Complete supersonic flowfields over blunt bodies in a generalized orthogonal coordinate system

A general orthogonal coordinate system is used to describe various axisymmetric and two-dimensional shapes. Close approximations to planetary probe configurations are possible. The full Navier-Stokes equations are discretized in this coordinate system in a manner based on Allen and Cheng's numerical procedure. The blow shock is treated as a discontinuity which floats between grid points. Completely coupled flows over the forebody, base, and near wake were calculated over a cylinder, sphere, and an approximation to the Viking Aeroshell. Some problem areas in determining the base flow for increasing Reynolds number are discussed. In particular, it is found that the mean free path of the fluid near the wall immediately below the corner of the Viking Aeroshell, which experiences a severe expansion, can become greater than the local mesh size required to resolve the boundary layer in the forebody

ENABLING LOCAL GOVERNMENTS TO DESIGN AND IMPLEMENT ANTI-CORRUPTION STRATEGIES THROUGH DYNAMIC PERFORMANCE MANAGEMENT AND GOVERNANCE. A CASE-STUDY OF AN ITALIAN MUNICIPALITY

Lo scopo principale di questa ricerca è quello di inquadrare le possibili relazioni causali fra corruzione negli approvvigionamenti pubblici e performance delle amministrazioni locali. A tal fine, viene adottato un disegno di ricerca che integra dinamicamente metodi quantitativi e qualitativi in ogni fase del processo di studio. Gli approcci Dynamic Performance Management (DPM) e Governance (DPG), supportati da interviste approfondite non-strutturate, modellazioni formali e simulazioni quantitative, sono qui adottati per analizzare un caso di studio rappresentativo di un piccolo comune italiano in cui si sono verificati alcuni episodi di corruzione nelle attività di approvvigionamento nei primi anni 2000. In particolare, l'Ente locale in questione è stato sciolto due volte per infiltrazioni di stampo mafioso e, attualmente, versa in una situazione di dissesto finanziario. Il lavoro analizza i possibili esiti di tali fatti sulla performance organizzativa dell'Ente nel suo complesso sulla base di tre fonti: dati primari qualitativi generati da interviste frontali convergenti non-strutturate; dati secondari estrapolati da sentenze passate in giudicato e da archivi ad accesso aperto; ed un'ampia rassegna della letteratura. All'inizio, una panoramica della letteratura aiuta il lettore a comprendere i contenuti, le teorie ed i confini della corruzione. Successivamente, viene proposto un esame delle strategie di misurazione e delle misure più diffuse per prevenirla e contrastarla. Nel complesso, una particolare attenzione è riservata agli approvvigionamenti nei contesti pubblici locali. A seguito di una discussione sui possibili vantaggi e svantaggi, in termini di opportunità e deterrenze corruttive, derivanti dall'adozione dei paradigmi di governance nel settore pubblico più diffusi, gli approcci DPM e DPG vengono analizzati per comprendere il loro contributo teorico nel supportare i responsabili politici ed i manager ad arginare i fenomeni di corruzione. Successivamente, sulla base di alcune tecniche di codifica applicate alle interviste frontali non-strutturate svolte con alcuni Pubblici Ufficiali, un approccio esplorativo-descrittivo del caso-studio selezionato consente di comprendere la misura in cui gli eventi corruttivi investigati in questa sede abbiano inciso nel tempo sulla performance complessiva del Comune preso in esame. In seguito, viene adottata una prospettiva sistemica e dinamica di performance management per inquadrare le relazioni di causa-effetto emergenti dal caso di studio. L'assunzione di un approccio DPM consente ai politici ed ai dirigenti pubblici di progettare, implementare e valutare strategie anticorruzione fattibili, efficaci ed efficienti a livello di governo locale. Più precisamente, l'utilizzo, in un grafico DPM, di driver di performance adeguati al rischio di corruzione legato alle sue cause strutturali ed individualistiche può porre rimedio non soltanto alle riconosciute ambiguità e carenze derivanti dall'adozione di “bandiere rosse” nei processi di approvvigionamento pubblico, ma anche ai fallimenti dei controlli direzionali meccanicistici nel rilevare l'effettiva presenza di corruzione, fornendo ai decisori tempestivi segnali derivanti dagli effetti deleteri prodotti da siffatte pratiche clandestine. Inoltre, enfatizzare il ruolo della moralità civica comunitaria a livello di sistema può supportare la comprensione di alcuni risultati controintuitivi della passata ricerca sulla corruzione negli approvvigionamenti pubblici e dedurre in che modo gli investimenti nelle tecnologie dell'informazione e della comunicazione (TIC) e la formazione del personale possano migliorare responsabilità e competenza dei governi locali. Per quanto riguarda la professionalità dei dirigenti e dello staff quale causa individualistica di corruzione, il patronage politico derivante da opportunità legali risulta, per il caso di studio, significativo nello spiegare il cattivo andamento degli approvvigionamenti pubblici nel tempo. All'interno di questo quadro, la visualizzazione DPM consente altresì di distinguere più dettagliatamente la corruzione dallo spreco di risorse dovuto ad azioni non corruttive. In sintesi, un approccio DPM può consentire ai manager pubblici di mantenere i loro “radar cognitivi” costantemente (re)attivi, in modo da: identificare e sopprimere pratiche illecite negli approvvigionamenti pubblici; rilevare illeciti emergenti che potrebbero essere trascurati dai tradizionali approcci diagnostici e interattivi del controllo direzionale; favorire l'apprendimento etico e migliorare il valore pubblico generato. Infine, la prospettiva DPG può essere efficace nel supportare la formulazione e la messa a punto di strategie anticorruzione basate sulla collaborazione multistakeholder, nonché nel sondarne la fattibilità e gli impatti nel tempo all'interno di aree locali caratterizzate da strutture di governance carenti. Pertanto, sulla base di precedenti progetti di successo realizzati da governi locali di diverse parti del mondo, nell'ultima parte di questa tesi di ricerca viene utilizzato un approccio DPG per delineare e valutare una strategia anticorruzione per il caso in esame secondo un'impostazione di collaborative governance, così da inquadrare possibili sinergie ed interdipendenze tra i soggetti rilevanti, quali leve critiche per contrastare il rischio sistemico di corruzione a livello locale.The main purpose of this research is to frame the possible causal relationships between corruption in public procurement and performance of local governments. With this aim, a fully-integrated research design is adopted to dynamically mix quantitative and qualitative methods at every phase of the research process. The Dynamic Performance Management (DPM) and Governance (DPG) approaches, supported by in-depth interviews, formal modelling and simulations, are here adopted to analyse a representative case-study of an Italian small Municipality, where some corruption episodes in procurement activities occurred in the early 2000s. In particular, the local Authority in question was disbanded twice for mafia-like infiltrations and is currently facing a financial instability. In the light of that, the overall work studies the possible outcomes of those facts on the organisational performance as a whole, based on three sources: qualitative primary data generated by face-to-face convergent interviews; secondary data retrieved from both documents describing legal cases and open-access repositories; an extensive literature review. At the beginning, a broad and composite literature overview helps the reader become aware about the contents, theories and boundaries of corruption. Thereafter, an examination of the most widespread measurement strategies and measures to either prevent or repress it is proposed. Overall, a special focus is set on procurement in local public contexts. Following a discussion on the possible advantages and disadvantages of the most common public sector paradigms in terms of opportunities and constraints for corruption, the DPM and DPG views are explored to understand their theoretical contribution in supporting policy- and decision-makers to curb corruption phenomena in heterogeneous governance contexts. Afterwards, based on coding techniques, an exploratory-descriptive approach of the selected case-study allows for a better understanding of the extent to which the investigated corruption events impacted on the overall performance of the Municipality under scrutiny over time, by means of non-structured face-to-face interviews held with some Public Officials in 2019. Therefore, a system perspective in performance management is adopted to frame the emerging cause-and-effect relationships of the case-study. Assuming a DPM approach allows politicians and public managers to design, implement and assess feasible, effective and efficient anti-corruption strategies at local government level. More precisely, the use in a DPM chart of performance drivers adjusted for the risk of corruption linked to its structural and individualistic causes may not only put right to ambiguities and flaws deriving from the adoption of ‘red-flags’ in public procurement, but also to failures of mechanistical controls in detecting the actual presence of corruption, thus providing decision-makers with prompt signals arising from the emergent effects of clandestine practices. In addition, emphasising the role of community civic morality at system level may back up the understanding of some counterintuitive results in the past research on corruption in public procurement and deduce to what extent investments in Information and Communication Technologies (ICTs) and personnel training may enhance local government accountability and expertise. With regard to managers’ and staff’s professionalism, as individualistic cause of corruption, political patronage stemming from legal opportunities results significant in explaining poor performance in public procurement over time. Within this framework, the DPM view also allows for better singling corruption out from resource waste due to non-corrupt actions. In summary, a DPM approach may lead public managers to constantly maintain their ‘cognitive radar’ reactive, so as to identify and suppress unlawful practices in procurement, detect emerging malfeasances that could be otherwise overlooked by traditional static diagnostical and interactive approaches, foster ethical learning and enhance community outcomes. Finally, the DPG perspective may be effective in supporting formulation and fine-tuning of collaboration-based anti-corruption strategies and probing their feasibility and impacts over time within local areas characterised by poor governance structures. Hence, on the basis of previous successful projects throughout the world, in the last part of this research thesis a DPG approach is used to outline and evaluate an anti-corruption strategy for the case under scrutiny according to collaboration settings, in a way to frame possible synergies and interdependencies among relevant participants as critical levers to hinder systemic risk of corruption at local level

Isospin influence on the IMFs production in the 78,86Kr+40,48Ca reactions at 10 AMeV

Some results of the analysis of the reactions 78,86Kr + 40,48Ca at 10AMeV are presented. In particular the neutron enrichment effects on the production mechanisms of the Intermediate Mass Fragments are investigated. The reaction products show different isotopic composition and relative richness between the two systems. An odd-even staggering effect is present in the charge distributions of the reaction products, in particular for the light fragments produced by the neutronpoor system. The kinematical characteristics of the IMFs indicate a high degree of relaxation of the degrees of freedom of the formed systems, indicating a production by equilibrated fission-like process

Simulation of Stagnation Region Heating in Hypersonic Flow on Tetrahedral Grids

Hypersonic flow simulations using the node based, unstructured grid code FUN3D are presented. Applications include simple (cylinder) and complex (towed ballute) configurations. Emphasis throughout is on computation of stagnation region heating in hypersonic flow on tetrahedral grids. Hypersonic flow over a cylinder provides a simple test problem for exposing any flaws in a simulation algorithm with regard to its ability to compute accurate heating on such grids. Such flaws predominantly derive from the quality of the captured shock. The importance of pure tetrahedral formulations are discussed. Algorithm adjustments for the baseline Roe / Symmetric, Total-Variation-Diminishing (STVD) formulation to deal with simulation accuracy are presented. Formulations of surface normal gradients to compute heating and diffusion to the surface as needed for a radiative equilibrium wall boundary condition and finite catalytic wall boundary in the node-based unstructured environment are developed. A satisfactory resolution of the heating problem on tetrahedral grids is not realized here; however, a definition of a test problem, and discussion of observed algorithm behaviors to date are presented in order to promote further research on this important problem

A Perspective on Computational Aerothermodynamics at NASA

The evolving role of computational aerothermodynamics (CA) within NASA over the past 20 years is reviewed. The paper highlights contributions to understanding the Space Shuttle pitching moment anomaly observed in the first shuttle flight, prediction of a static instability for Mars Pathfinder, and the use of CA for damage assessment in post-Columbia mission support. In the view forward, several current challenges in computational fluid dynamics and aerothermodynamics for hypersonic vehicle applications are discussed. Example simulations are presented to illustrate capabilities and limitations. Opportunities to advance the state-of-art in algorithms, grid generation and adaptation, and code validation are identified

Multi-Dimensional, Inviscid Flux Reconstruction for Simulation of Hypersonic Heating on Tetrahedral Grids

The quality of simulated hypersonic stagnation region heating on tetrahedral meshes is investigated by using a three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. Two test problems are investigated: hypersonic flow over a three-dimensional cylinder with special attention to the uniformity of the solution in the spanwise direction and hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problem provides a sensitive test for algorithmic effects on heating. This investigation is believed to be unique in its focus on three-dimensional, rotated upwind schemes for the simulation of hypersonic heating on tetrahedral grids. This study attempts to fill the void left by the inability of conventional (quasi-one-dimensional) approaches to accurately simulate heating in a tetrahedral grid system. Results show significant improvement in spanwise uniformity of heating with some penalty of ringing at the captured shock. Issues with accuracy near the peak shear location are identified and require further study

Semi-Analytic Reconstruction of Flux in Finite Volume Formulations

Semi-analytic reconstruction uses the analytic solution to a second-order, steady, ordinary differential equation (ODE) to simultaneously evaluate the convective and diffusive flux at all interfaces of a finite volume formulation. The second-order ODE is itself a linearized approximation to the governing first- and second- order partial differential equation conservation laws. Thus, semi-analytic reconstruction defines a family of formulations for finite volume interface fluxes using analytic solutions to approximating equations. Limiters are not applied in a conventional sense; rather, diffusivity is adjusted in the vicinity of changes in sign of eigenvalues in order to achieve a sufficiently small cell Reynolds number in the analytic formulation across critical points. Several approaches for application of semi-analytic reconstruction for the solution of one-dimensional scalar equations are introduced. Results are compared with exact analytic solutions to Burger s Equation as well as a conventional, upwind discretization using Roe s method. One approach, the end-point wave speed (EPWS) approximation, is further developed for more complex applications. One-dimensional vector equations are tested on a quasi one-dimensional nozzle application. The EPWS algorithm has a more compact difference stencil than Roe s algorithm but reconstruction time is approximately a factor of four larger than for Roe. Though both are second-order accurate schemes, Roe s method approaches a grid converged solution with fewer grid points. Reconstruction of flux in the context of multi-dimensional, vector conservation laws including effects of thermochemical nonequilibrium in the Navier-Stokes equations is developed

Updates to Multi-Dimensional Flux Reconstruction for Hypersonic Simulations on Tetrahedral Grids

The quality of simulated hypersonic stagnation region heating with tetrahedral meshes is investigated by using an updated three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. An earlier implementation of this algorithm provided improved symmetry characteristics on tetrahedral grids compared to conventional reconstruction methods. The original formulation however displayed quantitative differences in heating and shear that were as large as 25% compared to a benchmark, structured-grid solution. The primary cause of this discrepancy is found to be an inherent inconsistency in the formulation of the flux limiter. The inconsistency is removed by employing a Green-Gauss formulation of primitive gradients at nodes to replace the previous Gram-Schmidt algorithm. Current results are now in good agreement with benchmark solutions for two challenge problems: (1) hypersonic flow over a three-dimensional cylindrical section with special attention to the uniformity of the solution in the spanwise direction and (2) hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problems provide a sensitive indicator for algorithmic effects on heating. Additional simulations on a sharp, double cone and the shuttle orbiter are then presented to demonstrate the capabilities of the new algorithm on more geometrically complex flows with tetrahedral grids. These results provide the first indication that pure tetrahedral elements utilizing the updated, three-dimensional, upwind reconstruction algorithm may be used for the simulation of heating and shear in hypersonic flows in upwind, finite volume formulations

Conservation equations and physical models for hypersonic air flows in thermal and chemical nonequilibrium

The conservation equations for simulating hypersonic flows in thermal and chemical nonequilibrium and details of the associated physical models are presented. These details include the curve fits used for defining thermodynamic properties of the 11 species air model, curve fits for collision cross sections, expressions for transport properties, the chemical kinetics models, and the vibrational and electronic energy relaxation models. The expressions are formulated in the context of either a two or three temperature model. Greater emphasis is placed on the two temperature model in which it is assumed that the translational and rotational energy models are in equilibrium at the translational temperature, T, and the vibrational, electronic, and electron translational energy modes are in equilibrium at the vibrational temperature, T sub v. The eigenvalues and eigenvectors associated with the Jacobian of the flux vector are also presented in order to accommodate the upwind based numerical solutions of the complete equation set

A viscous shock-layer flowfield analysis by an explicit-implicit method

An implicit analogue of a widely used explicit method to external axisymmetric laminar flows with strong entropy gradients is extended. The details of the "numerics" of the implicit part are provided in a body oriented coordinate system with a moving outer (shock) boundary during the transient part of the solutions. The limiting values of the Courant number are obtained when the shock boundary is treated explicitly. The solution algorithm outlined includes the treatment of the source term associated with the equations in weak conservation form. From the results obtained for two sample problems, it becomes clear that accuracy of predictions is, indeed, very good at higher values of the Courant number. There is a significant saving in overall computing time, depending on the Courant number used and the flow Reynolds number. These properties combined with the simplicity of programming the implicit analog may appeal to researchers for using it in the analysis of 3-D flow problems