Richard Semaan

Progress in Efficient Active High-Lift

This paper presents some of the progress in research on efficient high-lift systems for future civil aircraft achieved by the Coordinated Research Centre CRC 880 sponsored by the German Research Foundation. Several new approaches to increasing the lift are applied as part of the design of a reference aircraft with short take-off and landing capability: The numerically predicted positive effect of Coanda jet blowing at the trailing edge flap is validated in water tunnel experiments. Robust miniature pressure and hot-fi�lm sensors are developed for the closed-loop control of a piezo-actuated blowing lip. A flexible leading-edge device utilizes composite materials, for which new structural designs are developed. Additionally, a potential de-icing system, as well as a lightning-strike protection are presented. A high power-density electrically driven compressor with a broad operating range is designed to provide the blowing air ow. Different propulsion systems for the reference aircraft are evaluated. An ultra-high bypass ratio engine is considered to be most promising, and thus a preliminary fan stage design process is established. The rotor dynamic influences of the engine on the aircraft structure are investigated through a hybrid approach using a multibody model and modal reduction.

Three-Component Laser-Doppler-Anemometry Measurements in Turbulent Swirling Jets

Three-component laser-Doppler-anemometry measurements were acquired in swirling jets with different swirl intensities and distributions. An uncertainty analysis covering the most relevant precision and bias errors was performed, and uncertainty related to the jet-center location was found to be dominant. An initial analysis of the data revealed some of the effects of swirl on hastening jet evolution. The measurements were compared with data from previous studies, and were found to be in good agreement. The range of conditions measured and the characterization of the data quality make the data set useful for guiding future experimental studies and for validating numerical approaches capable of capturing the effects of swirl on turbulence.

Challenges in the Experimental Quantification of the Momentum Coefficient of Circulation Controlled Wings

Based on three experiments in wind and water tunnels, the challenges in quantifying the momentum coefficient are investigated and solutions to minimize the associated uncertainties are proposed. It is shown that including the viscous losses, determining the blowing slot height changes under loading conditions, as well as measuring the jet pressure is crucial for accurately quantifying the momentum coefficient.

Approach Toward Similar Behavior of a Swirling Jet Flow

LDA measurements of a swirling and a non-swirling jet are analyzed considering a recently proposed similarity theory. Mean velocities and turbulent Reynolds stress profiles are assessed. The collapse of the scaled radial profiles at some position downstream of the nozzle exit and the the decay of their magnitudes indicate a behavior that is consistent with the similarity theory. The swirling jet is found to exhibit such behavior at a location closer to the nozzle exit than the non-swirling jet. At this location, the tangential velocities are still relatively significant compared to the axial velocities, a condition that lies outside the strict applicability range of the theory.

Three Component LDA Measurements in the Near and Far Field of Swirling Jets

Swirling jets with difierent swirl distributions and swirl intensities have been investigated. Measurements are made using a three-component Laser Doppler Anemometry (LDA) system in the near fleld, and, in two cases, the far fleld. The LDA measurements have been performed using two difierent conflgurations, where the measurements in one of the conflgurations is more susceptible to geometric positioning errors. Geometric uncertainties have been evaluated and their efiect on the measurements has been investigated. The present results have been found to be in agreement with the results from other studies, when comparable data exist. Higher swirling cases are shown to evolve faster with distance from the jet exit than their non-swirling counterparts with both the mean and second order quantities approaching self-similar proflles within the range of axial distances investigated. The mean quantities approached their self-similar proflles faster than the Reynolds stresses.

Optimized sensor placement using stochastic estimation for a flow over a 2D airfoil with Coanda blowing

This study investigates the optimal placement of sensors mounted over the flap of a twodimensional (2D) airfoil equipped with Coanda jet circulation control for the purpose of flow control. The analysis is based on flow field data obtained from 2D unsteady Reynolds averaged Navier-Stokes (uRANS) simulations of a high-lift airfoil with different jet blowing intensities and actuation frequencies, characterizing different flow separation states. Linear stochastic estimation of the proper orthogonal decomposition (POD) is used to estimate the time-coefficients. The optimal sensor locations for any number of sensors configuration are then determined by minimizing the root mean squared error between the determined and the estimated time-coefficients. The results are compared for two types of sensor inputs: pressure sensors and skin-friction sensors. The results show that it is possible to determine the state of flow more accurately using fewer pressure sensors placed at optimized locations than from using the same number of skin friction sensors.

Sparse Model of the Lift Gains of a Circulation Control Wing with Unsteady Coanda Blowing

The present study investigates and models the lift gains and losses generated by the superposition of a periodic actuation component onto a steady component on an airfoil with a highly deflected Coanda flap. The periodic actuation is provided by two synchronized specially-designed valves that deliver actuation frequencies up to 30 Hz and actuation amplitudes up to 20% of the mean blowing intensity. The lift gains/losses response surface is modeled using a data-driven sparse identification approach. The results clearly demonstrate the benefits of superimposing a periodic component onto the steady actuation component for a separated or partially-attached flow, where up to \(\varDelta C_l=0.47\) lift increase is achieved. On the other hand, this same superimposition for an attached flow is detrimental to the lift, with up to \(\varDelta C_l=-0.3\) lift reduction compared to steady actuation with similar blowing intensity is observed.

Shape Optimization of Active and Passive Drag-Reducing Devices on a D-shaped Bluff Body

Shape optimization of an active and a passive drag-reducing device on a two-dimensional D-shaped bluff body is performed. The two devices are: Coanda actuator, and randomly-shaped trailing-edge flap. The optimization sequence is performed by coupling the genetic algorithm software DAKOTA to the mesh generator Pointwise and to the CFD solver OpenFOAM. For the active device the cost functional is the power ratio, whereas for the passive device it is the drag coefficient. The optimization leads to total power savings of \({\approx } 70\%\) for the optimal Coanda actuator, and a 40% drag reduction for the optimal flap. This reduction is mainly achieved through streamlining the base flow and suppressing the vortex shedding. The addition of either an active or a passive device creates two additional smaller recirculation regions in the base cavity that shifts the larger recirculation region away from the body and increases the base pressure. The results are validated against more refined URANS simulations for selected cases.

Progress Toward Closed Loop Control of a Flow Around an Airfoil with Coanda Blowing

Progress toward developing a closed loop control of flow around an airfoil with a Coanda flap is presented. Two loop components were addressed and analysed for the reference no-blowing case: the estimator and its input signal. For the estimator, a Proper Orthogonal Decomposition (POD) Galerkin model based on unsteady Reynolds averaged Navier-Stocks (uRANS) data was evaluated. To compensate for the unresolved dissipative scales in uRANS and for truncation error, the POD Galerkin model was calibrated by introducing an eddy viscosity term. The calibrated POD Galerkin model succeeded in replicating the time coefficients of the first two modes but failed to replicate the higher modes. The sensor location over the flap was optimized using modified Linear Stochastic Estimation (mLSE). With an optimal sensor placement it was possible to determine the state of the flow more accurately than for the same number of evenly spaced sensors.

A Generalized Reduced-Order Model of Flow around an Airfoil with Circulation Control

A low-dimensional generalized model is proposed for a flow around an airfoil with circulation control, describing natural vortex shedding and steady actuation. The suggested application range of the model extends from the un-actuated natural state to the strongly actuated near-steady state. The form of the dynamical system has been based on generalized mean-field consideration. Time resolved PIV snapshots are employed to derive the POD time coefficients and to calibrate the system parameters. The model is solely dependent on the actuation blowing momentum coefficient, and makes a good candidate for flow control applications.