Natural Laminar Flow and Laminar Flow Control

Natural Laminar Flow and Laminar Flow Control

lcase/nasa LaRC Series Stability of Time Dependent and Spatially Varying Flows D.L. Dwoyer and M.Y. Hussaini (eds.) Studies of Vortex Dominated Flows M.Y. Hussaini and M.D. Salas (eds.) Finite Elements: Theory and Application D.L. Dwoyer, M.Y. Hussaini and RG. Voigt (eds.) Instability and Transition, Volumes I and II M.Y. Hussaini and RG. Voigt (eds.) Natural Laminar Flow and Laminar Flow Control RW. Barnwell and M.Y. Hussaini (eds.)

R.W. Barnwell Editors M.Y. Hussaini Natural Laminar Flow and Laminar Flow Control With 125 Illustrations Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Budapest

R.W. Barnwell Space Systems Division NASA Langley Research Center Hampton, VA 23665 USA M.Y. Hussaini ICASE NASA Langley Research Center Hampton, VA 23665 USA Library of Congress Cataloging-in-Publication Division Natural laminar flow and laminar flow control / [edited by] M.Y. Hussaini. p. cm. -- (ICASE/NASA LaRC series) Includes bibliographical references. ISBN-13:978-1-4612-7703-3 1. Laminar flow. 1. Hussaini, M. Y ousuff. II. Series. TL574.L3L36 1991 629.132'32--dc20 91-36758 Printed on acid-free paper. 1992 by Springer-Verlag New York, Inc. Softcover reprint of the hardcover 1st edition 1992 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA) except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not too be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Acts, may accordingly be used freely by anyone. Production managed by Karen Phillips; Manufacturing supervised by Jacqui Ashri. Camera-ready copy provided by the editors. 9 8 7 6 5 432 1 ISBN-13:978-1-4612-7703-3 00[: 10.1007/978-1-4612-2872-1 e-isbn -13: 978-1-4612-2872-1

Preface Research on laminar flow and its transition to turbulent flow has been an important part of fluid dynamics research during the last sixty years. Since transition impacts, in some way, every aspect of aircraft performance, this emphasis is not only understandable but should continue well into the future. The delay of transition through the use of a favorable pressure gradient by proper body shaping (natural laminar flow) or the use of a small amount of suction (laminar flow control) was recognized even in the early 1930s and rapidly became the foundation of much of the laminar flow research in the U.S. and abroad. As one would expect, there have been many approaches, both theoretical and experimental, employed to achieve the substantial progress made to date. Boundary layer stability theories have been formulated and calibrated by a good deal of wind tunnel and flight experiments. New laminar now airfoils and wings have been designed and many have been employed in aircraft designs. While the early research was, of necessity, concerned with the design of subsonic aircraft interest has steadily moved to higher speeds including those appropriate to planetary entry. Clearly, there have been substantial advances in our understanding of transition physics and in the development and application of transition prediction methodologies to the design of aircraft. The involvement of the NASA Langley Research Center in lami-nar now and transition physics as applied to airfoil and wing design dates from the early 1930s. Most identify Eastman Jacobs as the initiator, if not the originator, of much of the research which led to the development of the 2- through 7 -series laminar flow airfoils and the low turbulence tunnels in which they were tested. This work as well as a number of other studies concerning laminar flow control were carried out in the late thirties and early to mid forties; by 1950 laminar airfoil research was phased out to devote more resources to supersonic research. Interest in laminar flow and transition research was rekindled at the Langley Research Center following the oil embargo in 1973. By the end of the 1970s a wide variety of laminar flow research activities were under wav in stability theory, airfoil/wing design, and flight testing aimed at both laminar- wing operational problems and transition physics. Revolutionary improvements in computer and materials technologies provided important incentives. Research pertaining to laminar flow control continued throughout the eighties with many significant advances. In the light of progress made in the last decade, there is a need to document in one place some representative samples of the research accomplished and, where possible, to put it in context

vi with earlier work and future opportunities. This is the purpose of the present volume. Included in this volume are eight papers/chapters by well-known authorities in the field. The first article by J.N. Hefner contains a review of past and present laminar flow research programs at the NASA Langley Research Center and some suggestions as to the course of future work. Particular emphasis is placed on the potential of hybrid laminar flow control (HLFC), which is a combination oflaminar flow produced through airfoil/ wing shaping and that controlled by suction. Flight research, past and present, is the subject of the second article by R.D. Wagner et al. The third paper, authored by B.J. Holmes and C.J. Obara, concentrates on natural laminar flow (NLF) flight research. It contains valuable discussions of progress in test techniques and measurement technology and provides a listing of lessons learned. D.M. Somers is the author of the fourth article, which is devoted to the design of subsonic natural laminar flow airfoils. A historical background of laminar airfoil development is given, and design philosophy and experimental validation are discussed. The next paper by W. Pfenninger treats transonic laminar flow control. A design philosophy for long range LFC transports is outlined. The paper by P. Hall discusses the effect of wave interactions on the growth of distrubances in shear flows. Such interactions may have a significant impact on LFC predictions and have not been previously considered. The paper by D.M. Bushnell provides a succinct review of supersonic laminar flow control. He concludes that immediately available tools and experience should establish LFC as a viable and important component of SST /HSCT technology. The last paper, by P.J. Bobbitt et al., concerns the background of and results from the laminar flow control experiments carried out during the 1980s in the NASA Langley Research Center 8-foot Transonic Pressure Tunnel on a 23 degree swept airfoil model with a 7-foot chord. Details of the instrumentation, suction system, wind tunnel flow quality treatments and model fabrication are given. Results in the form of suction requirements, transition location, drag coefficients and boundary-layer stability calculations are presented. The editors would like to take this opportunity to thank the staff of Springer-Verlag for their patience and cooperation in the preparation of this volume. R.W. Barnwell M.Y. Hussaini

Contents Preface... v Laminar Flow Control: Introduction and Overview... 1 Jerry N. Hefner Laminar Flow Flight Experiments - A Review... 23 R.D. Wagner, D. V. Maddalon, D. W. Bartlett, F.S. Collier. Jr and A.L. Braslow Flight Research on Natural Laminar Flow Applications... 73 Bruce J. Holmes and Clifford J. Obara Subsonic Natural-Laminar-Flow Airfoils... 143 Dan M. Somers Design Philosophy of Long Range LFC Transports with Advanced Supercritical LFC Airfoils... 177 Werner Pfenninger and Chandra S. Vemuru Wave Interaction Theory and LFC... 223 Philip Hall Supersonic Laminar Flow Control... 233 D.M. Bushnell The Langley 8-Ft Transonic Pressure Tunnel Laminar-Flow-Control Experiment... 247 Percy J. Bobbitt, William D. Harvey. Charles D. Harris, and Cuyler W. Brooks, Jr.