ISO/TC205 WG2 on Energy Efficiency and as a Convenor for ISO/TC163 WG4 on Thermal Performance and Energy Use in the Built Environment. He was an ASHRAE Distinguished Lecturer and an Authorized Instructor for ASME. He also served as an ABET program evaluator (PEV). He was a member of the AIAA Green Engineering Program Committee as well as the AIAA Thermophysics Technical Committee, the AIAA Terrestrial Energy Systems Technical Committee, and the AIAA Gas Turbine Engines Technical Committee.The scientific contributions of Professor Khalil spanned many areas and have been recognized by many honors and awards. These include the Decor of Science and Arts of the First Order from former Egyptian President Anwar Sadat (1981), the National Award for Scientific Achievement in Engineering Sciences (1981), Member of L’Institut D’Egypte (2007), ASHRAE Presidential Award of Excellence (2009), ASHRAE Chapter Service Award (2009), ASME Westinghouse Gold Medal (2009), AIAA Energy Systems Award (2010), ASHRAE Regional Award of Merit (2010), AIAA Sustained Service Award (2011), ASHRAE Distinguished Service Award (2011), ASME James Harry Potter Gold Medal (2012), University of Wisconsin Milwaukee Distinguished Lecture Award (2013), ASME Egypt Achievement Award (2013), Syndicate of Egyptian Engineers Award of Excellence (2016), ASHRAE Exceptional Service Award (2017), and multiple Awards of Excellence from Cairo University.It is difficult to find appropriate words to express our emotions at this wistful moment. The scientific community will remember Professor Khalil as a prolific and exceptional scientist, mentor, teacher, and a highly respected colleague. He will also be remembered for his exceptional character as a human being who cared about his family, friends, students, and professional colleagues. Figures 1 through 5 show some memorable pictures of Professor Khalil with different colleagues, students, and friends. He will be sorely missed by all of us.

Liquid-ring vacuum pumps, by not having solid-solid contacts at interfaces where moving and stationary parts meet, are efficient and robust with considerable potential for further improvements on efficiency, performance, and range of operations. In this study, a physics-based reduced order model was developed for the preliminary design of liquid-ring pumps. The model developed accounts for the dominant physical processes created by the pump's key design and operating parameters: eccentricity, impeller-tip radius, impeller-hub radius, pressure at the pump's inlet and exit, and the impeller's rotational speed. The model developed can predict the shape of the liquid ring, the amount of air ingested and discharged by the pump, the power consumed by the pump as well as the pressure of the gas and liquid in the pump between the blades of the impeller as a function of those design and operating parameters. The predictions made by the model on the flow rates of the gas ingested by the pump and the power consumed by the pump were compared with experimental data, and good agreements were found.

In gas turbines, the hot gas exiting the combustor can have temperatures as high as 2000 °C, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the entering hot gas could damage the disks, its ingestion must be minimized. This is carried out by rim seals and by introducing a cooler flow from the compressor (sealing flow) into the wheelspace. Ingress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the ingress and egress driven by the rotor and its rotation. This is carried out by performing wall-resolved large eddy simulation (LES) around an axial seal in a rotor–stator configuration without vanes and blades. Results obtained show the mechanisms by which the rotor and its rotation induce ingress, egress, and flow trajectories. Kelvin–Helmholtz instability was found to create a wavy shear layer and displacement thickness that produces alternating regions of high and low pressures around the rotor side of the seal. Vortex shedding on the backward-facing side of the seal and its impingement on the rotor side of the seal also produces alternating regions of high and low pressures. The locations of the alternating regions of high and low pressures were found to be statistically stationary and to cause ingress to start on the rotor side of the seal. Vortex shedding and recirculating flow in the seal clearance also cause ingress by entrainment. With the effects of the rotor and its rotation on ingress and egress isolated, this study enables the effects of stator vanes and rotor blades to be assessed.