Wade W. Huebsch

Dynamic Roughness as a Means of Leading-Edge Separation Flow Control

The aircraft industry, as a whole, has been deeply concerned with improving the aerodynamic efficiency of current and future flight vehicles, particularly in the commercial and military markets. However, of particular interest to the field of aerodynamics is the elusive concept of a workable flow control mechanism. Effective flow control is a concept which if properly applied can increase aerodynamic efficiency. Various concepts and ideas to obtain successful flow control have been studied in an attempt to reap these rewards. Some examples include boundary layer blowing (steady and periodic), suction, and synthetic jets. The overall goal of flow control is to increase performance. The specific objectives of flow control include: 1) delay or eliminate flow separation, 2) delay boundary layer transition or 3) reduce skin friction drag. The purpose of this research is to investigate dynamic surface roughness as a novel method of flow control technology for external boundary layer flows. As opposed to standard surface roughness, dynamic roughness incorporates small time dependent perturbations to the surface of the airfoil. These surface perturbations are actual humps and/or ridges that are on the scale of the laminar boundary layer, and oscillate with an unsteady motion. Research has shown that this can provide a means to modify the instantaneous and mean velocity profile near the wall and favorably control the existing state of the boundary layer. The results of this study have shown that dynamic roughness can be a viable alternative in delaying and/or eliminating the leading edge laminar separation bubble and hence reaping some of the rewards of an effective flow control system, while also maintaining some physical advantages over other techniques.

Effects of Surface Ice Roughness on Dynamic Stall

A two-dimensional Navier-Stokes algorithm is used to investigate unsteady, incompressible viscous flow past an airfoil leading edge with surface roughness that is characteristic of early-growth ice accretion. The roughness is added to the surface through the use of a Prandtl transposition and can generate both small-scale and large-scale roughness geometries. The algorithm is used to simulate steady or unsteady flow at constant angle of attack or pitch up corresponding to dynamic-stall conditions. Investigations of the dynamic stall show that some types of surface roughness can significantly alter the unsteady flow separation pattern and the formation of the dynamic-stall vortex. This includes both small-scale and large-scale roughness

Two-dimensional simulation of dynamic surface roughness for aerodynamic flow control

This study addresses the issue of controlling flow separation through the use of dynamic surface roughness. The work focuses on two areas: 1) development of simulation tools for detailed analysis of moving flow boundaries and 2) investigation of the effects of dynamic roughness on aerodynamic flow separation. The process of generating a quality grid for a surface that contains complex roughness can be a labor-intensive project. The addition of dynamic surface roughness, or roughness that grows (or shrinks) in time, can further complicate this process. The current study proposes a method that not only accounts for the perturbations to the surface but also allows for the surface to move dynamically, which produces a robust gridding method that is well suited for this application. The method is applied to dynamic surface roughness in the leading-edge region of an airfoil but could also be used for analysis of internal surface roughness. The dynamic surface roughness examined in this study demonstrated a major effect on the flow field, with the resulting flow being significantly different than the flow found with similar static surface roughness. The dynamic roughness was able to delay or eliminate the unsteady flow separation for the conditions tested at both constant angle of attack and dynamic stall regimes and shows strong potential as an aerodynamic-flow-control mechanism.

Numerical prediction of unsteady vortex shedding for large leading-edge roughness

Abstract A full two-dimensional Navier–Stokes algorithm is used to investigate unsteady, incompressible viscous flow past an airfoil leading edge with surface roughness that is characteristic of ice accretion. The roughness is added to the surface through the use of a Prandtl transposition and can generate both small-scale and large-scale roughness. The focus of the study is a detailed flow analysis of the unsteady velocity fluctuations and vortex shedding induced by the surface roughness. The results of this study are compared to experimental data on roughness-induced transition for the same roughness geometry. A comparison is made between “fluctuation intensity” values from the current algorithm to experimentally determined turbulence intensity values. The effects of the roughness Reynolds number, Re k , are investigated and compared to experimental values of the critical roughness Reynolds number. The authors speculate that there may be a possible correlation between unsteady roughness-induced vortex shedding and the onset of experimentally measured transitional flow downstream of large-scale roughness.

Wind Tunnel Analysis of a Morphing Swept Wing Tailless Aircraft

Inspired by flight in nature, work done by Lippisch, the Hortens, and Northrop offered a chance at achieving the efficiency of bird flight with swept-wing tailless aircraft. Tailless designs have been forced incorporate aerodynamic compromises for control, which have inhibited potential advantages. A morphing mechanism, which changes the twist of wing and can provide pitch, roll and yaw control for a tailless swept wing aircraft. This research is investigating the design of a morphing wing to impro ve the flight characteristics of a tailless aircraft. Wind-tunnel testing is being used to evaluate the stability, control and efficiency of a morphing swept wing tailless aircraft. Preliminary data indicates that a morphing mechanism, which can change an aircrafts wing twist in flight, can provide adequate control forces and moments to control an UAV and potentially in a manned aircraft. This morphing wing can allow a swept wing tailless aircraft to fly in a cruise configuration without the added drag of b uilt in washout or winglets normally used to prevent adverse yaw during maneuvering resulting in lift to drag ratios in the cruise configuration for the morphing wing close to 15 % better then an elevon -equipped wing. Wind tunnel data also indicates that drag reductions of between 7% and 28 % during maneuvering flight may be possible.

Dynamic Surface Roughness for Aerodynamic Flow Control

This study addresses the issue of controlling flow separation through the use of dynamic surface roughness. The work focuses on two areas: 1) development of simulation tools for detailed analysis of moving flow boundaries and 2) investigation of the effects of dynamic roughness on aerodynamic flow separation. The process of generating a quality grid for a surface that contains complex roughness can be a laborintensive project. The addition of dynamic surface roughness, or roughness that grows (or shrinks) in time, can further complicate this process. The current study proposes a method that not only accounts for the perturbations to the surface, but also allows for the surface to move dynamically, which produces a robust gridding method that is well suited for this application. The method is applied to dynamic surface roughness in the leading-edge region of an airfoil, but could also be used for analysis of internal surface roughness. The dynamic surface roughness examined in this study showed that it can have a major impact on the flow field, with the resulting flow being significantly different that the flow found with similar static surface roughness. The dynamic roughness was able to delay or eliminate the unsteady flow separation for the conditions tested at both constant angle-of-attack and dynamic stall regimes and shows strong potential as an aerodynamic flow control mechanism.

Flight Simulation of a Hybrid Projectile to Estimate the Impact of Launch Angle on Range Extension

A Hybrid Projectile (HP) currently under design at West Virginia University was simulated to estimate the effects of barrel launch angle and flight position of wing deployment. The projectile is similar to a standard 60mm mortar, except that is has been equipped to achieve extended range. A Simulink model was developed based upon external ballistics. The flight performance of the WVU-HP-60 was compared to a standard M720 60mm mortar. The developed HP was considered to be a tube-launched UAV, that transforms, not directly after launch but sometime after for optimal gliding, and must be modeled with different flight profiles because after transformation the aerodynamics drastically change. Two models of the UAV were created to allow for design of controllers. They were the launch model and the projectile flight model. It was found that the projectile may exit the barrel with a two degree variation of launch angle. The simulations show that range extension is still viable, with this barrel exit variation, to within 10% of the maximum achievable range. A confidence area was also developed to determine how far the launch angle and wing deployment position could stray and still maintain a significant amount of range extension.Copyright

Aircraft Ice Accretion Prediction Based on Neural Networks

Many experimental research efforts in the past two decades have revealed that the complete picture of aircraft ice accretion has many components, resulting in a complex physical structure. Although overwhelmingly complex, the icing phenomenon needs to be understood because of its impact on aircraft performance and safety. This requires a detailed knowledge of ice accretion physics, subsequent flow over the aircraft, and the resulting modified aircraft performance. Experimental and numerical studies to address these issues have their own advantages, disadvantages, and limitations, which further limit the analysis of the icing phenomena. The motivation behind this study is the belief that complex phenomena in nature have an orderly structure on the large scale. Based on this premise, it is thought that icing phenomena also have orderly, albeit nonlinear, behavior that can be modeled by neural networks, which have a proven capability for modeling nonlinear systems. The methodology developed in the present study incorporates the Fourier series expansion of an ice shape following a conformal mapping, which suppresses the effect of airfoil geometry, and then utilizes neural networks to model the Fourier coefficients and the downstream extent of the ice shape. The neural network can be trained to make ice accretion predictions, given a set of data including the flight and atmospheric conditions, along with the Fourier coefficients and the extent of the resulting ice shape. The neural network also provides statistical output of the relative significance of the input parameters in the training. The preliminary results show that the proposed method has reasonable capabilities and has merit for further investment, because it can be coupled with other systems to create advanced computational ice accretion models and ice protection systems. Nomenclature ai, bi = coefficients of the cosine and sine functions of the Fourier series expansion, respectively f = actual perturbation geometry from the parabola surface ˜ f = approximated perturbation geometry LWC = liquid water content of oncoming air in grams per cubic meter M = number of Fourier terms for the truncated Fourier series expansion MVD = median volumetric diameter in micrometers N = number of data points of the actual ice geometry T∞ = static temperature in the oncoming air in kelvin V∞ = free stream velocity in meters per second x‐y = data coordinates of the experimental ice shape x � ‐y � = ice shape coordinates nondimensionalized by the leading-edge radius (LER) of the airfoil ξ ‐η = coordinates of the ice shape in the transformed plane ξ � ‐η � = coordinates of the ice shape after separation

Investigation of Relative Humidity and Induced-Vortex Effects on Aircraft Icing

Two new mechanisms for downstream ice growth (i.e., downstream of the primary ice shape) in aircraft icing scenarios were investigated. The first mechanism is local variation of relative humidity with its potential for water deposition due to supersaturation. The second mechanism is induced-vortex effects due to their potential impact on droplet paths. It was shown that for rough surfaces with an extended period of exposure, relative humidity effects can lead to additional growth. The resultant frost is a sandpaperlike roughness that can severely degrade the aerodynamic performance of the wings. It was also shown that the vortices induced by the existing ice-shape features are capable of altering the droplet paths. As a result, impingements occur beyond the limits predicted by the methods in other icing prediction codes.

Aerodynamic Drag Reduction of a Racing Motorcycle Through Vortex Generation

Aerodynamic Drag Reduction of a Racing Motorcycle through Vortex Generation