Drag reduction of a slanted-base cylinder using sweeping jets

2013

Active Flow Control (AFC) experiments performed at the Caltech Lucas Wind Tunnel on a generic airplane vertical tail model proved the effectiveness of sweeping jets in improving the control authority of a rudder. The results indicated that a momentum coefficient (C µ ) of approximately 2% increased the side force in excess of 50% at the maximum conventional rudder deflection angle in the absence of yaw. However, sparsely distributed actuators providing a collective C µ ≈ 0.1% were able to increase the side force in excess of 20%. This result is achieved by reducing the spanwise flow along the swept back rudder and its success is attributed to the large sweep back angle of the vertical tail. This current effort was sponsored by the NASA Environmentally Responsible Aviation (ERA) project. I.

Dec. 7-8, 2017 Paris (France) CCCME-17, MAIE-17, CAEBS-17, L2HSS-17 & LEBHM-17, 2017

This paper will discuss the simulation analysis of synthetic jet application effects on the Ahmed body model drag reduction.The purpose of this active airflow control is to improve the fuel consumption efficiency by reducing the wake area of the aerodynamic drag force. [1]Based on the fluid mechanic theory, the blow and the suction process of the membrane actuator of synthetic jet which produce vortex ring postpone the airflow separation in the rural area of the 70% reversed Ahmed body model.This phenomenon is believed that the vortex ring formation which formed by synthetic jet reduces the drag force by postponing the airflow separation. [2]The simulation is using k-Epsilon turbulence formulation feature on ANSYS student version software, Independent variables that applied on this simulation are the variation of the signal wave type, membrane vibration frequencies, and the airflow velocities.Types of signal waves are square, triangle, sinusoidal and frequencies ranges 90 Hz-130 Hz with the frequency interval is 10 Hz.The free stream velocity is 60 km/hr which represent the maximum allowed city car speed on the urban street.The free variable is the orifice diameter of cavity variations; there are 3 mm, 5 mm and 8 mm.Based on the simulation result, 110 Hz square wave of membrane frequency is the boundary condition which resulting the maximum drag reduction at the 3 mm diameter of the conical synthetic jet in three different free stream velocities.The drag reduction percentage of 3 mm of orifice diameter synthetic jet when the free stream velocities 11 m/s, 13.9 m/s and 16.7 m/s are 14.20%, 18.62%, 12.47%.

51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2013

Active Flow Control (AFC) experiments performed at the Caltech Lucas Adaptive Wall Wind Tunnel on a 12%-thick, generic vertical tail model indicated that sweeping jets emanating from the trailing edge (TE) of the vertical stabilizer significantly increased the side force coefficient for a wide range of rudder deflection angles and yaw angles at free-stream velocities approaching takeoff rotation speed. The results indicated that 2% blowing momentum coefficient (C µ) increased the side force in excess of 50% at the maximum conventional rudder deflection angle in the absence of yaw. Even C µ = 0.5% increased the side force in excess of 20% under these conditions. This effort was sponsored by the NASA Environmentally Responsible Aviation (ERA) project and the successful demonstration of this flow-control application could have far reaching implications. It could lead to effective applications of AFC technologies on key aircraft control surfaces and lift enhancing devices (flaps) that would aid in reduction of fuel consumption through a decrease in size and weight of wings and control surfaces or a reduction of the noise footprint due to steeper climb and descent.

Fluid-Structure-Sound Interactions and Control, 2021

Up to 40% drag reduction was achieved for a D-shaped cylinder in an experiment with robust model-based closed-loop control. The flow is actuated with on-off jet slots blowing in the stream-wise direction over the top and bottom edge. These jets are deflected inward with Coanda surfaces, thus realizing drag reduction by aerodynamic boat tailing. The flow state is monitored with pressure sensors at the trailing surface. The pressure fluctuation level is found to be closely related to drag. A starting point for control design is an optimized open-loop control, with a Strouhal number of 0.33 and duty cycle of 50%. Successful closed-loop drag reduction was achieved, in terms of a improving output stability and enhancing performance in term of settling time.

The objective of this paper is to appraise, the practicability of weakening the shock wave and hereby reducing the wave drag in transonic flight regime using flow control devices such as two dimensional contour bump, individual jet actuator, and also the hybrid control which includes both control devices together, and thereby to gain the desired improvements in aerodynamic performance of air-vehicle. To validate the numerical study, a natural laminar flow airfoil, Rae5243, is chosen and then comparisons with experimental data have been made before the optimization of flow control parameters. After validation study, an efficient Gradient Based optimization technique is used to optimize 2D bump parameters including the length, the maximum height, the bump position via shock location, and the crest position via bump and also the jet actuation parameters such as mass flow coefficient, suction/blowing angle, actuation location over the upper surface of the airfoil. The process generally consists of using the simulation code to obtain a flow solution for given parameters and then search the optimum parameters to reduce the total drag of the airfoil via the optimizer. Most importantly, it is shown that, the optimization yields 3:94% decrease in the total drag and 5:03% increase in lift, varying the design parameters of active and passive control devices.

54th AIAA Aerospace Sciences Meeting, 2016

This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs. The ERA systems analysis studies performed by NASA indicated that AFC-enhanced vertical tail could produce ~0.9% drag reduction for a large twin aisle aircraft and IAM coatings could enable ~1.2% drag reduction recovery for a potential total drag reduction of ~3.3% for a single aisle aircraft with a natural laminar flow (NLF) wing design. Nomenclature AFC = Active Flow Control APU = auxiliary power unit CFD = computational fluid dynamics C μ = momentum coefficient, %

FME Transactions, 2019

This paper presents an experimental and numerical study of the sweeping jet oscillation frequency which is a crucial parameter for effective separation control. Measurements of the time-resolved static pressure are made in the feedback channels using high-frequency pressure transducers. Experiments are performed for eight different inlet mass flow rates (from 1g/s to 8 g/s). The effects of geometry scaling are examined for the halfand double-size of the baseline actuator. The results reveal a relationship between the oscillating frequency and the inlet mass flow rate and demonstrate a linear trend of the Strouhal number versus the inlet Mach number for all the geometries. The experimental results are compared toresults obtained from numerical simulations using Ansys Fluent v17.2 software.A high correspondence is found between experimental results and numerical data from computationally inexpensive 2D-URANS simulations. This result opens possibilities of using these simple numerical models to perform extensive studies of the geometric parameters of the sweeping jet actuator in the future.

Experiments in Fluids, 2012

This paper highlights experimental flow control results obtained on an Ahmed model with slant angle of 25°. On this high drag configuration characterized by a large separation bubble along with energetic streamwise vortices, base flow is first presented. The influence of rear-end periodic forcing on the drag coefficient is then investigated using an open-loop control system. Four distinct configurations of flow control have been tested: rectangular pulsed jets with two different geometries on the roof end, and rectangular jets or a large open slot at the top of the rear slant. For each configuration, the influence of the forcing parameters (non-dimensional frequency, injected momentum) on the drag coefficient has been studied, along with their impact on the static pressure on various locations. Depending on the type and location of pulsed jets actuation, the maximum drag reduction is obtained for increasing injected momentum or welldefined optimal pulsation frequencies.

SAE Technical Paper Series, 2014

This study is focused on the detailed experimental investigation of jet boat-tail (JBT) passive flow control bluff body models to reduce the base pressure drag. The JBT technique is employed through an open inlet at the leading edge of the bluff body along with a circumferential jet at the trailing edge in order to energize the base flow using the high kinetic energy flow from freestream. As a consequence, entrainment of the main flow into base flow region is initiated earlier downstream. A reduction in the turbulent fluctuation of the wake can be observed in addition to a decrease of the recirculation region velocity. Using 2D/3C Particle Image Velocimetry (PIV), two models with different inlet sizes are tested. The large flow rate model is designed with an inlet area 4.7 times greater than the other JBT prototype. The wind tunnel experimental results show a substantial reduction in the wake width and depth for the two models, which indicates a significant drag reduction. Moreover, mean velocity vector plots from PIV measurements at the mid-plane location suggest their flow fields differ significantly due to the nature of the passive jets employed. The Jet1 model initiates the large coherent structures and flow entrainment earlier than the baseline model even though the jet momentum is small. The Jet2 generates paired vortices in the shear layer due to the high jet momentum and entrain main flow to the base region. The experimentation is performed at a Reynolds number of Re = 2.55×10 5. In order to investigate the effects at higher Reynolds numbers, Computational Fluid Dynamics (CFD) is used to model the flows using Large Eddy Simulation, which shows that the drag reduction is more effective at high Reynolds number.

Physics of Fluids

In this paper, a sweeping jet is applied to control the afterbody vortices behind a slanted-base cylinder for the first time at Reynolds numbers from 87 000 to 200 000. The control effects are examined using stereo particle image velocimetry and surface pressure measurements with the jet momentum coefficient (Cμ) varying from 0.056 to 0.893. It is found that the sweeping jet results in increasingly diffused and larger afterbody vortices as Cμ increases. While an increase in Cμ up to 0.167 leads to a reduction in the circulation of the afterbody vortices and their earlier detachment from the slanted base, a further increase in Cμ introduces additional vorticity into the afterbody vortices leading to higher vortex strength, which could be detrimental to the control purpose. The interaction mechanism of sweeping jets lies in that turbulence is injected into the afterbody vortices as the sweeping jet intersects with these vortices and this subsequently causes diffusion of velocity gradi...