This paper describes an investigation of the response of bluff body stabilized flames to harmonic oscillations. This problem involves two key elements: the excitation of hydrodynamic flow instabilities by acoustic waves, and the response of the flame to these harmonic flow instabilities. In the present work, data were obtained with inlet temperatures from 297 to 870 K and flow velocities from 38 to 170 m=s. These data show that the flame-front response at the acoustic forcing frequency first increases linearly with downstream distance, then peaks and decays. The corresponding phase decreases linearly with axial distance, showing that wrinkles on the flame propagate with a nearly constant convection velocity. These results are compared with those obtained from a theoretical solution of the G-equation excited by a harmonically oscillating, convecting disturbance. This kinematic model shows that the key processes controlling the response are 1) the anchoring of the flame at the bluff body, 2) the excitation of flame-front wrinkles by the oscillating velocity, 3) interference of wrinkles on the flame front, and 4) flame propagation normal to itself at the local flame speed. The first two processes control the growth of the flame response and the last two processes control the axial decrease observed farther downstream. These predictions are shown to describe many of the key features of the measured flame response characteristics. Nomenclature A = flame area D = burner depth d = bluff body width f = frequency f o = forcing frequency f BvK = Bénard-von Kármán instability frequency f KH = Kelvin-Helmholtz frequency G = isoscalar contour variable describing flame position H = burner height I t = edge detection threshold k = wave number L = flame position L 0 = fluctuation of flame position jL 0 j = gain of Fourier transformed flame position Q = heat release R 2 = goodness-of-fit parameter Re = Reynolds number S = distance along time-averaged flame front S L = laminar flame speed S T = turbulent flame speed t = time u = flow velocity in the x-direction u 0 = unsteady axial flow velocity u 0 = mean flow velocity u c;eff = effective convection velocity of a flame disturbance u c;v = convective velocity of a flow disturbance u 0 n = fluctuating flow velocity normal to the flame u t;0 = mean flow velocity tangential to the flame V = excitation voltage v = flow velocity in the y-direction W = burner width x = position along mean flow direction y = position perpendicular to mean flow direction = parametric flame-front angle " = nondimensionalized disturbance amplitude = time-averaged flame-front angle c = convective wavelength, u o =f 0 f = phase of a flame wrinkle x = phase of velocity perturbations in the x-direction y = phase of velocity perturbations in the y-direction ! = disturbance radial frequency

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A number of replacement fuels for JP-8 are currently under development to assure a secure source of fuel for aviation applications. Examples include Fischer-Tropsch derived liquids from coal or gas, or hydroprocessed fuels derived from vegetable oil or animal fats. The present effort focuses on examining how various candidate fuels behave upon injection into a subsonic crossflow. Characteristics such as droplet size, velocity, and dispersion are measured for the different fuels. As a result, the role of fuel type in the behavior of the spray can be assessed. In addition, the extent to which existing correlations or other models can describe the impact of the liquid properties on these characteristics is evaluated. The results show that systematic variation in liquid penetration occurs along with differences in column breaktime and frequency of the breakpoint motion. On the other hand, general droplet sizes, velocities, and volume flux profiles, at least measured on a time averaged basis exhibit little differences. The results suggest momentum flux captures the majority of the behavior as long as actual local values for the parameters are used (e.g., actual liquid jet velocity)

A number of "drop-in" replacement fuels for JP-8 are currently under development to assure a secure source of fuel for aviation applications. In the present work, evaluation of a liquid jet injected into a crossflow is carried out. Characteristics such as spray droplet size, velocity, and dispersion are measured for the different fuels. As a result, the role of fuel type in the behavior of the spray can be assessed. In addition, the extent to which existing correlations or other models can describe the impact of the liquid properties on these characteristics is evaluated. If confidence can be built in the use of design correlations, it can likely lead to simplification in the overall fuel assessment process when considering potential replacement fuels. The results show that some characteristics can be effectively captured (e.g., overall spray SMD) by simple models, whereas others cannot (e.g., spray penetration). This type of information can lead to the identification of areas of weakness relative to design tools that can be targeted for improvement though additional experimental studies and associated analyses. NomenclatureA = physical area d = diameter D32 = Sauter mean diameter Cd = discharge coefficient gc = gravitational constant p = pressure q = momentum flux ratio (defined in Eq. 2) Q = volume flow rate U = velocity  density  = liquid surface tension  = viscosity x,y,z = distance per sketch u,v,w = velocity component per sketch Subscripts g = gas l = liquid o = initial 1 = upstream 2 = downstream