David Rancourt

Method to Facilitate High-Dimensional Design Space Exploration Using Computationally Expensive Analyses

The emergence of adjoint design methods has been a breakthrough in the field of aerodynamic shape optimization. The strength of such methods lies in the fact that the adjoint formulation effectively removes the curse of dimensionality by drastically reducing the cost of computing the gradient. However, the curse of dimensionality is still very much alive when it comes to design space exploration, where gradient-free methods cannot be avoided. In attempt to solve this problem, this work presents a method called latent space gradient transformation, which facilitates gradient-free exploration for cases where function evaluations are expensive and dimensionality is high. The method builds upon previous work by applying principal component analysis to gradient information, something that had not been done before. This yields a low-rank transformation that maps a high-dimensional design space onto an equivalent, low-dimensional space in which gradient-free methods become more affordable. Concepts and limitatio...

Rim-Rotor Rotary Ramjet Engine, Part 2: Quasi-One-Dimensional Aerothermodynamic Design

The rim–rotor rotary ramjet engine is a new propulsion-system design with the potential to significantly improve power density and reduce complexity over conventional gas turbines, thus making it an interesting alternative for future transportation and stationary power systems. This paper presents a quasi-one-dimensional aerothermodynamic design model, taking into account the dominant physics of the rim–rotor rotary ramjet engine: 1) shock-wave compression, 2) high-g field combustion, 3) viscous losses, 4) heat transfer, 5) inlet and outlet periodic condition, and 6) windage losses. It is shown that high flame velocity due to buoyant forces leads to a very compact combustion chamber and possibly very low nitrogen oxides. A 500 kW rim–rotor rotary-ramjet-engine version is designed with the model and could produce 7:6 kW=kg at a tangential velocity of 1000 m=s, which is more than twicetheactualgas-turbinepowerdensity.Aproof-of-conceptprototypeistestedatlowspeed(Mach1),andshows good agreement with the model for both indicated power without combustion and windage losses. Combustion efficiency is measured to over 85% at 220;000g. These results confirm the design model capabilities, at least within the range of tested Mach numbers.

Design and Experimental Validation of a Supersonic Concentric Micro Gas Turbine

This paper presents the design and experimental results of a new micro gas turbine architecture exploiting counterflow within a single supersonic rotor. This new architecture, called the supersonic rim-rotor gas turbine (SRGT), uses a single rotating assembly incorporating a central hub, a supersonic turbine rotor, a supersonic compressor rotor, and a rim-rotor. This SRGT architecture can potentially increase engine power density while significantly reducing manufacturing costs. The paper presents the preliminary design of a 5 kW SRGT prototype having an external diameter of 72.5 mm and rotational speed of 125,000 rpm. The proposed aerodynamic design comprises a single stage supersonic axial compressor, with a normal shock in the stator, and a supersonic impulse turbine. A pressure ratio of 2.75 with a mass flow rate of 130 g/s is predicted using a 1D aerodynamic model in steady state. The proposed combustion chamber uses an annular reverse-flow configuration, using hydrogen as fuel. The analytical design of the combustion chamber is based on a 0D model with three zones (primary, secondary, and dilution), and computational fluid dynamics (CFD) simulations are used to validate the analytical model. The proposed structural design incorporates a unidirectional carbon-fiber-reinforced polymer rim-rotor, and titanium alloy is used for the other rotating components. An analytical structural model and numerical validation predict structural integrity of the engine at steady-state operation up to 1000 K for the turbine blades. Experimentation has resulted in the overall engine performance evaluation. Experimentation also demonstrated a stable hydrogen flame in the combustion chamber and structural integrity of the engine for at least 30 s of steady-state operation at 1000 K.

Principal Component Analysis Assisted Surrogate Modeling (PCA-SM) of Correlated Loads for Uncertainty Analysis of Design Load Envelopes

Target design load setting is one of the critical aspects in preliminary design phase of aircraft design process. Overestimation or underestimation of design loads lead to the aircraft’s performance and reliability implications, risk of costly re-desisgn, and specific design lead time. Selection of reliable design loads under uncertainties require a large number of analyses to evaluate loads for numerous flight conditions like maneuver loads, gust loads, ground loads, time dependent response under control deflection and so on leading to huge computational burden. To overcome this issue, Principal Component Analysis assisted Surrogate Modeling (PCA-SM) is developed in the current work for rapid reconstruction of correlated loads with relatively smaller number of analyses using Design of Experiments (DoE). The advantages of PCA-SM method over other surrogate modeling techniques have been discussed and demonstrated on a twin-aisle commercial transport aircraft case. Nomenclature λi i th eigenvalue of Σ Lg Data matrix of gust load data Lm Data matrix of static maneuver load data Λ Diagonal matrix containing eigenvalues of Σ φi i th eigenvectors of Σ Φ Matrix containing all the eigenvectors of Σ Φk Matrix containing k eigenvectors of Σ with largest k eigenvalues F Flight condition lm , lg Load vector for static maneuver and gust load respectively U Uncertain variable w Vector of weight or scores of x associated with eigenvectors stored in Φ X Data matrix consisting of all obeservation of x x Random vector Σ Correlation Matrix of X θ Polar angles Cg Convex hull for gust loads Cm Convex hull for static maneuver loads Fx, Fy, Fz Shear forces along x, y and z axis ∗PhD Candidate, School of Aerospace Engineering, Aerospace Systems Design Laboratory, Student Member. †Boeing Regents Professor of Advanced Aerospace Systems Analysis, School of Aerospace Engineering, AIAA Fellow ‡Loads technical skill leader for uncertainty management 1 of 15 American Institute of Aeronautics and Astronautics IQs Interesting quantities k Dimension of lower dimensional data representation Mx,My,Mz Moments about x, y and z axis p Dimension of random variable or load vector Si Sample covariance of i th descriptor xi of data t time xc, yc Centroid of all convex hull vertices zi Z-score of i th descriptor xi of data

Preliminary Wing Weight Estimation Under Probabilistic Loads for a Transport Aircraft

In preliminary design of aircraft wings, a common practice is to set target loads and target weights as governing parameters for more detailed design phases. These values must be reliable in the presence of uncertainty because overly conservative target estimates could result in over-design of the wing while non-conservative estimates could lead to costly latephase redesign to satisfy constraints. The process of confidently identifying these targets is typically very computationally expensive because a large multivariate space of flight scenarios and vehicle configurations must be investigated. Therefore, a method has been implemented to reduce the computational expense of reliability-based aero-structural preliminary design. To efficiently identify critical loading conditions for structural sizing, this method adaptively samples the discretized multivariate space with a kriging-based sequential routine. Each new sample point is identified by an expected improvement function based on the probabilistic distributions of internal structural loads. These distributions are determined by propagating uncertainty using Monte Carlo simulation through an aerostructural analysis code. This process is applied to the wing of a reference aircraft derived from the NASA Common Research Model, and the effect of reliability indices is shown on preliminary sizing and weight estimation.

High-g Field Combustor of a Rim–Rotor Rotary Ramjet Engine

High-g field combustion, such as in rotary ramjet engines, is a promising approach to reduce nitride oxides and combustor size by taking advantage of the flame acceleration due to the buoyancy of the products over the reactants. This paper presents a high-g field combustor design for a rim–rotor rotary ramjet engine. In this device, a premixed flow of air and fuel is ignited in the nonrotating inlet track and then swallowed and stabilized in the rotating combustion chamber. Outboard ignition frees the rotating structure from igniters, increasing the maximal tangential speed of the engine and thus its maximal efficiency. The rotating combustor design benefits from extreme centrifugal fields (105g to 107g) for both stabilizing the flame during ignition and maximize flame velocity. A simple buoyancy-driven combustion model allows estimating the combustor length and shows good agreement with numerical simulations, which demonstrate a combustion efficiency to be higher than 85%, even with some reactants bypass...

Autonomous Thrust-Assisted Perching of a Fixed-Wing UAV on Vertical Surfaces

We present the first fixed-wing drone that autonomously perches and takes off from vertical surfaces. Inspired by birds, this airplane uses a thrust-assisted pitch-up maneuver to slow down rapidly before touchdown. Microspines are used to cling to rough walls, while strictly onboard sensing is used for control. The effect of thrust on the suspension’s landing envelope is analyzed and a simple vertical velocity controller is proposed to create smooth and robust descents towards a wall. Multiple landings are performed over a range of flight conditions (a video of S-MAD is available at: http://createk.recherche.usherbrooke.ca/LM2017/).

Shock-Induced Combustion and Its Applications to Power and Thrust Generation

Due to the high pressure and temperature state produced by shock waves, they offer the possibility to greatly speed up combustion processes as compared to diffusive reaction mechanisms. Devices exploiting shock-induced combustion also have the potential for higher compression ratios, and thus better efficiency, and less complexity than systems using mechanical compression systems. These advantages can lead to lighter, more efficient, and more compact propulsion and power systems.

Integration of Electric Propulsion in Efficient Heavy-Lift VTOL Concept

Recent advances in conventional rotorcraft vehicles allow them to perform faster and more efficient cruise segments, with only incremental improvement in payload capabilities. Electric propulsion might enable ground breaking performance by allowing new design degrees of freedom. While many recent electric VTOL concepts are expected to have increased cruise capabilities, very few are addressing the payload limitations. The present paper aims at proposing a new electric VTOL concept: the Electric Powered Reconfigurable Rotor that uses the advantages of electric propulsion to perform efficient load lifting: unmanned electric tethered aircraft takeoff vertically, transition to a circular flight path to perform load lifting of a payload and can reconfigure to a side-by-side formation flight to perform efficient cruise segment. A review of various electric VTOL vehicle along with details on the proposed concept are given. Finally, a study on extreme operating altitude is used to outline the possible advantages of the proposed concept.

Inference of Aerodynamic Loads Under Uncertainty Using Strain Measurements and Bayesian Networks

The aerodynamic loads on a commercial transport aircraft are generally well known for a set of flight conditions. However, external phenomena such as wing contamination or the loss of natural laminar airflow (NLF) can create a slight shift in the aerodynamic loads. Although their effect on the loads is small, their consequence on the flight performance is important and current methods to detect those phenomena are rather complex. This paper presents a method based on Bayesian Networks (BN) to analyze the effect of adding strain sensors in a wing structure for two purposes. First, they could be used to reduce the uncertainty on the aerodynamic load prediction to possibly detect the loss of NLF or wing contamination (anomaly detection). Second, this method could contribute to inferring the flight condition with the objective of increasing the reliability of the monitoring system or reducing the number of sensors required on small aircraft such as Unmanned air vehicles (UAV). The methodology is applied to the Common Research Model (CRM), a B777 size aircraft augmented with an in-house designed structure. It is shown that the uncertainty on the aerodynamic loads can be reduced by 94% and that the flight conditions can be inferred within 5% for the Mach number and 9% for the fuel mass of the initial range by using only five strain measurements in the wing.