Saeed Farokhi

University of Kansas | KU · Department of Aerospace Engineering

View Video Presentation: https://doi.org/10.2514/6.2022-0412.vid A computational study to investigate the role of passive compliant coatings and trailing-edge noise is conducted on a flat plate in fully turbulent flow. Ffowcs Williams and Hawkings model is used to predict farfield noise generated by a flat plate with sharp trailing-edge. Noise was...

View Video Presentation: https://doi.org/10.2514/6.2022-2539.vid The temporal stability of inviscid parallel shear flows with embedded swirl is investigated in the limit of incompressible fluids. The base flow is divided into three regions: an inner irrotational jet flow, a thin swirl layer on the outer rim of the nozzle, and an external potential...

No PDF available ABSTRACT The temporal stability of inviscid parallel shear flows with embedded swirl is investigated. The base flow is divided into three regions: an inner irrotational jet flow, a thin swirl layer on the outer rim of the nozzle, and an external potential flow outside the nozzle. The swirl distribution in the thin shear layer is of...

No PDF available ABSTRACT With growing dependence on wind energy as a clean source of electricity, it is imperative to address the shortcomings in modern day wind turbines and ensure their widespread application. One such area to address is the trailing-edge noise from their rotor blades. The present computational study investigates the ability of...

Plane oblique shocks are formed in supersonic flows that cause abrupt flow deceleration, compression and turning. This behavior persists up to a maximum flow turning angle, θmax and a corresponding shock angle βmax for any upstream Mach number M1 with corresponding Mach angle, μ1. Beyond the maximum turning angle, the oblique shock becomes detached...

The Capstone design requirements have become an integral part of the most engineering curricula in the United States. They all share the goal of developing multidisciplinary designs for real-world problems/applications, often with industry sponsorship. In this paper, the three-capstone design options required by the aerospace engineering department...

Sustainable aviation demands renewable jet fuels to make future air travel environmentally friendly. This chapter addresses the challenges and opportunities in sustainable aviation fuels from renewable alternative jet fuels, to liquefied natural gas (LNG), liquid hydrogen, LH2, and fuel for compact fusion reactor. Based on the global abundance, i.e...

This chapter views aviation's impact on climate through the lens of combustion‐generated pollutants of fossil fuels and noise. It addresses aviation‐related sources and the magnitude of these anthropogenic, i.e. caused by human activities and emissions at the local and the global scale. Aviation noise generated in takeoff, climb, flyover, approach,...

This chapter addresses the specific pathways to sustainable aviation in key technologies, including the challenges in regulations and certifications, public confidence, and societal acceptance. Promising energy sources, as in renewable jet fuels and batteries, will continue to be the cornerstone of sustainable aviation. Cryogenic fuels, in particul...

This chapter reviews air‐breathing engine cycles and develops 1‐D, steady solution methodology based on thermodynamics and conservation laws for their performance parameters. The turbojet performance parameters are specific thrust, specific fuel consumption, thermal, propulsive, and overall efficiencies. The chapter presents a brief review of aircr...

This chapter reviews aircraft aerodynamics both at the fundamental and applied levels. Similarity parameters and boundary conditions in viscous, thermally conducting compressible flows are fundamental to the study of aircraft aerodynamics. In flows with a high Reynolds number, boundary‐layer formation and its behavior on bodies in motion hold the k...

Aviation contributes to about 12% of the greenhouse gas emissions in the transportation sector (i.e. road transport, rail, aviation, and shipping). The road to sustainable propulsion and power systems in commercial aviation goes through advanced gas turbine engines either as fully integrated propulsion‐air‐frame system or as hybrid electric propuls...

Undergraduate education in jet propulsion can benefit from a modern real-engine simulator. The traditional lecture/laboratory course in propulsion continues to emphasize fundamental aerothermodynamics and often includes a propulsion laboratory that tests small engines (e.g., micro-turbojet engines) mounted on a thrust stand. Modern engine simulator...

The evolution of vortex structures over flapping NACA0012 foils in shear flows and the corresponding aerodynamic performance are numerically studied using a two dimensional (2D) high-order accurate spectral difference Navier–Stokes flow solver, and further analyzed using the dynamic mode decomposition (DMD) method and vortex theory. Several types o...

A novel injector has been designed and cold flow injection tests were performed in a modified supersonic wind tunnel. To complement these experimental studies three dimensional STAR-CCM+CFD simulations were developed. The pulse width may be varied, with options of injecting gas for 33 %, 50 % and 66 % of the injection period. The scramjet combustor...

A rectangular jet emerging from a nozzle with embedded swirl vanes in its exit boundary layer is studied. The swirling shear layer imposes an external torque on the jet boundary where it causes jet rotation in the direction of axis switching, skew deformation as well as enhanced mixing. In moderate aspect ratio rectangular nozzles, e.g. AR = 5:1, a...

In this chapter we present the aerodynamics about two-dimensional lift-producing wing sections (airfoils) at low transonic conditions. It is shown how various design parameters influence the velocity distribution and the shock formation over an airfoil. The development of supercritical airfoils is explained from a historic perspective. First the ad...

The governing equations of motion for two and three-dimensional inviscid irrotational supersonic flows are derived. Although these equations are nonlinear, there are unique curves in the physical space, known as characteristics that turn the governing partial differential equations into ordinary differential equations that may be integrated along t...

In this chapter we (re-)familiarize the reader with concepts from mathematics, thermodynamics, and aerodynamics that are fundamental to the methods presented in the remainder of the book. This includes a short review of vector algebra and partial-differential equations to provide the mathematical insight into the governing equations of fluid flow....

In this chapter we discuss the aerodynamics of swept wings in transonic flow. To demonstrate the merits of swept-back wings, simple sweep theory is presented. It is shown why a swept wing can experience local supersonic flow while still being in subcritical conditions, thereby postponing the onset of strong shock waves and drag divergence. It is al...

Airliners and jet fighters are often designed for Mach numbers close to the speed of sound. At those speeds the flow domain is termed transonic and contains both subsonic and supersonic flow. Typical aerodynamic characteristics in this domain are shock waves, drag divergence, and transonic buffet. To suppress these adverse effects or postpone them...

This chapter develops the foundation of inviscid nonlinear shock-expansion theory on pointed bodies in supersonic flows. Fundamental equations of shock and expansion waves are derived and discussed. To extend the analysis to three-dimensional bodies, conical shock theory is derived. Examples from diamond and bi-convex airfoils are used to highlight...

This chapter starts the foundation with the small disturbance theory applied in the subsonic and supersonic flows. Both of these regimes are linear and thus fail at sonic speed, which is at the heart of transonic flow. Nonlinear small disturbance theory for the transonic regime is subsequently derived and discussed. With limited analytical options...

This chapter presents the sources of drag that are encountered by a nonlifting body that is moving at transonic Mach numbers. In inviscid conditions drag can be produced if the integrated pressure over a body has a component in the opposite direction to the flow (pressure drag). First, the reader is introduced to the relation between the geometry o...

Performance of an axial exhaust diffuser downstream of an un-shrouded turbine rotor is computationally analyzed. Three-dimensional analysis of two turbine stage-exhaust diffuser configurations has been performed. In one case, the turbine rotor is shrouded and in the second case, the rotor is un-shrouded. The static pressure recovery coefficient in...

The effect of mean flow shear on the wake vortical structure behind oscillating NACA0012 airfoils is numerically studied using a 2D high-order spectral difference Navier-Stokes flow solver. A shear flow with clockwise circulation is superposed on the uniform incoming flow to dynamically enhance or suppress the vortical structures in the wake vortex...

Mixing characteristics of under-expanded supersonic jets emerging from plane and notched rectangular nozzles are computationally studied using nozzle exit boundary layer swirl as a mean of passive flow control. The coupling of the rectangular jet instability modes, such as flapping, and the swirl is investigated. A three-dimensional unsteady Reynol...

A diffusing S-duct aircraft intake system is computationally studied for the effects of inlet icing and wall heat transfer on engine face distortion. A Reynolds-Averaged Navier-Stokes (RANS) code with k -ω SST turbulence model is used to simulate the compressible viscous flow in the duct. The glaze ice accretion on the inlet lip is simulated as a f...

A computational flow simulation is conducted to study underperformance of some stall regulated wind turbine blades. A hypothesis is proposed explaining the causes for the underperformance of an 8kW stall regulated wind turbine. The two main causes affecting the performance are due to poor manufacturing tolerances and the aerodynamic design of the a...

The effect of exit geometry of a rectangular nozzle on the instability modes and mixing characteristics of under-expanded supersonic jets is computationally investigated. The unsteady three-dimensional viscous simulation is based on the Proteus code developed at NASA Glenn Research Center. A shock adaptive grid generator was developed to enhance th...

Modeling and analysis of inventory systems in reverse logistics is more complex than in forwards logistics, because in reverse logistics not only amount of demand is not clear, but also uncertainty of product return is appeared in the system. In this paper, an inventory system with the possibility of product return is modeled by means of simulation...

In this paper, semi active control of non-ideal mechanical system with Magneto-Rheological (MR) damper is presented. The setup composed of a motor operating on a structure with mass M connected to a fixed frame by a non-linear spring and with a linear viscous damper. From the investigations carried out it is possible to observe the DC motor influen...

The effect of flow angularity on an S-duct inlet with icing is computationally investigated. Flow angularity is simulated through angle-of-attack, and sideslip in addition to asymmetrical ice accretion on the inlet lip. A commercial CFD code, STAR-CCM+ is used for the steadystate computations with the shear-stress transport (SST) k - ω turbulence...

The effects of a typical glaze ice accretion shape on the performance of the M2129 S-duct inlet are computationally investigated for a range of flight Mach numbers. A Reynolds-Averaged Navier-Stokes (RANS) code with k-omega) turbulence model is used to simulate the compressible viscous flow in the S-duct inlet. The glaze ice accretion on the cowl l...

In the present work, active control of a mass block-belt-motor system using impulse damper is presented. The system consists of a block located on a rough leather belt. The block is attached to a rigid fixed support through a linear spring. The belt moves over a pair of pulleys one of which is driven by a non-ideal motor. In the ideal problem, the...

Horizontal take -off and horizontal landing vehicles continue to be a subject of great interest for future space launch missions. For a hypersonic vehicl e, in order to operate through all Mach regimes, a combined -cycle propulsion system is the most promising concept. This paper describes the cycle analysis for a ramjet/ scramjet system consisting...

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO Includes bibliographical references. by Saeed Farokhi. Ph.D.

The ability of the shear-sensitive liquid crystal flow visualization technique to visualize flow separation, flow reattachment, shocks and vortices was demonstrated in a supersonic wind tunnel. This technique was performed employing an unsealed shear-sensitive thermo-chromic liquid crystal mixture on models with a convex surface and a cavity vortex...

An experimental flow visualization technique using shear-sensitive liquid crystals was used to capture the footprints of the flow separation ahead of a circular cylinder mounted on a flat surface. The experiments were conducted at the University of Kansas supersonic wind tunnel at a test Mach number of 2.0. In a single cylinder configuration, a cir...

The ability of shear-sensitive liquid crystals to visualize flow separation, flow reattachment, shocks and vortices were demonstrated at the University of Kansas supersonic wind tunnel facilities. This technique was performed using unsealed shear-sensitive liquid crystals on cavity vortex generator models with two-dimensional convex surfaces. Model...

The Federal Aviation Administration (FAA) has a continuing program to collect data and develop predictive methods for aircraft flight loads. Some of the most severe and potentially catastrophic flight loads are produced by separated flows. Structural response to the aerodynamic excitation produced by separated flows is defined as buffeting. A low-c...

Adverse flow environments pose challenging design constraints in aircraft engine components and component interactions. Some examples of such flow environments are: steep pressure gradients, random and periodic unsteadiness, shock wave interactions and 3-D boundary layer separation. These adverse flow environments and interactions promote the growt...

An experimental study was conducted to evaluate the pressure-sensitive paint (PSP) technique as a means of obtaining global surface pressure distribution on the inside surface of a supersonic nozzle at NASA Langley Research Center, In this experiment, the PSP technique was used to measure the surface pressure distribution for several configurations...

A theoretical/computational approach is developed to predict the change in near-field noise due to a momentum-deficit upstream of a propeller plane, specifically for a pylon wake in a pusher configuration. The acoustic pressure is computed using blade geometry and unsteady blade surface pressure history. The steady blade surface pressure is predict...

A new system for active how control using smart vortex generators (SVG) is presented. Increments in C-l max from modern vortex generators (VGs) are determined through wind-tunnel testing on a two-dimensional wing section. Using an optimized VG configuration, a system was built with 1) a shear-flow sensor that detected the onset and depth of stall,...

The performance of the NREL S807 airfoil is experimentally determined via wind tunnel testing. The tests are conducted at Reynolds numbers of 0.5, 1.0, and 1.5.106, with a clean surface, with two levels of leading edge surface roughness, and with surface roughness and large wishbone vortex generators. The results show that the S807 maximum lift coe...

Chordwise distribution of unsteady surface pressure is measured on a pylon-mounted pusher propeller in flight. Spectral decomposition of the fluctuating surface pressure signals reveals a strong presence of upstream wake interaction. The growth and decay behavior of the fundamental disturbance wave along the propeller chord exhibits the same charac...

A theoretical/computational approach is developed to predict the change in near-field noise due to a momentum-deficit upstream of a propeller plane, specifically for a pylon wake in a pusher configuration. The acoustic pressure is computed using blade geometry and unsteady blade surface pressure history. The steady blade surface pressure is predict...

As a building block in the development of smart lift-enhancement devices, a new concept for flow control using active vortex generators (AVGs) is presented. Ramp, wedge, and doublet wedge (Wheeler) VG configurations are investigated. The AVGs are designed to conform to the surface of the wing section at low alpha. As the section approaches the stal...

The current study is an application of CFD to a 'real' design and analysis environment. A subsonic, three-dimensional parabolized Navier-Stokes (PNS) code is used to construct stall margin design charts for optimum-length advanced exhaust systems' circular-to-rectangular transition ducts. Computer code validation has been conducted to examine the c...

Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a sw...

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flowfields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity incorporating the k-epsilon turbulence model are pro...

A propeller of an advanced turboprop testbed aircraft in pusher configuration is instrumented with 22 miniature blade-mounted transducers (BMTs) at two radii. Upstream pylon wake interaction with the propeller is the source of a one-per-cycle excitation for the blades in flight. The time history of fluctuating pressure signals over 26 flight condit...

In the present paper, the inadequacies of the traditional approach to undergraduate propulsion education are discussed. Propulsion as a system endeavor, in contrast to a single discipline, demands a system design education provided in a capstone engine design course in the senior year of aerospace engineering curricula. A suitable course content is...

The spatial instability of a swirling jet is investigated both experimentally and theoretically. A hydrodynamic stability analysis is applied to an inviscid incompressible top-hat jet, with a swirl distribution of solid-body rotation and free vortex in and outside the vortex core, respectively. Both plane and helical instability modes are examined....

A reduced Navier-Stokes (RNS) initial value space marching solution technique was applied to vortex generator and separated flow problems and demonstrated good predictions of the engine face flow field. This RNS solution technique using FLARE approximations can adequately describe the topological and topographical structure flow separation associat...

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows, the flow in a curved duct, and swirling flows are examples of flow fields where streamline curvature plays a dominant role. A comprehensive literature review on the effect of streamline curvature was conducte...

Miniature, high-frequency, pressure transducers were mounted on a pusher propeller at 75 and 90% radii. Time history of fluctuating surface pressure over 700 propeller revolutions and 26 flight conditions reveals intriguing phenomena. The anticipated pylon wake signature manifests itself as a negative pressure pulse over extended portions of the pr...

Miniature, high-frequency, pressure transducers were mounted on a pusher propeller at 3/4 and 90-percent radii. Time-history of fluctuating surface pressure over 700 revolutions and 26 flight conditions reveal intriguing phenomena. The anticipated pylon wake signature manifests itself as a negative pressure pulse over extended portions of the sucti...

An existing cold-jet facility at NASA Lewis Research Center was modified to produce swirling flows with controllable initial tangential velocity distribution. Distinctly different swirl velocity profiles were produced, and their effects on jet mixing characteristics were measured downstream of an 11.43 cm (4.5 in.) diameter convergent nozzle. It wa...

Unsteady aerodynamics of a pusher propeller operating in the wake of a pylon is investigated through analysis of flight test data. Twenty-two surface-mounted miniature pressure transducers were installed at the 75 and 90 percent radius locations on a propeller blade on a test-bed aircraft. Twenty-six different flight conditions were flown to cover...

A swirling jet with a swirl number of S = 0.12 is excited by plane acoustic waves at various Strouhal numbers (St = fD/U sub alpha). The maximum forcing amplitude of excitation was at 6.88 percent of the time-mean axial velocity at a Strouhal number of St = 0.39. The maximum time-mean tangential and axial velocities at the nozzle exit were 18 and 8...

Tip clearance flow is a major contributor to the losses in axial flow turbines. Tip shrouding reduces the extent of this loss at the expense of more structural complexity and increased centrifugal blade stresses. Recent technological advance in the area of active clearance control promises to minimize the tip clearance loss without the adverse tip...

A computer program is developed to optimize the shape of a nacelle installed in a supersonic aircraft for minimum drag. The program is also capable of optimizing the wind camber of the same aircraft. As a unique feature, the present code accounts for the aerodynamic forces on the entire airplane in contrast to previous wing camber optimization code...

Experimental results from acoustic excitation of a cold free turbulent jet with and without swirl are presented. A flow with a swirl number of 0.35 (i.e., moderate swirl) is excited internally by plane acoustic waves at a constant sound pressure level and at various frequencies. It is observed that the cold swirling jet is excitable by plane waves,...

An existing cold-jet facility at NASA Lewis Research Center was modified to produce swirling flows with controllable initial tangential velocity distribution. Two extreme swirl profiles, i.e., one with solid-body rotation and the other predominated by a free-vortex distribution, were produced at identical swirl number of 0.48. Mean centerline veloc...

An existing cold jet facility at NASA-Lewis was modified to produce swirling flows with controllable initial tangential velocity distribution. Distinctly different swirl velocity profiles were produced, and their effects on jet mixing characteristics were measured downstream of an 11.43 cm diameter convergent nozzle. It was experimentally shown tha...

In a modern gas turbine power plant, the axial exhaust diffuser accounts for up to 10% of the generator power. An unshrouded rotor, due to its highly energetic tip clearance flow, improves the pressure recovery characteristic of the exhaust diffuser, while the power production within the blading suffers a loss as a result of the tip leakage flow. I...

The present analytical formulation of unsteady, three-dimensional flow of a perfect fluid through a cascade of fluctuating lifting lines extends Hawthorne's (1973) generalized-functions approach to two-dimensional linearized perturbation analysis, and includes the effect of spanwise variation of circulation along the lifting lines on the induced fl...