'(NASA -cn-156 122) UNTAYN6DS-.DET78-20069 PROPULSIVE LIFT CONFIGURATIOUS.. PAET.C:

IDEV-Et OPENT OF EXPERIENTAI TECHNIQUES FOR INVES2IGTION OF UNSTEADY PRESSURES EEHIND A Unclas COLD. 1ODEL JET (-Virginia Univ.) 147 p HC G3/02 11880

RESEARCH LABORATORIES FOR THE ENGINEERING SCIENClW SCHOOL OF ENGINEERING AND

APPLIED SCIENCE

University of Virginia

Charlottesville, Virginia 22901

Technical Report

UNSTEADY LOADS DUE TO PROPULSIVE LIFT CONFIGURATIONS PART C - DEVELOPMENT OF EXPERIMENTAL TECHNIQUES FOR

INVESTIGATION OF UNSTEADY PRESSURES BEHIND A COLD MODEL

James C. Schroeder

Report No. UVA/528095/NAE78/l13

March 1978

https://ntrs.nasa.gov/search.jsp?R=19780012126 2018-05-18T08:21:48+00:00Z

RESEARCH LABORATORIES FOR THE ENGINEERING SCIENCES

Members of the faculty who teach at the undergraduate and graduate levels and a number of professional engineers and scientists whose primary activity is research generate and conduct the investigations that make up the school's research program. The School of Engineering and Applied Science of the University of Virginia believes that research goes hand in hand with teaching. Early in the development of its graduate training program, the School recognized that men and women engaged in research should be as free as possible of the administrative duties involved in sponsored research. In 1959, therefore, the Research Laboratories for the Engineering Sciences (RLES) was established and assigned the, administrative responsibility for such research within the School.

The director of RLES-himself a faculty member and researcher-maintains familiarity with the support requirements of the research under way. He is aided by an Academic Advisory Committee made up of a faculty representative from each academic department of the School. This Committee serves to inform RLES of the needs and perspectives of the research program.

In addition to administrative support, RLES is charged with providing certain technical assistance. Because it is not practical for each department to become self-sufficient in all phases of the supporting technology essential to present-day research, RLES makes services available through the following support groups: Machine Shop, Instrumentation, Facilities Services, Publications (including photographic facilities), and Computer Terminal Maintenance.

Technical Report

UNSTEADY LOADS DUE TO PROPULSIVE LIFT CONFIGURATIONS PART C - DEVELOPMENT OF EXPERIMENTAL TECHNIQUES FOR

INVESTIGATION OF UNSTEADY PRESSURES BEHIND A COLD METAL JET

Submitted to:

NASA Scientific and Technical Information Facility P. 0. Box 8757

Baltimore/Washington International Airport Maryland 21240

Submitted by:

J. K. Haviland

Professor

James C. Schroeder

Department of Mechanical and Aerospace Engineering

RESEARCH LABORATORIES FOR THE ENGINEERING SCIENCES

SCHOOL OF ENGINEERING AND APPLIED SCIENCE

UNIVERSITY OF VIRGINIA

CHARLOTTESVILLE, VIRGINIA

Report No. UVA/528095/MAE78/113 Copy No,

March 1978

ABSTRACT

As part of an overall study of the scaling laws for the fluctuating

pressures induced on the wings and flaps of STOL aircraft by jet engine

impingement, an experimental investigation has been made of the near

field fluctuating pressures behind a cold circular jet, both when it was

free and when it was impinging on a flat plate. Minature static pressure

probes were developed for measurements in the free jet and on the flat

plate; these were connected by plastic tubing to 1/8 inch microphones

which acted as pressure transducers. Using a digital correlator together

with an FFT program on the CDC 6400 computer, spectral densities, relative

amplitudes, phase lags, and coherences were also obtained for the signals

from pairs of these probes, and were used to calibrate these probes directly

against microphones. This system of instrumentation was employed to obtain

single point rms and third-octave surveys of the static pressures in the

free jet and on the surface of the plate. Also, two point cross-correlations

were obtained, and from these, relative amplitudes, phase lags, and coherences

were calculated for a more detailed characterization of the jet flow. These

measurements confirmed the existence of a vortex structure in the jet, and

demonstrated that the jet diameter, velocity and dynamic pressure are appro

priate scaling dimensions for characterizing fluctuating pressures behind

j ets.

OF POOR XS

iv

TABLE OF CONTENTS

Page

ACKNOITLEDGENTS ................ ................... iii

ABSTRACT ................... .............. ..... iv

LIST OF TABLES ............... ............... ...... vii

LIST OF FIGURES ......................... viii

LIST OF SYMBOLS. . .... ............ xiii

Chapter

1. INTRODUCTION ............ ................ ... 1

2. HISTORICAL AND THEORETICAL BACKGROUND .... ........ 4

2.0 Classical Model of a Circular Jet .... ......... 4

2.1 Vortex Model of a Circular Jet ..... ......... 6

2.2 Scaling Laws for a Circular Jet ... .......... .. 13

2.3 Jet Impingement ....... ................ . 14

3. INSTRUMENTATION AND DATA ANALYSIS TECHNIQUES FOR PRESSURE 14EASUREMENTS ................. ....... 17

3.0 Flow and Traverse System .... ............. . 17

3.1 Pressure Sensors ....... ........... ... 18

3.2 Data Analysis'Equipment . .... .......... 24

3.3 Fast Fourier Transform Analysis .... ........ . 26

4. EVALUATION OF DATA ANALYSIS TECHNIQUES AND PRESSURE SENSORS ......... .................. . 32

4.0 Evaluation of Data Analysis Techniques. . . ... 32

4.1 Theoretical Pressure Sensor Transfer Functions . . 38

4.2 Evaluation of Pressure Sensors ... .......... 48

4.3 Calculated Transfer Functions ... .......... 58

v

vi

TABLE OF CONTENTS (continued)

Chapter Page

5. EXPERIMENTAL RESULTS ...... ........... ... 65

5.0 Free Jet - Prms and Mean Dynamic Pressure Levels 65

5.1 Free Jet - 1/3 Octave Spectra .. .......... . 69

5.2 Free Jet - Correlation Coefficients. . .... 77

5.3 Free Jet - Phase'lag, Transfer Function Amplitude and Coherence ........ ......... ... 80

5.4 Jet Impingement --Flunctuating Pressure Levels . . 87

5.5 Jet Impingement - 1/3 Octave Spectra ..... . . 88

5.6 Jet Impingement - Correlation Coefficients . . . 103

5.7 Jet Impingement - Phase Lag, Transfer Function Amplitude and Coherence ... .......... ... 109

6. SUMM.ThARY .. ......... ................ 131

BIBLIOGRAPHY..... . . ...... .................... . 134

LIST OF TABLES

Table

1 Probe Correlation Coefficient Comparison . . ..... 49

2 Free Jet - Convection Celocities ... ........... . 87

3 Jet Impingement - Convection Velocities ...... .... 130

vii

LIST OF FIGURES

Figure Page

2.0.1 Classical Model of a Circular Jet ...... ........ 5

2.1.1 Vortex Model of a Circular Jet ...... ............. 7

2.1.2 a) Vortex Sheet Roll Up ......... ............ 9

2.1.2 b) Lobed Vortex Ring .... ........... ..... ... 9

2.1.3 Limits of Sheared Annulus ..... ........... .i. . 11

2.1.4 Vortex Model Fluctuations . ............... ... 12

3.0.1 Cold Jet Assembly ....... ................. .. 19

3.0.2 Data Acquisition Set-Up ....... ......... ... 20

3.1.1 Pressure Probes ......... ................. 22

3.1.2 Flat Impingement Plate ........ .......... ... 23

3.3.1 CROSSPECT Model ......... .................. .27

4.0.1 Power Spectra from 9.0 cm Downstream Location ...... .33

4.0.2 Power Spectra from 11.0 cm Downstream Locatiom. .... .. 34

4.0.3 Tran~fer Function Amplitude Output .... ....... .. 35

4.0.4 Phase Lag and Coherence Outputs ... ........... .. 36

4.0.5 Power Spectra from Normal Dynamic Range . ....... .. 37

4.0.6 Power Spectra from Extended Dynamic Range ... .... . 37

4.0.7 Power Spe&tra Output from CROSSPECT ... .......... 39

4.0.8 1/3 Octave Spectra ........ ............... ... 39

4.0.9 Comparison Between Power Spectra and 1/3 Octave . ... 40

4.1.1 Model for Analysis of Pressure Probes .. ......... .42

4.1.2 Pulsating Air Slug ........ .................. . 44

4.1.3 Pulsating Sphere .......... . ... .......... A4

viii

LIST OF FIGURES (continued)

Figure Page

4.1.4 Equivalent Piston ......... ............ . 46

4.1.5 Equivalent Pulsating Sphere .... ............. . 46

4.2.1 1/3 Octave Spectra: Total and Static .. ........ 50

4.2.2 Power Spectra: Static ....... ............ . 51

4.2.3 Power Spectra: Total .. ........... ...... 51

4.2.4 Transfer Function of Static Probe ........ . 53

4.2.5 Transfer Function of New Static Probe ..... .... 53

4.2.6 Special impingement plate ....... ...... ... 55

4.2.7 Transfer Function: Tubing Length = 0.5 m . ....... 56

4.2.8 Transfer Function: Tubing Length = 1.0 m ........ . 56

4.2.9 Transfer Function: Tubing Length = 2.0 m .. ........ 56

4.2.10 Transfer Function: Diameter = .01 m ..... .......... 5?

4.2.11 Transfer Function: Diameter = .02 m ... ......... 57

4.2.12 Transfer Function: Diameter = .04 m .. .......... 57

4.2.13 Comparison Between Microphone and Kulite .. ..... ... 59

4.2.14 Comparison Between Stainless and Plastic Tubi