Unsteady Aerodynamics of VSTOL Dual Impinging Jets - A Comprehensive Approach
Abstract
Short takeoff and vertical landing (STOVL) aircraft operating in hover mode suffersignificant adverse life cycle cost and operational constraints because of the unsteadiness associated with propulsive jet impingement on the ground plane (``ground effect ). Specific consequences include unsteady/unpredictable lift and lift loss, reduced aircraft stability, ground erosion and hot gas ingestion (HGI) into the engine inlets. Structural complications arise from accompanying high noise levels, which include high-amplitude discrete tones and aggravate the sonic fatigue problem. Fundamental studies of the unsteady fluid and acoustic phenomena associated with dissimilar STOVL jet pairs impinging on a surface are scarce. We seek to fill this gap with a comprehensive, tightly integrated experimental-computational study. In this work, we examine modal interactions between the two jets, with emphasis on the effect of the disparity in their properties (subsonic/supersonic, cold/hot respectively) and their interactions with the ground plane. The impact of jet-jet interactions on the thermo-mechanical loads, including spectral content and their correspondence to spatio/temporal coherent structures will be characterized. The properties of preferentially growing modes, and receptivity to (small) perturbations will be examined in high/hot and low/cold speed jets respectively. We propose a comprehensive parametric study to analyze these dynamics, bringing to bear anorderly approach combining the experimental strengths of Florida State University with the computational expertise of The Ohio State University. In the experimental thrust, the flow will be interrogated with conventional techniques (high bandwidth pressure sensors, whole-field schlieren and shadowgraphs) as well as advanced PIV methods (Stereoscopic, Tomographic and Phase-Conditioned) and Background Oriented Schlieren (including 3-D BOS). In the computational thrust, we will use a multi-fidelity approach, using ReynoldsAveraged Navier-Stokes equations concurrently with the experimental campaign, followed by highly resolved Large Eddy Simulations for select cases that encompass the principal regimes encountered. Validated simulations will be employed to perform studies to augment tunnel tests, by examining the effects of ground boundary layers. In addition to traditional analysis of unsteady loading and spectra, this research will reveal the most amplified modes, differential entrainment and discrete events, energetic interactions and flow sensitivity to various perturbations. The study will thus yield critical insight into thedynamics of this unsteady flow and help identify pathways towards physics-based management of STOVL generated ground effect.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 26, 2018
- Source ID
- N000141812506
Entities
People
- Farrukh S. Alvi
Organizations
- Florida State University
- Office of Naval Research
- United States Navy