Dionissios P. Margaris

Computational atmospheric trajectory simulation analysis of spin-stabilised projectiles and small bullets

A mathematical model is based on the full equations of motion set up in the no-roll body reference frame and is integrated numerically from given initial conditions at the firing site. The computational flight analysis takes into consideration the Mach number and total angle of attack effects by means of the variable aerodynamic coefficients. For the purposes of the present work, linear interpolation has been applied for aerodynamic coefficients from the official tabulated database. Static stability is examined. The aerodynamic jump has the most important effect and is examined more closely for projectile and bullet flight trajectories.

Stagnation Heat Transfer and Through-thickness Temperature Profile Calculation at Hypersonic Speeds

The aeroheating phenomenon that is being developed at the hypersonic speeds during a spacecrafts atmospheric reentry, leads to high thermal loads in the stagnation regions. The accurate calculation of the heat load is crucial for the optimum design (thickness and composition) of the spacecrafts Thermal Protection System (TPS). The heat load is being calculated using the Fay-Riddell theory. The wall temperature is calculated by the modified Fay-Riddell model. Finally an explicit numerical method is created for the through-thickness temperature profile calculation for various Thermal Protection System material models.

Entry Trajectory Aerothermodynamics of Space Vehicles in Planetary Atmospheres

A flexible synthetic metho d is developed for predicting the nominal entry trajectory of space vehicles without any simplifications, combining flight dynamics with parallel accurate aerothermodynamic analysis of the stagnation point region during hypersonic flight. For Earth atmosph ere the aerothermal estimation takes into consideration the real gas effects by means of the thermodynamic and transport properties of air as a thermochemical reacting gas in high entry temperatures. For the present work the Mollier chart of equilibrium ai r has been applied as transferred by polynomials. The accurate extreme convective stagnation heating loads are estimated and compared with other engineering analytical methods. The aerodynamic coefficients of the examined ballistic and lifting bodies are t aken for the hypersonic flight regime. The U.S. Standard Atmosphere model for Earth is applied whereas for other planetary atmospheres appropriate polynomial expressions taking from official tabulated data are used. The efficiency of the developed method i s proven by comparisons of velocity, stagnation point heat transfer and wall temperature results with corresponding computational and experimental data of known entry trajectories of Space Shuttle flight STS -40, Hermes spacecraft and a Apollo like capsule. Nomenclature r = distance of the vehicle from the planet’s center of gravity, m � = longitude of the vehicle’s position, rad � = latitude of the vehicle’s position, rad V = velocity relative to the planet, m/s � = flight path angle between the local hor izontal plane and velocity vector, rad � = heading angle between the local parallel of latitude and the projection of velocity vector on the horizontal plane, rad � = angle of attack of the vehicle, rad � = bank angle of the vehicle, rad n = angle of thrus t of the vehicle, rad m = vehicle mass, kg Lref = reference length, m Sref = reference area, m 2 RN = nose radius, m � = emissivity of vehicle wall

Aerodynamic Performance of a NREL S809 Airfoil in an Air-Sand Particle Two-Phase Flow

This paper opens up a new perspective on the aerodynamic performance of a wind turbine airfoil. More specifically, the paper deals with a steady, incompressible two-phase flow, consisting of air and two different concentrations of sand particles, over an airfoil from the National Renewable Energy Laboratory, NREL S809. The numerical simulations were performed on turbulence models for aerodynamic operations using commercial computational fluid dynamics (CFD) code. The computational results obtained for the aerodynamic performance of an S809 airfoil at various angles of attack operating at Reynolds numbers of Re = 1 × 106 and Re = 2 × 106 in a dry, dusty environment were compared with existing experimental data on air flow over an S809 airfoil from reliable sources. Notably, a structured mesh consisting of 80,000 cells had already been identified as the most appropriate for numerical simulations. Finally, it was concluded that sand concentration significantly affected the aerodynamic performance of the airfoil; there was an increase in the values of the predicted drag coefficients, as well as a decrease in the values of the predicted lift coefficients caused by increasing concentrations of sand particles. The region around the airfoil was studied by using contours of static pressure and discrete phase model (DPM) concentration.

Numerical and Computational Analysis of a New Vertical Axis Wind Turbine, Named KIONAS

This paper concentrates on a new configuration for a wind turbine, named KIONAS. The main purpose is to determine the performance and aerodynamic behavior of KIONAS, which is a vertical axis wind turbine with a stator over the rotor and a special feature in that it can consist of several stages. Notably, the stator is shaped in such a way that it increases the velocity of the air impacting the rotor blades. Moreover, each stage’s performance can be increased with the increase of the total number of stages. The effects of wind velocity, the various numbers of inclined rotor blades, the rotor diameter, the stator’s shape and the number of stages on the performance of KIONAS were studied. A FORTRAN code was developed in order to predict the power in several cases by solving the equations of continuity and momentum. Subsequently, further knowledge on the flow field was obtained by using a commercial Computational Fluid Dynamics code. Based on the results, it can be concluded that higher wind velocities and a greater number of blades produce more power. Furthermore, higher performance was found for a stator with curved guide vanes and for a KIONAS configuration with more stages.

A Six Degree of Freedom Trajectory Analysis of Spin‐Stabilized Projectiles

A full six degrees of freedom (6-DOF) flight dynami cs model is proposed for the accurate prediction of short and long-range trajectories of high and low spin-st abilized projectiles via atmospheric flight to fina l impact point. The projectile is assumed to be both rigid (non-flexibl e), and rotationally symmetric about its spin axis launched at low and high pitch angles. The projectile maneuvering motion dep ends on the most significant force and moment varia tions in addition to gravity and Magnus Effect. The computational flight analysis takes into consideration the Mach number and total angle of attack effects by means of the variable aerodynamic coefficients. For the purposes of the present work , linear interpolation has been applied from the tabulated database of McCoys book. The aforementioned variable flight model is c ompared with a trajectory atmospheric motion based on appropriate constant mean values of the aerodynamic projectile coefficients. Static stability, also called gyroscopic stability, is exa mined as a necessary condition for stable flight mo tion in order to locate the initial spinning projectile rotation. Static stabil ity examination takes into account the overturning moment variations with Mach number flight motion. The developed method gives satisfactory results compared with published dat a of verified experiments and computational codes on atmospheric dynamics model analysis.

Analytical Calculations of Spacecrafts Hypersonic Aerodynamic Characteristics based on Experimental Data

An analytical method is created for the calculation of the aerodynamic characteristics of Space Vehicles during their flight in hypersonic regime. The simplicity of this method lies on the fact that it only needs the Spacecrafts geometry in conjunction with a small number of experimental (wind tunnel) data. The analysis is based on the Newtonian Flow theory. Several basic assumptions are taken into account. The flow is considered inviscid, the pressure coefficient after the shockwave remains constant, the upper surface pressure coefficient is equal to zero and the lower surface pressure coefficient is given as a function of the Spacecrafts angle of attack. The Space Vehicle is modeled as a flat plate with constant unit-length wing span. The lift and drag coefficients during hypersonic flight can be calculated from the normal force coefficient and the Spacecrafts angle of attack. The lower surface of these Space Vehicles is considered be flat. Their dihedral angle is small. The wings top view is modeled with straight lines between known and predetermined points on the Spacecraft. Taking into account the fact that the Space Vehicles hypersonic aerodynamic attitude is similar to that of a flat plate, and it has finite and non-constant wing span which is modeled with straight lines as mentioned above, the Newtonian Flow theory is being developed for every Spacecraft separately. In the current analysis the Finite Wing Span Newtonian Flow (FWSNF) models for two specific Spacecrafts, the STS Shuttle Orbiter and the X-34 vehicle, are being developed in details.

Transient simulation of large scale gas transmission networks using an adaptive method of lines

The modern gas pipeline distribution networks is of such scale and complexity that operate under transient conditions most of the times. The accurate and rapid prediction of the time dependent flow magnitudes is essential in order to achieve optimum cumulative deliverability and safe and reliable operation.