Preface

Chapter 9 **Goal- and Object-Oriented Models of the Aerodynamic**

Chapter 10 **The Effects of Storage on Turbine Engine Fuels 193**

Chapter 11 **12-Pulse Active Rectifier for More Electric Aircraft**

**Coefficients 159** Jozsef Rohacs

**VI** Contents

David W. Johnson

**Applications 211** Mohamad Taha

Flight physics is a complex and interdisciplinary discipline, combining aerodynamics, fluid and solid mechanics, flight control and mechanics, and other scientific disciplines. In terms of aerody‐ namics, the study of flight combines wind tunnel testing, similarity scaling principles, analytical modeling, computational fluid dynamics (CFD) and empirical test data.

Aircraft development is triggered by the success of past years' research and development activi‐ ties resulting in increased lightweight performance of the aircraft, by using new materials and advanced manufacturing and design methods. Practical demands led to more complex aircraft architectures and consequently a need for higher efficiency and hence less conservative designs.

The dynamic behavior of aircraft is becoming more and more a design-driving topic. Considera‐ ble changes of aircraft design processes lead to significant reduction of development times, while including a number of disciplines in the early phases of design activities in order to find an opti‐ mum design. One of the main objectives in the aerospace industry is the reduction of aircraft de‐ velopment time and provision of robust solutions with improved quality. Simulation of the dynamic behavior is an important part of the design process and has a strong impact on safety and comfort. However, description and simulation of the dynamic behavior are also a challenging topic, since dynamic simulation requires detailed and advanced mathematical models. Improved simulation capabilities have a rather large impact on improving cost efficiency both with respect to aircraft development cost and aircraft operational cost.

The book offers a general overview of the concepts, theories and models underlying flight phys‐ ics. The book focuses on the synthesis of the fundamental disciplines and practical applications involved in the investigation, description, and analysis of aircraft flight including applied aerody‐ namics, aircraft propulsion, flight performance, stability, and control. The book covers the aero‐ dynamic models that describe the forces and moments on maneuvering aircraft, and provides an overview of the concepts and methods used in flight dynamics. A particular focus of the book is development of theoretical, computational and experimental methods in aerodynamics. The book covers some topics in depth while offering introductions and summaries of others. There are 11 chapters in the book covering different aspects related to flight physics.

#### **Learning from Nature: Unsteady Flow Physics in Bioinspired Flapping Flight**

The aerodynamics of free-flying insects is studied based on the approach combining high-speed photogrammetry, three-dimensional surface reconstruction, and computational fluid dynamics. The proposed approach is capable of measuring the wing kinematics, and surface deformation and simulating its aerodynamic performance. Four different species of insects (dragonfly, damsel‐ fly, butterfly, and cicada) are investigated to demonstrate the possibilities of the approach. A deep understanding of flapping wing mechanism, revealing the underlying flow physics for future de‐ signs and applications, is achieved.

#### **Helicopter Flight Physics**

The principles that constitute the fundamentals of helicopter flight physics, starting from the ba‐ sics of the main rotor aerodynamics and of the component parts related to flight control, are con‐ sidered. A short history of helicopter development is also presented. The main constructive solutions for helicopters and the basic equations of fluid mechanics are applied on a helicopter model with one main rotor and tail rotor. The ground effect, autorotation, stability and helicopter control are discussed, and the main factors that determine the helicopter performances are men‐ tioned.

#### **Flight Dynamic Modeling and Simulation of Large Flexible Aircraft**

The approach to modeling and simulation of large flexible aircrafts is presented. The approach requires a careful integration of aerodynamic models with models for structural dynamics. The coupled aero-structural model then provides forces and moments to the equations of motion. Two cases are used to demonstrate possibilities of the proposed methodology. The first case fo‐ cuses on aircraft response to a gust that has a spanwise varying profile, and the second case inves‐ tigates aircraft dynamics during control surface failure scenarios.

#### **Aerodynamic Characteristics and Longitudinal Stability of Tube-Launched Tandem-Scheme UAV**

Tube-launched unmanned aerial vehicles (UAVs) are often implemented with aerodynamic scheme with forward and rear wings (tandem scheme). UAV aerodynamic characteristics for dif‐ ferent wing rotation angles are discussed. The results show that UAV is unstable with wings' ro‐ tation angles up to 60 degrees because rear wings produce lift ahead of center of gravity. For large angles of wing rotation (low sweep angles), UAV model is stable in wide range of angles of at‐ tack.

#### **Airfoil Boundary Layer Optimization toward Aerodynamic Efficiency of Wind Turbines**

An airfoil optimization method for higher aerodynamic efficiency and laminar boundary layer enlargement is discussed, and advantages of laminar boundary layer expansion in airfoil of hori‐ zontal axis wind turbine blades are presented. The optimized airfoil shows enlarged laminar boundary layer region in all flow regime with a higher aerodynamic efficiency and the increased gliding ratio. The smaller laminar separation region and reduced stall regime of CFD simulations illustrate the desirable aerodynamics of the resulted airfoil.

#### **LES of Unsteady Aerodynamic Forces on a Long-Span Curved Roof**

Unsteady aerodynamic forceson long-span curved roofs with large eddy simulation (LES) techni‐ que are discussed. The forced vibration test in a turbulent boundary layer is simulated. The mod‐ els are force vibrated in the first antisymmetric modeto investigate the influences of a roof vibration on the wind pressure and flow field around a vibrating roof. The characteristics of un‐ steady aerodynamic forces in a wider range of reduced frequency of vibration are also investigat‐ ed. A comparison between the wind tunnel experiment and the LES indicates that the LES can be used effectively to evaluate the unsteady aerodynamic force.

#### **Wake Topology and Aerodynamic Performance of Heaving Wings**

Simulation of the three-dimensional flow features generated by heaving wings is a great chal‐ lenge for computational methods. The wake topology generated by oscillating rigid wings is studied. The unsteady laminar incompressible Navier-Stokes equations are solved on moving overlapping structured meshes using high-resolution numerical schemes. The numerical simula‐ tions are performed for a Reynolds number of Re=250 and different Strouhal numbers and heav‐ ing frequency.

#### **Aeroelastic Stability of Turboprop Aircraft: Whirl Flutter**

sidered. A short history of helicopter development is also presented. The main constructive solutions for helicopters and the basic equations of fluid mechanics are applied on a helicopter model with one main rotor and tail rotor. The ground effect, autorotation, stability and helicopter control are discussed, and the main factors that determine the helicopter performances are men‐

The approach to modeling and simulation of large flexible aircrafts is presented. The approach requires a careful integration of aerodynamic models with models for structural dynamics. The coupled aero-structural model then provides forces and moments to the equations of motion. Two cases are used to demonstrate possibilities of the proposed methodology. The first case fo‐ cuses on aircraft response to a gust that has a spanwise varying profile, and the second case inves‐

**Aerodynamic Characteristics and Longitudinal Stability of Tube-Launched Tandem-Scheme**

Tube-launched unmanned aerial vehicles (UAVs) are often implemented with aerodynamic scheme with forward and rear wings (tandem scheme). UAV aerodynamic characteristics for dif‐ ferent wing rotation angles are discussed. The results show that UAV is unstable with wings' ro‐ tation angles up to 60 degrees because rear wings produce lift ahead of center of gravity. For large angles of wing rotation (low sweep angles), UAV model is stable in wide range of angles of at‐

**Airfoil Boundary Layer Optimization toward Aerodynamic Efficiency of Wind Turbines**

An airfoil optimization method for higher aerodynamic efficiency and laminar boundary layer enlargement is discussed, and advantages of laminar boundary layer expansion in airfoil of hori‐ zontal axis wind turbine blades are presented. The optimized airfoil shows enlarged laminar boundary layer region in all flow regime with a higher aerodynamic efficiency and the increased gliding ratio. The smaller laminar separation region and reduced stall regime of CFD simulations

Unsteady aerodynamic forceson long-span curved roofs with large eddy simulation (LES) techni‐ que are discussed. The forced vibration test in a turbulent boundary layer is simulated. The mod‐ els are force vibrated in the first antisymmetric modeto investigate the influences of a roof vibration on the wind pressure and flow field around a vibrating roof. The characteristics of un‐ steady aerodynamic forces in a wider range of reduced frequency of vibration are also investigat‐ ed. A comparison between the wind tunnel experiment and the LES indicates that the LES can be

Simulation of the three-dimensional flow features generated by heaving wings is a great chal‐ lenge for computational methods. The wake topology generated by oscillating rigid wings is studied. The unsteady laminar incompressible Navier-Stokes equations are solved on moving overlapping structured meshes using high-resolution numerical schemes. The numerical simula‐ tions are performed for a Reynolds number of Re=250 and different Strouhal numbers and heav‐

**Flight Dynamic Modeling and Simulation of Large Flexible Aircraft**

tigates aircraft dynamics during control surface failure scenarios.

illustrate the desirable aerodynamics of the resulted airfoil.

used effectively to evaluate the unsteady aerodynamic force.

**Wake Topology and Aerodynamic Performance of Heaving Wings**

**LES of Unsteady Aerodynamic Forces on a Long-Span Curved Roof**

tioned.

VIII Preface

**UAV**

tack.

ing frequency.

The whirl flutter, which is the specific type of dynamic aeroelastic stability phenomenon, is stud‐ ied. Whirl flutter is caused by the effect of rotating parts of a turboprop power plant (propeller and gas turbine engine rotor). A brief historical overview and information regarding the occur‐ rence of whirl flutter in the aerospace practice are presented. The physical principles of whirl flut‐ ter are explained on a simple mechanical system with two degrees of freedom. The analytical solution to determine the aerodynamic forces caused by the gyroscopic motion on each of the propeller blades is provided, and the influences of the main structural parameters on the whirl flutter stability are mentioned.

#### **Goal- and Object-Oriented Models of the Aerodynamic Coefficients**

The study introduces some new models for aerodynamic coefficients and demonstrates how the different models can be applied in object-oriented solutions. General aspects related to generation of the aerodynamic forces and moments are also covered. Modeling of linear and nonlinear, and steady and unsteady aerodynamic coefficient structures and forms, is discussed.

#### **The Effects of Storage on Turbine Engine Fuels**

Modern aviation requires reliable and safe sources of fuel. The variable composition of fuel de‐ pending upon crude oil source and refining methods creates challenges for fuel storage. Other problems are related to the presence of water, both from contamination through leaks in the stor‐ age tanks and the general solubility of water in jet fuel. The study addresses some problems asso‐ ciated with the incompatibility and long-term fuel storage.

#### **12-Pulse Active Rectifier for More Electric Aircraft Applications**

The study presents analysis and simulation of 12-pulse active rectifier for electric aircraft applica‐ tions. Rather than using a fixed 400 Hz supply, variable frequency supply (360 to 800 Hz) is used depending on aircraft velocity.

The book promotes open discussion between research institutions, academia, and industry from around the globe on research and development of enabling technologies. The book covers many aspects of theory and simulation (physics, turbulence modeling, algorithms, applications, etc.) which deliver essential contributions, and provide their input and support to the cooperative efforts.

> **Dr. Konstantin Volkov** MEng, MSc, PhD, DSc, CEng, MIMechE, MInstP Department of Mechanical and Automotive Engineering School of Mechanical and Aerospace Engineering Faculty of Science, Engineering and Computing Kingston University, London, United Kingdom

**Provisional chapter**
