Summary Findings from the AVT-191 Project to Assess Sensitivity Analysis and Uncertainty Quantification Methods for Military Vehicle Design

A NATO symposium held in Greece in 2008 identified many promising sensitivity analysis and uncertainty quantification technologies, but the maturity and suitability of these methods for realistic applications was not clear. The NATO Science and Technology Organization, Task Group AVT-191 was established to evaluate the maturity and suitability of various sensitivity analysis and uncertainty quantification methods for application to realistic vehicle development problems. The program ran from 2011 to 2015, and the work was organized into four discipline-centric teams: external aerodynamics, internal aerodynamics, aeroelasticity, and hydrodynamics. This paper summarizes findings and lessons learned from the task group

A Discontinuous Galerkin Chimera scheme

The Chimera overset method is a powerful technique for modeling fluid flow associated with complex engineering problems using structured meshes. The use of structured meshes has enabled engineers to employ a number of high-order schemes, such as the WENO and compact differencing schemes. However, the large stencil associated with these schemes can significantly complicate the inter-grid communication scheme and hole cutting procedures. This paper demonstrates a methodology for using the Discontinuous Galerkin (DG) scheme with Chimera overset meshes. The small stencil of the DG scheme makes it particularly suitable for Chimera meshes as it simplifies the inter-grid communication scheme as well as hole cutting procedures. The DG-Chimera scheme does not require a donor interpolation method with a large stencil because the DG scheme represents the solution as cell local polynomials. The DG-Chimera method also does not require the use of fringe points to maintain the interior stencil across inter-grid boundaries. Thus, inter-grid communication can be established as long as the receiving boundary is enclosed by or abuts the donor mesh. This makes the inter-grid communication procedure applicable to both Chimera and zonal meshes. Details of the DG-Chimera scheme are presented, and the method is demonstrated on a set of two-dimensional inviscid flow problems

Relationship Between Intermittent Separation and Vortex Structure in a Three-Dimensional Shock/Boundary-Layer Interaction

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140686/1/1.J053905.pd

Development and Use of Engineering Standards for Computational Fluid Dynamics for Complex Aerospace Systems

Computational fluid dynamics (CFD) and other advanced modeling and simulation (M&S) methods are increasingly relied on for predictive performance, reliability and safety of engineering systems. Analysts, designers, decision makers, and project managers, who must depend on simulation, need practical techniques and methods for assessing simulation credibility. The AIAA Guide for Verification and Validation of Computational Fluid Dynamics Simulations (AIAA G-077-1998 (2002)), originally published in 1998, was the first engineering standards document available to the engineering community for verification and validation (V&V) of simulations. Much progress has been made in these areas since 1998. The AIAA Committee on Standards for CFD is currently updating this Guide to incorporate in it the important developments that have taken place in V&V concepts, methods, and practices, particularly with regard to the broader context of predictive capability and uncertainty quantification (UQ) methods and approaches. This paper will provide an overview of the changes and extensions currently underway to update the AIAA Guide. Specifically, a framework for predictive capability will be described for incorporating a wide range of error and uncertainty sources identified during the modeling, verification, and validation processes, with the goal of estimating the total prediction uncertainty of the simulation. The Guide's goal is to provide a foundation for understanding and addressing major issues and concepts in predictive CFD. However, this Guide will not recommend specific approaches in these areas as the field is rapidly evolving. It is hoped that the guidelines provided in this paper, and explained in more detail in the Guide, will aid in the research, development, and use of CFD in engineering decision-making

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Nozzle geometry effects on supersonic wind tunnel studies of shock–boundary-layer interactions

AbstractMany supersonic wind tunnel experiments investigate shock–boundary-layer interactions by measuring the response of tunnel wall boundary layers to an incident shock wave. To generate the supersonic flow, these facilities typically use two-dimensional contoured converging–diverging nozzles which can be arranged in two different ways. One configuration is symmetric about the centre height, whereas this symmetry plane defines the tunnel floor in the other asymmetric arrangement. In order to determine whether these nozzle configurations, which are widely thought to be equivalent, can influence experiments on shock–boundary-layer interactions, two different nozzle geometries are compared with one another in a single facility with rectangular cross section. For each setup, a full-span 8-degree wedge introduces an oblique shock to a Mach 2.5 flow. The two setups exhibit quite dissimilar behaviour, both in the corner regions and on the tunnel’s centre span, with a difference in central separation length of as much as 35% suggesting that nozzle geometry can have a profound impact on these interactions. The observed behaviour is caused by known secondary flows in the sidewall boundary layers which are driven by vertical pressure gradients in the nozzle region. The subsequent impact on the response of the floor boundary layer is consistent with expectations based on local flow momentum affecting corner separation size and on the displacement effect of this corner separation influencing the wider flow. Graphical abstract</jats:p

Nozzle geometry effects on supersonic wind tunnel studies of shock–boundary-layer interactions

AbstractMany supersonic wind tunnel experiments investigate shock–boundary-layer interactions by measuring the response of tunnel wall boundary layers to an incident shock wave. To generate the supersonic flow, these facilities typically use two-dimensional contoured converging–diverging nozzles which can be arranged in two different ways. One configuration is symmetric about the centre height, whereas this symmetry plane defines the tunnel floor in the other asymmetric arrangement. In order to determine whether these nozzle configurations, which are widely thought to be equivalent, can influence experiments on shock–boundary-layer interactions, two different nozzle geometries are compared with one another in a single facility with rectangular cross section. For each setup, a full-span 8-degree wedge introduces an oblique shock to a Mach 2.5 flow. The two setups exhibit quite dissimilar behaviour, both in the corner regions and on the tunnel’s centre span, with a difference in central separation length of as much as 35% suggesting that nozzle geometry can have a profound impact on these interactions. The observed behaviour is caused by known secondary flows in the sidewall boundary layers which are driven by vertical pressure gradients in the nozzle region. The subsequent impact on the response of the floor boundary layer is consistent with expectations based on local flow momentum affecting corner separation size and on the displacement effect of this corner separation influencing the wider flow. Graphical abstract</jats:p

Separated and nonseparated turbulent flows about axisymmetric nozzle afterbodies.

Extensive static pressure data were obtained on a model consisting of a cone-ogive-cylinder forebody, two interchangeable circular arc afterbody boattails having length-to-forebody diameter ratios of 0.80 and 1.77, and two interchangeable solid exhaust plume simulators of cylindrical and contoured geometry. Boundary-layer pitot data and photographic records of model tufts and schlieren data were also obtained. Data were collected over a Mach number range of 0.60 to 1.30 and a unit Reynolds number range of 3.2 to 13.12 million per m (1 to 4 million per ft) at zero angle of attack and sideslip for the purpose of obtaining experimental data suitable for comparison with theoretical predictions. Data are presented for two model configurations with cylindrical solid plume simulators at three flow conditions: (1) length-to-diameter ratio = 1.77 boattail at Mach number number 0.80 and Reynolds number 8.2 million per m for high subsonic, unseparated flow; (2) length-to-diameter ratio = 0.80 boattail at Mach number 0.60 and unit Reynolds number 8.2 million per m for subsonic, separated flow; and (3) length-to-diameter ratio = 0.80 boattail at Mach number 0.95 and unit Reynolds number 8.2 million per m for transonic, separated flow with boundary-layer-shock interaction. (Author)."October 1979.""Final Report: October 1, 1976 -- September 30, 1977."Includes bibliograpic references (page 15).Extensive static pressure data were obtained on a model consisting of a cone-ogive-cylinder forebody, two interchangeable circular arc afterbody boattails having length-to-forebody diameter ratios of 0.80 and 1.77, and two interchangeable solid exhaust plume simulators of cylindrical and contoured geometry. Boundary-layer pitot data and photographic records of model tufts and schlieren data were also obtained. Data were collected over a Mach number range of 0.60 to 1.30 and a unit Reynolds number range of 3.2 to 13.12 million per m (1 to 4 million per ft) at zero angle of attack and sideslip for the purpose of obtaining experimental data suitable for comparison with theoretical predictions. Data are presented for two model configurations with cylindrical solid plume simulators at three flow conditions: (1) length-to-diameter ratio = 1.77 boattail at Mach number number 0.80 and Reynolds number 8.2 million per m for high subsonic, unseparated flow; (2) length-to-diameter ratio = 0.80 boattail at Mach number 0.60 and unit Reynolds number 8.2 million per m for subsonic, separated flow; and (3) length-to-diameter ratio = 0.80 boattail at Mach number 0.95 and unit Reynolds number 8.2 million per m for transonic, separated flow with boundary-layer-shock interaction. (Author).Report supported by the Air Force Systems Command and prepared by ARO, Inc,, a Sverdrup Corporation Company, under Program Element,Mode of access: Internet

Effects of acoustic and vortical disturbances on the turbulent boundary layer at free-stream Mach number 0.5 /

An experimental investigation of the effects of free-stream disturbances on the development of a turbulent boundary layer is described. The data, obtained at a free-stream Mach number of 0.5, indicated: (1) compared to the baseline acoustic disturbances of 133 db, acoustic disturbances of up to 150 db did not significantly alter the turbulent boundary-layer skin friction, displacement thickness, or momentum thickness and (2) compared to the baseline vortical disturbances of 0.5 percent of the free-stream velocity, vortical disturbances of one percent of the free-stream velocity considerably altered the boundary-layer skin friction, displacement thickness, and momentum thickness, as well as their growth rates. (Author)."December 1977.""Final Report: July 1, 1974 -- June 30, 1976."Includes bibliographical references (pages 19-21).An experimental investigation of the effects of free-stream disturbances on the development of a turbulent boundary layer is described. The data, obtained at a free-stream Mach number of 0.5, indicated: (1) compared to the baseline acoustic disturbances of 133 db, acoustic disturbances of up to 150 db did not significantly alter the turbulent boundary-layer skin friction, displacement thickness, or momentum thickness and (2) compared to the baseline vortical disturbances of 0.5 percent of the free-stream velocity, vortical disturbances of one percent of the free-stream velocity considerably altered the boundary-layer skin friction, displacement thickness, and momentum thickness, as well as their growth rates. (Author).Report supported by the Air Force Systems Command and prepared by ARO, Inc, under Program Element,Mode of access: Internet